Effects of BM-573 on Endothelial Dependent Relaxation and Increased Blood Pressure at Early Stages of Atherosclerosis.

Endothelial dysfunction is considered to be an early event in atherosclerosis and plays a pivotal role in the development, progression and clinical complications of atherosclerosis. Previous studies have shown the beneficial effects of combined inhibition of thromboxane synthase and antagonism of thromboxane receptors by BM-573 on atherosclerosis; however our knowledge about the beneficial effects of BM-573 on endothelial function and increased blood pressure related to early stage of atherosclerosis is limited. In the present study, we investigated the effects of short-term (3 µM, 1 hour) and chronic (10 mg/L, 8 weeks) treatments with BM-573 on vasodilatory function, nitric oxide (NO) bioavailability, oxidative stress and systolic blood pressure in 15 weeks old apolipoprotein E-deficient (ApoE-KO) mice. ApoE-KO mice showed a reduced endothelium-derived relaxation. In addition, NO bioavailability was reduced and oxidative stress and blood pressure were increased in ApoE-KO mice versus wild-type mice. BM-573 treatments were able to improve the relaxation profile in ApoE-KO mice. Short-term effects of BM-573 were mainly mediated by an increased phosphorylation of both eNOS and Akt, whereas BM-573 in vivo treatment also reduced oxidative stress and restored NO bioavailability. In addition, chronic administration of BM-573 reduced systolic blood pressure in ApoE-KO mice. In conclusion, pharmacological modulation of TxA2 biosynthesis and biological activities by dual TP antagonism/TxAS inhibition with BM-573, already known to prevent plaque formation, has the potential to correct vasodilatory dysfunction at the early stages of atherosclerosis.

Antiplatelet Effects of Flavonoids Mediated by Inhibition of Arachidonic Acid Based Pathway.

Flavonoids, important components of human diet, have been claimed to possess a significant antiplatelet potential, in particular due to their effects on the arachidonic acid cascade. Due to variable and incomplete results, this study was aimed at delivering a detailed analysis of the effects of 29 structurally relevant, mainly natural flavonoids on three consecutive steps of the arachidonic acid cascade.Only the isoflavonoids genistein and daidzein were shown to possess a marked cyclooxygenase-1 inhibitory activity, which was higher than that of acetylsalicylic acid using the isolated ovine enzyme, and physiologically relevant, although lower than acetylsalicylic acid in human platelets. None of the tested flavonoids possesses an effect on thromboxane synthase in a clinically achievable concentration. Contrarily, many flavonoids, particularly those possessing an isolated 7-hydroxyl group and/or a 4'-hydroxyl group, acted as antagonists on thromboxane receptors. Interestingly, the substitution of the free 7-hydroxyl group by glucose might not abolish the activity.In conclusion, the consumption of few flavonoids in a diet, particularly of the isoflavonoids genistein and daidzein, may positively influence platelet aggregation.

Thromboxane inhibitors attenuate inflammatory and fibrotic changes in rat liver despite continued ethanol administrations.

BACKGROUND: Thromboxane levels are increased in rats fed ethanol (EtOH), whereas thromboxane inhibitors reduce alcoholic liver injury. The aim of this study is to determine whether thromboxane inhibitors could attenuate the already established alcoholic liver injury. METHODS: Rats were fed EtOH and liquid diet for 6 weeks by intragastric infusion to induce liver injury after which EtOH was continued for 2 more weeks, and the rats were treated with either a thromboxane synthase inhibitor (TXSI) or a thromboxane receptor antagonist (TXRA). Liver pathology, lipid peroxidation, nuclear factor-kappa-B (NF-κB) activity, tumor necrosis factor-α (TNF-α), cyclooxygenase-2 (COX-2), and transforming growth factor-beta1 (TGF-ß(1) ) were evaluated. RESULTS: Administration of fish oil and EtOH caused fatty liver, necrosis, inflammation and fibrosis accompanied by increased in lipid peroxidation, NF-κB activity, and expression of TNF-α, COX-2, and TGF-ß(1) . Treatment with the thromboxane inhibitors ameliorated a certain level of the pathological and biochemical abnormalities. In particular, TXSI in addition to reducing necrosis, inflammation and fibrosis also decrease the severity of fatty liver. CONCLUSIONS: Thromboxane inhibitors attenuated the alcoholic liver injury, inflammation and fibrotic changes despite continued EtOH administration. Inhibition of the production of thromboxane by thromboxane inhibitor and receptor antagonists may be a useful treatment strategy in clinical alcoholic liver disease.

Interaction of prostanoid EP3 and TP receptors in guinea-pig isolated aorta: contractile self-synergism of 11-deoxy-16,16-dimethyl PGE2.

BACKGROUND AND PURPOSE: Surprisingly high contractile activity was reported for 11-deoxy-16,16-dimethyl prostaglandin E2 (DX-DM PGE2) on pig cerebral artery when used as a selective EP3 receptor agonist. This study investigated the selectivity profile of DX-DM PGE2, focusing on the interaction between its EP3 and TP (thromboxane A2-like) agonist activities. EXPERIMENTAL APPROACH: Contraction of guinea-pig trachea (EP1 system) and aorta (EP3 and TP systems) was measured in conventional organ baths. KEY RESULTS: Strong contraction of guinea-pig aorta to sulprostone and 17-phenyl PGE2 (EP3 agonists) was only seen under priming with a second contractile agent such as phenylephrine, histamine or U-46619 (TP agonist). In contrast, DX-DM PGE2 induced strong contraction, which on the basis of treatment with (DG)-3ap (EP3 antagonist) and/or BMS-180291 (TP antagonist) was attributed to self-synergism arising from co-activation of EP3 and TP receptors. EP3/TP self-synergism also accounted for contraction induced by PGF(2α) and its analogues (+)-cloprostenol and latanoprost-FA. DX-DM PGE2 also showed significant EP1 agonism on guinea-pig trachea as defined by the EP1 antagonists SC-51322, (ONO)-5-methyl-1 and AH-6809, although AH-6809 exhibited poor specificity at concentrations ≥3 µM. CONCLUSIONS AND IMPLICATIONS: EP3/TP self-synergism, as seen with PGE/PGF analogues in this study, may confound EP3 agonist potency comparisons and the characterization of prostanoid receptor systems. The competitive profile of a TP antagonist may be distorted by variation in the silent/overt contraction profile of the EP3 system in different studies. The relevance of self-synergism to in vivo actions of natural prostanoid receptor agonists is discussed.

Additive anti-atherogenic effect of thromboxane receptor antagonism with 12/15lipoxygenase gene disruption in apolipoprotein E-deficient mice.

Previous studies in mouse models showed that 12/15lipoxygenase (12/15LO) gene disruption diminishes atherosclerosis. Pharmacologic suppression of thromboxane (Tx) A(2) biosynthesis or blockade of its receptor also reduces the development of the disease in the same models. We tested the hypothesis that simultaneous genetic absence of 12/15LO with TxA(2) receptor blockade might result in an additive anti-atherogenic effect. Apolipoprotein E (apoE)-deficient mice and apoE-deficient mice lacking 12/15LO were maintained on normal chow diet, or chow supplemented with BM-573, a selective TxA(2) receptor antagonist, for 12 weeks. Urinary TxA(2) and prostacyclin metabolites, isoprostaneF(2*)-III and atherosclerotic aortic lesions were assessed. 12/15LO gene disruption resulted in significantly reduced atherosclerotic lesion areas and decreased urinary isoprostaneF(2*)-III in apoE-deficient mice. TxA(2) receptor antagonism alone also afforded a significant reduction in atherosclerosis in apoE-deficient mice. However, thromboxane receptor blockade resulted in an additive and more potent anti-inflammatory and anti-atherogenic effect when administered to apoE-deficient mice lacking 12/15LO. These results suggest that the 12/15LO- and TxA(2) receptor-mediated pro-atherogenic effects are two distinct pathways and represent two separate therapeutic targets for a better anti-atherogenic strategy.

Preclinical evaluation of S18886 in an experimental model of coronary arterial thrombosis.

The specific thromboxane receptor antagonist, S18886, was evaluated for prevention of coronary arterial thrombosis and myocardial ischemia-reperfusion in anesthetized canines. For the primary thrombosis study in left circumflex (LCX) coronary artery, 26 dogs were randomized to receive either vehicle (n = 7) or intravenous S18886 (0.3 mg/kg, n = 6; 1.0 mg/kg, n = 6; and 3.0 mg/kg, n = 7). The respective times to occlusion after S18886 were as follows: 56.8 +/- 9.3, 83.5 +/- 14.9, and 92.4 +/- 15.7 minutes compared to 43.3 +/- 8.2 minutes after vehicle. S18886 caused a minimal increase in tongue bleeding time and a significant decrease in ex vivo platelet aggregation to arachidonic acid or U46619. Another 37 dogs were randomized to receive placebo (n = 12), clopidogrel 1.0 mg/kg p.o. QDX3 (n = 9), clopidogrel + S18886 0.3 (n = 9) or 1.0 (n = 7) mg/kg intravenous. Clopidogrel produced a 50% reduction in adenosine diphosphate-induced platelet aggregation and a slight increase in the time to occlusion. However, clopidogrel + S18886 1.0 mg/kg prevented occlusive thrombus formation in most of the coronary vessels over 6 hours. S18886 did not alter myocardial infarct size in the ischemia-reperfusion model. In conclusion, S18886 alone caused a dose-dependent prolongation in the time to primary occlusive coronary artery thrombosis, whereas S18886 + clopidogrel displayed effective in preventing occlusive thrombus formation with only a moderate increase of tongue-bleeding time.

Evaluation of BM-573, a novel TXA2 synthase inhibitor and receptor antagonist, in a porcine model of myocardial ischemia-reperfusion.

AIMS: To investigate whether BM-573 (N-tert-butyl-N'-[2-(4'-methylphenylamino)-5-nitro-benzenesulfonyl]urea), an original combined thromboxane A2 synthase inhibitor and receptor antagonist, prevents reperfusion injury in acutely ischemic pigs. METHODS: Twelve animals were randomly divided in two groups: a control group (n = 6) intravenously infused with vehicle, and a BM-573-treated group (n = 6) infused with BM-573 (10 mg kg(-1) h(-1)). In both groups, the left anterior descending (LAD) coronary artery was occluded for 60 min and reperfused for 240 min. Either vehicle or BM-573 was infused 30 min before LAD occlusion and throughout the experiment. Platelet aggregation induced by arachidonic acid ex vivo measured was prevented by BM-573. RESULTS: In both groups, LAD occlusion decreased cardiac output, ejection fraction, slope of stroke work--end-diastolic volume relationship, and induced end-systolic pressure-volume relationship (ESPVR) rightward shift, while left ventricular afterload increased. Ventriculo-arterial coupling and mechanical efficiency decreased. In both groups, reperfusion further decreased cardiac output and ejection fraction, while ESPVR displayed a further rightward shift. Ventriculo-arterial coupling and mechanical efficiency remained impaired. Area at risk, evidenced with Evans blue, was 33.2+/-3.4% of the LV mass (LVM) in both groups, and mean infarct size, revealed by triphenyltetrazolium chloride (TTC), was 27.3+/-2.6% of the LVM in the BM-573-treated group (NS). Histological examination and immunohistochemical identification of desmin revealed necrosis in the anteroseptal region similar in both groups, while myocardial ATP dosages and electron microscopy also showed that BM-573 had no cardioprotective effect. CONCLUSIONS: These data suggest that BM-573 failed to prevent reperfusion injury in acutely ischemic pigs.

S18886, a selective TP receptor antagonist, inhibits development of atherosclerosis in rabbits.

OBJECTIVE: To investigate the effect of S18886, a novel TP (thromboxane A2 and prostaglandin endoperoxide) receptor antagonist, on the development of aortic fatty streaks and advanced lesions in a rabbit model of atherosclerosis and restenosis. METHODS AND RESULTS: The right iliac artery of 96 rabbits (8 groups, n=12/group) was balloon injured, then the animals were fed a cholesterol-enriched diet for 6 weeks. In Groups 1-4, concomitant oral administration of S18886 at 5 mg/kg/day over the 6-week-period reduced the intima to media ratio of lesions in the uninjured aorta and injured iliac artery, the accumulation of macrophages and the expression of ICAM-1 compared with 1 mg/kg/day S18886, 30 mg/kg/day aspirin and placebo, with no effect on body weight or plasma cholesterol levels. In Groups 5-8, 2 weeks of treatment with 5 mg/kg/day S18886 reduced the intima to media ratio of restenosing lesions when pre-formed iliac artery lesions underwent a second balloon injury at week 6. The smaller lesions resulting from S18886 treatment correlated with a significant decrease in the neointimal area occupied by macrophages, as well as in ICAM-1 expression, with no effect on the smooth muscle component. Aspirin treatment had no significant effect on the neointimal smooth muscle component, but partially inhibited macrophage infiltration, without inhibiting ICAM-1 expression. CONCLUSION: Inhibition of the TP receptor using S18886 causes a significant decrease in the recruitment of monocyte/macrophages within fatty streaks in the uninjured aorta and within primary and restenosing atherosclerotic lesions in the iliac artery of rabbits. Since TP receptor agonists, such as thromboxane A2, prostanoid endoperoxides and isoprostanes participate in vessel wall inflammation and are localized and increased in atherosclerotic plaques, treatment with S18886 may enhance atherosclerotic lesion stability by attenuating inflammatory processes that ultimately lead to plaque rupture.

Antithrombotic properties of the thromboxane A2/prostaglandin H2 receptor antagonist S18886 on prevention of platelet-dependent cyclic flow reductions in dogs.

A potent thromboxane A2/PGH2 (TP)-receptor antagonist, S18886, was evaluated for its antithrombotic property in a dog model of acute periodic platelet-mediated thrombosis in stenosed coronary arteries with endothelial damage. After thrombosis had been obtained in 11 dogs, S18886 (300 microg/kg bolus) was administered IV. Heart rate, systemic blood pressure, and coronary blood flow were continuously recorded. Ex vivo whole blood platelet aggregation (PA), blood pH, hematocrit, platelet count, PO2, PCO2, and bleeding times were measured before and 30 minutes after administration of S18886. S18886 completely inhibited thrombosis in all dogs in approximately 5-10 minutes. No change in heart rate, blood pressure, pH, PO2, PCO2, platelet count, or bleeding time and a slight but significant elevation in hematocrit occurred. Infusion of epinephrine IV after complete inhibition of thrombosis by S18886 partially restored thrombosis in 3 of the 11 dogs. PA induced by collagen (4 microg/mL), collagen (0.25 microg/mL) plus epinephrine (1 microg/mL), collagen (1 microg/mL) plus epinephrine (1 microg/mL), ADP (40 microM) plus epinephrine (1 microg/mL), and phorbol 12-myristate 13-acetate (0.5 nM) were attenuated by 90 +/- 8% (P < 0.005), 98 +/- 2% (P < 0.05), 78 +/- 6% (P < 0.005), 70 +/- 10% (P < 0.005), and 28 +/- 8% (P < 0.05), respectively. In conclusion, S18886 is a potent platelet inhibitor that attenuates in vivo platelet-dependent thrombosis in the experimental dog model and reduces ex vivo platelet aggregation.

Thromboxane antagonism and cough in chronic bronchitis.

BACKGROUND: The increased eicosanoid synthesis has been suggested as the underlying mechanism of chronic productive cough in patients with chronic bronchitis. METHOD: The effects of the orally active thromboxane A2 (TxA2) receptor antagonist seratrodast and the cysteinyl leukotrienes (cLTs) receptor antagonist pranlukast on cough response to inhaled capsaicin were examined in sixteen patients with stable chronic bronchitis. Capsaicin cough threshold, defined as the lowest concentration of capsaicin eliciting five or more coughs, was measured as an index of airway cough sensitivity. RESULTS: The cough threshold was significantly increased compared with placebo after four-week treatment with seratrodast, but not after treatment with pranlukast. CONCLUSIONS: TxA2, but not cLTs, may be a possible modulator augmenting airway cough sensitivity in chronic bronchitis. Thromboxane antagonism may be considered to be one of the therapeutic options for the treatment of chronic productive cough.

Therapeutic potential of thromboxane inhibitors in asthma.

This paper reviews the role of thromboxane A(2) (TXA(2)) in the pathogenesis of pulmonary allergies, particularly asthma. The potential of TXA(2) modifiers in the prevention and/or treatment of pulmonary allergies is also discussed. Bronchial asthma is characterised by reversible airway obstruction, bronchial hyperresponsiveness and inflammation. Several studies have elucidated the role of arachidonic acid metabolites (leukotrienes, prostaglandins and TXA(2)) in the pathogenesis of asthma. Among those mediators, TXA(2) has attracted attention due to its strong physiological activity. Indeed, TXA(2) demonstrates not only potent bronchoconstrictive activity but is also believed to be involved both in late asthmatic responses and in bronchial hyperresponsiveness, a typical feature of this disease. Several thromboxane receptor antagonists (TXRAs) and thromboxane synthase inhibitors (TXSIs) have been studied with the aim of reducing or preventing asthma. As double-blind, placebo-controlled clinical trials have proven the efficiency of some TXA(2) modifiers in treating asthma, the TP receptor antagonist seratrodast (AA-2414) and the thromboxane synthase inhibitor ozagrel hydrochloride (OKY-046) are now available as anti-asthmatic agents in Japan. Moreover, seratrodast and ramatroban (BAY-U-3405), another thromboxane receptor antagonist, are currently under Phase III clinical evaluation in the US for the treatment of asthma.

Antagonistic effects of losartan on thromboxane A2-receptors in human isolated gastroepiploic artery and saphenous vein.

In addition to its AT1-receptor antagonist activity, losartan has been shown to antagonize thromboxane A2 (TXA2)-induced contraction of animal vessels. We investigated for the first time in human isolated gastroepiploic artery (GEA) and saphenous vein (SV) the TXA2/PGH2-receptor antagonist activity of losartan in the presence of indomethacin (1 microM) and N(omega)-nitro-L-arginine (100 microg). Losartan at concentrations of > or =1 microM on GEA and from 10 microM on SV significantly shifted U46619-induced contractions to the right. In addition, 100 microM losartan decreased by 34% the amplitude of the contraction to U46619 on both GEA and SV. The potency of losartan for the TXA2 receptor was 50- and 80-fold lower than that for the AT1 receptor on human GEA and SV, respectively. This inhibitory effect of losartan appeared selective for angiotensin II and TXA2-induced contractions because 100 microM losartan did not modify either endothelin-1- or KCl-induced contraction in human SV, although a reduction of norepinephrine- and 5-hydroxytryptamine-induced contraction was observed in human GEA and SV, respectively. In conclusion, losartan is an antagonist of TXA2 receptor on human GEA and SV. However, this antagonist activity occurred for a relative high dose of losartan, suggesting that it contributes at a low level, if any, to its antihypertensive effect.

Pharmacological antagonism of Anchietia salutaris extracts on the contraction induced by prostaglandin D2 and U46619 in guinea-pig lung parenchymal strips.

Anchietia salutaris tea is traditionally used in Brazil to treat allergies, suggesting it contains compounds with antagonistic activity on the allergic mediators. We have evaluated extracts and semi-purified fractions of Anchietia salutaris as a source of compounds having this type of antagonism on the contraction induced in guinea-pig lung parenchymal strips and on platelet aggregation and shape change. After 10 min pre-incubation dichloromethane extracts containing 30 or 100 microg mL(-1) inhibited the contraction induced by prostaglandin D2 (PGD2) in guinea-pig lung parenchymal strips with dose ratios (DR) of 0.76+/-0.14 and 0.93+/-0.19, respectively; the amount of inhibition depended both on the concentration and on the time of pre-incubation (DR after 30 min pre-incubation was 1.21+/-0.51). The dichloromethane extract and its semi-purified fractions also inhibited the contractions induced by U46619, a more potent, stable, synthetic agonist of thromboxane A2 (TxA2) prostanoid (TP) receptors, the receptors acted upon by PGD2 to produce lung contractions. The dichloromethane extract did not inhibit the lung parenchymal contractions induced by histamine, leukotriene D4 (LTD4) or platelet-activating factor (PAF). Platelet aggregation induced by U46619, adenosine 5'-diphosphate (ADP) or PAF was not inhibited by the dichloromethane extract. Indeed, the extract potentiated platelet aggregation induced by low concentrations of these agonists and also potentiated the shape change induced by U46619. These results imply that the dichloromethane extract of Anchietia salutaris and its semi-purified fractions contain an active principle that competitively inhibits TxA2 TP receptors, the stimulation of which causes lung parenchymal contraction. The inhibition seems to be selective for this receptor subtype, because the extract fails to inhibit platelet aggregation or shape change. This provides additional support of earlier reports suggesting the occurrence of TP receptor subtypes.

Relationship between basal NO release and cyclooxygenase products in the normal rat kidney.

We investigated the physiological regulation of renal function by nitric oxide (NO) and its interactions with the endothelial cyclooxygenase products in the conscious, chronically catheterized rat. A subpressor dose of NO inhibitor nitro-L-arginine methyl ester (L-NAME) produced renal vasoconstriction that was unaffected by cyclooxygenase inhibition with indomethacin (Indo). Acute, high-dose L-NAME produced a pressor response of approximately 40 mmHg and marked renal vasoconstriction. Indo selectively amplified the renal vasoconstriction, whereas inhibition of the thromboxane-endoperoxide receptor had no effect. Chronic NO inhibition for 5 wk led to sustained hypertension and renal vasoconstriction; the latter was amplified by acute Indo. These data suggest that in the normal, conscious rat the kidney is under important NO-dependent tone. There is no obvious interaction between NO and the cyclooxygenase products in control of basal renal function. When systemic NO inhibition is produced with either acute or chronic high-dose L-NAME, the kidney is severely vasoconstricted. The renal vasoconstriction is not ameliorated by thromboxane-endoperoxide antagonism but is exacerbated by cyclooxygenase blockade, suggesting that vasodilator cyclooxygenase products compensate for the renal hypoperfusion because of severe NO deficiency.

Differences between cytokine effects in the microcirculation of the rat.

We studied by in vivo microscopy in rat cremaster muscle the acute and delayed effects of short exposure to tumor necrosis factor (TNF), interleukin (IL)-1 beta, and IL-6 on basal tone and vascular reactivity of second- to fourth-order arterioles (A2-A4). A 20-min exposure to recombinant human (rh) TNF (0.1-10 ng/ml) induced a significant arteriolar vasodilation, but no significant changes in basal tone were found after exposure to the same doses of IL-1 beta. In contrast, the same exposure to IL-6 (0.1-10 ng/ml) induced a significant dose-dependent vasoconstriction (i.e., 8, 15, and 21% at 10 ng/ml in A2-A4 arterioles, respectively). This vasoconstriction was inhibited by the thromboxane A2 receptor antagonist SQ-29548. We did not find any significant effect of rhTNF or IL-6 on vascular reactivity to norepinephrine immediately after exposure to these two cytokines or 100 min after the end of the exposure. Contrastingly, a large dose-dependent decrease in reactivity to norepinephrine was found immediately after exposure to IL-1 beta and still persisted 100 min after the end of the exposure. Such a decrease was not found for the vasoconstriction in response to KCl. We conclude that, at the microvascular level, large differences exist between the three cytokines generally considered to mediate the harmful cardiovascular effects in sepsis. 1) TNF but not IL-1 beta is responsible for a vasodilatory effect, whereas the effect of IL-6 is a thromboxane A2-mediated vasoconstriction. 2) Short exposure to IL-1 beta but not to rhTNF or IL-6 diminishes the response of the arterioles to norepinephrine but not to KCl.

Effect of thromboxane A2-receptor antagonist on bradykinin-induced bronchoconstriction in asthma.

The role of the thromboxane A2 (TxA2) receptor in bradykinin-induced bronchial responses was investigated in this study by using a selective and potent TxA2-receptor antagonist BAY u 3405. Eleven asthmatic subjects were randomized to receive 50 mg of BAY u 3405 or matched placebo in a crossover and double-blind fashion. Ninety minutes after dosing, serum was taken for drug assay, and subjects underwent provocation with bradykinin or prostaglandin D2 (PGD2) to determine bronchial responsiveness [provocative concentration of agonist required to produce a 20% fall in forced expiratory volume in 1 s from the postdiluent baseline (PC20)]. Pretreatment with BAY u 3405 caused a twofold doubling-dilution reduction in bronchial reactivity to PGD2; the geometric mean PC20 values were 0.132 (0.015-0.871) and 0.034 (0.008-0.095) mg/ml, respectively, for active and placebo days (P = 0.001). There was, however, no significant difference in PC20 values for bradykinin between active and placebo treatment days. We have demonstrated that BAY u 3405 caused a significant inhibition of bronchconstriction induced by inhaled PGD2 but had no influence on bronchial responsiveness to inhaled bradykinin. This study suggests therefore that TxA2 receptors do not play a role in bradykinin-induced bronchoconstriction in asthma.

BAY u3405, a thromboxane A2 antagonist, reduces bronchial hyperresponsiveness in asthmatics.

OBJECTIVE: Thromboxane A2 (TXA2) is reported to induce bronchial hyperresponsiveness along with the well-documented bronchoconstrictor action on smooth muscles. We examined the effect of the TXA2 antagonist, BAY u3405, on bronchial hyperresponsiveness to methacholine (MCh) in asthmatics. PATIENTS: Twelve adult asthmatics were studied in a randomized, double-blind, placebo-controlled, crossover fashion. DESIGN: Following a 2-week run-in period, the subjects were administered 75 mg of BAY u3405 or placebo orally, twice a day for 2 weeks each in a crossover design, interposing a 2-week washout period. Bronchial hyperresponsiveness was measured by the astograph method. Briefly, the respiratory resistance (Rrs) was measured by the forced oscillation method during continuous inhalation of MCh in stepwise incremental concentrations, until Rrs reached twice the baseline value. Bronchial hyperresponsiveness was evaluated as the minimum cumulative dose (Dmin) of MCh that induced an increase in Rrs. Dmin was calculated so that 1 U of Dmin equals to 1 min of inhalation of aerosol solution at 1.0 mg/mL during quiet breathing. RESULTS: Three subjects were withdrawn from the evaluation because they had asthmatic attacks or wheezing during the study. The Dmin value of 0.533 U (GSEM 1.675) after the BAY u3405 treatment was significantly greater than that of 0.135 U (GSEM 1.969) after the placebo treatment (p = 0.0139). There were no safety concerns in either treatment group. CONCLUSION: We conclude that BAY u3405 may be a useful drug for attenuating bronchial hyperresponsiveness in bronchial asthma.

Thromboxane-blocked swine as an experimental model of severe intravascular inflammation and septic shock.

The cardiopulmonary response elicited by intravenous bacteria or endotoxin is well characterized in swine and has two major components. The first represents the acute pulmonary and broncho-constrictive phase (0-2 h) and the second phase (3-8 h) represents increased microvascular permeability, hypotension, and enhanced leukocyte-endothelial adhesion. The pulmonary vasoconstriction and bronchoconstriction of phase 1 results in acute pulmonary hypertension and airway dysfunction, which may result in rapid mortality. Because this acute pulmonary response may not mimic the development of human septic shock, we sought to block this early phase and examine the role of tumor necrosis factor in the latter septic phase (3-8 h). Employing a thromboxane A2 (TXA2) receptor antagonist (BAY U 3405) in the presence of LD100 Escherichia coli challenge, we blocked the acute pulmonary hypertensive phase and prevented early mortality, however, TXA2 blockade did not affect the latter development of septic shock and death. This latter lethal phase, characterized by prolonged leukopenia, was blocked in a dose-dependent manner by tumor necrosis factor monoclonal antibody. We conclude that the TXA2-blocked E. coli-challenged swine may provide a novel animal model in which to investigate the pathophysiology of acute septic shock.

Enhancement of thrombolytic efficacy of tissue-type plasminogen activator by adjuvants in the guinea pig thrombosis model.

Reocclusion following thrombolysis is a major limitation of thrombolytic therapy with recombinant tissue-type plasminogen activator (rt-PA). We investigated the effects of vapiprost ((1R-(1 alpha(Z),2 beta,3 beta,5 alpha))-7-(5-((1,1'-biphenyl)-4-yl-methoxy)- 3-hydroxy-2-(1-piperidinyl)cyclopentyl)-4-heptenoic acid, a thromboxane A2 receptor antagonist); argatroban ((2R,4R)-4-methyl-1-[N2-(3-methyl-1,2,3,4-tetrahydro-8-quinolinyl)sulfon yl] - L-arginyl)]-2-piperidine-carboxylic acid, a specific thrombin inhibitor) and MK-886 (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2,2- dimethylpropanoic acid, a specific leukotriene biosynthesis inhibitor) on the thrombolytic efficacy of rt-PA. The guinea pig femoral artery was thrombotically occluded by photochemical reaction between rose bengal and green light. Thirty min after the occlusion, rt-PA was administered and the time (T1) for reopening of the vessel and the frequency of reocclusion (Fro) 24 h after thrombolysis were monitored. With rt-PA alone, T1 was 28 +/- 7 min (n = 10) and Fro was 70%. T1 was reduced to 9 and 20 min by a combination of rt-PA with vapiprost and argatroban respectively. Fro was reduced by all three adjuvants. Histological observations revealed extensive adherence of polymorphonuclear leucocytes to the damaged endothelium at the site of thrombolysis. It is concluded that thromboxane A2, thrombin and leucocytes are involved in reocclusion after thrombolysis.

Protective effects of BAY U 3405, a thromboxane A2 receptor antagonist, in endotoxin shock.

The present study was designed to investigate the effects of BAY U 3405, a new thromboxane A2 (TxA2) receptor antagonist, in endotoxin shock. Endotoxin shock (ES) was induced in male rats by an i.v. injection of Salmonella enteritidis lipopolysaccharide (LPS; 20 mg kg-1). LPS administration caused animal death (survival = 0%, 48 h after endotoxin challenge), systemic hypotension, depressed phagocytosis and increased blood levels of TNF-alpha, TxB2 and 6-keto-PGF1 alpha, reduced white blood cell (WBC) count (ES = 5.9 +/- 1 x 10(3) mm-3; CTRL = 13.4 +/- 5 x 10(3) mm-3) and enhanced myeloperoxidase (MPO) activity, studied as a quantitative means for assessing leukocyte accumulation, in the ileum (ES = 0.24 +/- 0.7 U g-1 fresh tissue; CTRL = 0.13 +/- 0.04 U g-1 fresh tissue), in the heart (ES = 0.41 +/- 0.1 U g-1 fresh tissue; CTRL = 0.16 +/- 0.08 U g-1 fresh tissue) and in the lung (ES = 0.68 +/- 0.11 U g-1 fresh tissue; CTRL = 0.19 +/- 0.05 U g-1 fresh tissue). Furthermore, endotoxin administration produced characteristic damage of the gastric mucosa consisting of haemmorrhagic infiltrates. BAY U 3405 (30 mg kg-1 i.v., 30 min before endotoxin challenge) increased survival rate (45% survival rate 48 h after endotoxin challenge), reduced hypotension, decreased TNF-alpha levels in serum, enhanced phagocytic activity (ES = 25.6 +/- 1.9%, BAY U 3405 = 45.9 +/- 0.4%, P < 0.001) and lowered MPO activity in the ileum (0.14 +/- 0.05 U g-1 fresh tissue), in the heart (0.18 +/- 0.08 U g-1 fresh tissue) and in the lung (0.44 +/- 0.09 U g-1 fresh tissue). Finally, the gastric alterations were significantly reduced in rats pretreated with BAY U 3405. These data suggest that this thromboxane receptor antagonist might be a useful drug in shock conditions.