Leukotriene receptors

Discovery of agonist-antagonist pairs for the modulation of Ca [2]+ and voltage-gated K+ channels of large conductance that contain beta1 subunits

Large conductance, calcium/voltage-gated potassium channels (BK) regulate critical body processes, including neuronal, secretory and smooth muscle (SM) function. While BK-forming alpha subunits are ubiquitous, accessory beta1 subunits are highly expressed in SM. This makes beta1 an attractive target for pharmaceutical development to treat SM disorders, such as hypertension or cerebrovascular spasm. Compounds activating BK via beta1 have been identified, yet they exhibit low potency and off-target effects while antagonists that limit agonist activity via beta 1 remain unexplored. Beta1-dependent BK ligand-based pharmacophore modeling and ZINC database searches identified 15 commercially available hits. Concentration-response curves on BK alpha + beta1 subunit-mediated currents were obtained in CHO cells. One potent (EC50 = 20 nM) and highly efficacious activator (maximal activation = ×10.3 of control) was identified along with a potent antagonist (KB = 3.02 nM), both of which were dependent on beta1. Our study provides the first proof-of-principle that an agonist/antagonist pair can be used to control beta1-containing BK activity.

Montelukast suppresses the development of irritable bowel syndrome phenotype possibly through modulating NF-κB signaling in an experimental model

Irritable bowel syndrome (IBS) is a functional gut disorder with multi-factorial pathophysiology that causes recurring pain or discomfort in the abdomen, as well as altered bowel habits. Montelukast, a well-known cysteinyl leukotriene receptor 1 (CysLT1R) antagonist, is widely used for the anti-inflammatory management of asthma. The present study aimed to evaluate the effects of pharmacological inhibition of CysLT1R on acetic acid-induced diarrhea-predominant IBS (D-IBS) in rats. Behavioral pain responses to noxious mechanical stimulation were decreased in the montelukast-treated rats as compared to the model animals following colorectal distension (CRD)-induced visceral hypersensitivity. Stool frequency decreased dose-dependently by montelukast in IBS rats exposed to restraint stress. A significantly shorter immobility time was also observed in IBS rats who received montelukast vs IBS group in the forced swimming test (depression-like behavior). Furthermore, there were significant decreases in the NF-κB protein expression, inflammatory cytokine (TNF-α, and IL-1ß) levels, and histopathological inflammatory injuries concomitant with increased anti-inflammatory cytokine, IL-10, in montelukast-treated rats compared with the IBS group. Cysteinyl leukotriene production and CysLT1R mRNA expression showed no remarkable differences among the experimental groups. The present results suggest the possible beneficial effects of montelukast in the management of D-IBS symptoms. The molecular mechanism underlying such effects, at least to some extent, might be through modulating CysLT1R-mediated NF-κB signaling. Yet, more studies are required to demonstrate the clinical potential of this drug for IBS therapy.

Eicosanoid receptors as therapeutic targets for asthma

Eicosanoids comprise a group of oxidation products of arachidonic and 5,8,11,14,17-eicosapentaenoic acids formed by oxygenases and downstream enzymes. The two major pathways for eicosanoid formation are initiated by the actions of 5-lipoxygenase (5-LO), leading to leukotrienes (LTs) and 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), and cyclooxygenase (COX), leading to prostaglandins (PGs) and thromboxane (TX). A third group (specialized pro-resolving mediators; SPMs), including lipoxin A4 (LXA4) and resolvins (Rvs), are formed by the combined actions of different oxygenases. The actions of the above eicosanoids are mediated by approximately 20 G protein-coupled receptors, resulting in a variety of both detrimental and beneficial effects on airway smooth muscle and inflammatory cells that are strongly implicated in asthma pathophysiology. Drugs targeting proinflammatory eicosanoid receptors, including CysLT1, the receptor for LTD4 (montelukast) and TP, the receptor for TXA2 (seratrodast) are currently in use, whereas antagonists of a number of other receptors, including DP2 (PGD2), BLT1 (LTB4), and OXE (5-oxo-ETE) are under investigation. Agonists targeting anti-inflammatory/pro-resolving eicosanoid receptors such as EP2/4 (PGE2), IP (PGI2), ALX/FPR2 (LXA4), and Chemerin1 (RvE1/2) are also being examined. This review summarizes the contributions of eicosanoid receptors to the pathophysiology of asthma and the potential therapeutic benefits of drugs that target these receptors. Because of the multifactorial nature of asthma and the diverse pathways affected by eicosanoid receptors, it will be important to identify subgroups of asthmatics that are likely to respond to any given therapy.

Cysteinyl Leukotrienes Pathway Genes, Atopic Asthma and Drug Response: From Population Isolates to Large Genome-Wide Association Studies

Genetic variants associated with asthma pathogenesis and altered response to drug therapy are discussed. Many studies implicate polymorphisms in genes encoding the enzymes responsible for leukotriene synthesis and intracellular signaling through activation of seven transmembrane domain receptors, such as the cysteinyl leukotriene 1 (CYSLTR1) and 2 (CYSLTR2) receptors. The leukotrienes are polyunsaturated lipoxygenated eicosatetraenoic acids that exhibit a wide range of pharmacological and physiological actions. Of the three enzymes involved in the formation of the leukotrienes, arachidonate 5 lipoxygenase 5 (ALOX5), leukotriene C4 synthase (LTC4S), and leukotriene hydrolase (LTA4H) are all polymorphic. These polymorphisms often result in variable production of the CysLTs (LTC4, LTD4, and LTE4) and LTB4. Variable number tandem repeat sequences located in the Sp1-binding motif within the promotor region of the ALOX5 gene are associated with leukotriene burden and bronchoconstriction independent of asthma risk. A 444A > C SNP polymorphism in the LTC4S gene, encoding an enzyme required for the formation of a glutathione adduct at the C-6 position of the arachidonic acid backbone, is associated with severe asthma and altered response to the CYSLTR1 receptor antagonist zafirlukast. Genetic variability in the CysLT pathway may contribute additively or synergistically to altered drug responses. The 601 A > G variant of the CYSLTR2 gene, encoding the Met201Val CYSLTR2 receptor variant, is associated with atopic asthma in the general European population, where it is present at a frequency of ∼2.6%. The variant was originally found in the founder population of Tristan da Cunha, a remote island in the South Atlantic, in which the prevalence of atopy is approximately 45% and the prevalence of asthma is 36%. In vitro work showed that the atopy-associated Met201Val variant was inactivating with respect to ligand binding, Ca²⁺ flux and inositol phosphate generation. In addition, the CYSLTR1 gene, located at Xq13-21.1, has been associated with atopic asthma. The activating Gly300Ser CYSLTR1 variant is discussed. In addition to genetic loci, risk for asthma may be influenced by environmental factors such as smoking. The contribution of CysLT pathway gene sequence variants to atopic asthma is discussed in the context of other genes and environmental influences known to influence asthma.

Leukotrienes in pulmonary arterial hypertension

Leukotrienes (LTs) are lipid mediators derived from the 5-lipoxygenase (5-LO) pathway of arachidonic acid metabolism and are markers and mediators of pulmonary inflammation. Research over the past two decades has established that LTs modulate inflammation in pulmonary arterial hypertension (PAH). The purpose of this review was to summarize the current knowledge of LTs in the pathophysiology of PAH and to highlight a recent study that advances our understanding of how leukotriene B4 (LTB4) specifically contributes to pulmonary vascular remodeling. The results of these studies suggest that pharmacological inhibition of LT pathways, especially LTB4, has high potential for the treatment of PAH.

Unraveling the genetic basis of aspirin hypersensitivity in asthma beyond arachidonate pathways

Although aspirin-exacerbated respiratory disease (AERD) has attracted a great deal of attention because of its association with severe asthma, it remains widely under-diagnosed in the asthmatic population. Oral aspirin challenge is the best method of diagnosing AERD, but this is a time-consuming procedure with serious complications in some cases. Thus, development of non-invasive methods for easy diagnosis is necessary to prevent unexpected complications of aspirin use in susceptible patients. For the past decade, many studies have attempted to elucidate the genetic variants responsible for risk of AERD. Several approaches have been applied in these genetic studies. To date, a limited number of biologically plausible candidate genes in the arachidonate and immune and inflammatory pathways have been studied. Recently, a genome-wide association study was performed. In this review, the results of these studies are summarized, and their limitations discussed. In addition to the genetic variants, changes in methylation patterns on CpG sites have recently been identified in a target tissue of aspirin hypersensitivity. Finally, perspectives on application of new genomic technologies are introduced; these will aid our understanding of the genetic pathogenesis of aspirin hypersensitivity in asthma.

Cysteinyl leukotriene receptor assays

The cysteinyl leukotrienes (CysLTs), LTC4, LTD4 and LTE4, lipid products derived from arachidonic acid metabolism, have been implicated in the pathophysiology of several inflammatory diseases, in particular, asthma. This unit describes techniques and applications for the measurement of contractile responses to the CysLTs in isolated smooth muscle preparations. The contractions are assessed by standard methods for the isometric measurement of responses (contractile or relaxant) of isolated tissues to exogenous agonists, and a detailed description of the methods employed to assess CysLT-induced contractions in guinea-pig trachea is outlined. However, the same general methodology (other than parameters such as dissection for non-airway tissues) are appropriate for measuring CysLT-induced contractions in airway preparations from other animals, and in non-airways tissues (e.g., the gastrointestinal tract) from different species, and also in exploring the relaxant responses to the CysLTs that have been demonstrated in some tissues (e.g., pulmonary vein or artery).

Recent research and developmental strategy of anti-asthma drugs

Extensive research over the past decade has provided information about the pharmacotherapy of bronchial asthma (BA). Anti-asthma drugs are classified into two categories: relievers (for the relief of asthma attack symptoms) and controllers (for the prevention of asthma symptoms). This paper aims to review the recent advancements of anti-asthma drugs that are controller medicines. The controllers mainly act on immune and inflammatory responses in BA development. 1) Immunomodulators. Drugs that act on the immune response are classified into two categories: immunosuppressors and immunomodulators, including immunopotentiators. The immunomodulation of the Th1 and Th2 imbalance is the first strategy of the controller because allergic BA is thought to be caused by Th2-polarized immunity. Suplatast is a novel immunomodulator that can adjust the imbalance in the Th1/Th2 immune response and shows clear clinical efficacy against BA. The immunomodulator approach has shifted from a more theoretical and conceptual model to one supported by evidence of clinical efficacy.2) Anti-inflammatory agents. Corticosteroids,mast cell stabilizers and autacoid inhibitors are anti-inflammatory agents for BA. The clinical superiority of the combined therapy of inhaled corticosteroids and long-acting beta2 agonists is evident. This combined therapy shows a potent synergic anti-inflammatory effect compared to the effect by corticosteroids alone. Currently, the anti-inflammatory agents for BA under development are drugs affecting lipid mediators. The prostaglandin (PG) D2 antagonist, PGE2, EP3 agonist and PGI2 agonist are being considered in addition to well-established leukotriene and thromboxane A2 inhibitors. New development strategies and therapeutics for controllers are described in this review.

Protection of leukotriene receptor antagonist against aspirin-induced bronchospasm in asthmatics

PURPOSE

Leukotriene receptor antagonists (LTRAs) are used to treat aspirin-intolerant asthma (AIA); however, the protective effects of long-term LTRA administration against aspirin-induced bronchospasm have not been evaluated.

OBJECTIVES

We investigated the efficacy of a 12-week treatment with a LTRA in protecting against aspirin-induced asthma in AIA patients.

METHODS

Fifty-two adult patients with AIA underwent an aspirin challenge test just before administration of montelukast (10 mg/day) and just after 12 weeks of treatment. The protective effect was assessed as the disappearance of aspirin-induced bronchospasm after 12 weeks of treatment. The results were compared according to the patients' clinical and physiological parameters.

RESULTS

The decline in FEV1 following aspirin challenge was significantly reduced from 28.6+/-1.9% to 10.2+/-1.7% (P=0.0001) after 12 weeks of montelukast treatment. However, 14 subjects (30%) still showed a positive response (>15% decline in FEV1) to aspirin challenge. Grouping the subjects into good and poor responders according to post-treatment responses revealed that the pretreatment aspirin-induced FEV1 decline was significantly greater in the poor responders and that the triggering dose of aspirin and the induction time for a positive response were lower and shorter, respectively, in the poor responders. Histories of aspirin hypersensitivity and sinusitis were more prevalent among the poor responders than among the good responders.

CONCLUSIONS

Twelve weeks of treatment with montelukast protected against aspirin-induced bronchospasm in 70% of the AIA cases. A poor response was associated with more severe aspirin-induced bronchospasms before treatment and a history of aspirin hypersensitivity or sinusitis.

CLINICAL IMPLICATIONS

A severe response to aspirin challenge may be a predictor of poor responsiveness to leukotriene antagonist treatment.

Responsiveness to montelukast is associated with bronchial hyperresponsiveness and total immunoglobulin E but not polymorphisms in the leukotriene C4 synthase and cysteinyl leukotriene receptor 1 genes in Korean children with exercise-induced asthma (EIA)

BACKGROUND

As previous studies have shown that cysteinyl leukotrienes are important mediators in exercise-induced bronchoconstriction (EIB), and leukotriene receptor antagonists (LTRAs) such as montelukast have been shown to improve post-exercise bronchoconstrictor responses, we herein investigated whether clinical responsiveness to montelukast was associated with polymorphisms in the genes encoding leukotriene C4 synthase (LTC4S) and cysteinyl leukotriene receptor 1 (CysLTR1) and/or clinical parameters in Korean asthmatic children with EIB.

METHODS

The study population consisted of 100 asthmatic children with EIB. The individuals studied were given exercise challenge tests before and after receiving montelukast (5 mg/day) for 8 weeks. Responders were defined as children showing>10% post-treatment improvement in forced expiratory volume in 1 s (FEV1). The LTC4S A(-444)C and CysLTR1 T(+927)C polymorphisms were genotyped by PCR-restriction fragment length polymorphism analysis.

RESULTS

Of 100 enrolled children, 68 were classified as responders and 32 were classified as non-responders. No significant association was observed between montelukast responsiveness and LTC4S or CysLTR1 genotype, either alone or in combination. In contrast, montelukast-induced improvement in FEV(1) after exercise was correlated with higher pre-treatment PC20 (methacholine) values (r=0.210, P=0.036) and lower total IgE levels (r=-0.216, P=0.031).

CONCLUSIONS

The LTC4S A(-444)C and CysLTR1 T(+927)C genotypes do not appear to be useful for predicting clinical responsiveness to montelukast, whereas bronchial hyperresponsiveness and total IgE appear to predict the degree of montelukast responsiveness in Korean asthmatic children with EIB.

G-protein-coupled receptors and asthma endophenotypes: the cysteinyl leukotriene system in perspective

Genetic variation in specific G-protein coupled receptors (GPCRs) is associated with a spectrum of respiratory disease predispositions and drug response phenotypes. Although certain GPCR gene variants can be disease-causing through the expression of inactive, overactive, or constitutively active receptor proteins, many more GPCR gene variants confer risk for potentially deleterious endophenotypes. Endophenotypes are traits, such as bronchiole hyperactivity, atopy, and aspirin intolerant asthma, which have a strong genetic component and are risk factors for a variety of more complex outcomes that may include disease states. GPCR genes implicated in asthma endophenotypes include variants of the cysteinyl leukotriene receptors (CYSLTR1 and CYSLTR2), and prostaglandin D2 receptors (PTGDR and CRTH2), thromboxane A2 receptor (TBXA2R), beta2-adrenergic receptor (ADRB2), chemokine receptor 5 (CCR5), and the G protein-coupled receptor associated with asthma (GPRA). This review of the contribution of variability in these genes places the contribution of the cysteinyl leukotriene system to respiratory endophenotypes in perspective. The genetic variant(s) of receptors that are associated with endophenotypes are discussed in the context of the extent to which they contribute to a disease phenotype or altered drug efficacy.

Signalling pathways connecting mycotoxin production and sporulation

SUMMARY Mycotoxin contamination of food and feed presents a serious food safety issue on a global scale, causing tremendous yield and economic losses. These toxins, produced largely by members of the genera Aspergillus and Fusarium, represent a subset of the impressive array of secondary metabolites produced by filamentous fungi. Some secondary metabolites are associated temporally and functionally with sporulation. In Aspergillus and Fusarium, sporulation and mycotoxin production are both regulated by G protein signalling pathways. G protein signalling pathways commonly regulate fungal development, stress response and expression of virulence traits. In addition, fungal development is influenced by external factors. Among these are lipids, and in particular, oxylipin signals, which may be derived from either the fungus or infected seeds. Regardless of origin, oxylipins have the potential to elicit profound changes in both sporulation and mycotoxin production in the fungus. Signal transduction via G protein signalling pathways represents one mechanism by which oxylipin signals might elicit these changes. Therefore, in this review we integrate discussion of oxylipin signals and of G protein signalling cascades as regulators of fungal development.

Cysteinyl leukotriene 1 receptor expression in nasal polyps

OBJECTIVES

The pathogenesis of nasal polyps, thought to involve complex interactions between different factors, is currently not fully understood. Recent studies have suggested the involvement of cysteinyl leukotrienes (CysLTs) in nasal polyp development. To further understand the role of CysLTs in polyp pathogenesis, we studied the expression of CysLT1 receptors in nasal polyps.

METHODS

The study group comprised polyps removed endoscopically from 20 consecutive patients. Samples of ethmoid mucosa from 4 patients who underwent orbital decompression for Graves' ophthalmopathy were used as controls. The presence of CysLT1 receptors was determined with a rabbit anti-human anti-CysLT1 receptor polyclonal antibody. Cells with and without CysLT1 receptor expression were counted within the epithelial layer and stroma by means of light microscopy (40x magnification).

RESULTS

There were significantly more cells expressing CysLT1 receptors in the stroma than in the epithelium in both nasal polyps and control specimens. The stroma of polyps also contained more CysLT1 receptor-expressing cells than did controls (29 x 10(3) +/- 7 x 10(3) versus 3 x 10(3) +/- 3 x 10(3) cells per square millimeter; p < .01). In the epithelium of polyps, there was significantly higher expression of CysLT1 receptors than in controls (7 x 10(3) + 3 x 10(3) versus 0 cells per square millimeter; p = .02). No significant differences in polyps were found between patients with and patients without Samter's triad and asthma.

CONCLUSIONS

The significant up-regulation of CysLT1 receptors we found in both the stroma and the epithelium of nasal polyps suggests the presence of an inflammatory component in the pathogenesis of polyps, and possibly explains the efficacy of leukotriene modifiers in their treatment.

The G protein-coupled receptors: pharmacogenetics and disease

Genetic variation in G-protein coupled receptors (GPCRs) is associated with a wide spectrum of disease phenotypes and predispositions that are of special significance because they are the targets of therapeutic agents. Each variant provides an opportunity to understand receptor function that complements a plethora of available in vitro data elucidating the pharmacology of the GPCRs. For example, discrete portions of the proximal tail of the dopamine D1 receptor have been discovered, in vitro, that may be involved in desensitization, recycling and trafficking. Similar in vitro strategies have been used to elucidate naturally occurring GPCR mutations. Inactive, over-active or constitutively active receptors have been identified by changes in ligand binding, G-protein coupling, receptor desensitization and receptor recycling. Selected examples reviewed include those disorders resulting from mutations in rhodopsin, thyrotropin, luteinizing hormone, vasopressin and angiotensin receptors. By comparison, the recurrent pharmacogenetic variants are more likely to result in an altered predisposition to complex disease in the population. These common variants may affect receptor sequence without intrinsic phenotype change or spontaneous induction of disease and yet result in significant alteration in drug efficacy. These pharmacogenetic phenomena will be reviewed with respect to a limited sampling of GPCR systems including the orexin/hypocretin system, the beta2 adrenergic receptors, the cysteinyl leukotriene receptors and the calcium-sensing receptor. These developments will be discussed with respect to strategies for drug discovery that take into account the potential for the development of drugs targeted at mutated and wild-type proteins.

Association analysis of cysteinyl-leukotriene receptor 2 (CYSLTR2) polymorphisms with aspirin intolerance in asthmatics

OBJECTIVES AND METHODS

The cysteinyl leukotriene receptor 2 (CYSLTR2) gene on chromosome 13q14.12-q21.1 encodes a receptor for CYSLTs, potent biological mediators in the pathogenesis of asthma, particularly that associated with aspirin intolerance (AIA). In an effort to discover additional polymorphism(s), the variant(s) of which have been implicated in asthma and aspirin intolerance, we scrutinized genetic polymorphisms of the CYSLTR2 gene, and evaluated this locus as a potential candidate for asthma.

RESULTS

DNA sequencing in 24 Koreans of the 5-kb region of the CYSLTR2 gene, including the approximately 1500-bp promoter region, revealed four sequence variants: one in the 5'-flanking region (c.-819T>G), two in the 3'-flanking region (c.2078C>T and c.2534A>G), and one downstream of the gene (c.2545+297A>G). The SNP frequencies were 0.499 (c.-819T>G), 0.351 (c.2078C>T), 0.429 (c.2534A>G), and 0.088 (c.2545+297A>G), and five haplotypes were constructed. The SNPs and haplotypes were not associated with risk of asthma development, but were significantly associated with aspirin intolerance. The frequencies of rare alleles on c.-819T>G, c.2078C>T, and c.2534A>G were higher in subjects with AIA than in subjects with aspirin-tolerant asthma (P=0.013-0.031). Asthmatics who had rare alleles for c.-819T>G, c.2078C>T or c.2534A>G exhibited a more pronounced fall in FEV1 after aspirin provocation than did those who carried the common allele (P=0.03-0.009). Asthmatics carrying ht2 (TTGA) also showed a more pronounced decrease in FEV1% after aspirin provocation than those carrying ht1 (GCGA) (P=0.006). These associations were even stronger when combined with LTC4S polymorphisms (-444A>C [c.-444A>C]) gene.

CONCLUSION

CYSLTR2 polymorphisms are associated with aspirin intolerance in asthmatics.

The cysteinyl leukotriene receptors

The cysteinyl leukotriene (CysLT) receptors are putative 7 transmembrane spanning G protein-coupled receptors (GPCRs) of the rhodopsin subfamily of GPCRs. Two human and mouse CysLT receptors have been molecularly cloned and characterized. The properties of these receptors agrees well with previous pharmacological CysLT agonist and antagonist characterizations of the CysLT receptors.

Mesenteric microvascular inflammatory responses to systemic hypoxia are mediated by PAF and LTB4

Systemic hypoxia produces a rapid microvascular inflammatory response characterized by increased reactive oxygen species (ROS) levels, leukocyte-endothelial adherence and emigration, and increased vascular permeability. The lipid inflammatory mediator leukotriene B(4) (LTB(4)) is involved in the early hypoxia-induced responses (ROS generation and leukocyte adherence). Whether other lipid inflammatory mediators participate in this phenomenon is not known. The objective of these experiments was to study the role of platelet-activating factor (PAF) in the microvascular inflammatory response to hypoxia and its potential interactions with LTB(4) in this response. Intravital microscopy was used to examine mesenteric venules of anesthetized rats. We found that WEB-2086, a PAF receptor antagonist, completely prevented the increase in ROS levels and leukocyte adherence during a brief reduction in inspired Po(2) to anesthetized rats; administration of either WEB-2086 or the LTB(4) antagonist LTB(4)-DMA attenuated leukocyte emigration and the increase in vascular permeability to the same extent during prolonged systemic hypoxia in conscious rats. Furthermore, no additive effect was observed in either response when both antagonists were administered simultaneously. This study demonstrates a role for PAF in the rapid microvascular inflammatory response to hypoxia, as well as contributions of PAF and LTB(4) to the slowly developing responses observed during sustained hypoxia. The incomplete blockade of the hypoxia-induced increases in vascular permeability and leukocyte emigration by combined administration of both antagonists indicates that factors in addition to LTB(4) and PAF participate in these phenomena.

Actions of cysteinyl leukotrienes in the enteric nervous system of guinea-pig stomach and small intestine

Conventional intracellular microelectrodes, neuronal tracer injection techniques and immunohistochemistry were used to study the actions of cysteinyl leukotrienes (CysLTs) on electrical and synaptic behavior of enteric neurons in guinea-pig stomach and small intestine. Bath application of leukotriene C(4), leukotriene D(4) or leukotriene E(4) evoked a slowly activating depolarizing response in most of the myenteric and submucous plexus neurons in the small intestine while no effect was observed in gastric neurons. The depolarization evoked by cysteinyl leukotrienes in intestinal neurons was associated with increased input resistance and enhanced excitability. Suppression of hyperpolarizing after-potentials occurred in AH type neurons. The depolarizing action of cysteinyl leukotrienes was resistant to tetrodotoxin and cyclooxygenase inhibitors. Neither the CysLT(1) receptor antagonists (E)-3-[[[3-[2-(7-chloro-2-quinolinyl)ethenyl]phenyl][[3-dimethylamino)-3-oxopropyl]thio]methyl]thio]-propanoic acid (MK 571), 1-[2-hydroxy-3-propyl-4-[4-(1H-tetrazol-5-yl)butoxy]phenyl]-ethanone (LY 171883) and alpha-pentyl-3-(2-quinolinylmethoxy)-benzenemethanol (REV 5901), nor the dual CysLT(1)/CysLT(2) receptor antagonist 6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11(Z),14(Z)-eicosatetraenoic acid (BAY u9773) significantly altered the depolarizing action of the cysteinyl leukotrienes. Neurotransmission was unaffected by the cysteinyl leukotrienes. The results suggested involvement of cysteinyl leukotrienes in enteric immuno-neural communication through excitatory actions on enteric neurons. The receptor mediating these effects was distinct from currently recognized cysteinyl leukotriene receptor subtypes (CysLT(1) and CysLT(2) receptors) and may represent a new receptor subtype.

Roles of cysteinyl leukotrienes in airway inflammation, smooth muscle function, and remodeling

A new paradigm for asthma pathogenesis is presented in which exaggerated inflammation and remodeling in the airways are a consequence of abnormal injury and repair responses arising from a subject's susceptibility to components of the inhaled environment. An epithelial-mesenchymal trophic unit becomes activated to drive pathologic remodeling and smooth muscle proliferation through complex cytokine interactions. Histamine, prostanoids, and cysteinyl leukotrienes (CysLTs) are potent contractile agonists of airway smooth muscle (ASM). The CysLTs appear to play a central role in regulating human ASM motor tone and phenotypic alterations, manifested as hypertrophy and hyperplasia in chronic severe asthma. The CysLTs augment growth factor-induced ASM mitogenesis through activation of CysLT receptors. Although they mediate their contractile effects by increasing phosphoinositide turnover and inducing increased cytosolic calcium, new data suggest that part of the contractile effect may be independent of calcium mobilization. Prostaglandin E(2), the predominant eicosanoid product of the airway epithelium, is a potent inhibitor of mitogenesis, collagen synthesis, and mesenchymal cell chemotaxis and therefore can suppress inflammation and fibroblast activation. The capacity of the epithelium for CysLT synthesis is inversely related to its ability to make PGE(2). The ASM is capable of expressing both leukotriene-synthesizing enzymes and CysLT receptors, and cytokines upregulate the receptor expression. This may be an explanation for the CysLTs promoting airway hyperresponsiveness in asthma. The CysLTs play an important role in the airway remodeling seen in persistent asthma that includes increases of airway goblet cells, mucus, blood vessels, smooth muscle, myofibroblasts, and airway fibrosis. Evidence from a mouse model of asthma demonstrated that CysLT(1) receptor antagonists inhibit the airway remodeling processes, including eosinophil trafficking to the lungs, eosinophil degranulation, T(H)2 cytokine release, mucus gland hyperplasia, mucus hypersecretion, smooth muscle cell hyperplasia, collagen deposition, and lung fibrosis.

Differential peristaltic motor effects of prostanoid (DP, EP, IP, TP) and leukotriene receptor agonists in the guinea-pig isolated small intestine

1. Since the role of prostanoid receptors in intestinal peristalsis is largely unknown, the peristaltic motor effects of some prostaglandin (DP, EP, IP), thromboxane (TP) and leukotriene (LT) receptor agonists and antagonists were investigated. 2. Propulsive peristalsis in fluid-perfused segments from the guinea-pig small intestine was triggered by a rise of the intraluminal pressure and recorded via the intraluminal pressure changes associated with the peristaltic waves. Alterations of distension sensitivity were deduced from alterations of the peristaltic pressure threshold and modifications of peristaltic performance were reflected by modifications of the amplitude, maximal acceleration and residual baseline pressure of the peristaltic waves. 3. Four categories of peristaltic motor effects became apparent: a decrease in distension sensitivity and peristaltic performance as induced by the EP1/EP3 receptor agonist sulprostone and the TP receptor agonist U-46619 (1-1000 nM); a decrease in distension sensitivity without a major change in peristaltic performance as induced by PGD(2) (3-300 nM) and LTD(4) (10-100 nM); a decrease in peristaltic performance without a major change in distension sensitivity as induced by PGE(1), PGE(2) (1-1000 nM) and the EP1/IP receptor agonist iloprost (1-100 nM); and a decrease in peristaltic performance associated with an increase in distension sensitivity as induced by the EP2 receptor agonist butaprost (1-1000 nM). The DP receptor agonist BW-245 C (1-1000 nM) was without effect. 4. The peristaltic motor action of sulprostone remained unchanged by the EP1 receptor antagonist SC-51089 (1 micro M) and the DP/EP1/EP2 receptor antagonist AH-6809 (30 micro M), whereas that of U-46619 and LTD(4) was prevented by the TP receptor antagonist SQ-29548 (10 micro M) and the cysteinyl-leukotriene(1) (cysLT(1)) receptor antagonist tomelukast (10 micro M), respectively. 5. These observations and their pharmacological analysis indicate that activation of EP2, EP3, IP, TP and cysLT(1) receptors, but not DP receptors, modulate intestinal peristalsis in a receptor-selective manner, whereas activation of EP1 seems to be without influence on propulsive peristalsis. In a wider perspective it appears as if the effect of prostanoid receptor agonists to induce diarrhoea is due to their prosecretory but not peristaltic motor action.

Distal lung inflammation in asthma

OBJECTIVE

To review the role of distal lung inflammation in asthma.

DATA SOURCES AND STUDY SELECTION

Selected peer-reviewed research publications retrieved from MEDLINE search. Search was restricted to English-language publications only. Included articles were selected for their relevance to pathophysiology, diagnosis, and treatment. Bibliographies of selected papers served as an additional source of considered publications.

RESULTS

Inflammation in the small airways and alveolar tissue plays an important role in the clinical manifestations of asthma. Diagnostic modalities such as transbronchial biopsy and evolving radiologic techniques such as high-resolution computed tomography are improving our ability to evaluate this portion of the lung. New ultra-fine particle size metered-dose inhalers and oral agents such as cysteinyl leukotriene receptor antagonists offer new opportunities for treating small airways inflammation and need to be fully evaluated for their ability to target and treat distal lung inflammation.

CONCLUSIONS

Distal lung inflammation is an important component of airway inflammation in asthma. New modalities for evaluating distal airway inflammation and for targeting the distal lung with inhaled and systemic drugs are rapidly expanding our knowledge of the clinical importance of distal lung inflammation and may ultimately be of critical importance in asthma therapy.

Cysteinyl leukotriene receptors

The cysteinyl leukotrienes, leukotriene C4 (LTC4), leukotriene D4 (LTD4) and leukotriene E4 (LTE4), activate contractile and inflammatory processes via specific interaction with putative seven transmembrane-spanning receptors that couple to G proteins and subsequent intracellular signaling pathways. Pharmacological characterizations identified at least two subtypes of cysteinyl leukotriene (CysLT) receptor based on agonist and antagonist potency for biological responses. The rank potency of agonist activation for the CysLT1 receptor is LTD4 > LTC4 > LTE4 and for the CysLT2 receptor is LTC4 = LTD4 > LTE4. CysLT1 selective receptor antagonists are efficacious in the treatment of asthma. No selective CysLT2 receptor antagonists have been described. Molecular identification of the human and mouse CysLT1 and CysLT2 receptors has confirmed their structure as putative seven transmembrane domain G protein-coupled receptors and largely confirmed the previous pharmacological characterizations. The CysLT1 receptor is most highly expressed in spleen, peripheral blood leukocytes including eosinophils, and lung smooth muscle cells and interstitial lung macrophages. The CysLT2 receptor is most highly expressed in the heart, adrenal medulla, placenta and peripheral blood leukocytes. The molecular identification of the mouse CysLT1 and CysLT2 receptors show similar but not identical profiles to the orthologous human receptors.

Human mast cells express two leukotriene C(4) synthase isoenzymes and the CysLT(1) receptor

Cysteinyl-leukotrienes (cys-LTs) are potent smooth muscle contracting agents, especially in the respiratory tract and microcirculation, and play a key role in inflammatory and allergic diseases. The final step in the biosynthesis of LTC(4), the parent compound of cys-LTs, is catalyzed by a specific GSH transferase termed LTC(4) synthase, which is typically expressed in certain bone marrow-derived cells such as eosinophils and mast cells. Here we report that the human mast cell line HMC-1 as well as human mast cells derived from cord blood (CBMC) express a second enzyme capable of synthesizing leukotriene C(4), i.e., microsomal GSH transferase type 2. Furthermore, these cells abundantly express CysLT(1) receptors that are mostly located at the surface of both types of mast cells, as judged by immunohistochemistry. In addition, stimulation of CBMC with LTC(4) and LTD(4) elicits an immediate and dose-dependent (10(-7)-10(-11) M) mobilization of intracellular Ca(2+), which can be blocked with specific CysLT(1) receptor antagonists. Taken together, our data suggest that human mast cells are equipped with two enzymes that can catalyze the committed step in the biosynthesis of cys-LTs. Moreover, the expression of the cognate receptor CysLT(1) suggests that these lipid mediators may be involved in autocrine signaling pathways regulating mast cell functions.

Differential expression of cytokine genes in fibroblasts derived from skin biopsies of patients who developed minimal or severe normal tissue damage after radiotherapy

Curative radiotherapy for cancer patients requires the use of radiation doses that are limited by the tolerance of the surrounding normal tissues. Unfortunately, these tolerance doses vary not only between tissues but also between individuals. In a small proportion of sensitive patients, exposure to radiation can lead to severe irreversible morbidity and even death several months to years after treatment. At present these radiosensitive patients can be identified only retrospectively. Here we describe a cytokine microarray technique that was used to identify differentially expressed gene transcripts in fibroblasts obtained from a small group of patients who suffered either negligible or severe normal damage to tissues after radiotherapy. If our preliminary findings can be confirmed, the availability of such markers may eventually allow the prediction of outcome prior to commencement of radiotherapy, and thus allow modification of radiotherapy protocols to minimize adverse late effects, without compromising tumor control.

5-lipoxygenase inhibition reduces intrahepatic vascular resistance of cirrhotic rat livers: a possible role of cysteinyl-leukotrienes

BACKGROUND & AIMS

Cysteinyl-leukotrienes (Cys-LTs) increase intrahepatic vascular resistance in normal rat livers. CCl4 cirrhotic rat livers have increased Cys-LT production and 5-lipoxygenase messenger RNA (mRNA) expression. The aim of this study was to investigate the role of 5-lipoxygenase-derived eicosanoids regulating intrahepatic vascular tone in control and CCl4-induced cirrhotic rat livers.

METHODS

In different groups of portally perfused control and cirrhotic rat livers, the following were analyzed: a portal perfusion pressure (PP) dose-response curve to LTD4; the effects on PP caused by either vehicle, the selective 5-lipoxygenase inhibitor AA-861, the selective Cys-LT1 receptor antagonist MK-571, or the dual Cys-LT1 and Cys-LT2 receptor antagonist BAY u9773; and immunohistochemistry for 5-lipoxygenase in liver sections of cirrhotic and control livers.

RESULTS

Cirrhotic livers have a hyperesponse to LTD4. In control livers, AA-861 and MK-571 produced a moderate and similar reduction in PP. In cirrhotic livers, 5-lipoxygenase inhibition produced a marked and significantly greater reduction in PP than in controls. However, no effect on PP was observed after MK-571 or BAY u9773. 5-Lipoxygenase-positive cells were markedly increased in cirrhotic livers.

CONCLUSIONS

Our results suggest that 5-lipoxygenase-derived eicosanoids may contribute to the increased intrahepatic vascular resistance of cirrhotic rat livers and therefore the pathogenesis of portal hypertension.

The murine cysteinyl leukotriene 2 (CysLT2) receptor. cDNA and genomic cloning, alternative splicing, and in vitro characterization

Two classes of cysteinyl leukotriene receptor, CysLT(1) and CysLT(2), have been identified and pharmacologically characterized in human tissues. Although the CysLT(1) receptor mediates the proinflammatory effects of leukotrienes in human asthma, the physiological roles of CysLT(2) receptor are not defined, and a suitable mouse model would be useful in delineating function. We report here the molecular cloning and characterization of the mouse CysLT(2) receptor (mCysLT(2)R) from heart tissue. mCysLT(2)R cDNA encodes a protein of 309 amino acids, truncated at both ends compared with the human ortholog (hCysLT(2)R). The gene resides on the central region of mouse chromosome 14 and is composed of 6 exons with the entire coding region located in the last exon. Two 5'-untranslated region splice variants were identified with the short form lacking exon 3 as the predominant transcript. Although the overall expression of mCysLT(2)R is very low, the highest expression was detected in spleen, thymus, and adrenal gland by ribonuclease protection assay, and discrete sites of expression in heart were observed by in situ hybridization. Intracellular calcium mobilization in response to cysteinyl leukotriene administration was detected in human embryonic kidney 293T cells transfected with recombinant mCysLT(2)R with a rank order of potency leukotriene C(4)(LTC(4) ) = LTD(4)>>LTE(4). [(3)H]LTD(4) binding to membranes expressing mCysLT(2)R could be effectively competed by LTC(4) and LTD(4) and only partially inhibited by LTE(4) and BAYu9773. The identification of mCysLT(2)R will be useful for establishing CysLT(2)R-deficient mice and determining novel leukotriene functions.

Molecular cloning and functional characterization of murine cysteinyl-leukotriene 1 (CysLT(1)) receptors

We sought to clone and characterize the murine cysteinyl-leukotriene D(4) receptor (mCysLT(1)R) to complement our studies with leukotriene-deficient mice. A cDNA, cloned from trachea mRNA by reverse transcriptase-polymerase chain reaction, has two potential initiator ATG codons that would encode for polypeptides of 352 and 339 amino acids, respectively. These two potential forms, predicted to be seven transmembrane-spanning domain proteins, have 87% amino acid identity with the human CysLT(1) receptor (hCysLT(1)R). Membrane fractions of Cos-7 cells transiently expressing the short mCysLT(1)R demonstrated high affinity and specific binding for leukotriene D(4) (LTD(4), K(d) = 0.25 +/- 0.04 nM). In competition binding experiments, LTD(4) was the most potent competitor (K(i) = 0.8 +/- 0.2 nM) followed by LTE(4) and LTC(4) (K(i) = 86.6 +/- 24.5 and 100.1 +/- 17.1 nM, respectively) and LTB(4) (K(i) > 1.5 microM). Binding of LTD(4) was competitively inhibited by the specific CysLT(1) receptor antagonists MK-571 [(+)-3-(((3-(2-(7-chloro-2-quinolinyl)ethenyl)phenyl) ((3-(dimethylamino)-3-oxopropyl)thio)methyl)thio)propanoic acid], pranlukast (Onon), and zafirlukast (Accolate), while the CysLT(1)/CysLT(2) receptor antagonist BAY-u9773 [6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E),11(Z),14(Z)-eicosatetrenoic acid] was 1000 times less potent than LTD(4). In transiently transfected HEK293-T cells expressing either the long or short form of mCysLT(1)R, LTD(4) induced an increase of intracellular calcium. In Xenopus laevis melanophores transiently expressing either isoform, LTD(4) induced the dispersion of pigment granules, consistent with the activation by LTD(4) of a G(alphaq) (calcium) pathway. Functional elucidation of mCysLT(1)R properties as described here will enable further experiments to clarify the selective role of LTD(4) in murine models of inflammation and asthma.

Atypical lambda/iota PKC conveys 5-lipoxygenase/leukotriene B4-mediated cross-talk between phospholipase A2s regulating NF-kappa B activation in response to tumor necrosis factor-alpha and interleukin-1beta

The transcription factor nuclear factor kappaB (NF-kappaB) plays crucial roles in a wide variety of biological functions such as inflammation, stress, and immune responses. We have shown previously that secretory nonpancreatic (snp) and cytosolic (c) phospholipase A(2) (PLA(2)) regulate NF-kappaB activation in response to tumor necrosis factor (TNF)-alpha or interleukin (IL)-1beta activation and that a functional coupling mediated by the 5-lipoxygenase (5-LO) metabolite leukotriene B(4) (LTB(4)) exists between snpPLA(2) and cPLA(2) in human keratinocytes. In this study, we have further investigated the mechanisms of PLA(2)-modulated NF-kappaB activation with respect to specific kinases involved in TNF-alpha/IL-1beta-stimulated cPLA(2) phosphorylation and NF-kappaB activation. The protein kinase C (PKC) inhibitors RO 31-8220, Gö 6976, and a pseudosubstrate peptide inhibitor of atypical PKCs attenuated arachidonic acid release, cPLA(2) phosphorylation, and NF-kappaB activation induced by TNF-alpha or IL-1beta, thus indicating atypical PKCs in cPLA(2) regulation and transcription factor activation. Transfection of a kinase-inactive mutant of lambda/iotaPKC in NIH-3T3 fibroblasts completely abolished TNF-alpha/IL-1beta-stimulated cellular arachidonic acid release and cPLA(2) activation assayed in vitro, confirming the role of lambda/iotaPKC in cPLA(2) regulation. Furthermore, lambda/iotaPKC and cPLA(2) phosphorylation was attenuated by phosphatidyinositol 3-kinase (PI3-kinase) inhibitors, which also reduced NF-kappaB activation in response to TNF-alpha and IL-1beta, indicating a role for PI3-kinase in these processes in human keratinocytes. TNF-alpha- and IL-1beta-induced phosphorylation of lambda/iotaPKC was attenuated by inhibitors toward snpPLA(2) and 5-LO and by an LTB(4) receptor antagonist, suggesting lambda/iotaPKC as a downstream effector of snpPLA(2) and 5-LO/LTB(4) the LTB(4) receptor. Hence, lambda/iotaPKC regulates snpPLA(2)/LTB(4)-mediated cPLA(2) activation, cellular arachidonic acid release, and NF-kappaB activation induced by TNF-alpha and IL-1beta. In addition, our results demonstrate that PI3-kinase and lambda/iotaPKC are involved in cytokine-induced cPLA(2) and NF-kappaB activation, thus identifying lambda/iotaPKC as a novel regulator of cPLA(2).

Functional coupling between secretory and cytosolic phospholipase A2 modulates tumor necrosis factor-alpha- and interleukin-1beta-induced NF-kappa B activation

Tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta are potent activators of the transcription factor NF-kappaB, induced during inflammatory conditions. We have previously shown that both secretory and cytosolic phospholipase A(2) (PLA(2)) are involved in TNF-alpha- and IL-1beta-induced NF-kappaB activation. In this study, we have addressed the mechanism of PLA(2) involvement with respect to downstream arachidonic acid (AA) metabolites and the functional coupling between PLA(2)s mediating NF-kappaB activation. We show that in addition to inhibitors of secretory and cytosolic PLA(2)s, 5-lipoxygenase inhibitors attenuate TNF-alpha- and IL-1beta-stimulated NF-kappaB activation. Exogenous addition of leukotriene B(4) (LTB(4)) restored NF-kappaB activation reduced by 5-lipoxygenase inhibitors or an LTB(4) receptor antagonist, thus identifying LTB(4) as a mediator in signaling to NF-kappaB. TNF-alpha- and IL-1beta-induced AA release from cellular membranes was accompanied by phosphorylation of cytosolic PLA(2). Inhibitors of secretory PLA(2) and of 5-lipoxygenase/LTB(4) functionality markedly reduced AA release and nearly completely abolished cytosolic PLA(2) phosphorylation. This demonstrates that secretory PLA(2), through 5-lipoxygenase metabolites, is an essential upstream regulator of cytosolic PLA(2) and AA release. Our results therefore suggest the existence of a functional link between secretory and cytosolic PLA(2) in cytokine-activated keratinocytes, providing a molecular explanation for the participation of both secretory and cytosolic PLA(2) in arachidonic acid signaling and NF-kappaB activation in response to proinflammatory cytokines.

Receptor nomenclature guidelines

Receptors are typically characterized via two distinct approaches: (1) the identification and pharmacological characterization of a receptor-mediated response using classical pharmacological and/or radioligand approaches in tissues and animal models using selective agonist and antagonist ligands, and; (2) the cloning and expression of proteins with structural homology to known receptors, the function of which is subsequently established by studying the structure activity relationship (SAR) of receptor-mediated responses. An additional means to characterize receptors proceeded, and evolved, with the structural approach, namely classification in terms of signal transduction mechanisms. The International Union of Pharmacology (IUPHAR) created guidelines and selected working groups for each receptor family to establish a common nomenclature system. Reports from those groups that have reached some degree of consensus have been summarized in this appendix.

Leukotriene D(4)-induced Rho-mediated actin reorganization in human bronchial smooth muscle cells

We investigated the role of cysteinyl leukotriene (CysLT) receptors on leukotriene D(4)-induced actin reorganization and the signaling pathways of the response in human bronchial smooth muscle cells. The effects of leukotriene D(4) on actin reorganization in human bronchial smooth muscle cells were evaluated by dual-fluorescence labeling of filamentous (F) and monomeric (G) actin with fluorescein isothiocyanate (FITC)-labeled phalloidin and Texas Red-labeled DNase I, respectively. Leukotriene D(4) (100 nM) induced actin reorganization in the presence and absence of extracellular Ca(2+). The CysLT type 1 (CysLT(1)) receptor antagonist ONO 1078 (4-oxo-8(-)[p-(4-phenylbutyloxy) benzoylamino]-2-(tetrazol-5-yl)-4H-1-benzopyran hemihydrate) inhibited leukotriene D(4)-induced actin reorganization. Pretreatment with pertussis toxin, C3 exoenzyme, or tyrosine kinase inhibitors significantly reduced leukotriene D(4)-induced actin reorganization. However, phosphatidylinositol-3-kinase and protein kinase C inhibitors had little effect on these responses. These results suggest that leukotriene D(4)-induced actin reorganization in human bronchial smooth muscle cells is extremely dependent on the CysLT(1) receptor coupled with pertussis toxin-sensitive G protein, Rho GTPases and tyrosine phosphorylation pathways.

Expression of the cysteinyl leukotriene 1 receptor in normal human lung and peripheral blood leukocytes

The cysteinyl leukotrienes (CysLTs) are important mediators of human asthma. Pharmacologic and clinical studies show that the CysLTs exert most of their bronchoconstrictive and proinflammatory effects through activation of a putative, 7-transmembrane domain, G-protein-coupled receptor, the CysLT1 receptor. The initial molecular characterization of the CysLT1 receptor showed by in situ hybridization, the presence of CysLT1 receptor messenger RNA (mRNA) in human lung smooth-muscle cells and lung macrophages. We confirmed the results of these in situ hybridization analyses for the CysLT1 receptor, and produced the first immunohistochemical characterization of the CysLT1 receptor protein in human lung. The identification of the CysLT1 receptor in the lung is consistent with the antibronchoconstrictive and antiinflammatory actions of CysLT1 receptor antagonists. We also report the expression of CysLT1 receptor mRNA and protein in most peripheral blood eosinophils and pregranulocytic CD34+ cells, and in subsets of monocytes and B lymphocytes.

Molecular cloning and characterization of a second human cysteinyl leukotriene receptor: discovery of a subtype selective agonist

The cysteinyl leukotrienes (CysLTs) are potent biological mediators in the pathophysiology of inflammatory diseases, in particular of airway obstruction in asthma. Pharmacological studies have suggested the existence of at least two types of CysLT receptors, designated CysLT(1) and CysLT(2). The CysLT(1) receptor has been cloned recently. Here we report the molecular cloning, expression, localization, and functional characterization of a human G protein-coupled receptor that has the expected characteristics of a CysLT(2) receptor. This new receptor is selectively activated by nanomolar concentrations of CysLTs with a rank order potency of LTC(4) = LTD(4) >> LTE(4). The leukotriene analog BAY u9773, reported to be a dual CysLT(1)/CysLT(2) antagonist, was found to be an antagonist at CysLT(1) sites but acted as a partial agonist at this new receptor. The structurally different CysLT(1) receptor-selective antagonists zafirlukast, montelukast, and MK-571 did not inhibit the agonist-mediated calcium mobilization of CysLT(2) receptors at physiological concentrations. Localization studies indicate highest expression of CysLT(2) receptors in adrenal glands, heart, and placenta; moderate levels in spleen, peripheral blood leukocytes, and lymph nodes; and low levels in the central nervous system and pituitary. The human CysLT(2) receptor gene is located on chromosome 13q14.12-21.1. The new receptor exhibits all characteristics of the thus far poorly defined CysLT(2) receptor. Moreover, we have identified BAY u9773 as a CysLT(2) selective agonist, which could prove to be of immediate use in understanding the functional roles of the CysLT(2) receptor.

Characterization of the human cysteinyl leukotriene 2 receptor

The contractile and inflammatory actions of the cysteinyl leukotrienes (CysLTs), LTC(4), LTD(4), and LTE(4), are thought to be mediated through at least two distinct but related CysLT G protein-coupled receptors. The human CysLT(1) receptor has been recently cloned and characterized. We describe here the cloning and characterization of the second cysteinyl leukotriene receptor, CysLT(2), a 346-amino acid protein with 38% amino acid identity to the CysLT(1) receptor. The recombinant human CysLT(2) receptor was expressed in Xenopus oocytes and HEK293T cells and shown to couple to elevation of intracellular calcium when activated by LTC(4), LTD(4), or LTE(4). Analyses of radiolabeled LTD(4) binding to the recombinant CysLT(2) receptor demonstrated high affinity binding and a rank order of potency for competition of LTC(4) = LTD(4) LTE(4). In contrast to the dual CysLT(1)/CysLT(2) antagonist, BAY u9773, the CysLT(1) receptor-selective antagonists MK-571, montelukast (Singulair(TM)), zafirlukast (Accolate(TM)), and pranlukast (Onon(TM)) exhibited low potency in competition for LTD(4) binding and as antagonists of CysLT(2) receptor signaling. CysLT(2) receptor mRNA was detected in lung macrophages and airway smooth muscle, cardiac Purkinje cells, adrenal medulla cells, peripheral blood leukocytes, and brain, and the receptor gene was mapped to chromosome 13q14, a region linked to atopic asthma.

Genetic factors determine the contribution of leukotrienes to acute inflammatory responses

Leukotrienes (LT) are potent lipid mediators synthesized by the 5-lipoxygenase pathway of arachidonic acid (AA) metabolism. LT have been implicated in a broad spectrum of inflammatory processes. To investigate the influence of genetic factors on the contribution of LT to acute inflammation, we generated congenic 5-lipoxygenase-deficient 129, C57BL/6 (B6), and DBA/1Lac (DBA) mouse lines. Topical application of AA evoked a vigorous inflammatory response in 129 and DBA mice, whereas only a modest response was seen in B6 animals. The response to AA in 129 and DBA strains is LT dependent. In contrast, LT make little contribution to this response in B6 mice. AA-induced inflammation in B6 mice is prostanoid dependent, since this response was substantially reduced by treating B6 mice with a cyclooxygenase inhibitor. These data suggest that prostanoids are essential for AA-induced cutaneous inflammation in B6 mice, whereas LT are the major mediators of this response in 129 and DBA strains. In contrast, the response to AA in the peritoneal cavity is robust in the 129 and B6 strains, but was significantly blunted in DBA mice, showing that strain differences in the response to AA are tissue specific. Variations in these and other experimental models of inflammation appear to correlate directly with the ability of a particular mouse strain and a specific tissue to respond to LT, specifically LTC4. Taken together, these findings indicate that the relative contribution of prostanoids and LT to inflammatory responses is variable not only between strains but also between different tissues within these inbred mouse lines.

A random rapid equilibrium mechanism for leukotriene C4 synthase

Kinetic studies performed on the conjugation reaction catalyzed by LTC4 synthase proved to conform to a random rapid equilibrium mechanism which was further substantiated by competition patterns ruling out other possible mechanisms. Most cytosolic Gst's investigated to date appear to follow a random kinetic mechanism although are mainly responsible for detoxification purposes. Conversely, LTC4 synthase possesses a very different biological role yet still follows a similar mechanism. Therefore, it can be concluded that most GSTs function in a consistent manner regardless of their biological function. Of interest are the mechanisms of the other members of the MAPEG family which in some respects are closer to conventional GSTs than to LTC4 synthase, yet they remain to be deciphered.

Montelukast in the prophylaxis of migraine: a potential role for leukotriene modifiers

OBJECTIVE

Clinical observation of a decrease in migraine frequency in patients with comorbid asthma taking montelukast, a specific D4 leukotriene receptor antagonist, or zafirlukast, another leukotriene receptor antagonist, prompted us to explore a possible role for leukotriene modifiers in the treatment of migraine. (A further prompt was a pharmacist colleague's observation that a number of patients on these agents reported a decreased sensitivity to perfume triggers and improvement in migraine.)

BACKGROUND

Nonsteroidal anti-inflammatory agents have been used widely in the treatment of migraine. Another class of anti-inflammatory agents, known as leukotriene modifiers, have not been studied to date with regard to their possible role in the treatment of migraine. The name "leukotriene is derived both from the parent molecule, which was originally isolated from leukocytes, and from its three double-bond carbon backbone or triene structure. Both prostaglandins and leukotrienes are derived from the metabolism of arachidonic acid, with prostaglandins coming off the cyclooxygenase pathway and leukotrienes derived via the enzyme 5-lipoxygenase. Both prostaglandins and leukotrienes mediate inflammatory responses. The latter have been studied with regard to their role in the pathophysiology of asthma.

METHODS

A prospective, open-label study evaluating the efficacy of montelukast, 10 mg or 20 mg, in the prophylaxis of migraine in 17 patients is presented in this paper. All 17 patients completed the study that consisted of a 2-month baseline run-in period and a 3-month treatment phase.

RESULTS

Montelukast was extremely well tolerated, and no adverse events were reported by any of the patients. Fifty-three percent showed a reduction of greater than 50% (P<.025) in the frequency of severe attacks, with 41% showing a reduction of greater than 60%. Responders, including modest responders, rated the drug as excellent.

CONCLUSIONS

We conclude, given the limitations of an open-label study design and the small sample size, that montelukast shows potential as an effective, well-tolerated prophylactic agent in migraine. Double-blinded, placebo-controlled studies are warranted. In addition, the leukotrienes, as suggested previously in the literature, may play a role in the pathogenesis of migraine.

Identification, molecular cloning, expression, and characterization of a cysteinyl leukotriene receptor

The cysteinyl leukotrienes (CysLTs) have been implicated in the pathophysiology of inflammatory disorders, in particular asthma, for which the CysLT receptor antagonists pranlukast, zafirlukast, and montelukast, have been introduced recently as novel therapeutics. Here we report on the molecular cloning, expression, localization, and pharmacological characterization of a CysLT receptor (CysLTR), which was identified by ligand fishing of orphan seven-transmembrane-spanning, G protein-coupled receptors. This receptor, expressed in human embryonic kidney (HEK)-293 cells responded selectively to the individual CysLTs, LTC(4), LTD(4), or LTE(4), with a calcium mobilization response; the rank order potency was LTD(4) (EC(50) = 2.5 nM) > LTC(4) (EC(50) = 24 nM) > LTE(4) (EC(50) = 240 nM). Evidence was provided that LTE(4) is a partial agonist at this receptor. [(3)H]LTD(4) binding and LTD(4)-induced calcium mobilization in HEK-293 cells expressing the CysLT receptor were potently inhibited by the structurally distinct CysLTR antagonists pranlukast, montelukast, zafirlukast, and pobilukast; the rank order potency was pranlukast = zafirlukast > montelukast > pobilukast. LTD(4)-induced calcium mobilization in HEK-293 cells expressing the CysLT receptor was not affected by pertussis toxin, and the signal appears to be the result of the release from intracellular stores. Localization studies indicate the expression of this receptor in several tissues, including human lung, human bronchus, and human peripheral blood leukocytes. The discovery of this receptor, which has characteristics of the purported CysLT(1) receptor subtype, should assist in the elucidation of the pathophysiological roles of the CysLTs and in the identification of additional receptor subtypes.

Chemical probes that differentially modulate peroxisome proliferator-activated receptor alpha and BLTR, nuclear and cell surface receptors for leukotriene B(4)

Peroxisome proliferator-activated receptor alpha (PPARalpha)is a nuclear receptor for various fatty acids, eicosanoids, and hypolipidemic drugs. In the presence of ligand, this transcription factor increases expression of target genes that are primarily associated with lipid homeostasis. We have previously reported PPARalpha as a nuclear receptor of the inflammatory mediator leukotriene B(4) (LTB(4)) and demonstrated an anti-inflammatory function for PPARalpha in vivo (Devchand, P. R., Keller, H., Peters, J. M., Vazquez, M., Gonzalez, F. J., and Wahli, W. (1996) Nature 384, 39-43). LTB(4) also has a cell surface receptor (BLTR) that mediates proinflammatory events, such as chemotaxis and chemokinesis (Yokomizo, T., Izumi, T., Chang, K., Takuwa, Y., and Shimizu, T. (1997) Nature 387, 620-624). In this study, we report on chemical probes that differentially modulate activity of these two LTB(4) receptors. The compounds selected were originally characterized as synthetic BLTR effectors, both agonists and antagonists. Here, we evaluate the compounds as effectors of the three PPAR isotypes (alpha, beta, and gamma) by transient transfection assays and also determine whether the compounds are ligands for these nuclear receptors by coactivator-dependent receptor ligand interaction assay, a semifunctional in vitro assay. Because the compounds are PPARalpha selective, we further analyze their potency in a biological assay for the PPARalpha-mediated activity of lipid accumulation. These chemical probes will prove invaluable in dissecting processes that involve nuclear and cell surface LTB(4) receptors and also aid in drug discovery programs.

Characterization of the human cysteinyl leukotriene CysLT1 receptor

The cysteinyl leukotrienes-leukotriene C4(LTC4), leukotriene D4(LTD4) and leukotriene E4(LTE4)-are important mediators of human bronchial asthma. Pharmacological studies have determined that cysteinyl leukotrienes activate at least two receptors, designated CysLT1 and CysLT2. The CysLT1-selective antagonists, such as montelukast (Singulair), zafirlukast (Accolate) and pranlukast (Onon), are important in the treatment of asthma. Previous biochemical characterization of CysLT1 antagonists and the CysLT1 receptor has been in membrane preparations from tissues enriched for this receptor. Here we report the molecular and pharmacological characterization of the cloned human CysLT1 receptor. We describe the functional activation (calcium mobilization) of this receptor by LTD4 and LTC4, and competition for radiolabelled LTD4 binding to this receptor by the cysteinyl leukotrienes and three structurally distinct classes of CysLT1-receptor antagonists. We detected CysLT1-receptor messenger RNA in spleen, peripheral blood leukocytes and lung. In normal human lung, expression of the CysLT1-receptor mRNA was confined to smooth muscle cells and tissue macrophages. Finally, we mapped the human CysLT1-receptor gene to the X chromosome.

Demonstration of cell-specific phosphorylation of LTC4 synthase

PMA-induced leukotriene C4 synthase (LTC4S) phosphorylation was investigated over a period of 8 h in a monocytic cell line (THP-1). The level of LTC4S phosphorylation was increased 3-5 fold over a 4 h period decreasing to basal levels after 8 h. This phosphorylation event was found to be specific to THP-1 cells as there was a lack of LTC4S phosphorylation in both COS-7 and K-562 cells, and was also found to be dependent on the cellular confluency. In the presence of specific protein kinase C (PKC) inhibitors, a dose-dependent inhibition of the phosphorylation of LTC4S became evident, an effect not seen with PKA and tyrosine kinase inhibitors. This represents the first direct demonstration of LTC4S phosphorylation in whole cells.

Leukotriene binding, signaling, and analysis of HIV coreceptor function in mouse and human leukotriene B4 receptor-transfected cells

The mouse leukotriene B4 receptor (m-BLTR) gene was cloned. Membrane fractions of human embryonic kidney 293 cells stably expressing m-BLTR demonstrated a high affinity and specific binding for leukotriene B4 (LTB4, Kd = 0.24 +/- 0.03 nM). In competition binding experiments, LTB4 was the most potent competitor (Ki = 0.23 +/- 0.05 nM) followed by 20-hydroxy-LTB4 (Ki = 1.1 +/- 0.2 nM) and by 6-trans-12-epi-LTB4 and LTD4 (Ki > 1 microM). In stably transfected Chinese hamster ovary cells, LTB4 inhibited forskolin-activated cAMP production and induced an increase of intracellular calcium, suggesting that this receptor is coupled to Gi- and Go-like proteins. In Xenopus laevis melanophores transiently expressing m-BLTR, LTB4 induced the aggregation of pigment granules, confirming the inhibition of cAMP production induced by LTB4. BLT receptors share significant sequence homology with chemokine receptors (CCR5 and CXCR4) that act as human immunodeficiency virus (HIV) coreceptors. However, among the 16 HIV/SIV strains tested, the human BLT receptor did not act as a coreceptor for virus entry into CD4-expressing cells based on infection and cell-cell fusion assays. In 5-lipoxygenase-deficient mice, the absence of leukotriene B4 biosynthesis did not detectably alter m-BLT receptor binding in membranes obtained from glycogen-elicited neutrophils. Isolation of the m-BLTR gene will form the basis of future experiments to elucidate the selective role of LTB4, as opposed to cysteinyl-leukotrienes, in murine models of inflammation.

Pharmacology of airway smooth muscle

Airway smooth muscle contributes to changes in airway caliber not only through the variations in its tone but also through its contribution to thickness of the airway wall. Until recently, most attention was paid to the agents that altered airway smooth muscle tone, their receptors, the signal transduction pathways they activated, and the mechanisms of contraction and relaxation themselves. Lately, the regulation of smooth muscle proliferation has received increasing attention, and, most recently, the possible role of smooth muscle as a source of inflammatory mediators has been recognized. Airway smooth muscle cells are now seen as playing an important interactive role with inflammatory and structural cells in the response to injury and repair of the airways.

Effects of LTD4 on human airway smooth muscle cell proliferation, matrix expression, and contraction In vitro: differential sensitivity to cysteinyl leukotriene receptor antagonists

The cysteinyl leukotrienes (CysLTs) mimic many of the features of asthma and are implicated in its pathophysiology. Little, however, is known about the effects of the CysLTs on airways remodeling. In this study the effects of leukotriene D4 (LTD4) on human airway smooth muscle (HASM) cell proliferation and expression of extracellular matrix proteins were investigated. LTD4 (0.1-10 microM) alone had no effect on DNA synthesis in HASM. LTD4, however, markedly augmented proliferation induced by the mitogen, epidermal growth factor (EGF, 1 ng/ml). The potentiating effect of LTD4 (1 microM) on EGF-induced DNA synthesis was abolished by pranlukast (1 microM) or pobilukast (30 microM), but unaffected by zafirlukast (1 microM). In contrast, pranlukast (pKB = 6.9), pobilukast (pKB = 7.0), and zafirlukast (pKB = 6.5) had equivalent potencies for inhibition of LTD4-induced contraction in human bronchus. LTD4 (0.1 or 10 microM) did not increase the total messenger RNA expression of the extracellular matrix proteins (pro-alpha[I] type I or alpha1[IV] type IV collagen), elastin, biglycan, decorin, and fibronectin, and did not influence tumor growth factor-beta (10 ng/ml)-induced effects on the expression of these proteins in HASM cells. These data indicate that LTD4 augments growth factor-induced HASM proliferation but does not alter the expression of various extracellular matrix components. The observed differences in sensitivity to the antagonists suggests that the former phenomenon may be mediated by a CysLT receptor distinct from that which mediates LTD4-induced HASM contraction. Collectively, these results provide preliminary evidence that CysLTs may play a role in airways remodeling in asthma.

The inflammatory mediator leukotriene D4 triggers a rapid reorganisation of the actin cytoskeleton in human intestinal epithelial cells

Epithelial cells play an important role in maintaining the intestinal mucosa barrier, a barrier that is impaired in several inflammatory conditions. The mechanisms behind this impairment are not known, but it can be presumed that structural alterations of the epithelial cells are involved. In support of this notion, we here show the inflammatory mediator leukotriene D4 (LTD4) triggered first a rapid (10 s) increase and immediately thereafter (30 s) a sustained decrease in the cellular filamentous actin (F-actin) level in intestinal epithelial cells. The initial LTD4-induced increase in F-actin content was effectively blocked by preincubating the cells with either pertussis toxin or the tyrosine kinase inhibitor genistein. A possible involvement of the tyrosine kinase-dependent phosphatidylinositol-3-kinase (PI-3-kinase) in the polymerisation of actin was supported by the observations that LTD4 induced a translocation to a membrane fraction of PI-3-kinase and by the findings that wortmannin, a PI-3-kinase inhibitor, totally abolished both this translocation of PI-3-kinase as well as the initial LTD4-induced polymerisation of actin. In addition, pertussis toxin and genistein, both known to interfere with the LTD4-induced calcium signal, completely or partially reversed the actin-depolymerising effect of LTD4. The calcium ionophore ionomycin (30s) induced actin depolymerisation to the same extent as LTD4 (30 s) did, but lacked the initial effect on actin polymerisation. In cells loaded with the calcium chelator MAPT, LTD4 induced a normal actin polymerisation response but the subsequent depolymerisation was completely inhibited. Similar results were obtained when the cells were preincubated with the protein kinase A inhibitor Rp-cAMPS, which has been shown to impair the LTD4-induced calcium signal in these epithelial cells. The present results show that the inflammatory mediator LTD4 triggers a reorganisation of the actin network in intestinal epithelial cells that is likely to contribute to the impairment of the intestinal barrier function.