Thromboxane Synthetase Inhibitor Research Articles

Age- and hypertension-induced changes in abnormal contractions in rat aorta.

The current investigation explored the potential age-dependant modulation of abnormal spontaneous constrictions (thromboxane-like) in the spontaneously hypertensive rat (SHR) aorta, observed only after the inhibition of endogenous production of nitric oxide (NO). Aortic rings from SHR and Wistar-Kyoto (WKY) control rats of varying ages (4, 8, 12, and 18 months) were mounted in organ baths, and changes in tension were monitored. Inhibition of NO with Nomega-nitro-L-arginine (NOLA) unmasked a slow contraction, which appeared to be age dependent (p < 0.05). This contraction was found in SHRs of all age groups and in older WKY rats. Denuding the endothelium in young SHRs did not influence the constriction, confirming a nonendothelial cell origin, while in the older groups this led to a 30-40% reduction in contraction. Comparable attenuation of the constrictor response was observed after incubation of endothelium intact rings with superoxide dismutase (100 U/ml) or 3-amino-1,2,4-triazole. Of the residual activity that was unaffected by free radical scavengers or de-endothelialization, 60-70% was sensitive to cyclooxygenase inhibition by indomethacin and/or ibuprofen. The thromboxane (TxA ) receptor antagonist SQ29548 induced a complete reversal of the abnormal constriction. In contrast, thromboxane synthetase inhibition had no effect, ruling out any involvement of TxA in mediating this abnormality. Collectively, these observations support the view that as compared with the normotensive setting, contraction induced by NO inhibition in the SHR develops prematurely and deteriorates more rapidly during the aging process. In aged rats, prostaglandin endoperoxide intermediates PGG /H and endothelium-derived free radicals rather than TxA per se appear to contribute to the NOLA-dependent TxA -like vasoconstriction.

Effects of the selective inhibition of platelet thromboxane synthesis on the platelet-subendothelium interaction.

1. Drugs that inhibit TxA(2) synthesis are used to reduce platelet aggregation. The aim of this study was to compare the effects of a cyclo-oxygenase (COX) inhibitor (acetylsalicylic acid, ASA), a thromboxane synthetase (TxS) inhibitor (dazoxiben) and a dual TxS inhibitor and TxA(2) receptor blocker (DT-TX 30) on platelet aggregation and the platelet-subendothelium interaction in flow conditions. 2. The techniques used in this in vitro study were platelet aggregometry in whole blood, and measurement of platelet thromboxane B(2) and prostaglandin E(2) production and leucocyte production of 6-keto-PGF(1alpha). The platelet-subendothelium interaction was evaluated in rabbit aorta subendothelium preparations exposed to flowing blood at a shear stress of 800 s(-1). Morphometric methods were used to calculate the percentage of subendothelium occupied by platelets. 3. The 50% inhibitory concentration (IC(50)) of DT-TX 30 in whole blood was in the range of 10(-7) micro M (induced with collagen or arachidonic acid) to 10(-5) micro M (induced with thrombin) or 10(-4) (induced with ADP). IC(50) values under all experimental conditions were lower with DT-TX 30 than with ASA. For thromboxane B(2) the IC(50) were: ASA 0.84+/-0.05 micro M, dazoxiben 765+/-54 micro M, DT-TX 30 8.54+/-0.60 micro M. Prostaglandin E(2) was inhibited only by ASA (IC(50) 1.21+/-0.08 micro M). Leucocyte 6-keto-PGF(1alpha) was inhibited by ASA (IC(50) 6.58+/-0.76 micro M) and increased by dazoxiben and DT-TX 30. The greatest reduction in percentage subendothelial surface occupied by platelets after blood perfusion was seen after treatment with DT-TX 30 in the range of concentrations that inhibited collagen-induced platelet aggregation (control group: 31.20+/-3.8%, DT-TX 30 at 0.1 micro M: 10.71+/-0.55%, at 1.0 micro M: 6.53+/-0.44%, at 5.0 micro M; 1.48+/-0.07%). All three drugs reduced thrombus formation, although ASA (unlike dazoxiben or DT-TX 30) increased the percentage surface occupied by adhesions. 4. In conclusion, the effect of specific blockage of TxS together with blockage of membrane receptors for TxA(2) can surpass the effect of ASA in inhibiting the platelet-subendothelium interaction in flow conditions.

Modulation of Prostacyclin and Thromboxane Secretion by Cytotrophoblasts from Normal and Pre-eclamptic Human Pregnancies

We and others have previously observed an imbalance in cytotrophoblast secretion of the vasoactive prostanoids prostacyclin and thromboxane A2 in pre-eclampsia. To examine the effects of potential modulators of this imbalance, cytotrophoblasts isolated from normal and pre-eclamptic pregnancies were incubated in the presence of lipopolysaccharide, the calcium ionophore A23187, tumour necrosis factor α, or interleukin 1β, with or without the cyclo-oxygenase inhibitor, indomethacin. Further incubations included the drugs tranylcypromine, a prostacyclin synthetase inhibitor (0.1, 10μm ), or the thromboxane synthetase inhibitor, pirmagrel (0.001, 1μm ). Results showed that cytotrophoblasts from pre-eclamptic pregnancies had increased thromboxane production and significant stimulation of prostacyclin production by lipopolysaccharide and calcium ionophore. Lipopolysaccharide stimulated thromboxane production in normal cytotrophoblasts, while indomethacin almost completely inhibited production of both prostanoids. Tranylcypromine mildly inhibited prostacyclin production in normal cytotrophoblasts only, whereas pirmagrel strongly inhibited thromboxane production in a dose-related manner, with reciprocal increase in prostacyclin production occurring in cytotrophoblasts from pre-eclamptic pregnancies. This study confirmed that cytotrophoblasts from pre-eclamptic women had increased thromboxane production and showed that pirmagrel, at the relatively low dose of 0.001μm , was able to normalize the imbalance of thromboxane and prostacylin production and may therefore warrant further investigation as a treatment for pre-eclampsia.

Effects of the thromboxane synthetase inhibitor and receptor antagonist terbogrel in patients with primary pulmonary hypertension

Background Circulating mediators, including thromboxane A2, the vasoconstrictor, platelet aggregant, and smooth muscle mitogen, may contribute to the progression of vascular narrowing in primary pulmonary hypertension (PPH). Methods To further understand the contribution of thromboxane and to provide novel therapy for PPH, we administered the potent orally active thromboxane synthetase inhibitor and thromboxane receptor antagonist terbogrel for 12 weeks to patients with New York Heart Association functional classification II and III PPH. The study had a multicenter randomized placebo-controlled design. The primary endpoint was a change in the distance walked during 6 minutes. The pharmacologic effects of terbogrel on thromboxane and prostacyclin metabolism also were studied. Results Although the planned enrollment was 135 patients, the study was halted after only 71 patients had been randomized because of the unforeseen side effect of leg pain, which occurred almost exclusively in patients with terbogrel treatment. Only 52 patients completed the 12-week study, and only 22 patients (31%) were fully compliant with the study medication. The leg pain confounded the primary endpoint of walking distance. On an intention-to-treat analysis, no improvements in 6-minute walk distance or in hemodynamics in patients with terbogrel treatment were seen. However, terbogrel was effective from a pharmacologic standpoint, reducing thromboxane metabolites by as much as 98% (P <.0001), with a modest but statistically insignificant (39%) rise in prostacyclin metabolites. Conclusion Inhibition of thromboxane with an orally active agent is feasible in PPH, but the incidence of severe leg pain with terbogrel precludes its use in this disorder. Similar therapeutic efforts, with other thromboxane inhibitors, should be considered. (Am Heart J 2002;143:e4)

Effect of ozagrel hydrochloride, a thromboxane synthetase inhibitor, on alcoholic beverage-induced bronchoconstriction in asthmatic patients

Acetaldehyde is thought to be a main factor of alcohol-induced asthma. The thromboxane (TX) synthetase inhibitor, ozagrel hydrochloride, inhibits acetaldehyde-induced bronchoconstriction in asthmatic patients. The present study evaluated the involvement of TXA2 on alcoholic beverage-induced bronchoconstriction. Four patients with alcohol-induced asthma received ozagrel (400 mg for 4 days) or placebo using a single-blind, randomized, cross-over design. On two separate study days, each subject drank the same brand and volume of alcoholic beverage (beer or Japanese sake) and bronchoconstriction was assessed as the change in peak expiratory flow (PEF). The effect of ozagrel on the aerosolized challenge of acetaldehyde was investigated in the same subjects. Although aerosolized acetaldehyde-induced bronchoconstriction was significantly prevented by ozagrel, there were no differences in the time course of the decrease in PEF or the maximum fall in PEF after alcohol intake between placebo and ozagrel. We conclude that TXA2 is not involved in alcoholic beverage-induced bronchoconstriction.

Involvement of thromboxane A(2) in airway mucous cells in asthma-related cough.

The aim of this study was to elucidate the role of thromboxane A(2) (TxA(2)) on asthma-related cough in guinea pigs. Animals were immunosensitized and repeatedly challenged with ovalbumin as an antigen. Coughs were induced by the inhalation of 10(-5) M capsaicin solution for 10 min. Thromboxane synthetase (TxS) inhibitor OKY-046 and thromboxane-receptor antagonist AA-2414 significantly inhibited cough responses in repeatedly challenged animals. Inhalation of TxA(2) mimic STA-2- potentiated cough responses in normal and immunosensitized animals but not in repeatedly challenged ones. Moreover, STA-2-potentiated coughs were inhibited by administration of neurokinin-receptor antagonist FK-224. In repeatedly challenged animals, concentration of TxB(2) in airway lavage fluid, expression of TxS mRNA in tracheal epithelia, and the immunostaining intensity against TxS in mucous cells of the epithelium significantly increased compared with normal and sensitized animals. These results suggest that TxA(2) derived from mucous cells potentiated cough responses to capsaicin in allergic airway inflammation.

Design, synthesis and pharmacological evaluation of novel pyrazolo[3,4- b]thieno[2,3- d]pyridine acid derivatives: a new class of anti-inflammatory and anti-platelet agents

A series of pyrazolo[3,4- b]thieno[2,3- d]pyridine alkanoic acid derivatives has been synthesized and evaluated as thromboxane synthetase inhibitors and leukotriene D 4 receptor antagonists. The glutaric acid derivative LASSBio341 ( 6 ) was shown to be active in arachidonic acid-induced platelet aggregation (IC 50=0.14 μM) and inhibition of the contraction of guinea pig tracheal strip induced with LTD 4 (IC 50=43.7 μM), displaying still in vivo anti-inflammatory profile.

The preventive effect of ketoconazole on experimental metastasis from a human pancreatic carcinoma may be related to its effect on prostaglandin synthesis.

Arachidonic acid metabolites known to affect platelet function also interfere with tumor growth and metastases. The purpose of this study was to evaluate the anti-metastatic potential of ketoconazole, a thromboxane synthetase and 5-lipoxygenase inhibitor, on hepatic metastasis from a human pancreatic adenocarcinoma in nude mice and its effect on serum prostaglandin levels. The human pancreatic tumor cells (RWP-2) were injected intrasplenically in nude mice grouped into control, ketoconazole (270 microg), ketoconazole (360 microg), and ketoconazole (540 microg). The agent was administered intraperitoneally 30 min before and every 24 h after the tumor cell inoculation for 8 days. In a separate experiment thromboxane B2 (TxB2), prostaglandin D2 (PGD2), prostaglandin E2 (PGE2) and 6-Keto-F1a (stable prostacyclin derivative) were measured on blood from controls, tumor bearing animals and animals bearing tumors treated with 270 microg of ketoconazole. Statistically significant differences were observed between the control and three-treatment groups on the reduction of liver tumor nodules (p < 0.001), and in the liver surface areas occupied by tumor (p < 0.001). The TxB2 levels decreased from 150.6 ng/mL in the tumor bearing to 104.8 ng/mL in the ketoconazole treated animals (p < 0.05). PGD2, PGE2 and 6-keto-F1a levels increased to 7.1 ng/mL, 8.3 ng/mL, and 13.6 ng/mL from 3 ng/mL, 5.8 ng/mL, and 0.02 ng/mL respectively (p < 0.001). These results indicate that ketoconazole significantly reduced hepatic metastases from the human pancreatic carcinoma RWP-2 in the nude mouse model, and inhibited thromboxane B2 formation, potentiating a concomitant redirection of platelet endoperoxide metabolism into PGD2, PGE2, and 6-keto-F1a. It is hypothesized that the changes in the arachidonic acid metabolism mediate the ameliorating effect of ketoconazole on experimental hepatic metastasis.

Serotonin Hypersensitivity in Aorta of Two Kidney-Two Clip Hypertensive Rats: Calcium Contribution and Prostanoids-Nitric Oxide Interactions

Previous studies from our own laboratory have shown that abdominal aorta rings from two kidney ­ two clip hypertensive rats (HT) develop hypersensitivity to serotonin (SER) which is related to a decreased nitric oxide (NO) availability and enhanced thromboxane A2 production. In the present study we investigated whether calcium and prostanoid-NO interactions are involved in these findings. To this purpose, the aortic responses to SER were analyzed in calcium-free medium and in calcium-depleted aorta placed in normal medium. Moreover, effects of ridogrel (RID, an antagonist of TxA 2 /PGH 2 receptors and inhibitor of thromboxane synthetase) were analysed by cumulative dose-response curves to SER in the presence and in the absence of the NO synthase inhibitor N γ -nitro-L-arginine (NOLA). Vascular responses to SER in vessels from HT rats were associated with increased intracellular calcium mobilization. In addition, hypersensitivity to SER in HT group respect to sham group (SH) disappeared in the presence of RID, NOLA and RID plus NOLA. RID decreases the maximum tension to SER and this effect was prevented by NOLA. This inhibition was of a greater magnitude in rings from sham rats (SH): 34 ± 6% than in HT rats: 15 ± 6% (p < 0.05). Besides, RID decreased the sensibility to SER in the presence of NOLA only in the HT group. In conclusion, the present study suggests that SER hypersensitivity observed in HT rats is related to a facilitated intracellular calcium mobilization and enhanced TxA 2 –endoperoxide response. Changes in membrane SER-gated calcium channels opening are observed only during the early hypertensive period. Besides, the lower depressor effect of RID on the maximal tension to SER in aorta rings from HT rats are related with a decreased NO availability in this model of renovascular hypertension.

Platelet-Activating Factor Contributes to Postischemic Vasospasm

Background. The purpose of the present study was to determine if platelet-activating factor is an important mediator that produces vasospasm during reperfusion after ischemia in skeletal muscle.Materials and Methods. A vascular isolated cremaster muscle in male Sprague–Dawley rats was coupled with local intraarterial drug infusion as a model to study microcirculation responses to ischemia/reperfusion injury. Arteriole diameters and capillary perfusion were measured using intravital microscopy.Group 1: platelet-activating factor dose response.Group 2: Effects of a cyclooxygenase inhibitor; indomethacin, and a thromboxane synthetase inhibitor, imidazole, on the response to platelet-activating factor.Group 3: Effects of nitric oxide synthesis inhibitor; Nω-nitro-l-arginine methyl ester, on the response to platelet-activating factor.Group 4: Effects of a platelet-activating factor receptor antagonist, CV-3988, indomethacin, and imidazole after 4 h of warm ischemia and reperfusion.Results. Intraarterial infusion of platelet-activating factor produced a dose-related but mild vasoconstriction. Pretreatment with indomethacin or imidazole resulted in significant vasodilation actually emanating from platelet-activating factor infusion. Nitric oxide inhibition (with Nω-nitro-l-arginine methyl ester) enhanced the vasoconstriction produced by platelet-activating factor. Pretreatment with CV-3988, indomethacin, or imidazole significantly attenuated ischemia/reperfusion-induced vasospasm and capillary no-reflow in the cremaster muscles.Conclusions. Ischemia/reperfusion-induced vasoconstriction is at least in part mediated by platelet-activating factor and thromboxane A2.

Effects of Tetrodotoxin and OKY-046 in Renal Ischemia Reperfusion

Ischemia reperfusion injury (IRI) contributes significantly to posttransplant graft dysfunction. An emphasis, therefore, has been directed toward the identification of novel renoprotective agents. In this study, the renoprotective effect of tetrodotoxin (TTX) alone, or in combination with a thromboxane synthetase inhibitor (OKY-046), was investigated in a 60-min warm ischemia, 72-h reperfusion, IRI rodent model.Unilateral nephrectomized rats were treated with the test vehicle alone, 1, 2, or 4 μg/kg of TTX or 2 mg/kg of OKY-046 intravenously, either 15 min pre- or postischemia, or 2 μg/kg TTX administered simultaneously with OKY-046 (2 mg/kg), following the ischemic interval. Baseline, 24, and 72 h mean plasma creatinine (Cr) and urea nitrogen (BUN) were compared.Maximal renoprotection was demonstrated by significantly improved 72-h Cr and BUN levels with the 2 μg/kg of TTX or with 2 mg/kg of OKY-046, each administered after ischemia (ischemic control Cr = 8.01 ± 1.07 mg/dl vs TTX = 3.84 ± 0.80 mg/dl, P = 0.008; vs OKY-046 = 4.0 ± 1.5, P + 0.008; ischemic control BUN = 241.3 mg/dl ± 32.8 vs TTX = 85.7 mg/dl ± 18.7, P < 0.008; vs OKY-046 = 52.6 ± 22.5, P = 0.008). The combination therapy utilizing TTX with OKY-046 resulted in reduced animal survival, demonstrating no renoprotection as measured with the biochemical parameters.These results support the renoprotective effects of TTX in a severe, rodent IRI model. The exact mechanism of action, as well as the therapeutic potential of TTX in preservation/transplantation, warrants further study.

Phospholipase A2 augments contraction and intracellular calcium mobilization through thromboxane A2 in bovine tracheal smooth muscle.

Phospholipase A2 (PLA2) induces hyper-sensitivity to muscarinic agonists in airway smooth muscle in vitro. The precise mechanism of this is unknown, but might involve altered calcium homeostasis. In order to elucidate the effects of PLA2, on bovine tracheal smooth muscle contraction, isometric tension and intracellular calcium concentration ([Ca2+]i) were simultaneously measured in fura 2-loaded muscle strips. A high concentration of PLA2 (0.5 microg x mL(-1)) caused the muscle strips to contract, and this contractile response was significantly attenuated by pretreatment with indomethacin (IND; 10 microM), but not by nordihydroguaiaretic acid (NDGA; 10 microM). A low concentration of PLA2 (0.02 microg x mL(-1)) did not directly contract muscle strips. However a low concentration PLA2 significantly enhanced the threshold of the contractile response and that of the [Ca2+]i response to acetylcholine (ACh), but not that of the response to a high K+ concentration. These augmented responses to ACh returned to control levels after pretreatment with IND, a thromboxane (TX) synthetase inhibitor (OKY-046; 10 microM) or a TXA2 receptor antagonist (ONO-3708; 10 microM), but not after NDGA pretreatment. These results suggest that a low concentration of phospholipase A2 enhances smooth muscle responsiveness to acetylcholine by agonist-mediated Ca2+ mobilization facilitated by thromboxane A2. It is concluded that phospholipase A2 plays an important role in bronchial hypersensitivity involving thromboxane A2. It remains to be examined whether similar abnormalities in calcium homeostasis and muscarinic receptor function or coupling are involved in the pathogenesis of asthma.

Placental transfer of the thromboxane synthetase inhibitor ridogrel in the late-pregnant ewe

Objectives: To assess the occurrence of placental transfer of the thromboxane synthetase inhibitor ridogrel in the pregnant ewe and to determine its effect on prostanoid levels in the ewe and fetal lamb, on uterine contractility and on maternal and fetal hemodynamics. Study design: Five chronically instrumented pregnant ewes at 122 days of gestation received intravenous infusions of 5 mg/kg/3 h ridogrel and solvent. Maternal and fetal arterial samples were obtained at predetermined intervals to determine concentrations of ridogrel and prostaglandin metabolites TXB 2, 6-keto-PGF 1α, PGF 2α, and PGE 2. Maternal and fetal responses of blood flow and pressures were determined. Results: Fetal ridogrel levels were 25% of maternal concentrations. Ridogrel showed rapid and marked thromboxane synthetase inhibition and augmentation of levels of prostaglandin metabolites. There was no evidence of change in amniotic pressure, uterine blood flow, maternal and fetal blood pressure and heart rate. Conclusion: Ridogrel is a potent thromboxane synthetase inhibitor which passes the sheep placenta, does not influence maternal and fetal hemodynamics and uterine contractility, and shows similar antiplatelet activity in the ewe and the fetal lamb.

Effects of thromboxane synthetase inhibitor (RS-5186) on experimentally-induced cerebral vasospasm

RS-5186, which inhibits thromboxane A2 (TXA2) synthetase activity, ameliorated delayed cerebral vasospasm in a canine two-hemorrhage model. Subarachnoid hemorrhage was induced in 15 dogs, which were divided into two groups. In the RS-5186-treated group (9 dogs), 50 mg kgof RS-5186 was administered twice a day for seven days. The remaining six dogs without administration of RS-5186 were used as a control group. In the RS-5186-treated group, the angiographic diameter of the basilar artery on Day 7 after subarachnoid hemorrhage was constricted to 60.9% ± 11.6% fn = 9, mean±SD) of that on Day 0, before subarachnoid hemorrhage. The corresponding value was 42.8%±6.1% (n = 6) in the control group. There was a statistically significant difference between these percentages. In the RS-5186-treated group, plasma thromboxane B2 level on Day 7 was 144.3 ± 28.1 pg mh1 fn = 4), which was lower than the 815.5± 162.0 pg ml–1 fn = 4) in the control group (p < 0.0005). The plasma 6-keto-prostaglandin F1a level on Day 7 was 180.5 ± 66.5 pg ml*1 fn = 4J in the RS-5186-treated group, and higher than 107.3± 12.4 pg mh1 fn = 4) in the control group fp = 0.0734). Thus, administration of RS-5186 reduced TXA2 plasma level and had a beneficial effect on angiographically-detected delayed vasospasm. [Neurol Res 1999; 21: 513–516]

Endothelial dysfunction in DOCA-salt hypertension Possible involvement of prostaglandin endoperoxides

The effects of the arachidonic acid metabolism inhibitors on the acetylcholine responses of aortae from control (CR) and deoxycorticosterone acetate (DOCA)-salt hypertensive (HR) rats were investigated. The acetylcholine decreased response observed in HR relaxation % : CR 95.5 ± 2.7, n = 4; HR 52.0 ± 6.3, n = 5, p < 0.05 was restored by the cyclooxygenase inhibitor piroxicam relaxation % : CR 99.8 ± 0.2, n = 4; HR 86.0 ± 4.0, n = 5 and by the thromboxane synthetase inhibitor and the thromboxane A 2/prostaglandin H 2 receptor antagonist ridogrel relaxation % : CR 92.1 ± 4.4, n = 7; HR 93.1 ± 2.0, n = 7 but not by the inhibitors of thromboxane synthetase, prostacyclin synthetase, cytochrome P-450 monooxygenase, and lipoxygenase. So, endoperoxide intermediates seem to be involved in the decreased endothelium-dependent relaxation to acetylcholine in DOCA-salt hypertension.

Ureteral obstruction reverses glomerular proliferation in immune complex glomerulonephritis

We investigated an effect of ureteral obstruction on a progressive immune complex glomerulonephritis in murine lupus erythematosus. Unilateral ureteral obstruction for 8 days significantly decreased the expanded glomerular mesangial area, as measured by computer-assisted morphometry (4.44 ± 0.33 × 10−4 mm2 to 3.60 ± 0.34 × 10−4 mm2, P < .05), and reduced the staining for IgG, C3, and extracellular matrix components, whereas the nephritis was exacerbated in the contralateral non-obstructed kidney. The renal concentration of prostaglandin E2 (PGE2) and 6-keto-prostaglandin F1α (6-keto-PGF1α) in the obstructed kidneys 8 days after obstruction significantly exceeded that of kidneys in sham-operated controls (344.2 ± 83.9 pg/mg tissue protein vs 50.0 ± 27.5 pg/mg tissue protein, P < .01; 71.9 ± 11.4 pg/mg tissue protein vs 9.5 ± 2.3 pg/mg tissue protein, P < .01), whereas thromboxane B2 (TxB2) levels were similar in the two groups (33.9 ± 4.5 pg/mg tissue protein vs 31.3 ± 2.6 pg/mg tissue protein). Next, an experiment was performed to evaluate the role of renal eicosanoids in the amelioration in the immune complex glomerulonephritis after ureteral obstruction. Treatment with the cyclooxygenase inhibitor indomethacin abolished the decrease in mesangial area induced by ureteral obstruction (7.7% ± 6.9%). CV-4151, a thromboxane synthetase inhibitor, had no effect on the decrease in mesangial area (−25.8% ± 6.8%, P < .05). We conclude that unilateral ureteral obstruction quickly decreased the mesangial expansion in immune complex glomerulonephritis, and vasodilatory eicosanoids such as PGE2 and PGI2 at least partly contribute to the amelioration of glomerular histology.

Effect of DP-1904, a thromboxane synthetase inhibitor, on antigen- and spasmogen-induced bronchoconstriction in rodents

The effect of DP-1904 [6-(1-imidazolylmethyl)-5, 6, 7, 8-tetra-hydronaphthalene-2-carboxylic acid hydrochloride], a selective thromboxane synthetase inhibitor, was examined on antigen- and spasmogen-induced bronchoconstriction in rodents. Oral administration of DP-1904 (1, 3, 10 mg/kg) as well as OKY-046 (sodium ( E)-3[4-(1-imidazolylmethyl)-phenyl]-2-propanoate, 100 mg/kg), significantly inhibited immunoglobulin G-mediated bronchoconstriction in actively sensitized guinea pigs. Immunoglobulin E-mediated bronchoconstriction in actively sensitized rats was also inhibited by both DP-1904 (1, 10 mg/kg) and OKY-046 (100 mg/kg). DP-1904 (3–30 mg/kg) and OKY-046 (30 mg/kg) suppressed leukotriene D 4-induced bronchoconstriction in guinea pigs. In these models, the endogenous levels of thromboxanes significantly increased following the stimulus (antigen and leukotriene D 4). DP-1904 (10 mg/kg) inhibited the increase in thromboxane level in both plasma and bronchial alveolar lavage fluid. These actions of DP-1904 persisted for more than 12 h, indicating a long-lasting effect of DP-1904 on bronchoconstriction. The results showed that the biological activity of DP-1904 in our rodents models is more potent than that of OKY-046 (Ozagrel), which is available as an anti-asthma agent in Japan.

Monocyte prostaglandins inhibit procollagen secretion by human vascular smooth muscle cells: implications for plaque stability

Extracellular matrix remodelling occurs during atherosclerosis dictating the structure of the plaque and thus the resistance to rupture. Monocytes and macrophages are believed to play a role in this remodelling. In the present study, filter-separated co-culture has been used to study the effect of monocytes on procollagen turnover by human vascular smooth muscle cells (VSMC). In this system, freshly isolated human peripheral blood monocytes inhibited procollagen secretion from VSMC without affecting either degradation of procollagen, or DNA synthesis by the VSMC. Insertion of a 12 kDa dialysis membrane between the two cell types and treatment with indomethacin showed that the inhibitory factor was of low molecular weight and was cyclooxygenase-dependent. Pre-incubation of each cell type with indomethacin demonstrated that monocyte, but not VSMC cyclooxygenase was required. Thus, the inhibitory effect on procollagen secretion was due, most likely, to monocyte prostaglandins. Neither inhibition of thromboxane synthetase, nor blocking IL-1 activity, reduced the inhibitory activity. Addition of prostaglandins PGE 1, PGE 2 and PGF 2 α to VSMC cultures caused a reduction in procollagen secretion which was equivalent to, but was not additive with, the maximal effect achieved by monocytes. Monocytes and macrophages are a major source of prostaglandins and these molecules are likely to play an important role in collagen turnover within lesions.

A possible involvement of thromboxane A2and peptide leukotrienes in hyperresponsiveness of Sephadex-treated rat lung parenchyma

An augmented contraction and elevated thromboxane (TX) B2release were observed, when the isolated parenchyma from Sephadex-treated rats was stimulated by 5-hydroxytryptamine (5-HT). Release of peptide leukotrienes (pLTs) was also increased by the stimuli. In the Sephadex-induced hyperresponsiveness model, DP-1904, a novel TX synthetase inhibitor, at the concentrations of 3 × 10-7~3 × 10-6 M, reduced the augmented contraction. Also, indomethacin (3 × 10-6 M), a histamine H1antagonist and AA-2414 (10-6 M, a TXA2antagonist, significantly attenuated the hyperresponsiveness to 5-HT. ICI-198,615 (10-7 M), a leukotriene receptor antagonist, partially but significantly reduced the augmented contraction. In an ex vivo study, oral DP-1904 significantly inhibited both the augmented contraction and elevated TXB2release from Sephadex-treated rat parenchyma, but did not affect the blood eosinophilia induced by Sephadex-treatment.These results suggested that the ability to synthesize newly generated lipid mediators such as TXA2and pLTs to exogenous 5-HT was altered upward by Sephadex injection, and so could lead to augmented contraction of established hyperresponsiveness in rats.

Effects of DP-1904, a thromboxane synthetase inhibitor, on the antigen-induced airway hyperresponsiveness and infiltration of inflammatory cells in guinea-pigs

The effect of DP-1904, a novel thromboxane (TX) synthetase inhibitor, on airway hyperresponsiveness was studied in actively sensitized guinea-pigs. Airway hyperresponsiveness to intravenous ACh was observed at 3 and 7 h after aerosolized antigen challenge. In the model, a significant correlation between increases of respiratory resistance and microvascular leakage was observed, corresponding to the elevation of TXB 2 in bronchoalveolar lavage fluid (BALF) in the early phase. DP-1904, at doses of 3 mg/kg or higher given orally one hour prior to the antigen challenge, inhibited the TXB 2 production and the development of airway hyperresponsiveness in the early phase. Further, DP-1904 significantly suppressed the accumulation of lymphocytes in BALF and airway hyperresponsiveness in the late phase, although it only slightly decreased the mobilization of eosinophils and neutrophils. The results suggest that TXA 2 is possibly involved in the development of airway hyperresponsiveness, and DP-1904 prevented the airway hyperresponsiveness via inhibition of TXA 2 production and regulation of inflammatory cells.