Cysteinyl Leukotriene Receptor Antagonist Research Articles

Method for screening cysteinyl leukotriene receptor 2 antagonists and preliminary screening of compounds

To establish a method for screening cysteinyl leukotriene receptor 2 (CysLT(2)) antagonists and to preliminarily screen a series of synthetic compounds. Rat glioma cell line (C6 cells) highly expressing CysLT(2) receptor was used. Intracellular calcium concentration was measured after stimulation with the agonist LTD(4),which was used to screen compounds with antagonist activity for CysLT(2) receptor. Bay u9773, a CysLT1/CysLT(2) receptor non-selective antagonist, and AP-100984, a CysLT(2) receptor antagonist, were used as control. PT-PCR showed a higher expression of CysLT(2) receptor in C6 cells. LTD(4) at 1 mumol/L significantly increased intracellular calcium in C6 cells; the maximal effect was about 37.5% of ATP, a positive stimulus.LTD(4)-induced increase of intracellular calcium was blocked by CysLT(2) receptor antagonists, but not by CysLT(1) receptor antagonists. Among the synthetic compounds, D(XW-)1,2,13,23,29 and 30 inhibited LTD(4)-induced increase of intracellular calcium. LTD(4)-induced change in intracellular calcium in C6 cells can be used as a screening method for CysLT(2) receptor antagonists. The compounds, D(XW-)1,2,13,23,29 and 30, possess antagonist activity for CysLT(2) receptor.

Inhaled montelukast inhibits cysteinyl-leukotriene-induced bronchoconstriction in ovalbumin-sensitized guinea-pigs: The potential as a new asthma medication

Oral cysteinyl-leukotriene (LT) receptor antagonists such as montelukast are used for reducing airway inflammation and exacerbations. However, inhaled therapy using LT receptor antagonists has not been studied. In the present study, the effect of inhaled montelukast was investigated on airway hyperresponsiveness measured by cysteinyl-LT induced bronchoconstriction in an animal model of asthma. Bronchoconstriction responses were induced by inhaled LTC4 and LTD4 (0.2 µg/ml each) or three doses of intravenous LTC4 and LTD4 (0.3, 1, 3 µg/kg) in ovalbumin (OVA)-sensitized Hartley male guinea-pigs. The response was measured by the change in peak pressure of airway opening (Pao). The effect of montelukast was evaluated by the comparison of bronchoconstriction responses between the groups of animals pre-treated with 15-min inhalation of 10 mg/ml montelukast and saline. To evaluate the tissue injury which might be caused by montelukast inhalation, lung tissues were examined for the histology. The broncoconstriction responses induced by inhaled LTC4 and LTD4 were enhanced by OVA sensitization in the guinea-pigs. In sensitized animals, the significant increases in peak Pao were 18.5 ± 2.1 cmH 2O by LTC4 inhalation and 25.0 ± 1.6 cmH 2O by LTD4 inhalation on average. Prior treatment of inhaled montelukast potently suppressed the peak Pao increases induced by both inhaled and intravenous LTC4 and LTD4 (all P < 0.01 vs. saline control). Moreover, the suppression of inhaled montelukast against LTD4-induced bronchoconstriction was observed for at least up to 24 h. According to the histological examination, montelukast inhalation produced no injury to the lung tissue. Inhaled montelukast, a cysteinyl-LT receptor antagonist, was effective in inhibiting cysteinyl-LT-induced acute bronchoconstriction, and may have the potential for clinical use as a new asthma drug.

Genetics and pharmacogenetics of the leukotriene pathway

Leukotrienes are now established contributors to the inflammatory process in asthma, and leukotriene modifiers are mainstays in the therapy of asthma. This review focuses on published association studies implicating the role of leukotriene pathway genes in asthma pathogenesis and treatment response, specifically focusing on those genetic variants associated with asthma affection status, the development of aspirin-exacerbated respiratory disease, and pharmacogenetic response. Although published studies have been limited by small sample sizes and a lack of independent replication, multiple loci within multiple leukotriene pathway genes have now been associated in more than 1 study related to asthma or asthma treatment response. Those specific variants include 2 variants in the 5-lipoxygenase gene (ALOX5) that are both associated with response to 5-lipoxygenase inhibition and to leukotriene receptor antagonists, variants in genes encoding the 2 established cysteinyl leukotriene receptor antagonists (CYSLTR1 and CYSLTR2) that are both associated with asthma susceptibility in at least 2 independent populations, and a leukotriene C(4) synthase promoter polymorphism (LTC4s) that has been associated with asthma affection status and asthma-exacerbated respiratory disease. Despite these successes, genetic investigations into this pathway remain in their formative stages. Future studies aimed at providing a broader scope of investigation through increased sample sizes and through genome-wide approaches are needed.

Participation of 5-lipoxygenase-derived LTB 4 in 4-hydroxynonenal-enhanced MMP-2 production in vascular smooth muscle cells

5-Lipoxygenase (5-LO) has been suggested as a modulator of atherosclerotic plaque instability, however, its role in MMP production in vascular smooth muscle cells (VSMC) is still unclear. Thus, this study investigated the role of 5-LO in HNE-enhanced MMP-2 production in VSMC, and the mechanisms by which this enzyme could be activated by HNE. VSMC stimulated with HNE (1 μM) produced MMP-2, which was markedly attenuated in 5-LO-deficient VSMC as well as in cells pretreated with a FLAP inhibitor, MK886, confirming a role for 5-LO metabolites in HNE-enhanced MMP-2 production. Related to these results, HNE increased nuclear translocation of 5-LO promoting 5-LO activity, which was attenuated not only by SB203580, a p38 MAPK inhibitor, but also by PD98059, an ERK inhibitor. In parallel, phosphorylation of p38 MAPK and ERK occurred as early as 15 min after exposure to HNE, suggesting a potential role for p38 MAPK and ERK pathways in HNE-induced activation of 5-LO. Among leukotriene (LT) receptor antagonists, U-75302, a BLT receptor antagonist, but not MK-571 and Rev-5901, cysLT receptor antagonists, showed an inhibitory effect on HNE-enhanced MMP-2 production. Moreover, MMP-2 production in VSMC was also significantly increased by LTB 4, but not by LTC 4 and LTD 4. Collectively, these data suggest that 5-LO mediates HNE-enhanced MMP-2 production via LTB 4-BLT receptor pathways, consequently leading to atherosclerotic plaque instability.

Synthesis and structure–activity relationships of γ-carboline derivatives as potent and selective cysLT1 antagonists

A γ-carboline series of cysLT1 receptor antagonists has been prepared. Some of the compounds show good potencies both, in vitro and in vivo, compared to the standard compounds.

5-Lipoxygenase: mechanisms of regulation

5-lipoxygenase (5-LO) catalyzes two steps in biosynthesis of leukotrienes (LTs), a group of lipid mediators of inflammation derived from arachidonic acid (AA). LT antagonists are used in treatment of asthma; more recently a potential role also in atherosclerosis has raised considerable interest. Furthermore, possible effects of 5-LO metabolites in relation to tumorigenesis have emerged. Thus, an understanding of the biochemistry of this lipoxygenase has potential implications for treatment of various diseases.

Quantification of montelukast, a selective cysteinyl leukotriene receptor (CysLT1) antagonist in human plasma by liquid chromatography–mass spectrometry: validation and its application to a human pharmacokinetic study

A highly sensitive, rapid assay method has been developed and validated for the estimation of montelukast (MTK) in human plasma with liquid chromatography coupled to tandem mass spectrometry with electro spray ionization in the positive-ion mode. Liquid-liquid extraction was used to extract MTK and amlodipine (internal standard, IS) from human plasma. Chromatographic separation was achieved with 10 mM ammonium acetate (pH 6.4): acetonitrile (15:85, v/v) at a flow rate of 0.50 mL/min on a Discovery HS C(18) column with a total run time of 3.5 min. The MS/MS ion transitions monitored were 586.10 --> 422.10 for MTK and 409.20 --> 238.30 for IS. Method validation and clinical sample analysis were performed as per FDA guidelines and the results met the acceptance criteria. The lower limit of quantitation achieved was 0.25 ng/mL and linearity was observed from 0.25 to 800 ng/mL. The intra-day and inter-day precisions were 5.97-8.33 and 7.09-10.13%, respectively. This novel method has been applied to a pharmacokinetic study of MTK in humans.

Cedar and Cypress Pollinosis and Allergic Rhinitis: Quality of Life Effects of Early Intervention with Leukotriene Receptor Antagonists

Background: Allergic rhinitis involves inflammation of the nasal passages. The use of nasal steroids is generally very effective in providing significant symptom relief. However, compliance for their use is sometimes poor. Methods: To examine the efficacy of early intervention (before pollen dispersal) with oral cysteinyl leukotriene receptor antagonists (LTRA) on pollinosis in patients with allergy to cedar and Japanese cypress pollens, groups of subjects were treated with LTRA or a placebo for 4 weeks at the beginning of the cedar pollen dispersal season. Subsequently, all patients received nasal steroid therapy concomitantly with LTRA throughout the remaining period of the pollen dispersal season. The effects of such early treatment with LTRA on pollinosis were investigated using symptom scores from an allergy diary and quality of life (QOL) scores. Results: Sneezing and nasal congestion scores were significantly lower in the LTRA-pretreated subjects than observed in the placebo-pretreated patients between weeks 4 and 6 and weeks 3 and 5, respectively. QOL scores improved significantly in all domains after concomitant therapy with nasal steroids. The percent improvement in the nasal congestion score after the concomitant therapy was significantly higher in the LTRA group (69%) than in the placebo group (41%). Conclusion: Significant differences observed in symptoms and in QOL effects between LTRA- and placebo-pretreated patients and the absence of major adverse effects noted in these studies suggest that early intervention with LTRA is beneficial and safe and should be considered in the management of pollinosis-associated allergic rhinitis.

Cysteinyl Leukotrienes Induce Monocyte Chemoattractant Protein-1 in Human Monocyte/Macrophages via Mitogen-Activated Protein Kinase and Nuclear Factor-κB Pathways

Background: We have previously demonstrated that cysteinyl leukotriene (CysLT) induced monocyte chemoattractant protein-1 (MCP-1) production in monocytes/macrophages. The intracellular signal transduction pathway of MCP-1 production induced by CysLT in human monocytes/macrophages is unclear. Methods: The activation of mitogen-activated protein kinase (MAPK), including extracellular signal-regulated kinases 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK) and p38 MAPK by phosphorylation, and nuclear factor-κB (NF-κB) by leukotriene (LT) D₄ and LTC₄ was determined in THP-1 cells, a human monocytic leukemia cell line, and peripheral blood CD14+ monocytes/macrophages. We examined the inhibitory effects of inhibitors of ERK1/2, JNK, p38 MAPK and NF-κB and pranlukast as a CysLT1 receptor antagonist on induction of MCP-1 production by LTD₄ and LTC₄. Results: LTD₄ and LTC₄ induced significant phosphorylations of ERK1/2 and JNK, but not p38 MAPK, in THP-1 cells and peripheral blood CD14+ monocytes/macrophages. Pretreatment with the ERK1/2 inhibitor PD98059 and JNK inhibitor SP600125 attenuated MCP-1 production by CysLTs. NF-κB activation was induced by addition of LTD₄ and LTC₄. Pretreatment with the NF-κB inhibitors caffeic acid phenylethyl ester and MG-132 inhibited MCP-1 production by CysLTs. Pranlukast inhibited phosphorylation of ERK1/2 and JNK, NF-κB activation, and the MCP-1 production induced by CysLTs. Conclusion: CysLTs induce MCP-1 and this induction is mediated by ERK1/2 and JNK in MAPK, and NF-κB pathways via the CysLT1 receptor, for the most part, in human monocytes/macrophages.

Pranlukast Attenuates Ischemia-like Injury in Endothelial Cells Via Inhibiting Reactive Oxygen Species Production and Nuclear Factor-κB Activation

The anti-inflammatory effects of pranlukast, an antagonist of cysteinyl leukotriene receptor 1, may be rendered not only by antileukotriene activity but also by other pharmacological activities. Previous studies indicate that pranlukast reduces ischemic tissue injury partially through decreasing vascular permeability, but its effect on ischemic injury in endothelial cells is not known. Thus, in this study, we investigated the effect of pranlukast on ischemia-like injury induced by oxygen-glucose deprivation (OGD) in EA.hy926 cells, a human endothelial cell line, and the possible mechanisms. We found that cell viability was reduced, lactate dehydrogenase release was increased 4-8 hours after OGD, and necrosis was induced 8 hours after OGD. Production of reactive oxygen species (ROS) increased by 211%, 176%, and 128%, respectively, 0.5, 1, and 2 hours after OGD. Nuclear factor-kappaB (NF-kappaB) was translocated to the nuclei 4-8 hours after OGD. Pranlukast ameliorated the reduced viability, the increased lactate dehydrogenase release, and necrosis after OGD. It also reduced ROS production and inhibited NF-kappaB nuclear translocation after OGD. The ROS scavenger, edaravone, inhibited OGD-induced nuclear translocation of NF-kappaB as well. Edaravone and pyrrolidine dithiocarbamate (a specific NF-kappaB inhibitor) protected endothelial cells from the OGD-induced injury. However, zileuton, a 5-lipoxygenase inhibitor, did not affect the cell injury, ROS production, and NF-kappaB nuclear translocation after OGD. The exogenous leukotriene D4 did not induce cell injury, ROS production, and NF-kappaB translocation. Thus, we conclude that pranlukast protects endothelial cells from ischemia-like injury via decreasing ROS production and inhibiting NF-kappaB activation, which is leukotriene independent.

Montelukast: Pharmacology, Safety, Tolerability and Efficacy

Allergic rhinitis and asthma are common disorders effecting large percentages of the population of Western countries. There are multiple treatment options available for allergic rhinitis and asthma and stepwise approaches to therapy have been recommended. Montelukast is a cysteinyl leukotriene receptor antagonist that has been found to be effective both in the treatment of allergic rhinitis and asthma. This paper will describe the pharmacology, safety, efficacy and tolerability of montelukast. It will examine the comparative efficacy of montelukast to other medications for the treatment of allergic rhinitis and asthma, as well as discuss the recent studies of combination therapy.

Cysteinyl-leukotriene receptor antagonist montelukast decreases blood–brain barrier permeability but does not prevent oedema formation in traumatic brain injury

Introduction: Traumatic brain injury is highly associated with the over-production of reactive oxygen species. The aim of this study was to investigate the putative neuroprotective effect of montelukast, a cysteinyl-leukotriene receptor antagonist, in a rat model of traumatic brain injury (TBI).Methods: Sprague Dawley rats were subjected to TBI with a weight-drop device using 300 g-1 m weight-height impact. The groups were: control (saline), montelukast (10 mg kg −1 per day, ip), trauma and trauma + montelukast. Two days post-trauma, neurological examination scores were measured and animals were decapitated and the brain tissues were taken for the histologic and biochemical [malondialdehyde (MDA)—an index for lipid peroxidation, reduced glutathione (GSH), myeloperoxidase (MPO)—an index for neutrophil infiltration and Na +/K +-ATPase activity] evaluations. Brain oedema and blood–brain barrier (BBB) permeability were also evaluated.Results: The neurological examination scores mildly increased in trauma groups at 48 hours. Although the scores were decreased in the montelukast treated group, they were still significantly higher than the control. The trauma caused a significant increase in brain water content and Evans blue (EB) extravasation. Montelukast treatment reduced BBB permeability. It also decreased lipid peroxidation and MPO activity.Conclusion: The present study suggests that montelukast may have beneficial effects against TBI-induced oxidative stress of the brain.

Leukotriene D4 Stimulates the Migration but Not Proliferation of Endothelial Cells Mediated by the Cysteinyl Leukotriene CysLT1 Receptor via the Extracellular Signal-Regulated Kinase Pathway

The actions of cysteinyl leukotrienes (CysLTs) are mediated by activating CysLT receptors, CysLT1, and CysLT2. The CysLT1 receptor mediates vascular responses to CysLTs; however, its effect on the proliferation and migration of endothelial cells is not clarified. To determine this effect, we observed proliferation and migration in EA.hy926 cells, a human endothelial cell line, and the involvement of activation of mitogen-activated protein kinases (MAPKs). We found that LTD4 did not affect the proliferation, but significantly stimulated the migration of endothelial cells. LTD4 also induced the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2, but not those of p38 or JNK. The LTD4-induced migration and ERK1/2 phosphorylation were blocked by the CysLT1-receptor antagonist montelukast and the dual antagonist Bay u9773, but not by the CysLT2-receptor antagonist Bay cysLT2; the migration was also inhibited by the ERK1/2 inhibitor U0126. Our findings indicate that LTD4 stimulates the CysLT1 receptor–mediated migration of endothelial cells; this may be regulated by the ERK1/2 pathway.

Montelukast inhibits neutrophil pro‐inflammatory activity by a cyclic AMP‐dependent mechanism

The objective of this study was to characterize the effects of the cysteinyl leukotriene receptor antagonist, montelukast (0.1-2 micromol x L(-1)), on Ca(2+)-dependent pro-inflammatory activities, cytosolic Ca(2+) fluxes and intracellular cAMP in isolated human neutrophils activated with the chemoattractants, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (1 micromol x L(-1)) and platelet-activating factor (200 nmol x L(-1)). Generation of reactive oxygen species was measured by lucigenin- and luminol-enhanced chemiluminescence, elastase release by a colourimetric assay, leukotriene B(4) and cAMP by competitive binding ELISA procedures, and Ca(2+) fluxes by fura-2/AM-based spectrofluorimetric and radiometric ((45)Ca(2+)) procedures. Pre-incubation of neutrophils with montelukast resulted in dose-related inhibition of the generation of reactive oxygen species and leukotriene B(4) by chemoattractant-activated neutrophils, as well as release of elastase, all of which were maximal at 2 micromol x L(-1) (mean percentages of the control values of 30 +/- 1, 12 +/- 3 and 21 +/- 3 respectively; P < 0.05). From a mechanistic perspective, treatment of chemoattractant-activated neutrophils with montelukast resulted in significant reductions in both post-peak cytosolic Ca(2+) concentrations and store-operated Ca(2+) influx. These montelukast-mediated alterations in Ca(2+) handling by the cells were associated with a significant elevation in basal cAMP levels, which resulted from inhibition of cyclic nucleotide phosphodiesterases. Montelukast, primarily a cysteinyl leukotriene (CysLT(1)) receptor antagonist, exhibited previously undocumented, secondary, neutrophil-directed anti-inflammatory properties, which appeared to be cAMP-dependent.

Regulatory effects of arachidonate 5-lipoxygenase on hepatic microsomal TG transfer protein activity and VLDL-triglyceride and apoB secretion in obese mice

As 5-lipoxygenase (5-LO) is an emerging target in obesity and insulin resistance, we have investigated whether this arachidonate pathway is also implicated in the progression of obesity-related fatty liver disease. Our results show that 5-LO activity and 5-LO-derived product levels are significantly elevated in the liver of obese ob/ob mice with respect to wild-type controls. Treatment of ob/ob mice with a selective 5-LO inhibitor exerted a remarkable protection from hepatic steatosis as revealed by decreased oil red-O staining and reduced hepatic triglyceride (TG) concentrations. In addition, 5-LO inhibition in ob/ob mice downregulated genes involved in hepatic fatty acid uptake (i.e., L-FABP and FAT/CD36) and normalized peroxisome proliferator-activated receptor alpha (PPARalpha) and acyl-CoA oxidase expression, whereas the expression of lipogenic genes [i.e., fatty acid synthase (FASN) and SREBP-1c] remained unaltered. Furthermore, 5-LO inhibition restored hepatic microsomal TG transfer protein (MTP) activity in parallel with a stimulation of hepatic VLDL-TG and apoB secretion in ob/ob mice. Consistent with these findings, 5-LO products directly inhibited MTP activity and triggered cytosolic TG accumulation in CC-1 cells, a murine hepatocyte cell line. Taken together, these findings identify a novel steatogenic role for 5-LO in the liver through mechanisms involving the regulation of hepatic MTP activity and VLDL-TG and apoB secretion.

A Double-Blind, Placebo-Controlled, Randomized Trial of Montelukast for Acute Bronchiolitis

Cysteinyl leukotrienes are implicated in the inflammation of bronchiolitis. Recently, a specific cysteinyl leukotriene receptor antagonist, montelukast (Singulair [MSD, Haarlem, Netherlands]), has been approved for infants in granule sachets. Our goal was to evaluate the effect of montelukast on clinical progress and on cytokines in acute bronchiolitis. This was a randomized, placebo-controlled, double-blind, parallel-group study in 2 medical centers. Fifty-three infants (mean age: 3.8+/-3.5 months) with a first episode of acute bronchiolitis were randomly assigned to receive either 4-mg montelukast sachets or placebo, every day, from hospital admission until discharge. The primary outcome was length of stay, and secondary outcomes included clinical severity score (maximum of 12) and changes in type 1 and 2 cytokine levels (including interleukin4/IFN-gamma ratio as a surrogate for the T-helper 2/T-helper 1 ratio) in nasal lavage. Both groups were comparable at baseline, and cytokine levels correlated positively with disease severity. There were neither differences in length of stay (4.63+/-1.88 [placebo group] vs 4.65+/-1.97 days [montelukast group]) nor in clinical severity score and cytokine levels between the 2 groups. No differences in interleukin 4/IFN-gamma ratio between the 2 groups were seen. There was a slight tendency for infants in the montelukast group to recover more slowly than those in the placebo group (clinical severity score at discharge: 6.1+/-2.4 vs 4.8+/-2.2, respectively). Montelukast did not improve the clinical course in acute bronchiolitis. No significant effect of montelukast on the T-helper 2/T-helper 1 cytokine ratio when given in the early acute phase could be demonstrated.

Anti-atherogenic effects of montelukast associated with reduced MCP-1 expression in a rabbit carotid balloon injury model

Atherosclerosis is characterized by inflammatory responses of the arterial wall to “injury”, which is prominently driven by inflammatory mediators. Montelukast, a selective CysLT1 receptor antagonist, has potent anti-inflammatory effects in diverse animal models. However, the role of montelukast in regulating inflammatory progression of atherosclerosis has not been elucidated. Therefore, we investigated the effect of montelukast on atherosclerosis compared with that of atorvastatin. Twenty-six male New Zealand White rabbits were randomized into four groups including a negative control group. The rabbits were fed a normal diet or an atherogenic diet for 12 weeks. The rabbits, except the negative control group, received right carotid artery balloon-injury 2 weeks after initiation of the atherogenic diet. Animals were then treated with montelukast (1mg/kg/day), atorvastatin (1.5mg/kg/day) or placebo for 4 weeks, respectively. At the end of the treatment, animals were killed and carotids were dislodged and detected. The results indicated that the placebo group had significant progression of atherosclerosis compared with the negative control group. In contrast, montelukast or atorvastatin treated rabbits showed a significant reduction of neointima, decreased macrophage content, increased SMC content and inhibited expression of MCP-1. Between two drugs, there were no significant differences in reducing neointima and decreasing the level of MCP-1. However, montelukast had no influence on plasma lipids, while atorvastatin down-regulated the levels of TC, TG and LDL. These results suggest that montelukast produces anti-atherogenic effects unrelated to plasma lipid modulation but related to MCP-1 down regulation.

The effects of montelukast on random pattern skin flap survival: An experimental study in rats

Background: A variety of methods to improve skin flap survival, including the use of pharmacologic agents, have been intensively investigated. Decreasing neutrophil-mediated inflammation and tissue injury has been reported to be effective in improving flap survival. Montelukast is a selective reversible cysteinyl leukotriene receptor-1 antagonist that has been found to have protective effects against renal ischemia reperfusion injury and burn-induced oxidative injury of the skin in rats. However, its effects on skin flap survival have not been previously reported. Objective: The aim of this study was to investigate the effects of montelukast on neutrophil-mediated random pattern skin flap survival. Methods: Male Sprague-Dawley rats weighing 230 to 250 g were randomly divided into 2 groups—the montelukast-treated group and the control group. Caudally based rectangular random pattern skin flaps 3 × 9 cm were elevated on the backs of the rats. The flaps were sutured into their original places. In the montelukast group, 1 mL of solution containing 10 mg/kg montelukast was administered intraperitoneally (IP) 30 minutes before surgery and then daily for 6 days. In the control group, 1 mL of saline was administered IP 30 minutes before surgery and then daily for 6 days. To observe the effects of montelukast, myeloperoxidase (MPO) activity, an index of tissue neutrophil infiltration, was measured from extracted skin tissue 12 hours after flap elevation. Flap viability was evaluated 7 days after surgery by measuring necrotic flap area and total flap area. Results: Sixteen rats (mean [SD] weight, 240.6 [6.6] g) were equally divided between the 2 groups. All rats survived throughout the study period. Mean (SD) MPO activity in flap tissue was significantly lower in the montelukast group than in the control group (14.57 [2.33] vs 21.28 [4.86] U/g protein; P = 0.005). The percentage of necrotic flap area was significantly lower in the montelukast group than in the control group (17.17 [7.95] vs 37.51 [10.72]; P = 0.001). Conclusion: This small, experimental, in vivo animal study found that montelukast was associated with both lower MPO activity and a lower percentage of necrotic random pattern skin flap area. Future studies are needed to clarify these findings.

Cysteinyl leucotriene receptor type 1 mediates contraction in human and guinea‐pig oesophagus

Leucotriene D(4) (LTD(4)) causes contraction of the guinea-pig and cat oesophagus. Effects of cysteinyl leucotrienes in the human oesophagus were unknown. To investigate and compare the cysteinyl leucotriene effects in the human oesophagus with those in the guinea-pig oesophagus, we measured contraction of muscularis mucosae strips isolated from the human and guinea-pig oesophagus caused by cysteinyl leucotrienes, LTC(4), LTD(4) and LTE(4), as well as the dihydroxy leucotriene, LTB(4). Effects of leucotrienes in human were similar to those in guinea-pig oesophagus. LTC(4) and LTD(4) caused moderate, whereas LTE(4) caused mild, concentration-dependent contraction. LTE(4) was a partial agonist. In contrast, LTB(4) did not cause any contraction. The relative potencies for cysteinyl leucotrienes to cause contraction were LTD(4) = LTC(4) > LTE(4). The LTD(4)-induced contraction was moderately inhibited by two selective CysLT(1) receptor antagonists, montelukast and zafirlukast, in both human and guinea-pig oesophagus. In addition, the LTD(4)-induced contraction was not and only slightly inhibited by BAY u9773, the CysLT(1) and CysLT(2) receptor antagonist, in the human and guinea-pig oesophageal muscularis mucosae respectively. These indicate the existence of the CysLT(1) mediating oesophageal contraction in both human and guinea-pig oesophagus. The LTD(4)-induced contraction was not affected by tetrodotoxin, atropine or capsaicin, suggesting a direct effect. These results demonstrate that cysteinyl leucotrienes but not the dihydroxy leucotriene cause contraction in the human and guinea-pig oesophagus. CysLT(1) mediates contraction in both human and guinea-pig oesophagus.

Protective Potential of Montelukast Against Hepatic Ischemia/Reperfusion Injury in Rats

Ischemia and reperfusion (I/R) injury is characterized by significant oxidative stress, characteristic changes in the antioxidant system and organ injury leading to significant morbidity and mortality. This study was designed to assess the possible protective effect of montelukast, a selective antagonist of cysteinyl leukotriene receptor 1 (CysLT1), on hepatic I/R injury in rats. Wistar albino rats through clamping hepatic artery, portal vein, and bile duct, were subjected to 45 min of hepatic ischemia followed by 60 min reperfusion period. Montelukast (10 mg/kg; i.p.) was administered 15 min prior to ischemia and immediately before reperfusion period. At the end of the reperfusion period, the rats were killed by decapitation. Aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH) activity, and proinflammatory cytokines (TNF-alpha and IL-1beta) were determined in blood samples. Malondialdehyde (MDA), and glutathione (GSH) levels and myeloperoxidase (MPO) and Na+, K+-ATPase activities were determined in the liver tissue samples while formation of reactive oxygen species was monitored by using chemiluminescence (CL) technique with luminol and lucigenin probes. Tissues were also analyzed histologically. Serum ALT, AST, and LDH activities were elevated in the I/R group, while this increase was significantly decreased by montelukast treatment. Hepatic GSH levels and Na+, K+-ATPase activity, significantly depressed by I/R, were elevated back to control levels in montelukast-treated I/R group. Furthermore, increases in tissue luminol and lucigenin CL, MDA levels, and MPO activity due to I/R injury were reduced back to control levels with montelukast treatment. Since montelukast administration alleviated the I/R-induced liver injury and improved the hepatic structure and function, it seems likely that montelukast with its anti-inflammatory and antioxidant properties may be of potential therapeutic value in protecting the liver against oxidative injury due to ischemia-reperfusion.