Levels of cysteinyl leukotriene receptor mRNA in human peripheral leucocytes: significantly higher expression of cysteinyl leukotriene receptor 2 mRNA in eosinophils

Cysteinyl leukotriene receptor-1 as a potential target for host-directed therapy during chronic schistosomiasis in murine model

Schistosomiasis remains the most devastating neglected tropical disease, affecting over 240 million people world-wide. The disease is caused by the eggs laid by mature female worms that are trapped in host's tissues, resulting in chronic Th2 driven fibrogranulmatous pathology. Although the disease can be treated with a relatively inexpensive drug, praziquantel (PZQ), re-infections remain a major problem in endemic areas. There is a need for new therapeutic drugs and alternative drug treatments for schistosomiasis. The current study hypothesized that cysteinyl leukotrienes (cysLTs) could mediate fibroproliferative pathology during schistosomiasis. Cysteinyl leukotrienes (cysLTs) are potent lipid mediators that are known to be key players in inflammatory diseases, such as asthma and allergic rhinitis. The present study aimed to investigate the role of cysLTR1 during experimental acute and chronic schistosomiasis using cysLTR1-/- mice, as well as the use of cysLTR1 inhibitor (Montelukast) to assess immune responses during chronic Schistosoma mansoni infection. Mice deficient of cysLTR1 and littermate control mice were infected with either high or low dose of Schistosoma mansoni to achieve chronic or acute schistosomiasis, respectively. Hepatic granulomatous inflammation, hepatic fibrosis and IL-4 production in the liver was significantly reduced in mice lacking cysLTR1 during chronic schistosomiasis, while reduced liver pathology was observed during acute schistosomiasis. Pharmacological blockade of cysLTR1 using montelukast in combination with PZQ reduced hepatic inflammation and parasite egg burden in chronically infected mice. Combination therapy led to the expansion of Tregs in chronically infected mice. We show that the disruption of cysLTR1 is dispensable for host survival during schistosomiasis, suggesting an important role cysLTR1 may play during early immunity against schistosomiasis. Our findings revealed that the combination of montelukast and PZQ could be a potential prophylactic treatment for chronic schistosomiasis by reducing fibrogranulomatous pathology in mice. In conclusion, the present study demonstrated that cysLTR1 is a potential target for host-directed therapy to ameliorate fibrogranulomatous pathology in the liver during chronic and acute schistosomiasis in mice.

Gene-diet interactions associated with complex trait variation in an advanced intercross outbred mouse line

Phenotypic variation of quantitative traits is orchestrated by a complex interplay between the environment (e.g. diet) and genetics. However, the impact of gene-environment interactions on phenotypic traits mostly remains elusive. To address this, we feed 1154 mice of an autoimmunity-prone intercross line (AIL) three different diets. We find that diet substantially contributes to the variability of complex traits and unmasks additional genetic susceptibility quantitative trait loci (QTL). By performing whole-genome sequencing of the AIL founder strains, we resolve these QTLs to few or single candidate genes. To address whether diet can also modulate genetic predisposition towards a given trait, we set NZM2410/J mice on similar dietary regimens as AIL mice. Our data suggest that diet modifies genetic susceptibility to lupus and shifts intestinal bacterial and fungal community composition, which precedes clinical disease manifestation. Collectively, our study underlines the importance of including environmental factors in genetic association studies.

Complex traits associate with genetic variation and environment and their interaction. Here, the authors study the influence of different diets on trait variability in 1154 outbred mice from an advanced intercross line and find gene-diet interactions associated with spontaneous autoimmunity development in these animals.

Hypersensitivity reactions to nonsteroidal anti-inflammatory drugs: an update on pharmacogenetics studies

Nonsteroidal anti-inflammatory drugs are the medications most frequently involved in hypersensitivity reactions to drugs. These can be induced by specific immunological and nonimmunological mechanisms, being the latter the most frequent. The nonimmunological mechanism is related to an imbalance of inflammatory mediators, which is aggravated by the cyclooxygenase inhibition. Genetic studies suggest that multiples genes and additional mechanisms might be involved. The proposals of this review is summarize the contribution of variations in genes involved in the arachidonic acid, inflammatory and immune pathways as well as the recent genome-wide association studies findings related to cross-intolerant nonsteroidal anti-inflammatory drugs hypersensitivity reactions. In addition, using integration of different genetic studies, we propose new target genes. This will help to understand the underlying mechanism of these reactions.

Leukotriene receptors as potential therapeutic targets

Leukotrienes, a class of arachidonic acid-derived bioactive molecules, are known as mediators of allergic and inflammatory reactions and considered to be important drug targets. Although an inhibitor of leukotriene biosynthesis and antagonists of the cysteinyl leukotriene receptor are clinically used for bronchial asthma and allergic rhinitis, these medications were developed before the molecular identification of leukotriene receptors. Numerous studies using cloned leukotriene receptors and genetically engineered mice have unveiled new pathophysiological roles for leukotrienes. This Review covers the recent findings on leukotriene receptors to revisit them as new drug targets.

A new CysLT1 and CysLT2 receptors-mediated anaphylaxis guinea pig model

Although the effectiveness of CysLT₁ receptor antagonists on asthma has been clinically established, the effects of CysLT₂ receptor antagonists are still unclear. The purpose of this study was to develop a new CysLT₁ and CysLT₂ receptors-mediated anaphylaxis guinea pig model using S-hexyl GSH, a γ-glutamyl transpeptidase (GTP) inhibitor, to suppress conversion of LTC₄ to LTD₄. Actively sensitized guinea pigs were challenged with OVA in the absence or presence of S-hexyl GSH, and survival rate following anaphylactic response was monitored. OVA-induced fatal anaphylaxis in the absence of S-hexyl GSH was almost completely inhibited by montelukast, a CysLT₁ receptor antagonist, but not by the CysLT₂ receptor antagonist BayCysLT₂RA. However, under treatment with S-hexyl-GSH, the inhibitory effect of motelukast was dramatically diminished, whereas that of BayCysLT₂RA was markedly increased. The dual CysLT_1/2 receptor antagonist ONO-6950 effectively inhibited anaphylactic response in both S-hexyl GSH-treated and non-treated animals. LC/MS/MS analysis revealed that S-hexyl GSH treatment actually inhibited LTC₄ metabolism in the blood and lung tissues. Using S-hexyl GSH, we developed a novel CysLT₁ and CysLT₂ receptors-mediated anaphylaxis guinea pig model that can be useful for not only screening both CysLT₂ and CysLT_1/2 receptors antagonists, but also for functional analysis of CysLT₂ receptors.

Expression of CysLTR1 and 2 in Maturating Lymphocytes of Hyperplasic Tonsils Compared to Peripheral Cells in Children

Cysteinyl-leukotriene receptors 1 and 2 (CysLTR1 and 2) are related to allergic inflammatory responses. Recent studies demonstrated their role in lymphocyte division and maturation in the bone marrow. Few data are available about CysLTRs function in lymphocyte maturation in tonsils. The objectives of this study are to compare CysLTRs expression in peripheral blood lymphocytes with expression in maturating lymphocytes of hyperplasic tonsil and to check the influence of respiratory allergies in this process. Leukocytes of peripheral blood (PL) and hyperplasic tonsils of children were immunostained for CysLTR1, CysLTR2, CD3 (T cells), and CD19 (B cells) and read in flow cytometer. Lymphocyte of tonsils were divided in differentiating small cells (SC) and mitotic large cells (LC); percentage of B and T cells expressing CysLTRs was determined, and comparison was done using ANOVA and Tukey's tests. Data were analyzed as a whole and categorizing patients according the presence of allergies. Sixty children were enrolled in this study. There was a large expression of CysLTR1 and 2 in CD3+ LC, and such expression decreased progressively in SC and PL. In B cells, the highest expression of CysLTR1 and 2 was found in PL while SC showed the lowest and LC showed the intermediate expression. This pattern kept unchanged in groups of allergic and non-allergic individuals. CysLTRs seem to be involved in lymphocyte maturation that occurs in tonsils, without influence of allergies. New studies aiming the clinic treatment of tonsil hyperplasia must be targeted to the development of drugs capable of blocking both CysLTR1 and 2.

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.

CysLT2 receptor activation is involved in LTC4-induced lung air-trapping in guinea pigs

CysLT₁ receptors are known to be involved in the pathogenesis of asthma. However, the functional roles of CysLT₂ receptors in this condition have not been determined. The purpose of this study is to develop an experimental model of CysLT₂ receptor-mediated LTC₄-induced lung air-trapping in guinea pigs and use this model to clarify the mechanism underlying response to such trapping. Because LTC₄ is rapidly converted to LTD₄ by γ-glutamyltranspeptidase (γ-GTP) under physiological conditions, S-hexyl GSH was used as a γ-GTP inhibitor. In anesthetized artificially ventilated guinea pigs with no S-hexyl GSH treatment, i.v. LTC₄-induced bronchoconstriction was almost completely inhibited by montelukast, a CysLT₁ receptor antagonist, but not by BayCysLT₂RA, a CysLT₂ receptor antagonist. The inhibitory effect of montelukast was diminished by treatment with S-hexyl GSH, whereas the effect of BayCysLT₂RA was enhanced with increasing dose of S-hexyl GSH. Macroscopic and histological examination of lung tissue isolated from LTC₄-/S-hexyl-GSH-treated guinea pigs revealed air-trapping expansion, particularly at the alveolar site. Inhaled LTC₄ in conscious guinea pigs treated with S-hexyl GSH increased both airway resistance and airway hyperinflation. On the other hand, LTC₄-induced air-trapping was only partially suppressed by treatment with the bronchodilator salmeterol. Although montelukast inhibition of LTC₄-induced air-trapping was weak, treatment with BayCysLT₂RA resulted in complete suppression of this air-trapping. Furthermore, BayCysLT₂RA completely suppressed LTC₄-induced airway vascular hyperpermeability. In conclusion, we found in this study that CysLT₂ receptors mediate LTC₄-induced bronchoconstriction and air-trapping in S-hexyl GSH-treated guinea pigs. It is therefore believed that CysLT₂ receptors contribute to asthmatic response involving air-trapping.

Expression of CysLT2 receptors in asthma lung, and their possible role in bronchoconstriction

BACKGROUND

The expression and functional role of CysLT2 receptors in asthma have not been clarified. In this study, we evaluated CysLT2 receptors expression, and effects of CysLT2-and CysLT1/2-receptor antagonists on antigen-induced bronchoconstriction using isolated lung tissues from both asthma and non-asthma subjects.

METHODS

CysLT1 and CysLT2 receptors expression in asthma and non-asthma lung tissue preparations was examined in immunohistochemistry experiments, and their functional roles in antigen-induced bronchoconstriction were assessed using ONO-6950, a dual CysLT1/2-receptor antagonist, montelukast, a CysLT1 receptor antagonist, and BayCysLT2RA, a CysLT2 receptor-specific antagonist.

RESULTS

CysLT1 receptors were expressed on the bronchial smooth muscle and epithelium, and on alveolar leukocytes in 5 in 5 non-asthma subjects and 2 in 2 asthma subjects. On the other hand, although degrees of CysLT2 receptors expression were variable among the 5 non-asthma subjects, the expression in the asthma lung was detected on bronchial smooth muscle, epithelium and alveolar leukocytes in 2 in 2 asthma subjects. In the non-asthma specimens, antagonism of CysLT2 receptors did not affect antigen-induced bronchial contractions, even after pretreatment with the CysLT1-receptor specific antagonist, montelukast. However, in the bronchus isolated from one of the 2 asthma subjects, antagonism of CysLT2 receptors suppressed contractions, and dual antagonism of CysLT1 and CysLT2 receptors resulted in additive inhibitory effect on anaphylactic contractions.

CONCLUSIONS

CysLT2 receptors were expressed in lung specimens isolated from asthma subjects. Activation of CysLT2 receptors may contribute to antigen-induced bronchoconstriction in certain asthma population.

Effects of ONO-6950, a novel dual cysteinyl leukotriene 1 and 2 receptors antagonist, in a guinea pig model of asthma

We assessed in this study the anti-asthmatic effects of ONO-6950, a novel cysteinyl leukotriene 1 (CysLT1) and 2 (CysLT2) receptors dual antagonist, in normal and S-hexyl glutathione (S-hexyl GSH)-treated guinea pigs, and compared these effects to those of montelukast, a CysLT1 selective receptor antagonist. Treatment with S-hexyl GSH reduced animals LTC4 metabolism, allowing practical evaluation of CysLT2 receptor-mediated airway response. ONO-6950 antagonized intracellular calcium signaling via human and guinea pig CysLT1 and CysLT2 receptors with IC50 values of 1.7 and 25 nM, respectively (human receptors) and 6.3 and 8.2 nM, respectively (guinea pig receptors). In normal guinea pigs, both ONO-6950 (1 or 0.3 mg/kg, p.o.) and the CysLT1 receptor antagonist montelukast (0.3 or 0.1 mg/kg, p.o.) fully attenuated CysLT1-mediated bronchoconstriction and airway vascular hyperpermeability induced by LTD4. On the other hand, in S-hexyl GSH-treated guinea pigs ONO-6950 at 3 mg/kg, p.o. or more almost completely inhibited bronchoconstriction and airway vascular hyperpermeability elicited by LTC4, while montelukast showed only partial or negligible inhibition of these airway responses. In ovalbumin sensitized guinea pigs, treatment with S-hexyl GSH on top of pyrilamine and indomethacin rendered antigen-induced bronchoconstriction sensitive to both CysLT1 and CysLT2 receptor antagonists. ONO-6950 strongly inhibited this asthmatic response to the level attained by combination therapy with montelukast and BayCysLT2RA, a selective CysLT2 receptor antagonist. These results clearly demonstrate that ONO-6950 is an orally active dual CysLT1/LT2 receptor antagonist that may provide a novel therapeutic option for patients with asthma.

Discovery of Gemilukast (ONO-6950), a Dual CysLT1 and CysLT2 Antagonist As a Therapeutic Agent for Asthma

An orally active dual CysLT1 and CysLT2 antagonist possessing a distinctive structure which consists of triple bond and dicarboxylic acid moieties is described. Gemilukast (ONO-6950) was generated via isomerization of the core indole and the incorporation of a triple bond into a lead compound. Gemilukast exhibited antagonist activities with IC50 values of 1.7 and 25 nM against human CysLT1 and human CysLT2, respectively, and potent efficacy at an oral dose of 0.1 mg/kg given 24 h before LTD4 challenge in a CysLT1-dependent guinea pig asthmatic model. In addition, gemilukast dose-dependently reduced LTC4-induced bronchoconstriction in both CysLT1- and CysLT2-dependent guinea pig asthmatic models, and it reduced antigen-induced constriction of isolated human bronchi. Gemilukast is currently being evaluated in phase II trials for the treatment of asthma.

Discovery of a potent, orally available dual CysLT₁ and CysLT₂ antagonist with dicarboxylic acid

A potent, orally available dual CysLT₁ and CysLT₂ receptor antagonist with a dicarboxylic acid is described. 4-(3-(Carboxymethyl)-4-{(E)-2-[4-(4-phenoxybutoxy)phenyl]vinyl}-1H-indol-1-yl)butanoic acid (15: ONO-4310321, IC₅₀: CysLT₁=13nM, CysLT₂=25 nM) showed excellent pharmacokinetic profiles (%Frat=100) compared with our previously reported compound 1 (%Frat=1.5). In addition, we describe a new rule for dicarboxylic acid derivatives to show good oral bioavailability (%Frat⩾40) in rats (HBDs: ⩽2, ClogP: >6.5 and TPSA: <100). Especially, reduction of only one hydrogen-bond donor (HBDs) showed dramatically improved oral bioavailability. This small change of HBDs in dicarboxylic acid derivatives is generally a very effective modification.

Leukotriene C4 induces bronchoconstriction and airway vascular hyperpermeability via the cysteinyl leukotriene receptor 2 in S-hexyl glutathione-treated guinea pigs

Cysteinyl leukotrienes act through G-protein-coupled receptors termed cysteinyl leukotriene 1 (CysLT1) and cysteinyl leukotriene 2 (CysLT2) receptors. However, little is known about the pathophysiological role of CysLT2 receptors in asthma. To elucidate the possible involvement of CysLT2 receptors in bronchoconstriction and airway vascular hyperpermeability, we have established a novel guinea pig model of asthma. In vitro study confirmed that CHO-K1 cells, expressing guinea pig CysLT2 and CysLT1 receptors are selectively stimulated by LTC4 and LTD4, respectively. However, when LTC4 was intravenously injected to guinea pigs, the resulting bronchoconstriction was fully abrogated by montelukast, a CysLT1 receptor antagonist, indicating rapid metabolism of LTC4 to LTD4 in the lung. We found that treatment with S-hexyl glutathione (S-hexyl GSH), an inhibitor of gamma-glutamyl transpeptidase, significantly increased LTC4 content and LTC4/(LTD4 plus LTE4) ratio in the lung. Under these circumstances, LTC4-induced bronchoconstriction became resistant to montelukast, but sensitive to Compound A, a CysLT2 receptor antagonist, depending on the dose of S-hexyl GSH. Combination with montelukast and Compound A completely abrogated this spasmogenic response. Additionally, we confirmed that LTC4 elicits airway vascular hyperpermeability via CysLT2 receptors in the presence of high dose of S-hexyl GSH as evidenced by complete inhibition of LTC4-induced hyperpermeability by Compound A, but not montelukast. These results suggest that CysLT2 receptors mediate bronchoconstriction and airway vascular hyperpermeability in guinea pigs and that the animal model used in this study may be useful to elucidate the functional role of CysLT2 receptors in various diseases, including asthma.

The role of leukotrienes in allergic diseases

Leukotrienes (LTs), both LTB4 and the cysteinyl LTs (CysLTs) LTC4, LTD4 and LTE4, are implicated in a wide variety of inflammatory disorders. These lipid mediators are generated from arachidonic acid via multistep enzymatic reactions through which arachidonic acid is liberated from membrane phospholipids through the action of phospholipase A2. LTB4 and CysLTs exert their biological effects by binding to cognate receptors, which belong to the G protein-coupled receptor superfamily. LTB4 is widely considered to be a potent chemoattractant for most subsets of leukocytes, whereas CysLTs are potent bronchoconstrictors that have effects on airway remodeling. LTs play a central role in the pathogenesis of asthma and many other inflammatory diseases. This review will provide an update on the synthesis, biological function, and relevance of LTs to the pathobiology of allergic diseases, and examine the current and future therapeutic prospects of LT modifiers.

Discovery of Highly Potent Dual CysLT1 and CysLT2 Antagonist

The benzoxazine derivative, (2S)-4-(3-carboxypropyl)-8-{[4-(4-phenylbutoxy)benzoyl]amino}-3,4-dihydro-2H-1,4-benzoxazine-2-carboxylic acid (19, ONO-2050297), was identified as the first potent dual CysLT1 and CysLT2 antagonist with IC50 values of 0.017 μM (CysLT1) and 0.00087 μM (CysLT2), respectively.

A review on leukotrienes and their receptors with reference to asthma

OBJECTIVE AND METHODS

Leukotrienes (LTs) including cysteinyl leukotrienes (CysLTs) and LTB4 are the most potent inflammatory lipid mediators and play a central role in the pathophysiology of asthma and other inflammatory diseases. These biological molecules mediate a plethora of contractile and inflammatory responses through specific interaction with distinct G protein-coupled receptors (GPCRs). The main objective of this review is to present an overview of the biological effects of CysLTs and their receptors, along with the current knowledge of mechanisms and role of LTs in the pathogenesis of asthma.

RESULTS

CysLTs including LTC4, LTD4 and LTE4 are ligands for CysLT1 and CysLT2 receptors, and LTB4 is the agonist for BLT1 and BLT2 receptors. The role of CysLT1 receptor is well established, and most of the pathophysiological effects of CysLTs in asthma are mediated by CysLT1 receptor. Several CysLT1 antagonists have been developed to date and are currently in clinical practice. Most common among them are classical CysLT1 receptor antagonists such as montelukast, zafirlukast, pranlukast, pobilukast, iralukast, cinalukast and MK571. The pharmacological role of CysLT2 receptor, however, is less defined and there is no specific antagonist available so far. The recent demonstration that mice lacking both known CysLT receptors exhibit full/augmented response to CysLT points to the existence of additional subtypes of CysLT receptors. LTB4, on the other hand, is another potent inflammatory leukotriene, which acts as a strong chemoattractant for neutrophils, but weaker for eosinophils. LTB4 is known to play an important role in the development of airway hyper-responsiveness in severe asthma. However there is no LTB4 antagonist available in clinic to date.

CONCLUSION

This review gives a recent update on the LTs including their biosynthesis, biological effects and the role of anti-LTs in the treatment of asthma. It also discusses about the possible existence of additional subtypes of CysLT receptors.

Proinflammatory and immunoregulatory roles of eicosanoids in T cells

Eicosanoids are inflammatory mediators primarily generated by hydrolysis of membrane phospholipids by phospholipase A2 to ω-3 and ω-6 C20 fatty acids that next are converted to leukotrienes (LTs), prostaglandins (PGs), prostacyclins (PCs), and thromboxanes (TXAs). The rate-limiting and tightly regulated lipoxygenases control synthesis of LTs while the equally well-controlled cyclooxygenases 1 and 2 generate prostanoids, including PGs, PCs, and TXAs. While many of the classical signs of inflammation such as redness, swelling, pain, and heat are caused by eicosanoid species with vasoactive, pyretic, and pain-inducing effects locally, some eicosanoids also regulate T cell functions. Here, we will review eicosanoid production in T cell subsets and the inflammatory and immunoregulatory functions of LTs, PGs, PCs, and TXAs in T cells.

Leukotriene D4 and interleukin-13 cooperate to increase the release of eotaxin-3 by airway epithelial cells

INTRODUCTION

Airway epithelial cells play a central role in the physiopathology of asthma. They release eotaxins when treated with T(H)2 cytokines such as interleukin (IL)-4 or IL-13, and these chemokines attract eosinophils and potentiate the biosynthesis of cysteinyl leukotrienes (cysLTs), which in turn induce bronchoconstriction and mucus secretion. These effects of cysLTs mainly mediated by CysLT(1) and CysLT(2) receptors on epithelial cell functions remain largely undefined. Because the release of inflammatory cytokines, eotaxins, and cysLTs occur relatively at the same time and location in the lung tissue, we hypothesized that they regulate inflammation cooperatively rather than redundantly. We therefore investigated whether cysLTs and the T(H)2 cytokines would act in concert to augment the release of eotaxins by airway epithelial cells.

METHODS

A549 cells or human primary bronchial epithelial cells were incubated with or without IL-4, IL-13, and/or LTD(4). The release of eotaxin-3 and the expression of cysLT receptors were assessed by ELISA, RT-PCR, and flow cytometry, respectively.

RESULTS

IL-4 and IL-13 induced the release of eotaxin-3 by airway epithelial cells. LTD(4) weakly induced the release of eotaxin-3 but clearly potentiated the IL-13-induced eotaxin-3 release. LTD(4) had no effect on IL-4-stimulated cells. Epithelial cells expressed CysLT(1) but not CysLT(2). CysLT(1) expression was increased by IL-13 but not by IL-4 and/or LTD(4). Importantly, the upregulation of CysLT(1) by IL-13 preceded eotaxin-3 release.

CONCLUSIONS

These results demonstrate a stepwise cooperation between IL-13 and LTD(4). IL-13 upregulates CysLT(1) expression and consequently the response to cysLTs This results in an increased release of eotaxin-3 by epithelial cells which at its turn increases the recruitment of leukocytes and their biosynthesis of cysLTs. This positive amplification loop involving epithelial cells and leukocytes could be implicated in the recruitment of eosinophils observed in asthmatics.

Montelukast inhibits leukotriene stimulation of human dendritic cells in vitro

BACKGROUND

Leukotrienes are potent inflammatory mediators which modulate immune responses and induce bronchoconstriction in susceptible individuals. Montelukast (MK) is a leukotriene receptor (CysLT1) antagonist that has been shown to prevent exacerbation of asthma. Considering the plethora of potential cellular targets for MK, specific mechanisms for its therapeutic action are still not fully understood. In vitro, we determined whether human dendritic cell function could be affected by leukotriene C(4) (LTC(4)) treatment and whether MK had potential in modulating this response. We also studied the effect of LTC(4) in the context of response to an airway virus (respiratory syncytial virus, RSV).

METHODS

Human monocyte-derived dendritic cells (moDCs) exposed to LTC(4), MK, or both, were cocultured with autologous T cells, with or without RSV. The effects of LTC(4) and MK on cell function were determined by ELISA and proliferation assays.

RESULTS

Both moDCs and their precursors--monocytes--express LTC(4) receptor CysLT1, making them potential targets for MK. moDCs cultured with LTC(4) release the eosinophil chemoattractant RANTES (CCL5) and induce greater T cell proliferation. Both were blocked by the presence of MK. MK treatment, albeit anti-inflammatory, did not interfere with the moDC-dependent T cell-proliferative responses induced by RSV.

CONCLUSIONS

LTC(4), chronically present in the airways of asthma patients, could induce an exaggerated inflammatory response to airway infection via dendritic cell activation, which would be prevented by MK. Our study provides additional insight into the mechanisms of action of this leukotriene receptor antagonist.

Leukotrienes as modifiers of preclinical atherosclerosis?

Preclinical atherosclerosis represents a crucial period associated with several pathophysiological reactions in the vascular wall. Failure to diagnose preclinical atherosclerosis at this stage misses a major opportunity to prevent the long-term consequences of this disease. Surrogate biological and structural vascular markers are available to determine the presence and the extension of preclinical vascular injury in the general population. Examples of surrogate markers are carotid intima media thickness and biomarkers including high-sensitivity C-reactive protein, cell adhesion molecules and matrix metalloproteinases, and leukotrienes. Recently, leukotrienes have been implicated as mediators, biomarkers, and possible therapeutic targets in the context of subclinical atherosclerosis. The aim of this short paper is to focus on the relation between preclinical atherosclerosis and leukotrienes, with particular attention to the recent development on the use of leukotriene modifiers in the treatment of atherosclerosis.

Expression of cysLT1 and cysLT2 receptor in chronic hyperplastic eosinophilic sinusitis

Elevated production of cysteinyl leukotrienes (cysLTs) from sinus tissues and abundant sinus eosinophils are characteristic features of chronic hyperplastic eosinophilic sinusitis (CHS). CysLTs exert their action through G-protein-coupled receptors named cysLTs receptor type I (cysLT1R) and type II (cysLT2R). These expressions of cysLT receptors in the sinus mucosa have yet to be clarified and the relationship between eosinophilia and the expression of these receptors remains obscure. We compared the expressions of cysLT1R and cysLT2R in the sinus mucosa in patients with CHS, non-eosinophilic chronic sinusitis (NECS), and control sinus tissues; and analyzed the correlation between the expression of CysLTRs and the presence of sinus eosinophils by immunohistochemistry and real-time PCR. A significantly higher percentage of eosinophils expressing cysLT2R protein was observed in patients with CHS compared with NECS and controls. In addition, cysLT2R mRNA expression in CHS was significantly higher than in NECS and controls. Furthermore, a positive correlation was observed between cysLT2R mRNA expression and the number of infiltrated eosinophils. In contrast, the cysLT1R mRNA expression did not differ significantly among these groups. The effect of cysLTs on sinus eosinophils may be mediated through the cysLT2R in patients with CHS. These results may suggest the therapeutic benefit of cysLT2R antagonists in CHS.

Variable expression of cysteinyl leukotriene type I receptor splice variants in asthmatic females with different promoter haplotypes

BACKGROUND

Cysteinyl leukotrienes are potent inflammatory mediators implicated in the pathogenesis of asthma. Human cysteinyl leukotriene receptor 1 (CYSLTR1) gene contains five exons that are variably spliced. Within its promoter few polymorphisms were described. To date, there has been no evidence about the expression of different splice variants of CysLT1 in asthma and their association with CYSLTR1 promoter polymorphisms.The goal of our study was to investigate CysLT1 alternative transcripts expression in asthmatic patients with different CYSLTR1 promoter haplotypes.The study groups consisted of 44 patients with asthma, diagnosed according to GINA 2008 criteria and 18 healthy subjects. Genomic DNA and total RNA was extracted from peripheral blood mononuclear cells. Real-time PCR was performed with specific primers for transcript I [GenBank:DQ131799] and II [GenBank:DQ131800]. Fragments of the CYSLTR1 promoter were amplified by PCR and sequenced directly to identify four single nucleotide polymorphisms: C/T [SNP:rs321029], A/C [SNP:rs2637204], A/G [SNP:rs2806489] and C/T [SNP:rs7066737].

RESULTS

The expression of CysLT1 transcript I and II in asthma did not differ from its expression in healthy control group. However, in major alleles homozygotic CAAC/CAAC women with asthma we found significantly higher expression of transcript I as compared to heterozygous CAAC/TCGC women in that loci. CysLT1 transcript I expression tended to negative correlation with episodes of acute respiratory infection in our asthmatic population. Moreover, expression of CysLT1 transcript II in CAAC/CAAC homozygotic women with asthma was significantly lower than in CAAC/CAAC healthy control females.

CONCLUSIONS

Genetic variants of CYSLTR1 promoter might be associated with gender specific expression of CysLT1 alternative transcripts in patients with asthma. CysLT1 splice variants expression might also correlate with the susceptibility to infection in asthmatic population.

Genetic effect of CysLTR2 polymorphisms on its mRNA synthesis and stabilization

BACKGROUND

We previously demonstrated that single nucleotide polymorphism (SNP) and haplotypes were associated with aspirin hypersensitivity in asthmatics. We investigated the genetic effects of the SNPs and haplotypes on the expression of the CysLTR2 gene.

METHODS

We measured CysLTR2 protein and mRNA expression in EB virus-infected B cell lines from asthmatics having ht1+/+ and ht2+/+. A gel retardation assay was used to identify nuclear protein binding to the c.-819 promoter site. The function of promoter and 3'-UTR were assessed using pGL3 luciferase and pEGFP reporter system, respectively.

RESULTS

We found that the expression of CysLTR2 protein was higher in B cell lines of asthmatics having ht2+/+ than in those having ht1+/+. PMA/ionomycin induced higher mRNA expression of CysLTR2 in B cell lines from ht2+/+ asthmatics than those from ht1+/+ asthmatics. A nuclear protein from the B cell lines showed stronger DNA binding affinity with a probe containing c.-819T than one containing c.-819G. The luciferase activity of the c.-819T type of CysLTR2 promoter was higher than that of the c.-819G type. EGFP expression was higher in the EGFP-c.2078T 3'-UTR fusion construct than in the c.2078C construct.

CONCLUSION

The sequence variants of CysLTR2 may affect its transcription and the stability of its mRNA, resulting in altered expression of CysLTR2 protein, which in turn causes some asthmatics to be susceptible to aspirin hypersensitivity.

Leukotriene signaling in atherosclerosis and ischemia

INTRODUCTION

The inflammatory process of atherosclerosis is associated with several pathophysiological reactions within the vascular wall. The arachidonic acid released by phospholipase A(2) serves as substrate for the production of a group of lipid mediators known as the leukotrienes, which induce pro-inflammatory signaling through activation of specific BLT and CysLT receptors.

DISCUSSION

Leukotriene signaling has been implicated in early lipid retention and foam cell accumulation, as well as in the development of intimal hyperplasia and advanced atherosclerotic lesions. Furthermore, the association of leukotrienes with degradation of extracellular matrix has suggested a role in atherosclerotic plaque rupture. Finally, studies of either myocardial or cerebral ischemia and reperfusion indicate that leukotriene signaling in addition may be involved in the development of ischemic injury.

CONCLUSION

Both leukotriene synthesis inhibitors and leukotriene receptor antagonists have been suggested to induce beneficial effects at different stages of the atherosclerosis process.

Expanding roles for leukotrienes in airway inflammation

Leukotrienes (LTs) are lipid mediators derived from the 5-lipoxygenase pathway of arachidonic acid metabolism. Cysteinyl (cys) LTs C(4), D(4), and E(4) are long known to contribute to airway contractile responses via ligation of the cysLT1 receptor, and cysLT1 antagonists are beneficial in some patients with asthma. Research advances over the past several years suggest that cysLT1 also mediates the ability of cysLTs to modulate inflammation, immune responses, and airway remodeling. Although less is known about an additional receptor, cysLT2, emerging evidence indicates that it likely also contributes to cysLT actions promoting inflammation, vascular permeability, and perhaps fibrosis. LTB(4), best known as a neutrophil chemoattractant, is now recognized to exert other important effects contributing to inflammatory and immune responses. These recent data highlight a growing appreciation for LTs as pleiotropic effectors, which are integral components in the network of molecules that mediate the expression of asthma.

Cysteinyl leukotriene receptor CysLT1 as a novel therapeutic target for allergic rhinitis treatment

BACKGROUND

Cysteinyl leukotrienes (cys-LTs) play an important role in allergic rhinitis because CysLT(1) receptor antagonists relieve the symptoms of allergic rhinitis.

OBJECTIVE

I overview the clinical pharmacology of CysLT(1) receptor antagonists and their potential role in patients with allergic rhinitis.

METHODS

I review the evidence regarding the release of cys-LTs and localization of CysLT(1) receptor on nasal mucosa, and evaluate the clinical efficacy of CysLT(1) receptor antagonist in allergic rhinitis.

RESULTS/CONCLUSION

Immunohistochemical studies show that in allergic rhinitis, the major target of CysLT(1) receptor antagonists are the vascular bed and infiltrated leukocytes such as mast cells, eosinophils and macrophages. CysLT(1) receptor antagonists provide a new opportunity for simultaneous management of allergic diseases of the upper and lower respiratory tract.

Cysteinyl leukotriene-1 receptor activation in a human bronchial epithelial cell line leads to signal transducer and activator of transcription 1-mediated eosinophil adhesion

We studied the effect of leukotriene D(4) (LTD(4)) on a human bronchial epithelial cell line (16HBE) overexpressing the cysteinyl leukotriene (CysLT) (1) receptor (HBECysLT(1)R), looking at the associated signal transduction mechanisms as well as at effects on inflammatory cell adhesion. The results obtained showed that LTD(4) increases the phosphorylation of extracellular signal-regulated protein kinase (ERK) 1/2 and of the signal transducer and activator of transcription 1 (STAT-1) in serine 727 (STAT-1Ser727), resulting in increased eosinophil adhesion to HBECysLT(1)R, associated with enhanced surface expression of intercellular adhesion molecule (ICAM) 1. Pretreatment with a CysLT(1)R-selective antagonist or with a selective inhibitor of protein kinase C (PKC) or with a selective inhibitor of the mitogen-activated protein kinase kinase (MEK) successfully suppressed both LTD(4)-induced STAT-1Ser727 phosphorylation and the associated increase in eosinophil adhesion. The use of the MEK inhibitor and of the selective CysLT(1)R antagonist in electrophoretic mobility shift assay experiments showed that LTD(4) promotes the nuclear translocation of STAT-1 through the activation of ERK1/2 pathway. The key role of STAT-1 in leukotriene D(4) transduction signaling was confirmed by RNA interference experiments, where silencing of STAT-1 expression abolished the effect of leukotriene D(4) on eosinophil adhesion. In conclusion, for the first time, we provide evidence of the involvement of STAT-1 in the signal transduction mechanism of the CysLT(1) receptor; phosphorylation of STAT-1, through PKC and ERK1/2 activation, causes enhanced ICAM-1 surface expression and eosinophil adhesion. Effective CysLT(1)R antagonism may therefore contribute to the control of the chronic inflammatory condition that characterizes human airways in asthma.

Cysteinyl-leukotrienes and their receptors in asthma and other inflammatory diseases: critical update and emerging trends

Cysteinyl-leukotrienes (cysteinyl-LTs), that is, LTC4, LTD4, and LTE4, trigger contractile and inflammatory responses through the specific interaction with G protein-coupled receptors (GPCRs) belonging to the purine receptor cluster of the rhodopsin family, and identified as CysLT receptors (CysLTRs). Cysteinyl-LTs have a clear role in pathophysiological conditions such as asthma and allergic rhinitis (AR), and have been implicated in other inflammatory conditions including cardiovascular diseases, cancer, atopic dermatitis, and urticaria. Molecular cloning of human CysLT1R and CysLT2R subtypes has confirmed most of the previous pharmacological characterization and identified distinct expression patterns only partially overlapping. Interestingly, recent data provide evidence for the immunomodulation of CysLTR expression, the existence of additional receptor subtypes, and of an intracellular pool of CysLTRs that may have roles different from those of plasma membrane receptors. Furthermore, genetic variants have been identified for the CysLTRs that may interact to confer risk for atopy. Finally, a crosstalk between the cysteinyl-LT and the purine systems is being delineated. This review will summarize and attempt to integrate recent data derived from studies on the molecular pharmacology and pharmacogenetics of CysLTRs, and will consider the therapeutic opportunities arising from the new roles suggested for cysteinyl-LTs and their receptors.

Eicosanoid regulation of pulmonary innate immunity post-hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) is a therapeutic option for a number of malignant and inherited disorders. However, the efficacy of this therapy is limited by a number of serious infectious and noninfectious complications. Pulmonary infections represent a significant cause of morbidity and mortality post-HSCT and can occur both pre- and post-hematopoietic reconstitution. Susceptibility to Gram-negative bacterial infections despite full hematopoietic engraftment suggests that innate immunity remains impaired months to years post-HSCT. This review will describe the process and complications of HSCT and will summarize what is known about innate immune reconstitution post-HSCT. Data from the literature as well as our own laboratory will be presented to suggest that an eicosanoid imbalance characterized by over-production of prostaglandins and under-production of leukotrienes leads to impaired lung phagocyte function post-HSCT. Of therapeutic interest, strategies which limit production of prostaglandins can improve pulmonary host defense in animal HSCT models, which suggests that this may also be beneficial for human HSCT recipients.

Mast cells and eicosanoid mediators: a system of reciprocal paracrine and autocrine regulation

When activated by specific antigen, complement, or other transmembrane stimuli, mast cells (MCs) generate three eicosanoids: prostaglandin (PG)D(2), leukotriene (LT)B(4), and LTC(4), the parent molecule of the cysteinyl leukotrienes (cysLTs). These diverse lipid mediators, which are generated from a single cell membrane-associated precursor, arachidonic acid, can initiate, amplify, or dampen inflammatory responses and influence the magnitude, duration, and nature of subsequent immune responses. PGD(2) and cysLTs, which were originally recognized for their bronchoconstricting and vasoactive properties, also serve diverse and pivotal functions in effector cell trafficking, antigen presentation, leukocyte activation, matrix deposition, and fibrosis. LTB(4) is a powerful chemoattractant for neutrophils and certain lymphocyte subsets. Thus, MCs can contribute to each of these processes through eicosanoid generation. Additionally, MCs express G-protein-coupled receptors specific for cysLTs, LTB(4), and another eicosanoid, PGE(2). Each of these receptors can regulate MC functions in vivo by autocrine and paracrine mechanisms. This review focuses on the biologic functions for MC-associated eicosanoids, the regulation of their production, and the mechanisms by which eicosanoids may regulate MC function in host defense and disease.

Eosinophils and asthma

Recruitment and activation of eosinophils into the airways of asthma patients is suggested to be a contributing causative agent in the histopathologies and lung dysfunction that are characteristic of asthma. Recent studies in mouse models of asthma and in human patients implicate eosinophils in immune regulation and remodeling in the lung in addition to their hypothesized role as destructive agents. Specifically, eosinophils not only participate in release of granule proteins, lipid mediators, reactive oxygen species, cytokines, and growth factors but also function through complex cell-cell interactions to elicit chronic T helper 2 inflammation in the lung. This review highlights the roles of eosinophils in asthma.

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.

Cysteinyl leukotrienes: multi-functional mediators in allergic rhinitis

Cysteinyl leukotrienes (CysLTs) are a family of inflammatory lipid mediators synthesized from arachidonic acid by a variety of cells, including mast cells, eosinophils, basophils, and macrophages. This article reviews the data for the role of CysLTs as multi-functional mediators in allergic rhinitis (AR). We review the evidence that: (1) CysLTs are released from inflammatory cells that participate in AR, (2) receptors for CysLTs are located in nasal tissue, (3) CysLTs are increased in patients with AR and are released following allergen exposure, (4) administration of CysLTs reproduces the symptoms of AR, (5) CysLTs play roles in the maturation, as well as tissue recruitment, of inflammatory cells, and (6) a complex inter-regulation between CysLTs and a variety of other inflammatory mediators exists.

Cysteinyl leukotriene receptor 1 promoter polymorphism is associated with aspirin-intolerant asthma in males

BACKGROUND

Cysteinyl leukotrienes (CysLTs) play important roles in the pathogenesis of eosinophilic airway inflammation characterized by bronchoconstriction, mucus secretion and airway hyper-responsiveness via cysteinyl leukotriene receptor 1 (CysLTR1)-mediated mechanism. CysLTR1-selective antagonists have anti-bronchoconstrictive and anti-inflammatory effects in asthma, particularly aspirin-intolerant asthma (AIA).

METHODS

To investigate the association of CysLTR1 with AIA development, we identified three single nucleotide polymorphisms (SNPs), -634C>T, -475A>C, -336A>G, in the 5' upstream region of CysLTR1 gene using a direct sequencing method in 105 AIA patients, 110 ASA-tolerant asthma (ATA) patients and 125 normal healthy controls (NC).

RESULTS

Significant differences were observed in allele frequencies of the three SNPs within male subjects; Male AIA patients had higher frequencies of the minor alleles of these three SNPs than male control groups (P=0.03 for AIA vs. NC; P=0.02 for AIA vs. ATA). Moreover, three-SNP haplotype, ht2 [T-C-G], was associated with increased disease risk (odds ratio (OR)=2.71, P=0.03 for AIA vs. NC; OR=2.89, P=0.02 for AIA vs. ATA) in males. CysLTR1 haplotypes were also associated with altered gene expression; luciferase activity was significantly enhanced with the ht2 [T-C-G] construct in comparison with the ht1 [C-A-A] construct in human Jurkat cells (P=0.04).

CONCLUSION

These results suggest that genetic variants of CysLTR1 are associated with AIA in a Korean population, and may modulate CysLTR1 expression.

Determination of structure and transcriptional regulation of CYSLTR1 and an association study with asthma and rhinitis

Pharmacologic studies have revealed that cysteinyl leukotrienes (CYSLTs) act through two receptors, cysteinyl leukotriene receptor 1 (CYSLTR1) and CYSLTR2. CYSLTR1 antagonists are widely used to treat asthma and rhinitis. In this study, we characterized the genomic structure and transcriptional regulation of CYSLTR1 and examined associations between CYSLTR1 polymorphisms and asthma/rhinitis. The experiment of rapid amplification of cDNA end revealed that CYSLTR1 contains three exons and that the entire open reading frame is located in exon 3. Reverse transcriptase-polymerase chain reaction showed that there were multiple splice variants of CYSLTR1 and that the transcript expression patterns differed from tissues and cell types. The promoter region of CYSLTR1 is from -665 to -30 bp relative to the transcription start site. We identified four polymorphisms (c.-618-434T/C, c.-618-275C/A, c.-618-136G/A, and 927C/T), and transmission disequilibrium tests revealed that none of these polymorphisms was associated with the development of asthma/rhinitis. However, the TCG and CAA haplotypes in the promoter region caused different transcriptional activity. Our findings indicate that CYSLTR1 polymorphisms are not likely to be involved in the development of asthma/rhinitis, but it is possible that these polymorphisms could influence drug responses in individuals with atopic diseases.

Interferon-gamma up-regulates expression of cysteinyl leukotriene type 2 receptors on eosinophils in asthmatic patients

STUDY OBJECTIVES

Cysteinyl leukotrienes (cysLTs) are strong bronchoconstrictive mediators that play a key role in asthma inflammation. They act through specific receptors including cysLT type 1 receptor (CysLT1R) and cysLT type 2 receptor (CysLT2R). Although these two receptors are co-expressed on inflammatory cells, little is known about CysLT2R in patients with asthma. The aims of this study were to investigate the changes in cysLT receptors (CysLTRs) during asthma exacerbations and to determine which cytokine modulates CysLTR expression on eosinophils.

METHODS

We assessed protein expression and messenger RNA of CysLT1R and CysLT2R in peripheral blood eosinophils and measured urinary leukotriene E(4) levels in 36 patients with stable asthma, 23 subjects with asthma exacerbation, and 15 healthy subjects. We also evaluated the modulation of these receptors by interleukin (IL)-1beta, IL-4, IL-5, IL-13, interferon (IFN)-gamma and tumor necrosis factor-alpha in cultured eosinophils.

RESULTS

Expression of both CysLT1R and CysLT2R on eosinophils during asthma exacerbations was significantly higher (p < 0.05) than in stable asthma and healthy subjects. A greater expression of CysLT2R in exacerbation was found in nonatopic asthmatics. Only IFN-gamma up-regulated cell-surface expression of CysLT2R in a dose-dependent manner and enhanced messenger RNA levels. No cytokine affected CysLT1R expression or messenger RNA level.

CONCLUSIONS

CysLT2R expression on eosinophils was increased in patients, especially in nonatopic subjects, during asthma exacerbation, and was up-regulated by IFN-gamma; therefore we speculate that a pathway through CysLT2R might modulate exacerbations of asthma.

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.

Association between a polymorphism in cysteinyl leukotriene receptor 2 on chromosome 13q14 and atopic asthma

OBJECTIVE

Cysteinyl leukotriene receptor 2 (CYSLTR2) is one of the receptors for the cysteinyl leukotrienes (CYSLTs), which cause bronchoconstrictions, vascular hyperpermeability and mucus hypersecretion in asthmatic patients. CYSLTR1 antagonists have been shown to be effective in the treatment of chronic asthma. CYSLTR2 is located approximately 300 kb from D13S153, which is reportedly linked to asthma in several populations. We characterized the genomic structure of humans CYSLTR2, determined the putative major promoter region and conducted association studies pertaining to polymorphisms in CYSLTR2 and asthma.

METHODS AND RESULTS

We identified three novel exons in the 5' untranslated region of CYSLTR2 by rapid amplification of cDNA ends and identified eight novel polymorphisms in CYSLTR2 by direct sequencing. A transmission disequilibrium test with 137 Japanese asthmatic families revealed that the -1220A > C polymorphism is associated with the development of asthma (P = 0.0066). In addition, a polymorphism in the putative promoter region caused different promoter activities in vitro.

CONCLUSION

Our results suggest that CYSLTR2 is one of the genes that contributes to susceptibility to asthma in the Japanese population.

Cysteinyl leukotrienes and their receptors: cellular distribution and function in immune and inflammatory responses

The cysteinyl leukotrienes (cys-LTs) are a family of potent bioactive lipids that act through two structurally divergent G protein-coupled receptors, termed the CysLT(1) and CysLT(2) receptors. The cloning and characterization of these two receptors has not only reconciled findings of previous pharmacologic profiling studies of contractile tissues, but also has uncovered their expression on a wide array of circulating and tissue-dwelling leukocytes. With the development of receptor-selective reagents, as well as mice lacking critical biosynthetic enzymes, transporter proteins, and the CysLT(1) receptor, diverse functions of cys-LTs and their receptors in immune and inflammatory responses have been identified. We review cys-LT biosynthesis; the molecular biology and distribution of the CysLT(1) and CysLT(2) receptors; the functions of cys-LTs and their receptors in the recruitment and activation of effector leukocytes and induction of adaptive immunity; and the development of fibrosis and airway remodeling in animal models of lung injury and allergic inflammation.

Targeted Gene Disruption Reveals the Role of the Cysteinyl Leukotriene 2 Receptor in Increased Vascular Permeability and in Bleomycin-induced Pulmonary Fibrosis in Mice

The cysteinyl leukotrienes (cys-LTs) mediate both acute and chronic inflammatory responses in mice, as demonstrated by the attenuation of the IgE/antigen-mediated increase in microvascular permeability and of bleomycin-induced pulmonary fibrosis, respectively, in a strain with targeted disruption of leukotriene C(4) synthase to prevent cys-LT synthesis. Our earlier finding that the acute, but not the chronic, injury was attenuated in a strain with targeted disruption of the cysteinyl leukotriene 1 (CysLT(1)) receptor suggested that the chronic injury might be mediated through the CysLT(2) receptor. Thus, we generated CysLT(2) receptor-deficient mice by targeted gene disruption. These mice developed normally and were fertile. The increased vascular permeability associated with IgE-dependent passive cutaneous anaphylaxis was significantly reduced in CysLT(2) receptor-null mice as compared with wild-type mice, whereas plasma protein extravasation in response to zymosan A-induced peritoneal inflammation was not altered. Alveolar septal thickening after intratracheal injection of bleomycin, characterized by interstitial infiltration with macrophages and fibroblasts and the accumulation of collagen fibers, was significantly reduced in CysLT(2) receptor-null mice as compared with the wild-type mice. The amounts of cys-LTs in bronchoalveolar lavage fluid after bleomycin injection were similar in the CysLT(2) receptor-null mice and the wild-type mice. Thus, in response to a particular pathobiologic event the CysLT(2) receptor can mediate an increase in vascular permeability in some tissues or promote chronic pulmonary inflammation with fibrosis.

Urinary 3-bromotyrosine and 3-chlorotyrosine concentrations in asthmatic patients: lack of increase in 3-bromotyrosine concentration in urine and plasma proteins in aspirin-induced asthma after intravenous aspirin challenge

BACKGROUND

Eosinophil peroxidase and myeloperoxidase halogenate tyrosine residues in plasma proteins and generate 3-bromotyrosine (BY) and 3-chlorotyrosine (CY), respectively.

OBJECTIVES

(1) To estimate urinary concentrations of BY and CY in asthmatic patients. (2) To investigate BY concentration in relation to urinary leukotriene E4 (LTE4) concentration in order to evaluate the activation of eosinophils in patients with aspirin-induced asthma (AIA).

METHODS

BY and CY were quantified with a gas chromatograph-mass spectrometer using (13)C-labelled compounds as internal standards.

RESULTS

(1) Activation of eosinophils and neutrophils by immobilized IgG1 induced preferential formation of BY and CY, respectively. (2) A significantly higher concentration of BY was observed in the urine from asthmatic patients than in that from healthy control subjects (45+/-21.7 vs. 22.6+/-10.8 ng/mg-creatinine, P<0.01). CY concentration was also elevated in the urine from asthmatic patients (4.4+/-3.2 vs. 1.5+/-1.0 ng/mg-creatinine, P<0.01). (3) After intravenous aspirin challenge of aspirin-induced asthmatic patients, the concentration of BY in urine did not significantly change. No significant change was also observed in the ratio of BY concentration to total tyrosine concentration in plasma proteins. In contrast, the concentration of urinary LTE4 significantly increased after the intravenous aspirin challenge.

CONCLUSION

Determination of BY and CY concentrations may be useful for monitoring the activation of eosinophils and neutrophils in asthmatic patients, respectively. After aspirin challenge of AIA patients, the increased concentration of urinary LTE4 did not accompany changes in BY concentration in both urine and plasma proteins. These results may preclude the activation of eosinophils after aspirin challenge in patients with AIA.

Eosinophil activation and cysteinyl leukotriene production in infants with respiratory syncytial virus bronchiolitis

BACKGROUND

It has been suggested that acute infantile bronchiolitis associated with respiratory syncytial virus (RSV) may share some pathogenic features with atopic asthma in that virus-specific IgE is produced and cysteinyl leukotrienes (cLTs) and eosinophil cationic protein (ECP) have been detected in airway secretions. ECP is a specific marker of eosinophil activation although leukotrienes can be released from a variety of cells including mast cells, eosinophils and monocytes.

OBJECTIVE

To test the association between eosinophil activation and cysteinyl leukotriene production in the upper airway secretions of infants with RSV positive (RSV+ve) bronchiolitis.

METHODS

Nasal lavage samples were performed in 78 infants (0.0-11.5 months) admitted to hospital with RSV+ve bronchiolitis soon after admission (0-48 h). Leukotriene C4 (LTC4) was assayed by enzyme immunoassay (EIA) and eosinophil cationic protein (ECP) by fluoroimmunoassay (FIA).

RESULTS

LTC4 was detectable in 51 and ECP in 57 of 78 samples with a significant positive relationship between LTC4 and ECP (r=0.557, P<0.001).

CONCLUSION

In the majority of our subjects with RSV+ve bronchiolitis ECP and LTC4 were detectable in upper airway secretions and were significantly associated with each other. In this clinical setting much of the detected LTC4 within upper airway secretions is likely to originate from the eosinophil, an observation that may have implications for clinical management and for delineation of the underlying mechanisms associated with this illness.