6-ketoprostaglandin-f1-alpha and pirmagrel

Although thromboxane A2 is a potent platelet agonist and vasoconstrictor in vitro, our knowledge of its pathophysiologic importance in human disease is limited. To facilitate the elucidation of its role in vivo, we sought to define a human syndrome in which pharmacologic interventions designed to inhibit the biosynthesis or biologic actions of thromboxane A2 might be appropriately assessed. Patients with severe peripheral vascular disease were selected on the basis of elevated plasma beta-thromboglobulin and circulating platelet aggregates and compared with healthy, age-matched control subjects. In addition to the platelet indexes, their bleeding time was shorter and excretion of 2,3-dinor-thromboxane B2, a noninvasive index of thromboxane formation in vivo, and 2,3-dinor-6-keto-prostaglandin F 1 alpha, the major urinary metabolite of prostacyclin, was markedly increased. A selective inhibitor of thromboxane synthase, imidazo (1,5-2) pyridine-5-hexanoic acid, was administered to these patients under randomized, double-blind, controlled conditions. Platelet aggregation ex vivo, the circulating platelet aggregate ratio, and the bleeding time were all unaltered, despite almost maximal inhibition of platelet thromboxane formation 1 hr after dosing. By contrast, pronounced inhibition of aggregation was observed when platelet cyclooxygenase was inhibited by aspirin. During long-term dosing with the synthetic inhibitor, inhibition of thromboxane biosynthesis was incomplete, which would permit continued thromboxane-dependent platelet aggregation to occur. However, the failure of enzyme blockade to influence platelet function at the time of maximal drug action, despite efficient inhibition of serum thromboxane B2, suggests that accumulation of proaggregatory endoperoxides is also likely to have contributed to the persistence of platelet activation. We have characterized a human preparation in which platelet activation coexists with increased thromboxane biosynthesis. In this setting, platelet activation persists despite long-term administration of a thromboxane synthase inhibitor in a dosing regimen representative of that employed in clinical trials. Prolongation of drug action and combination with antagonists of the shared endoperoxide/thromboxane A2 receptor may be necessary to assess the potential of selective inhibition of thromboxane synthase as a therapeutic strategy in man.

Topics: 6-Ketoprostaglandin F1 alpha; Aged; Arteriosclerosis; beta-Thromboglobulin; Epoprostenol; Female; Humans; Imidazoles; Male; Middle Aged; Platelet Aggregation; Platelet Factor 4; Pyridines; Thromboxane B2; Thromboxane-A Synthase

Neutralization of heparin anticoagulation by protamine produces catastrophic hemodynamic reactions in some patients. Using a canine model, we tested effects of thromboxane synthetase inhibition (CGS-13080) and glucocorticoid pretreatment on the cardiorespiratory effects of protamine. In control dogs, protamine decreased mean arterial pressure and cardiac output and increased mean pulmonary artery pressure, systemic and pulmonary vascular resistances (SVR, PVR), and airway pressure. Both CGS-13080 and methylprednisolone ameliorated some effects of protamine. CGS-13080 infusion decreased mean pulmonary artery pressure, SVR, and airway pressure after protamine injection relative to controls. Cardiac output and PVR were unaffected by the drug, whereas the decrease in mean arterial pressure was prolonged. Plasma thromboxane A2 metabolite (TXB2) concentrations were lower and prostacyclin metabolite (6-keto PGF1 alpha) concentrations were higher compared with that of controls. These experiments support a role for TXA2 in the response to protamine. Methylprednisolone pretreatment produced larger cardiac output and lower airway pressure after protamine injection compared with controls. Mean arterial pressure was improved, but not significantly. Mean pulmonary artery pressure, SVR, and PVR were not different from that of controls; TXB2 and 6-keto PGF1 alpha were unaffected. The effects of methylprednisolone appear unrelated to arachidonic acid metabolism, as TXB2 and 6-keto PGF1 alpha levels were unaffected.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Dogs; Drug Interactions; Hemodynamics; Imidazoles; Methylprednisolone; Protamines; Pyridines; Thromboxane B2; Thromboxane-A Synthase

Pulmonary hypertension occurs after the intravascular activation of complement. However, it is unclear which activated complement fragments are responsible for the pulmonary vascular constriction. We investigated the 21-carboxy-terminal peptide of C3a (C3a57-77) to see if it would cause pulmonary vascular constriction when infused into isolated buffer-perfused rat lungs. Injection of C3a57-77 (225 to 450 micrograms) caused mean pulmonary arterial pressure (Ppa) to rapidly increase. However, the response was transient, with Ppa returning to baseline within 10 min of its administration. C3a57-77 also resulted in an increase in lung effluent thromboxane B2 (TXB2), concomitant with the peak increase in Ppa. C3a57-77 did not affect the amount of 6-keto-PGF1 alpha in the same effluent samples. Indomethacin inhibited the C3a57-77-induced pulmonary artery pressor response and the associated TXB2 production. Indomethacin also decreased lung effluent 6-keto-PGF1 alpha. The thromboxane synthetase inhibitors CGS 13080 and U63,357 inhibited the C3a57-77-induced pulmonary artery pressor response and TXB2 production without affecting 6-keto-PGF1 alpha. These inhibitors did not inhibit pulmonary artery pressor responses to angiotensin II. Tachyphylaxis to C3a57-77 occurred because a second dose of C3a57-77 administered to the same lung failed to cause a pulmonary artery pressor response or TXB2 production. The loss of the pressor response was not due to a C3a57-77-induced decrease in pulmonary vascular responsiveness because pressor responses elicited by angiotensin II were not altered by lung contact with C3a57-77. Thus, C3a57-77 caused thromboxane-dependent pulmonary vascular constriction in isolated buffer perfused rat lungs.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Benzofurans; Blood Pressure; Complement C3a; Cyclooxygenase Inhibitors; Imidazoles; In Vitro Techniques; Indomethacin; Lung; Male; Peptide Fragments; Perfusion; Pyridines; Rats; Thromboxane B2; Thromboxane-A Synthase; Vasoconstriction

The effects of the thromboxane synthase inhibitor CGS13080 on the in vivo synthesis of thromboxane and prostacyclin were determined in six healthy volunteers. Two different doses (0.08 and 0.25 mg/kg x h) were infused for six hours under strictly controlled conditions and 2,3-dinor-TxB2 and 2,3-dinor-6-keto-PGF1 alpha were measured in urine using gaschromatography--mass spectrometry. The in vivo synthesis of thromboxane was inhibited by 80-75% while there was no effect on the in vivo prostacyclin synthesis.

Topics: 6-Ketoprostaglandin F1 alpha; Adult; Epoprostenol; Humans; Imidazoles; Male; Pyridines; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

While platelets have been shown to be capable of supplying prostaglandin (PG) H2 to endothelial cells in culture for PGI2 synthesis, endothelial cells have been shown unable to supply PGH2 to platelets for thromboxane (TX) A2 synthesis. We incubated rings of the bovine coronary artery (BCAR) with human platelets treated with aspirin (to inhibit cyclooxygenase) or CGS 13080 (to inhibit TXA2 synthase) in the presence of 20 microM arachidonic acid. BCAR, with damaged endothelium, produced significantly less PGI2 than that with intact endothelium. However, co-incubation with CGS 13080-treated platelets resulted in an increase in PGI2 independent of endothelium, demonstrating a shunt of PGH2 from platelets to BCAR. Co-incubation of BCAR with aspirin-treated platelets resulted in a net increase in TXA2 demonstrating a shunt of PGH2 from BCAR to platelets. Employing [14C]PGH2 as substrate, BCAR with and without intact endothelium produced similar amounts of 6-keto-[14C]PGF1 alpha. Likewise, homogenates (50 micrograms protein) of intimal and subintimal regions of BCAR and BCAR converted similar amounts of PGH2 to 6-keto-PGF1 alpha. These data suggest that vascular production of PGH2 is more dependent on an intact endothelium than is the conversion of PGH2 to PGI2. These data also suggest a potential for a bidirectional exchange of PGH2 between platelets and vascular wall during platelet-vascular wall interactions.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Arachidonic Acid; Arachidonic Acids; Aspirin; Blood Platelets; Cattle; Coronary Vessels; Cyclooxygenase Inhibitors; Cytochrome P-450 Enzyme System; Epoprostenol; Humans; Imidazoles; Intramolecular Oxidoreductases; Isomerases; Prostaglandin Endoperoxides; Prostaglandin Endoperoxides, Synthetic; Prostaglandin H2; Prostaglandins H; Pyridines; Thromboxane B2; Thromboxane-A Synthase

Prostacyclin (PGI2) is an inhibitor of platelet function in vitro. We tested the hypothesis that PGI2 is formed in biologically active concentrations at the platelet-vascular interface in man and can be pharmacologically modulated to enhance its inhibitory properties. This became feasible when we developed a microquantitative technique that permits the measurement of eicosanoids in successive 40-microliters aliquots of whole blood emerging from a bleeding time wound. In 13 healthy volunteers the rate of production of thromboxane B2 (TXB2) gradually increased, reaching a maximum of 421 +/- 90 (mean +/- SEM) fg/microliters per s at 300 +/- 20 s. The hydration product of PGI2, 6-keto-PGF1 alpha, rose earlier and to a lesser degree, reaching a peak (68 +/- 34 fg/microliters per s) at 168 +/- 23 s. The generation of prostaglandins PGE2 and D2 resembled that of PGI2. Whereas the threshold concentration of PGI2 for an effect on platelets in vitro is approximately 30 fg/microliters, only less than 3 fg/microliters circulates under physiological conditions. By contrast, peak concentrations of 6-keto-PGF1 alpha obtained locally after vascular damage averaged 305 fg/microliters. Pharmacological regulation of PG endoperoxide metabolism at the platelet-vascular interface was demonstrated by administration of a TX synthase inhibitor. The rate of production of PGI2, PGE2, and PGD2 increased coincident with inhibition of TXA, as reflected by three indices; the concentration of TXB2 in bleeding time blood and serum, and excretion of the urinary metabolite, 2,3-dinor-TXB2. These studies indicate that PGI2 is formed locally in biologically effective concentrations at the site of vessel injury and provide direct evidence in support of transcellular metabolism of PG endoperoxides in man.

Topics: 6-Ketoprostaglandin F1 alpha; Bleeding Time; Blood Platelets; Blood Vessels; Epoprostenol; Gas Chromatography-Mass Spectrometry; Humans; Imidazoles; Prostaglandin Endoperoxides; Pyridines; Reference Values; Thromboxane A2; Thromboxane B2

Pulmonary hypertension with an elevated pulmonary vascular resistance was observed during the immediate recovery period in patients who underwent mitral valve surgery. In eight such patients, intravenous infusion of CGS-13080, imidazo(1,5-a)pyridine-5-hexanoic acid (a thromboxane synthetase inhibitor), at a dose range of 0.08-0.1 mg/kg/hr, effectively reduced pulmonary hypertension (from a mean pulmonary arterial pressure of 36 +/- 2 to 31 +/- 2 torr) and pulmonary vascular resistance (from 339 +/- 38 to 238 +/- 37 dynes.sec.cm-5) within 30 minutes and remained reduced for the entire infusion period (48 hours in five patients and 18 hours in three patients). Mean arterial pressure or systemic vascular resistance were not significantly affected by the drug infusion. Serum thromboxane B2 levels (a stable metabolic product of thromboxane A2) were significantly reduced after administration of the compound, with the maximum effect of greater than 90% reduction. All patients tolerated the drug infusion without significant side effects.

Topics: 6-Ketoprostaglandin F1 alpha; Cardiopulmonary Bypass; Heart Valve Prosthesis; Hemodynamics; Humans; Hypertension, Pulmonary; Imidazoles; Mitral Valve; Postoperative Complications; Pulmonary Circulation; Pyridines; Thromboxane B2; Thromboxane-A Synthase; Vascular Resistance

Pretreatment with the thromboxane synthase inhibitor OKY-046 but not the cyclo-oxygenase inhibitor ibuprofen protects against ischemia-induced acute tubular necrosis. However, ibuprofen together with the vasodilating agent prostaglandin E1 is protective. This suggests that a high prostaglandin to thromboxane ratio is the major factor operative in preventing tubular necrosis, the subject of this study. Rats that had unilateral nephrectomy (n = 60) with the exception of rats that had sham operations (n = 8) underwent 45 minutes of left renal pedicle clamping. Thirty minutes before the operation, the rats received either a saline solution or a thromboxane synthase inhibitor that was given intravenously. The inhibitors OKY-046 (2 milligrams per kilogram, n = 10), UK38485 (1 milligram per kilogram, n = 9) and U63357A (10 milligrams per kilogram, n = 10) were given as a single bolus while the inhibitor CGS13080 (0.1 milligram per kilogram, n = 9, and 1.0 milligram per kilogram, n = 7) was given by constant infusion and continued for 60 minutes after reperfusion. With saline solution therapy, five minutes after reperfusion, thromboxane B2 increased from 154 to 2,537 picograms per milliliter (p less than 0.00001) and 6-keto-prostaglandin F1 alpha increased from 51 to 266 picograms per milliliter (p less than 0.004). At 24 hours, the creatinine level increased from 0.5 to 2.8 milligrams per deciliter (p less than 0.00001). Only OKY-046 yielded a creatinine level at 24 hours of 1.2 milligrams per deciliter, a value lower than that for those in the saline solution control group (p less than 0.002). Furthermore, OKY-046 led to the highest prostaglandin to thromboxane ratio (p less than 0.035). The five other ratios which occurred after drug therapy were inversely related to the decrease in the creatinine value (r = -0.93, p less than 0.02). Histologically, OKY-046 was the only thromboxane synthase inhibitor to prevent acute tubular necrosis (p less than 0.05). Results show that a high prostaglandin to thromboxane ratio protects against acute tubular necrosis.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Benzofurans; Creatinine; Evaluation Studies as Topic; Ibuprofen; Imidazoles; Ischemia; Kidney; Kidney Tubular Necrosis, Acute; Male; Methacrylates; Pyridines; Rats; Thromboxane B2; Thromboxane-A Synthase

The effects of intravenously administered collagen on the circulatory platelet count, TxB2, 6-keto PGF1 alpha and 51Cr-labelled platelet accumulation in the thorax have been evaluated in the guinea-pig. Administration of collagen induced a dose-related peripheral thrombocytopenia and a concomitant increase in 51Cr-labelled platelets in the thorax. There was also a transient dose-related increase in plasma TxB2 but no change in plasma 6-keto PGF1 alpha levels. The thromboxane synthetase inhibitors tested, reduced the platelet accumulation, but only CGS 13080 significantly inhibited TxB2 production. In contrast all the cyclooxygenase inhibitors tested impaired the elevation of plasma TxB2 after collagen, but only diclofenac inhibited the 51Cr-labelled platelet accumulation. The greater effect of thromboxane synthetase inhibitors compared to cyclooxygenase inhibitors on platelet accumulation in this system cannot be completely explained by the changes measured in the circulating prostanoids.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Platelets; Chromium Radioisotopes; Collagen; Cyclooxygenase Inhibitors; Diclofenac; Dose-Response Relationship, Drug; Guinea Pigs; Imidazoles; Injections, Intravenous; Platelet Aggregation; Platelet Count; Prostaglandins; Pyridines; Thorax; Thromboxane B2; Thromboxanes

The hematological and pharmacological effects of a new thromboxane synthetase inhibitor, CGS-13080 (imidazo[1,5-alpha]pyridine-5-hexanoic acid), were investigated during cardiopulmonary bypass in a blinded, randomized manner in dogs. Compared with placebo, CGS-13080 suppressed thrombin-stimulated platelet thromboxane B2 production by 90% during cardiopulmonary bypass (p less than .001), an effect that persisted for two hours after stopping the infusion. In the CGS-13080-treated group, plasma 6-keto-prostaglandin F1 alpha levels significantly increased over time (p less than .03) and were somewhat higher when compared with those in the placebo-treated group. This observation suggests that an "endoperoxide shunt" may have occurred. In the control group, an inverse correlation between platelet count and level of thromboxane B2 per platelet following in vitro thrombin stimulation (r = .5, p less than .001) was apparent, but there was no correlation between these two variables (r = .18, p less than .10) in the CGS-13080-treated group. No adverse hemodynamic or other effects attributable to CGS-13080 occurred during or immediately following cardiopulmonary bypass. These results suggest that CGS-13080 is an effective inhibitor of thromboxane B2 production during cardiopulmonary bypass in dogs and has no adverse physiological effects.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood; Cardiopulmonary Bypass; Dogs; Double-Blind Method; Drug Evaluation, Preclinical; Female; Hemodynamics; Imidazoles; Male; Platelet Count; Pyridines; Random Allocation; Thromboxane B2; Thromboxane-A Synthase; Time Factors

Increase in thromboxane A2 (TXA2) generation has been proposed as a mechanism of dynamic vaso-occlusion and in vivo platelet thrombus formation. We have examined the effects of CGS-13080, an imidazole derivative, on rabbit and human TXA2-prostacyclin (PGI2) "balance." In rabbits given CGS-13080, serum levels of TXB2 (stable metabolite of TXA2) were inhibited 81% at 2 hours and 56% at 24 hours (both P less than or equal to 0.01). Collagen-induced platelet aggregation was inhibited at 2 hours after CGS-13080 administration. In contrast, serum levels of 6-keto-PGF1 alpha (stable hydrolysis product of PGI2) increased 587% compared with control values at 2 hours (P less than or equal to 0.01). Platelet and white blood cell counts were not significantly altered. In human blood incubated in vitro with CGS-13080, serum TXB2 was completely inhibited, whereas PGI2 generation was stimulated (both P less than or equal to 0.001). In other experiments, we demonstrated uptake of platelet-generated cyclic endoperoxides by leukocytes and generation of PGI2 in the presence of CGS-13080 but not indomethacin. Thus, CGS-13080 inhibits TXA2 and stimulates PGI2 production in rabbit and human blood. Increase in PGI2 generation with TXA2 inhibition may be of potential benefit in conditions characterized by platelet hyperactivity.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Platelets; Calcimycin; Calcium Chloride; Collagen; Epoprostenol; Imidazoles; Indomethacin; Leukocytes; Oxidoreductases; Platelet Aggregation; Pyridines; Rabbits; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes

Topics: 6-Ketoprostaglandin F1 alpha; Arachidonic Acid; Arachidonic Acids; Aspirin; Blood Platelets; Cyclooxygenase Inhibitors; Dose-Response Relationship, Drug; Double-Blind Method; Humans; Imidazoles; Male; Oxidoreductases; Pyridines; Thromboxane-A Synthase; Time Factors

CGS 13080 inhibited cell-free thromboxane synthetase with an IC50 of 3 nM. It was at least five orders of magnitude less potent toward other key enzymes involved in arachidonic acid metabolism. Submicromolar concentrations inhibited calcium ionophore-induced formation of thromboxane B2 by intact human platelets with concomitant accumulation of prostaglandin E2. Oral doses lower than 1 mg/kg in rats suppressed the elevations of plasma thromboxane B2 induced by calcium ionophore. This was attended by shunting of endoperoxide substrate to 6-keto-prostaglandin F1 alpha and prostaglandin E2. CGS 13080 is one of the most potent and selective thromboxane synthetase inhibitors yet identified.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Platelets; Humans; Imidazoles; In Vitro Techniques; Male; Oxidoreductases; Prostaglandins E; Pyridines; Rats; Rats, Inbred Strains; Thromboxane B2; Thromboxane-A Synthase

N(7-Carboxyheptyl) imidazole, 4-[2-(1H-imidazol-1-yl) ethoxy] benzoic acid (dazoxiben) and imidazo [1,5-alpha] pyridine-5-hexanoic acid (CGS 13080) are potent selective inhibitors of platelet thromboxane synthetase that have little or no effect on the cyclooxygenase activity. Oral doses of the substances given to rats inhibited platelet thromboxane B2 production induced by intra-venous administration of collagen (100 micrograms/kg). Plasma concentrations of immunoreactive 6-keto PGF1 alpha in treated animals were increased above corresponding concentrations in untreated animals. There were small effects on the thrombocytopenia with CGS 13080 and carboxyheptylimidazole but not with dazoxiben. However these results did not always achieve statistical significance. Confirmation that the immunoreactive prostaglandin measured was actually 6-keto PGF1 alpha was obtained by the facts that indomethacin abolished its appearance in plasma and that the other prostaglandins were not present in sufficient quantities to cross-react with the antiserum to 6-keto PGF1 alpha. Two different antisera to 6-keto PGF1 alpha detected the same changes. Administration of thromboxane synthetase inhibitors to rats causes redirection of prostaglandin production from thromboxane to prostacyclin when platelets are stimulated with collagen in vivo.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Blood Platelets; Collagen; Imidazoles; Indoles; Indomethacin; Male; Oxidoreductases; Pyridines; Radioimmunoassay; Rats; Rats, Inbred Strains; Thrombocytopenia; Thromboxane B2; Thromboxane-A Synthase; Thromboxanes