L-arginine supplementation and thromboxane synthase inhibition increases cerebral blood flow in experimental cerebral malaria.

Cerebral malaria pathogenesis involves vascular dysfunction with low nitric oxide (NO) bioavailability, vasoconstriction and impaired vasodilation, leading to ischemia, tissue hypoxia and ultimately death. Cerebral blood flow (CBF) involves NO and other pathways, including arachidonic acid (AA)-derived metabolites. Here we show that mice with experimental cerebral malaria (ECM) by P. berghei ANKA showed marked decreases in CBF (as assessed by laser speckle contrast imaging - LSCI) and that administration of L-arginine supplementation (50 mg/kg) and/or of the thromboxane synthase inhibitor Ozagrel (100 mg/kg) induced immediate increases in CBF. L-arginine in combination with artesunate (32 mg/kg) induced immediate reversal of brain ischemia in the short-term (1 hour), but the effect subsided after 3 and 6 hours. Neither L-arginine nor Ozagrel reversed blood brain barrier breakdown. Mice with ECM showed brain levels of selected AA-derived metabolites with a vasoconstrictor profile, with increased levels of 8-isoprostanes, 20-HETE and 14,15-DHET, whereas mice infected with a non-ECM-inducing strain of P. berghei (NK65) showed a vasodilator profile, with normal levels of 20-HETE and 14,15-DHET and increased levels of PGE2. L-arginine is capable of partially reversing cerebral ischemia and AA metabolites may play a role in the cerebrovascular dysfunction in ECM.

4-Methylcatechol, a Flavonoid Metabolite with Potent Antiplatelet Effects.

SCOPE: Intake of flavonoids from the diet can be substantial, and epidemiological studies suggest that these compounds can decrease the incidence of cardiovascular diseases by involvement with increased platelet aggregation. Although parent flavonoids possess antiplatelet effects, the clinical importance is disputable due to their very low bioavailability. Most of them are metabolized by human colon bacteria to smaller phenolic compounds, which reach higher plasma concentrations than the parent flavonoids. In this study, a series of 29 known flavonoid metabolites is tested for antiplatelet potential. METHODS AND RESULTS: Four compounds appear to have a biologically relevant antiplatelet effect using whole human blood. 4-Methylcatechol (4-MC) is clearly the most efficient being about 10× times more active than clinically used acetylsalicylic acid. This ex vivo effect is also confirmed using a potentially novel in-vivo-like ex ovo hen's egg model of thrombosis, where 4-MC significantly increases the survival of the eggs. The mechanism of action is studied and it seems that it is mainly based on the influence on intracellular calcium signaling. CONCLUSION: This study shows that some flavonoid metabolites formed by human microflora have a strong antiplatelet effect. This information can help to explain the antiplatelet potential of orally given flavonoids.

Improved Biological Activities of Isoepoxypteryxin by Biotransformation.

Isoepoxypteryxin is the major coumarin of a Japanese medicinal plant Angelica shikokiana. This research was designed to study the effect of structural changes through fungal biotransformation on the reported biological activities of isoepoxypteryxin. Among the tested microorganisms, only Cordyceps sinensis had enzymes that could catalyze the ester hydrolysis and the reductive cleavage of the epoxide ring of isoepoxypteryxin, separately, to give two more polar metabolites (+)-cis-khellactone (P1) and a new coumarin derivative (+)-cis-3'-[(2-methyl-3-hydroxybutanoyl)oxy]-4'-acetoxy-3',4'-dihydroseselin (P2), respectively. The polar metabolite P2 showed stronger cytotoxicity and higher selectivity than isoepoxypteryxin. On the molecular level, P2 showed more in vitro inhibition of both tubulin polymerization and histone deacetylase 8 (HDAC8). Similarly, P2 showed more neuroprotection against amyloid beta fragment 1 - 42 (Aß1 - 42 )-induced neurotoxicity in human neuroblastoma cells (SH-SY5Y) and exhibited more inhibition of the in vitro aggregation of Aß1 - 42 . Both metabolites showed stronger antiplatelet aggregation by increased inhibition of thromboxane-A2 synthase (TXS) activity and thromboxane-A2 (TXA2) production. This study is the first to describe the improved cytotoxic, neuroprotective, and antiplatelet aggregation activities of isoepoxypteryxin through its biotransformation by C. sinensis.

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.

Alditols and monosaccharides from sorghum vinegar can attenuate platelet aggregation by inhibiting cyclooxygenase-1 and thromboxane-A2 synthase.

ETHNOPHARMACOLOGICAL RELEVANCE: Vinegar has been used as both a common seasoning and a traditional Chinese medicine. Sorghum vinegar is an excellent source of physiological substances with multiple health benefits. AIM OF THIS STUDY: To evaluate the antiplatelet aggregation activity of alditols and monosaccharides extracted from sorghum vinegar and analysis its mechanism. MATERIALS AND METHODS: Alditol and monosaccharide extract (AME) from sorghum vinegar was first evaluated for antiplatelet activity using the turbidimetric method. Blood was collected from healthy volunteer donors. The platelet aggregation was induced by arachidonic acid (AA), collagen, adenosine diphosphate (ADP) and thrombin in vitro. AME was divided into three experimental groups with the concentration were 0.10, 0.25 and 0.50 mg/mL. In order to determine the inhibitory activity of AME on COX1, TXS and TXA2 production experiments were conducted using the COX1, TXS and TXB2 EIA kit. Computational docking was used to find the docking pose of monosaccharides and alditols with COX1. RESULTS: AME showed significant induction of antiplatelet activity by arachidonic acid (AA), collagen, adenosine diphosphate (ADP) and thrombin in a concentration-dependent manner (p<0.05). AME (0.50 mg/mL) reduced the AA-induced aggregation rate to 10.35%±0.46%, which was comparable to acetylsalicylic acid (aspirin, ASA) (0.50 mg/mL, 6.35%±0.58%), a medical standard. Furthermore, AME strongly inhibited cyclooxygenase-1 (COX1) and thromboxane-A2 synthase (TXS), and subsequently attenuated thromboxane-A2 (TXA2) production. These findings indicated that AME attenuates platelet aggregation through the AA metabolism pathway. Computational docking showed that alditols (L-erythritol, L-arabitol, xylitol and D-sorbitol), monosaccharides (D-glucopyranose, D-fructofuranonse, D-xylopyranose, D-galactopyranose and D-ribose), ethyl glucoside and 3,4-(methylenedioxy) mandelic acid could dock directly into the active site of COX1. CONCLUSION: Alditols and monosaccharides from sorghum vinegar inhibit multiple steps in the platelet aggregation pathway, and may be beneficial for the treatment of cardiovascular diseases.

Attenuation of alpha-adrenergic-induced vasoconstriction by dietary wild blueberries (Vaccinium angustifolium) is mediated by the NO-cGMP pathway in spontaneously hypertensive rats (SHRs).

The role of wild blueberries (WB) on key signaling steps of nitric oxide (NO) and cyclooxygenase (COX) pathways was examined in spontaneously hypertensive rats (SHRs) after eight weeks on a control (C) or an 8% w/w WB diet. Aortic rings from SHRs were stimulated with phenylephrine (Phe) in the absence or presence of inhibitors of: soluble guanylyl cyclase (sGC), phosphodiesterase-5 (PDE(5)), prostaglandin I(2) (PGI(2)) synthase and thromboxane A(2) (TXA(2)) synthase. Additionally, enzymatic activities in these pathways were determined by the concentration of NO, cyclic guanosine monophosphate (cGMP), PGI(2) and TXA(2). In the WB-fed SHR, attenuation of Phe-induced vasoconstriction was mediated by an increased synthesis or preservation of cGMP. Despite an increased release of PGI(2) in the WB group, neither inhibition of PGI(2) or TXA(2) synthase resulted in a different response to Phe between the control and the WB rings. Hence, in the SHR, WB decrease Phe-mediated vasoconstriction under basal conditions by enhancing NO-cGMP signaling without a significant involvement of the COX pathway.

Effects of continuous ingestion of hesperidin and glucosyl hesperidin on vascular gene expression in spontaneously hypertensive rats.

Hesperidin (HES) and glucosyl hesperidin (GHES) have antihypertensive effects. In the present study, to clarify the antihypertensive mechanisms, we compared the effects of continuous ingestion of HES and GHES in spontaneously hypertensive rats (SHRs). HES and GHES ingestion for 8 wk significantly prevented hypertension and suppressed the mRNA expression of NADPH oxidase subunits and thromboxane A2 synthase in SHR aortas. Further, hesperetin, a common metabolite of HES and GHES, reduced thromboxane B2 release from SHR aortas. These findings indicate that continuous ingestion of HES and GHES prevents hypertension via regulating the gene expression related to the modulation of vascular tone.

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.

In vitro platelet antiaggregatory properties of 4-methylcoumarins.

Platelets play a crucial role in physiological haemostasis. However, in coronary arteries damaged by atherosclerosis, enhanced platelet aggregation, with subsequent thrombus formation, is a precipitating factor in acute myocardial infarction. Current therapeutic approaches are able to reduce approximately one quarter of cardiovascular events, but they are associated with an increased risk of bleeding and in some resistant patients are not efficient. Some coumarins possess antiplatelet activity and, due to their additional antioxidant effects, may be promising drugs for use in combination with the present therapeutic agents. The aim of this study was to analyse a series of simple 4-methylcoumarins for their antiplatelet activity. Human plasma platelet suspensions were treated with different aggregation inducers [arachidonic acid (AA), collagen and ADP] in the presence of the 4-methylcoumarins. Complementary experiments were performed to explain the mechanism of action. 5,7-Dihydroxy-4-methylcoumarins, in particular those containing a lipophilic side chain at C-3, reached the activity of acetylsalicylic acid on AA-induced aggregation. Other tested coumarins were less active. Some of the tested compounds mildly inhibited either collagen- or ADP-induced aggregation. 5,7-Dihydroxy-4-methylcoumarins did not interfere with the function of thromboxane synthase, but were competitive antagonists of thromboxane A(2) receptors and inhibited cyclooxygenase-1 as well. 5,7-Dihydroxy-4-methylcoumarins appear to be promising candidates for the extension of the current spectrum of antiplatelet drugs.

Chlorella powder inhibits the activities of peptidase cathepsin S, PLA2, cyclooxygenase-2, thromboxane synthase, tyrosine phosphatases, tumor necrosis factor-alpha converting enzyme, calpain and kinases.

A Chlorella powder was tested in 118 in vitro enzyme assay systems. The powder showed potent inhibitions of peptidase cathepsin S, thromboxane A(2) synthase and cyclooxygenase-2 in a dose-concentration manner with IC(50)+/-standard error of the mean values of 3.46+/-0.93 microg/ml, 3.23+/-0.69 microg/ml, and 44.26+/-9.98 microg/ml, respectively. Other activities observed were inhibitions of tumor necrosis factor-alpha converting enzyme, protein tyrosine phosphatase (SHP-2), calpain, protein kinases and protein tyrosine phosphatases. Chlorella powder had no significant effect on cyclooxygenase-1. These actions to inhibit cyclooxygenase-2 and thromboxane synthase could contribute to the purported anti-inflammatory and anti-thrombotic effects of Chlorella. These results reveal important potential biochemical activities to be developed that, if confirmed by in vivo studies, might be exploited for the prevention or treatment of several serious pathologies, including inflammatory diseases, immune and cancer.

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.

Involvement of brain thromboxane A in hypotension induced by haemorrhage in rats.

1. In the present study, we aimed to determine the involvement of brain thromboxane A2 (TXA2) in blood pressure decreases evoked by acute and/or graded haemorrhage in rats. 2. Sprague-Dawley rats were used throughout the study. Acute haemorrhage was achieved by withdrawing a total volume of 2.1 and 2.5 mL blood/100 g bodyweight over a period of 10 min. A microdialysis study was performed in a hypothalamic area to measure extracellular TXA2 levels. Graded haemorrhage was conducted successively by withdrawing carotid arterial blood (0.55 mL/100 g bodyweight) over a 10 s period four times (S1-S4) at 5 min intervals. Furegrelate (125, 250 and 500 microg), a TXA2 synthase inhibitor, was injected intracerebroventricularly (i.c.v.) 60 min before acute or graded haemorrhage was initiated. U-46619 (0.5, 1 and 2 microg, i.c.v.), a synthetic TXA2 analogue, was administered 5 min before acute haemorrhage (2.1 mL/100 g bodyweight). 3. Acute haemorrhage produced a severe and long-lasting decrease in blood pressure and had a tendency to increase heart rate. Both haemorrhage protocols (2.1 or 2.5 mL/100 g) generated similar approximate twofold increases in extracellular hypothalamic TXA2 levels. Intracerebroventricular furegrelate (250 microg) pretreatment completely blocked the TXA2 increases induced by acute haemorrhage. Furegrelate administration (100, 250 and 500 microg, i.c.v.) attenuated the fall in arterial pressure evoked by acute haemorrhage and caused significant increases in heart rate at all doses injected. 4. Graded haemorrhage progressively lowered arterial pressure and increased plasma vasopressin and adrenaline levels in the last period. Furegrelate-injected rats were greatly resistant to the hypotensive effect of haemorrhage for all degrees of blood removed. Plasma adrenaline and vasopressin levels were significantly elevated in furegrelate-pretreated rats compared with the saline-treated group during S2-S3 and S4, respectively. U-46619 administration caused small but statistically significant decreases in arterial pressure induced by haemorrhage. 4. The results show that acute hypotensive haemorrhage increases extracellular hypothalamic TXA2 levels. The increase in brain endogenous TXA2 levels involves a decrease in blood pressure evoked by haemorrhage because the blockade of TXA2 synthesis by furegrelate pretreatment attenuated the haemorrhagic hypotension. Increases in plasma adrenaline and vasopressin levels may mediate this effect.

Pharmacological evaluation of both enantiomers of (R,S)-BM-591 as thromboxane A2 receptor antagonists and thromboxane synthase inhibitors.

The aim of this work is to evaluate the anti-thromboxane activity of two pure enantiomers of (R,S)-BM-591, a nitrobenzene sulfonylurea chemically related to torasemide, a loop diuretic. The drug affinity for thromboxane A2 receptor (TP) of human washed platelets has been determined. In these experiments, (R)-BM-591 (IC50 = 2.4+/-0.1 nM) exhibited a significant higher affinity than (S)-BM-591 (IC50 = 4.2+/-0.15 nM) for human washed platelets TP receptors. Both enantiomers were stronger ligands than SQ-29548 (IC50 = 21.0+/-1.0 nM) and sulotroban (IC50 = 930+/-42 nM), two reference TXA2 receptor antagonists. Pharmacological characterisations of (S)-BM-591 and (R)-BM-591 were compared in several models. Thus, (R)-BM-591 strongly prevented platelet aggregation induced by arachidonic acid (AA) (600 microM) and U-46619 (1 microM) while (S)-BM-591 showed a lower activity. On isolated tissues pre-contracted by U-46619, a stable TXA2 agonist, (S)-BM-591 was more potent in relaxing guinea-pig trachea (EC50 = 0.272+/-0.054 microM) and rat aorta (EC50 = 0.190+/-0.002 microM) than (R)-BM-591 (EC50 of 9.60+/-0.63 microM and 0.390+/-0.052 microM, respectively). Moreover, at 1 microM, (R)-BM-591 totally inhibited TXA2 synthase activity, expressed as TXB2 production from human platelets, while at the same concentration, (S)-BM-591 poorly reduced the TXB2 synthesis (22%). Finally, in rats, both enantiomers lost the diuretic activity of torasemide. In conclusion, (R)-BM-591 exhibits a higher affinity and antagonism on human platelet TP receptors than (S)-BM-591 as well as a better thromboxane synthase inhibitory potency. In contrast, (S)-BM-591 is more active than the (R)-enantiomer in relaxing smooth muscle contraction of rat aorta and trachea guinea pig. Consequently, (R)-BM-591 represents the best candidate for further development in the field of thrombosis disorders.

Proinflammatory actions of thromboxane receptors to enhance cellular immune responses.

Metabolism of arachidonic acid by the cyclo-oxygenase (COX) pathway generates a family of prostanoid mediators. Nonsteroidal anti-inflammatory drugs (NSAIDs) act by inhibiting COX, thereby reducing prostanoid synthesis. The efficacy of these agents in reducing inflammation suggests a dominant proinflammatory role for the COX pathway. However, the actions of COX metabolites are complex, and certain prostanoids, such as PGE(2), in some circumstances actually inhibit immune and inflammatory responses. In these studies, we examine the hypothesis that anti-inflammatory actions of NSAIDs may be due, in part, to inhibition of thromboxane A(2) synthesis. To study the immunoregulatory actions of thromboxane A(2), we used mice with a targeted disruption of the gene encoding the thromboxane-prostanoid (TP) receptor. Both mitogen-induced responses and cellular responses to alloantigen were substantially reduced in TP(-/-) spleen cells. Similar attenuation was observed with pharmacological inhibition of TP signaling in wild-type splenocytes, suggesting that reduced responsiveness was not due to subtle developmental abnormalities in the TP-deficient mice. The absence of TP receptors reduced immune-mediated tissue injury following cardiac transplant rejection, an in vivo model of intense inflammation. Taken together, these findings show that thromboxane augments cellular immune responses and inflammatory tissue injury. Specific inhibition of the TP receptor may provide a more precise approach to limit inflammation without some of the untoward effects associated with NSAIDs.

The antiplatelet activity of Geiji-Bokryung-Hwan, Korean traditional formulation, is mediated through inhibition of phospholipase C and inhibition of TxB(2) synthetase activity.

Geiji-Bokryung-Hwan (GBH), consisting of herbes of Cinnamomi ramulus (Geiji), Poria cocos (Bokryun), Mountan cortex radicis (Mokdanpi), Paeoniae radix (Jakyak), and Persicae semen (Doin), on antiplatelet activity in human platelet suspensions was studied. The mechanism involved in the antiplatelet activity of GBH in human platelet suspensions was investigated. GBH did not significantly affect the thromboxane synthetase activity of aspirin-treated platelet microsomes and GBH (15 and 30 microg/ml) significantly inhibited [3H]arachidonic acid released in collagen-activated platelets but not in unactivated-platelets. Nitric oxide (NO) production in human platelets was measured by a chemiluminesence detection method in this study. GBH did not significantly affect nitrate production in collagen (10 microg/ml)-induced human platelet aggregation. Various concentrations of GBH (0, 5, 10, 15, and 30 microg/ml) dose-dependently inhibited [3H]inositol monophosphate formation stimulated by collagen (10 microg/ml) in [3H]myoinositol-loaded platelets at different incubation times (1, 2, 3, and 5 min). These results indicated that the antiplatelet activity of GBH may possibly be due to the inhibition of phospholipase C (PLC) activity, leading to reduce phosphoinositide breakdown, followed by the inhibition of thromboxane A(2) formation, and then inhibition of [Ca(2+)](i) mobilization of platelet aggregation stimulated by agonists. In conclusion, GBH suppressed PLC in a dose-dependent manner, and may have pharmaceutical applications. These data suggest that GBH extracts merit investigation as a potential anti-atherosclerogenic agent in humans.

Radical scavenging glycoprotein inhibiting cyclooxygenase-2 and thromboxane A2 synthase from aloe vera gel.

An active glycoprotein fraction containing 58 % protein was isolated from Aloe vera gel by precipitation with 55 % ammonium sulfate followed by gel permeation using DEAE-Sephacel A-25, Sepharose 6B and Sephadex G-50 columns in a yield of 3 x 10 -3 %. The glycoprotein fraction showed a single band corresponding to a subunit of verectin at the same position when stained with both Coomassie brilliant blue and periodic acid-Schiff reagents on 18 % SDS-PAGE. The molecular weight (14 kDa) was confirmed by Sephadex G-50 column chromatography. The glycoprotein fraction showed a radical scavenging activity against superoxide anion generated by the xanthine-xanthine oxidase system as well as inhibition of cyclooxygenase-2 and reduction of thromboxane A 2 synthase level in vitro.

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 microM) and inhibition of the contraction of guinea pig tracheal strip induced with LTD(4) (IC(50) = 43.7 microM), displaying still in vivo anti-inflammatory profile.

Effects of selective cyclooxygenase-2 inhibition on vascular responses and thrombosis in canine coronary arteries.

BACKGROUND: Prostanoid synthesis via the action of cyclooxygenase-2 (COX-2) is a component of the inflammatory response. Prostacyclin, a product of COX-2 in vascular endothelium, has important physiological roles, such as increasing blood flow to injured tissues, reducing leukocyte adherence, and inhibiting platelet aggregation. We examined the possibility that selective COX-2 inhibition could suppress the protective effects of prostacyclin, resulting in an alteration of the hemostatic balance and vascular tone. METHODS AND RESULTS: Circumflex coronary artery thrombosis was induced in dogs by vascular electrolytic injury. Orally administered celecoxib (COX-2 inhibition) or high-dose aspirin (HDA) (COX-1 and COX-2 inhibition) did not alter time to occlusive thrombus formation compared with controls (celecoxib 77.7+/-7.2 minutes, HDA 72.0+/-18.5 minutes, control 93.0+/-21.8 minutes). Oral HDA with an endothelial recovery period (HDA-ER) (COX-1 inhibition) produced a significant increase in time to vessel occlusion (257.0+/-41.6 minutes). The observed increase in time to occlusion was abolished when celecoxib was administered to animals dosed with HDA-ER (80.7+/-20.6 minutes). The vasomotor effect of endothelium-derived prostacyclin was examined by monitoring coronary flow during intracoronary administration of arachidonic acid or acetylcholine. In celecoxib-treated animals, vasodilation in response to arachidonic acid was reduced significantly compared with controls. CONCLUSIONS: The results indicate important physiological roles for COX-2-derived prostacyclin and raise concerns regarding an increased risk of acute vascular events in patients receiving COX-2 inhibitors. The risk may be increased in individuals with underlying inflammatory disorders, including coronary artery disease.

Ridogrel enemas in distal ulcerative colitis.

OBJECTIVE: To evaluate the effect of Ridogrel enemas (Janssen Research Foundation, Beerse, Belgium) on disease activity and mucosal inflammatory mediators in patients with active left-sided ulcerative colitis. DESIGN AND METHODS: Eleven patients with active left-sided ulcerative colitis were evaluated in an open non-placebo-controlled pilot study. All patients were treated with Ridogrel enemas (300 mg/40 ml once daily) over four weeks. A disease activity score based on clinical, endoscopic and histological criteria was obtained before and after treatment with Ridogrel. The concentrations of thromboxane B2 (TxB2), prostaglandin E2 (PGE2), interleukin-6 (IL-6) and tumour necrosis factor alpha (TNF-alpha) were measured in mucosal biopsies before and after treatment. RESULTS: One patient discontinued treatment because of progression of disease, the other ten patients tolerated the Ridogrel enemas well. Mucosal TxB2 concentration decreased significantly in all patients. The mucosal concentrations of the other inflammatory mediators (PGE2, IL-6 and TNF-alpha) were unaltered. The disease score decreased in five patients. However, clinical improvement was not always associated with a decrease in endoscopic and/or histological scores. CONCLUSIONS: This pilot study shows that Ridogrel enemas selectively reduce mucosal TxB2 concentration.

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 kg-1 of 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% (n = 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 ml-1 (n = 4), which was lower than the 815.5 +/- 162.0 pg ml-1 (n = 4) in the control group (p < 0.0005). The plasma 6-keto-prostaglandin F1 alpha level on Day 7 was 180.5 +/- 66.5 pg ml-1 (n = 4) in the RS-5186-treated group, and higher than 107.3 +/- 12.4 pg ml-1 (n = 4) in the control group (p = 0.0734). Thus, administration of RS-5186 reduced TXA2 plasma level and had a beneficial effect on angiographically-detected delayed vasospasm.