thromboxane-a2 and isbogrel

Topics: Animals; Electric Stimulation; Enzyme Inhibitors; Fatty Acids, Monounsaturated; Graft Rejection; Guinea Pigs; Heart Transplantation; In Vitro Techniques; Isoquinolines; Nitroglycerin; Platelet Activating Factor; Platelet Aggregation Inhibitors; Pyridines; Pyridinium Compounds; Rats; Rats, Inbred Strains; Tetrahydroisoquinolines; Thromboxane A2; Transplantation, Heterologous; Ventricular Function, Left

In rabbit platelet-rich plasma, a specific TXA2 synthase inhibitor, CV-4151 (isbogrel) alone modestly inhibited the platelet aggregation induced by arachidonic acid (AA); even at 10(-4) M the inhibition was less than 50% (IC40 value: 8.1 x 10(-5) M). Aspirin-treated rat aortic rings alone inhibited the AA-induced platelet aggregation by 7%. However, CV-4151 exhibited a potent antiplatelet action in the presence of the aortic rings and its IC40 value was 8.3 x 10(-8) M. Thus, the aortic rings caused 1000-fold enhancement of the antiplatelet action of CV-4151. Next, we investigated the effect of CV-4151 on the production of two highly biologically active prostanoids, TXA2 and PGI2, and the contribution of these prostanoids to the antiplatelet action of CV-4151. TXA2 and PGI2 were measured by a radioimmunoassay of their stable metabolites, TXB2 and 6-keto-PGF1 alpha, respectively. Under the experimental conditions, CV-4151 simultaneously inhibited TXA2 generation and enhanced PGI2 generation. There was a positive linear relationship (r = 0.975, p < 0.01) between % inhibition of platelet aggregation and PGI2 generation and a significant negative linear relationship (r = 0.994, p < 0.001) between % inhibition of platelet aggregation and TXA2 generation. CV-4151 exhibits a potent antiplatelet action in the presence of PGI2 synthase, which is the in vivo situation, by simultaneously inhibiting TXA2 generation and enhancing PGI2 generation.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Aorta; Arachidonic Acid; Aspirin; Cytochrome P-450 Enzyme System; Enzyme Inhibitors; Epoprostenol; Fatty Acids, Monounsaturated; In Vitro Techniques; Intramolecular Oxidoreductases; Isomerases; Male; Platelet Aggregation; Platelet Aggregation Inhibitors; Prostaglandins; Pyridines; Rabbits; Rats; Rats, Sprague-Dawley; Thromboxane A2; Thromboxane-A Synthase

Effects of thromboxane A2 (TXA2) synthase inhibitors (CV-4151 and ozagrel) on cerebral thrombosis and cerebral damage were examined in a rat middle cerebral artery (MCA) thrombosis model and their potencies were compared with the conventional antithrombotic agents, aspirin and ticlopidine. CV-4151 significantly inhibited photochemically induced MCA thrombosis by oral (1 and 10 mg/kg) and intravenous (1 mg/kg) administration. Ozagrel (10 mg/kg, p.o.) also inhibited it. The potency of CV-4151 was about 10 times stronger than that of ozagrel, being comparable with the inhibition of blood TXA2 generation. Aspirin (100 mg/kg, p.o.) and ticlopidine (300 mg/kg, p.o.) showed an inhibitory tendency on MCA thrombosis. Twenty-four h after photochemical stimulation, cerebral edema and cerebral infarction were observed, and the lactate content in the brain increased. CV-4151 and ozagrel prevented this edema, and the antiedema effects of the drugs were correlated with the antithrombotic effect on thrombotic MCA occlusion. CV-4151 (10 mg/kg, p.o.), furthermore, significantly reduced the infarct size and inhibited the increase in lactate content. These results indicate that TXA2 synthase inhibitors inhibit cerebral damage by inhibition of MCA occlusion with thrombosis, probably resulting from the inhibition of TXA2 generation, and their effects are superior to those of aspirin and ticlopidine. TXA2 might play an important role in cerebral damage in the MCA thrombosis model. CV-4151 might be a useful drug for the treatment of cerebral thrombosis and for the prevention of cerebral infarction.

Topics: Animals; Aspirin; Brain Chemistry; Brain Edema; Cerebral Arteries; Cerebral Infarction; Drug Evaluation, Preclinical; Fatty Acids, Monounsaturated; Fibrinolytic Agents; Guinea Pigs; Intracranial Embolism and Thrombosis; Lactates; Lactic Acid; Magnetic Resonance Imaging; Magnetic Resonance Spectroscopy; Male; Methacrylates; Photochemistry; Potassium; Pyridines; Rabbits; Rats; Rats, Sprague-Dawley; Rose Bengal; Sodium; Thromboxane A2; Ticlopidine

We established an experimental model of late asthmatic response (LAR) using conscious guinea pigs actively sensitized by antigen aerosol inhalation. In actively sensitized guinea pigs, antigen challenge by aerosol inhalation caused an immediate increase in specific airway resistance (SRaw) (immediate airway response; IAR) followed by a LAR which occurred 4 to 8 hr after antigen challenge. SRaw in the challenged animals was still increased 23 hr after antigen challenge. Examination of bronchoalveolar lavage (BAL) fluid and histology of the lungs revealed increases in eosinophils and neutrophils during LAR. The beta-2 agonist salbutamol inhibited only IAR and not LAR. Dexamethasone inhibited LAR but not IAR. A low dose of theophylline had little effect on both IAR and LAR. A novel thromboxane A2 (TXA2) receptor antagonist, AA-2414, orally administered before antigen challenge dose-dependently inhibited both IAR and LAR, and oral administration of AA-2414 after the IAR inhibited LAR. Also, thromboxane synthetase inhibitors, CV-4151 and OKY-046, reduced both IAR and LAR. Salbutamol significantly reduced the increase in neutrophils in BAL fluid, and dexamethasone significantly reduced the increase in eosinophils and neutrophils in BAL fluid. Theophylline also reduced the increase in eosinophils in BAL fluid. However, AA-2414 did not inhibit the accumulation of these inflammatory cells in BAL fluid or the airway tissues. These results suggest that asthmatic responses in guinea pigs are similar to those in asthmatic subjects and that TXA2 plays an important role in both IAR and LAR but not in inflammatory cell infiltration in this model of allergic asthma.

Topics: Acetylcholine; Airway Resistance; Animals; Antibodies; Asthma; Benzoquinones; Bronchoalveolar Lavage Fluid; Disease Models, Animal; Fatty Acids, Monounsaturated; Guinea Pigs; Heptanoic Acids; Leukocytes; Male; Methacrylates; Ovalbumin; Pyridines; Theophylline; Thromboxane A2

The effects of CV-4151 on post-ischemic brain hypoperfusion and thromboxane (Tx)A2 production in a canine model of total global brain ischemia were studied. Complete cerebral ischemia for 5 min was produced in adult mongrel dogs by temporary ligation of the venae cavae and aorta. In the non-treated group, cerebral blood flow (CBF) increased during the first 20 to 30 min post-ischemia followed by a gradual decline and then stayed below preischemic level; CBF at 2 hr after the reperfusion was significantly reduced to ca 77% of the pre-ischemic level. Water content in the cerebral cortex at 2 hr after the reperfusion in the non-treated group was 78.15 +/- 0.21%, higher than the content in the control group, 76.70 +/- 0.07%. The concentration of TxB2 in the sagittal sinus was significantly increased at 30 min post ischemia. CV-4151 (1.0 mg/kg, i.v.) almost completely inhibited the post-ischemic hypoperfusion, significantly inhibited the increase in water content and almost completely inhibited the production of TxB2 in the post-ischemic period and increased the production of 6-keto PGF1 alpha. OKY-046 (10 mg/kg, i.v.) had no significant effects on both post-ischemic hypoperfusion and increase in water content in the cerebral cortex. We conclude that CV-4151 ameliorates post-ischemic cerebral hypoperfusion and that this improvement is associated with decreased sagittal sinus levels of TxB2.

Topics: Animals; Body Water; Brain Ischemia; Cerebral Cortex; Cerebrovascular Circulation; Disease Models, Animal; Dogs; Fatty Acids, Monounsaturated; Female; Male; Pyridines; Reperfusion Injury; Thromboxane A2; Thromboxane-A Synthase

Topics: Arterial Occlusive Diseases; Aspirin; Chronic Disease; Epoprostenol; Fatty Acids, Monounsaturated; Humans; Methacrylates; Polydeoxyribonucleotides; Pyridines; Thromboxane A2; Thromboxane-A Synthase

To clarify the role of thromboxane (TX) A2 in arterial thrombus formation, we examined the antithrombotic effects of both a TXA2 synthetase inhibitor (CV-4151) and a TXA2 receptor antagonist (AA-2414) on the rabbit common carotid artery thrombosis which was induced by injury of the endothelium by treatment with 0.25% pronase solution. CV-4151 (1,10 mg/kg, p.o.) and AA-2414 (10 mg/kg, p.o.) significantly inhibited thrombus formation. Furthermore, the combined use of CV-4151 and AA-2414 (0.1 mg/kg, p.o. each) significantly inhibited thrombus formation, though these drugs at the same doses had no effect when administered singly. The plasma level of 11-dehydro TXB2 increased significantly during thrombus formation, and CV-4151 (10 mg/kg) markedly inhibited this increase. There was a significant correlation between the in vivo antithrombotic effects of these drugs and their ex vivo inhibitory effects on arachidonic acid-induced platelet aggregation. The antithrombotic effect of CV-4151 also correlated significantly with its ability to inhibit the production of serum TXA2. These results show that TXA2 may play an important role in the thrombus formation in arterial thrombosis.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Arachidonic Acid; Arachidonic Acids; Benzoquinones; Carotid Artery Thrombosis; Disease Models, Animal; Endothelium, Vascular; Fatty Acids, Monounsaturated; Heptanoic Acids; Male; Platelet Aggregation; Pyridines; Quinones; Rabbits; Thromboxane A2; Thromboxane B2; Thromboxane-A Synthase

Thromboxane A2 synthase is a cytochrome P450-type enzyme and its interaction with imidazole or pyridine-based inhibitors could be studied by absolute and difference spectroscopy with the solubilized as well as the purified enzyme. Nitrogenous bases shift the 418-nm Soret absorption by 4-6 nm to the red and among them the best inhibitors of enzyme activity showed a stoichiometric binding to the enzyme. The structural and energetic prerequisites for such high binding affinities were primarily the liganding of the basic nitrogen to the hemin but also the attachment of a hydrophobic carboxylic side chain to the active site at an about 1 nm distance from the nitrogen. In addition, the side chain seemed to be oriented almost parallel to the plane of the heme. If this geometry was changed, a decrease in affinity was observed and if the ligand binding was sterically hindered, a spectral shift to a five-coordinated complex absorbing at 390 nm occurred. This is best explained by the displacement of an endogenous oxygen ligand, presumably water, from the sixth coordination position of the heme. From these results it can be concluded that the inhibitors mimic the binding of prostaglandin H2 (PGH2) with its carboxylic group at the carboxyl side chain and the endoperoxide oxygen atom at C9 as previously reported. The methyl side chain of PGH2 does not seem to play a role in the formation of the enzyme-substrate complex.

Topics: Blood Platelets; Chromatography, Thin Layer; Computers; Cytochrome P-450 Enzyme System; Enzyme Inhibitors; Fatty Acids, Monounsaturated; Fatty Acids, Unsaturated; Heme; Humans; Kinetics; Prostaglandin Endoperoxides, Synthetic; Prostaglandin H2; Prostaglandins H; Pyridines; Solubility; Spectrophotometry; Structure-Activity Relationship; Thromboxane A2; Thromboxane-A Synthase

When CV-4151, a specific thromboxane (TX) A2 synthetase inhibitor, was given orally to 4 week old (4w) spontaneously hypertensive rats (SHR) daily for 3 weeks, the initiation of hypertension was delayed by about one week. The agent increased urinary excretion of water, sodium and creatinine, reduced that of TXA2 (as TXB2), increased that of PGI2 (as 6-keto-PGF1 alpha) and enhanced urinary PGI2/TXA2. In 4w Wistar-Kyoto rats (WKY) and 18w SHR was established hypertension, the agent had little effect on blood pressure and renal function. In isolated, perfused kidneys of 6w SHR, CV-4151 markedly inhibited both arachidonic acid-induced pressor action and production of TXA2. TXA2 synthetase activity in renal cortical microsomes of 5w SHR was approximately 1.5 times higher than that in age-matched WKY. CV-4151 inhibited TXA2 synthetase activity of medullary and cortical microsomes more effectively in 5w SHR than in age-matched WKY. Thus, in young SHR, the TXA2 synthetase inhibitor seemed to improve renal function by altering the balance of renal TXA2 and PGI2 biosynthesis and subsequently caused a delay in the initiation of hypertension. The present findings lend support to the idea that an imbalance in the renal TXA2-PGI2 biosynthesis may be involved in the initiation of hypertension in SHR.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Blood Pressure; Fatty Acids, Monounsaturated; Heart Rate; Hypertension; Kidney; Male; Oxidoreductases; Prostaglandins; Pyridines; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Renin; Thromboxane A2; Thromboxane-A Synthase; Thromboxanes; Vasoconstriction