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

Functional polymorphism and differential regulation of CYSLTR1 transcription in human airway smooth muscle and monocytes

Cysteinyl leukotrienes play an important role in the pathophysiology of many inflammatory disorders, including asthma. The aim of this study was to characterize the mechanisms underlying transcriptional regulation of the human cysteinyl leukotriene receptor 1 (hCYSLTR1) gene. 5'RACE was performed on human airway smooth muscle (HASM) and peripheral blood mononuclear cells. A1128-bp region of the hCYSLTR1 main putative promoter was screened for polymorphisms by sequencing of 48 individuals. Luciferase reporter gene assays were performed using fragments of the core promoter (232 bp to 1128 bp) in HASM and THP1 cells. Three hCYSLTR1 transcripts were found, one representing 90% of all messenger RNA identified. The genomic location of the transcription start sites suggested there are two putative hCYSLTR1 promoters. The majority of the transcriptional activity of the main putative promoter was detected between -232 and -679 bp. Four singlenucleotide polymorphisms in strong linkage disequilibrium were found in the region studied: -561 (rs7066737), -642 (rs2806489), -781 (rs2637204), and -940 (rs321029), with three haplotypes observed. In THP1 cells, the G allele (-642) caused a twofold decrease in luciferase expression compared to the Aallele. These data suggest that the majority of hCYSLTR1 transcripts in HASM and monocytes arise from a single promoter located immediately upstream of the 5\' untranslated region, although rarer transcripts can also occur. This study also raises the possibility that cell-type-dependent differences in transcriptional activity caused by the presence of specific haplotypes within the main CYSLTR1 promoter may be a predictor of disease risk or treatment response.

Agonist- and T(H)2 cytokine-induced up-regulation of cysteinyl leukotriene receptor messenger RNA in human monocytes

BACKGROUND

The cysteinyl leukotrienes (CysLTs) are lipid mediators that have been implicated in the pathogenesis of allergic diseases, and their actions are mediated via specific receptors named CysLT1 receptor (CysLT1R) and CysLT2 receptor (CysLT2R). Little information is known about the role of T(H)2 cytokines in the regulation of both CysLT1R and CysLT2R expression.

OBJECTIVE

To investigate the possible modulation of both CysLT1R and CysLT2R messenger RNA (mRNA) expression, we have developed a real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR) assay based on the TaqMan fluorescence method to quantify CysLT1R and CysLT2R mRNA in human monocytes.

METHODS

Human monocytes were stimulated with leukotriene D4 or interleukin (IL) 4 or IL-13, and the levels of CysLT1R and CysLT2R mRNA were measured by the quantitative RT-PCR.

RESULTS

CysLT1R and CysLT2R mRNA was increased after stimulation with leukotriene D4. CysLT1R mRNA was augmented 150-fold after treatment with IL-4; however, no significant increase was observed in CysLT2R mRNA level. IL-13 could induce a biphasic augmentation of CysLT1R mRNA level. In contrast to IL-4, IL-13 enhanced CysLT2R mRNA level, with a maximal effect at 2 hours of incubation.

CONCLUSIONS

CysLT1R and CysLT2R expression can be regulated by CysLT itself and T(H)2 cytokines at the transcriptional level.

Specific leukotriene receptors couple to distinct G proteins to effect stimulation of alveolar macrophage host defense functions

Leukotrienes (LTs) are lipid mediators implicated in asthma and other inflammatory diseases. LTB(4) and LTD(4) also participate in antimicrobial defense by stimulating phagocyte functions via ligation of B leukotriene type 1 (BLT1) receptor and cysteinyl LT type 1 (cysLT1) receptor, respectively. Although both Galpha(i) and Galpha(q) proteins have been shown to be coupled to both BLT1 and cysLT1 receptors in transfected cell systems, there is little known about specific G protein subunit coupling to LT receptors, or to other G protein-coupled receptors, in primary cells. In this study we sought to define the role of specific G proteins in pulmonary alveolar macrophage (AM) innate immune responses to LTB(4) and LTD(4). LTB(4) but not LTD(4) reduced cAMP levels in rat AM by a pertussis toxin (PTX)-sensitive mechanism. Enhancement of FcgammaR-mediated phagocytosis and bacterial killing by LTB(4) was also PTX-sensitive, whereas that induced by LTD(4) was not. LTD(4) and LTB(4) induced Ca(2+) and intracellular inositol monophosphate accumulation, respectively, highlighting the role of Galpha(q) protein in mediating PTX-insensitive LTD(4) enhancement of phagocytosis and microbicidal activity. Studies with liposome-delivered G protein blocking Abs indicated a dependency on specific Galpha(q/11) and Galpha(i3) subunits, but not Galpha(i2) or G(beta)gamma, in LTB(4)-enhanced phagocytosis. The selective importance of Galpha(q/11) protein was also demonstrated in LTD(4)-enhanced phagocytosis. The present investigation identifies differences in specific G protein subunit coupling to LT receptors in antimicrobial responses and highlights the importance of defining the specific G proteins coupled to heptahelical receptors in primary cells, rather than simply using heterologous expression systems.

A putative link of PUFA, GPR40 and adult-born hippocampal neurons for memory

Long chain polyunsaturated fatty acids (PUFA) such as docosahexaenoic and arachidonic acids, which are enriched in the brain, are important for multiple aspects of neuronal development and function including neurite outgrowth, signal transduction and membrane fluidity. Recent studies show that PUFA are capable of improving hippocampal long-term potentiation, learning ability of aged rats, and cognitive function of humans with memory deficits, although the underlying mechanisms are unknown. There have been several reports studying physiological roles of G-protein coupled receptor 40 (GPR40) in the pancreas, but no studies have focused on the function of GPR40 in the brain. As GPR40 was recently identified in neurons throughout the brain, it is probable that certain PUFA may act, as endogenous ligands, on GPR40 at their cell surface. However, the effects of PUFA upon neuronal functions are still not clearly understood. Here, although circumferential, a combination of in vitro and in vivo data is introduced to consider the effects of docosahexaenoic and arachidonic acids on brain functions. GPR40 was found in the newborn neurons of the normal and postischemic hippocampi of adult macaque monkeys, while the positive effects of PUFA upon Ca(2+) mobilization and cognitive functions were demonstrated in both GPR40 gene-transfected PC12 cells and human subjects with memory deficits. The purpose of this review is to propose a putative link among PUFA, GPR40, and hippocampal newborn neurons by discussing whether PUFA can improve memory functions through GPR40 activation of adult-born neurons. At present, little is known about PUFA requirements that make possible neurogenesis in the adult hippocampus. However, the idea that 'PUFA-GPR40 interaction might be crucial for adult neurogenesis and/or memory' should be examined in detail using various experimental paradigms.

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.

3-Arylamino-2H-1,2,4-benzothiadiazin-5-ol 1,1-dioxides as novel and selective CXCR2 antagonists

A series of 3-arylamino-2H-1,2,4-benzothiadiazin-5-ol 1,1-dioxides were prepared and shown to be novel and selective antagonists of the CXCR2 receptor. Synthesis, structure and activity relationships, selectivity, and some developability properties are described.

The role of antileukotriene drugs in management of rhinitis and rhinosinusitis

Antileukotriene drugs have been studied for more than 15 years. In this review we examine the role of leukotrienes in rhinitis and rhinosinusitis, and explore the clinical literature supporting the use of anti-leukotriene agents in these diseases. Although these medications clearly are efficacious in rhinitis, it is unclear where in the armamentarium they should be used. The evidence for use in sinusitis has not been well studied except in sinusitis-associated aspirin-exacerbated respiratory disease. In this circumstance there is information that allows use of antileukotriene agents to be considered efficacious. We provide our rationale for use and await future clinical studies to answer this important question.

IFN-gamma induces cysteinyl leukotriene receptor 2 expression and enhances the responsiveness of human endothelial cells to cysteinyl leukotrienes

Cysteinyl leukotrienes (cysLTs) are important mediators of cell trafficking and innate immune responses, involved in the pathogenesis of inflammatory processes, i.e., atherosclerosis, pulmonary fibrosis, and bronchial asthma. The aim of this study was to examine the regulation of cysLT signaling by IFN-gamma in human primary endothelial cells. IFN-gamma increased cysLT receptor 2 (CysLTR2) mRNA expression and CysLTR2-specific calcium signaling in endothelial cells. IFN-gamma signaled through Jak/STAT1, as both AG490, a Jak2 inhibitor, and expression of a STAT1 dominant-negative construct, significantly inhibited CysLTR2 mRNA expression in response to IFN-gamma. To determine mechanisms of IFN-gamma-induced CysLTR2 expression, the human CysLTR2 gene structure was characterized. The CysLTR2 gene has a TATA-less promoter, with multiple transcription start sites. It consists of six variably spliced exons. Eight different CysLTR2 transcripts were identified in endothelial and monocytic cells. Gene reporter assay showed potent basal promoter activity of a putative CysLTR2 promoter region. However, there were no significant changes in gene reporter and mRNA t(1/2) assays in response to IFN-gamma, suggesting transcriptional control of CysLTR2 mRNA up-regulation by IFN-gamma response motifs localized outside of the cloned CysLTR2 promoter region. Stimulation of endothelial cells by cysLTs induced mRNA and protein expression of early growth response genes 1, 2, and 3 and cycloxygenase-2. This response was mediated by CysLTR2 coupled to G(q/11), activation of phospholipase C, and inositol-1,4,5-triphosphate, and was enhanced further 2- to 5-fold by IFN-gamma stimulation. Thus, IFN-gamma induces CysLTR2 expression and enhances cysLT-induced inflammatory responses.

Montelukast decreases plasma endothelin-1 and serum eosinophil cationic protein levels in paediatric atopic asthma

BACKGROUND AND OBJECTIVE

Endothelin-1 (ET-1) is produced by vascular endothelial cells and epithelial cells, T-lymphocytes and phagocytes. Increased ET-1 levels have been demonstrated in the bronchial epithelium of asthma patients. In vitro, ET-1 stimulates mucus secretion, activates proinflammatory cells - macrophages and mast cells - and serves as a mitogenic stimulus for fibroblasts and smooth muscle. In addition, ET-1 activates phospholipase 2. Compared with healthy individuals, asthma patients have increased ET-1 levels during an attack and following stabilisation. Our study was designed to examine plasma ET-1 (P-ET) levels in paediatric atopic patients newly diagnosed with persistent mild bronchial asthma and 1 month after initiation of montelukast therapy.

METHODS

Patients' histories were examined, and their blood eosinophil leucocyte count and levels of total serum immunoglobulin E (S-IgE), serum eosinophil cationic protein (S-ECP) and P-ET were determined. Thirty-six patients with persistent mild bronchial asthma were treated with the leukotriene receptor antagonist montelukast, administered once a day for 4 weeks. Second P-ET and S-ECP level determinations were made 4 weeks later with all the children included in the study. P-ET levels were also determined in a group of 27 healthy children who had no atopy in their medical histories and were taking no drugs (including montelukast), and who served as controls.

RESULTS

The mean +/- SD pretreatment P-ET level in the 36 study children was 11.542 +/- 6.408 pg/L, and this decreased to 5.636 +/- 4.419 pg/L after 1 month's therapy with montelukast (statistically significant difference; p < 0.0001). Both of these values were significantly higher (p < 0.0001 and p < 0.031, respectively) than the mean level in the control group of 27 children (3.543 +/- 2.497 pg/L). The mean pretreatment S-ECP level was 35.78 +/- 19.58 microg/L, and this decreased to 19.54 +/- 13.86 microg/L after 1 month's therapy (p < 0.001).

CONCLUSIONS

This study demonstrated a decrease in P-ET levels in children with mild asthma receiving montelukast. This indicates a reduction in the severity of the inflammatory response and, hence, provides evidence for the anti-inflammatory effect of montelukast. Monitoring both ET-1 and ECP levels at regular follow-up may be useful in assessing these two facets of activity of chronic inflammation in bronchial asthma.

Differential effects of G protein coupled receptors on hematopoietic progenitor cell growth depend on their signaling capacities

We have shown that CD34(+) hematopoietic progenitor and stem cells (HPCs) consistently express several G protein-coupled receptors (GPCRs): the chemokine receptor CXCR4, the cysteinyl-leukotriene receptor cysLT1, and receptors for sphingosine 1-phosphate (S1P), particularly S1P1. These GPCRs differentially mediate chemotactic, adhesive, and proliferative responses in HPCs. To elucidate the diversity of the responses observed, we compared their signaling capacities in CD34(+) cells. In primary CD34(+) progenitors, the strongest effects on calcium signaling (intracellular calcium fluxes) were mediated by cysLT1. Analyses in CD34(+) cell lines revealed that calcium signaling induced by cysLT1 was only partially inhibited by pertussis toxin (PTX), while responses induced by CXCR4 and S1P receptors were completely blocked. These findings indicate that cysLT1 signals via Gi and Gq proteins, while CXCR4 and also S1P receptors (e.g., S1P1) only induce Gi protein-mediated effects. By analysis of downstream signaling, we could provide further evidence that combined activation of PTX-insensitive (Gq-mediated) and PTX-sensitive (Gi-mediated) pathways by cysLT1 may explain the strong and broad effects of cysteinyl-leukotrienes in early hematopoietic cells, while signaling of CXCR4 and S1P1 solely depends on Gi proteins, resulting in effects mainly restricted to migration and adhesion.

Modification of Cysteinyl Leukotriene Receptor Expression in Capsular Contracture

The development of a fibrotic capsule around foreign material in the body is a physiologic reaction undertaken by the body to protect itself from a material it does not recognize. The periprosthetic capsule can pathologically contract, pressing on the implant; it can cause pain, firmness, and sometimes implant extrusion. The pathogenesis of capsular contracture is still unclear, but most reports indicate a multifactorial explanation. The aim of this study is to investigate the role of cysteinyl leukotriene receptors (cysLTR) on the inflammatory cells involved in the development of the capsular contracture. We recruited 20 patients affected by severe capsular contracture (Baker III-IV) and a control group composed of normal patients who had undergone implant substitution. In both groups, we performed a semiquantitative analysis of mRNA encoding for cysLTR1, cysLTR2, tumor necrosis factor-alpha (TNF-alpha) and interleukin 10 (IL-10) on myofibroblasts and macrophages of the periprosthetic capsular tissue. The molecular analysis showed an increase in the cysLTR2, TNF-alpha gene expression but no change in the cysLTR1 and IL-10 genes in patients affected by capsular contracture. These preliminary findings suggest a primary role for cysteinyl leukotrienes in the activation and up-regulation of capsular contraction mechanisms.

Spatio-temporal expression of cysteinyl leukotriene receptor-2 mRNA in rat brain after focal cerebral ischemia

Cysteinyl leukotrienes (CysLTs) induce inflammatory responses mediated by activating CysLT(1) and CysLT(2) receptors. We have recently reported that CysLT(1) receptor expression is increased in rat brain after focal cerebral ischemia and the increased expression is spatio-temporally related to acute neuronal injury and late astrocyte proliferation. Here we report spatio-temporal expression of CysLT(2) receptor mRNA in rat brain after focal cerebral ischemia induced by 30min of middle cerebral artery occlusion. We found that the neuron density was gradually decreased or disappeared in the ischemic core and boundary zone during 14 days after reperfusion, and the astrocyte population in the boundary zone was increased 3-14 days after reperfusion. In the ischemic core, the expression of CysLT(2) receptor mRNA was increased at 6, 12 and 24h and then recovered at 3, 7 and 14 days after reperfusion. In the boundary zone, the expression was significantly increased 3, 7 and 14 days after reperfusion. The results suggest that CysLT(2) receptor may be related to the acute neuronal injury and late astrocyte proliferation in the ischemic brain.

Treating asthma in the older patient: is there a place for leukotriene modifiers?

Asthma is a common airway disease found in people of all ages, although most studies of asthma therapies are focused on adolescent and young adults. Little information exists on the use of asthma therapeutics in the older patient (>65 years of age). The newest therapeutic class to be released in the US for the treatment of asthma is the leukotriene modifiers. These medications (either receptor antagonists or enzyme inhibitors) have been found to be beneficial in younger patients with asthma, but their potential role in older patients is less clear. In this review, the data regarding the use of these medications in older patients are examined, as are the epidemiological and pathophysiological issues regarding asthma in this growing patient population. On the basis of the two published reports of leukotriene modifiers in the older patient, we conclude that leukotriene modifiers are useful in this population, but like other controller therapies for asthma, they are less effective in the older population.

Cysteinyl leukotriene receptors CysLT1 and CysLT2 are upregulated in acute neuronal injury after focal cerebral ischemia in mice

AIM

To determine whether cysteinyl leukotriene receptors (CysLT1 and CysLT2) are upregulated in acute neuronal injury after focal cerebral ischemia in mice, and to confirm CysLT1 receptor localization.

METHODS

After permanent focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO), neurological deficits and neuron loss were determined at various time points within 48 h. The mRNA expressions of CysLT1 and CysLT2 receptors in the brain were analyzed by RT-PCR. CysLT1 receptor localization was detected by double immunofluorescence.

RESULTS

Neurological deficits and neuron loss were found 6, 24 and 48 h after MCAO. The mRNA expressions of both CysLT1 and CysLT2 receptors were upregulated in the ischemic hemisphere 1, 24, and 48 h after MCAO with peaks at 24 h. The CysLT1 receptor was selectively localized in neurons 24 h after MCAO.

CONCLUSION

CysLT1 and CysLT2 receptors are upregulated in acute neuronal injury after focal cerebral ischemia, and the CysLT1 receptor is localized in neurons after ischemia.

Cysteinyl leukotriene receptor 1 is involved in N-methyl-D-aspartate-mediated neuronal injury in mice

AIM

To determine whether cysteinyl leukotriene receptor 1 (CysLT1 receptor) is involved in N-methyl-D-aspartate (NMDA)-induced excitotoxic injury in the mouse brain.

METHODS

Brain injury was induced by NMDA microinjection (50-150 nmol in 0.5 microL) into the cerebral cortex. The changes in CysLT1 receptor expression 24 h after NMDA injection and the effects of a CysLT1 receptor antagonist, pranlukast (0.01 and 0.1 mg/kg), an NMDA receptor antagonist, ketamine (30 mg/kg), and an antioxidant, edaravone (9 mg/kg) were observed.

RESULTS

In the NMDA-injured brain, the CysLT1 receptor mRNA, and protein expression were upregulated, and the receptor was mainly localized in the neurons and not in the astrocytes. Pranlukast, ketamine and edaravone decreased NMDA-induced injury; pranlukast (0.1 mg/kg) and ketamine inhibited the upregulated expression of the CysLT1 receptor.

CONCLUSION

CysLT1 receptor expression in neurons is upregulated after NMDA injection, and NMDA-induced responses are inhibited by CysLT1 receptor antagonists, indicating that the increased CysLT1 receptor is involved in NMDA excitotoxicity.

The cysteinyl-leukotriene type 1 receptor polymorphism 927T/C is associated with atopy severity but not with asthma

BACKGROUND

The cysteinyl-leukotriene receptor type 1 (CysLT1) mediates the bronchoconstrictor and pro-inflammatory actions of cysteinyl-leukotrienes (LTC4, LTD4, LTE4) in asthma and is the molecular target of the lukast class of oral anti-leukotriene drugs. We screened the CYSLTR1 gene on chromosome Xq13-21 for coding region polymorphisms, and investigated their associations with allergy and asthma.

METHODS

Solid-phase chemical cleavage was used to screen polymorphisms in the coding region of CYSLTR1. A TaqMan allelic discrimination assay was used to genotype a 927T/C SNP and oligonucleotide ligation assays were used to genotype the previously reported 617T/C and 898G/A SNPs of CYSLTR1 in 341 asthmatic families from the UK. Associations with asthma diagnosis, atopic status, serum-specific IgE and severity of allergy and asthma were examined.

RESULTS

Family-based association tests showed that the 927 T allele was associated with atopy severity, especially in female subjects, but not with asthma diagnosis or severity, atopic status, bronchial hyper-responsiveness to methacholine or forced expiratory volume in 1 s.

CONCLUSION

Mutation screening identified only one polymorphism, 927T/C, in the coding region of the CysLT1 receptor. This polymorphsim is predictive of atopy severity, but not associated with asthma.

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.

Distribution of specific binding sites for cysteinyl leukotriene 1 receptor antagonist in human nasal mucosa

CONCLUSION

The high density of [3H]-pranlukast binding sites on the local leukocytes in human nasal mucosa suggests that CysLT1 receptor antagonists may directly modulate cellular function of the local leukocytes through binding to CysLT1 receptor on allergic nasal mucosa.

OBJECTIVES

The cysteinyl leukotrienes (CysLTs) are lipid mediators that have been implicated in the pathogenesis of allergic diseases. Pharmacological studies using CysLTs indicate that two classes of receptors named CysLT1 and CysLT2 receptor exist. The former is sensitive to the CysLT1 receptor antagonist currently used to treat asthma and allergic rhinitis. To confirm the binding sites of CysLT1 receptor antagonist in human nasal mucosa, the autoradiographic distribution of CysLT1 receptor was studied in human nasal inferior turbinates.

MATERIALS AND METHODS

Cryostat sections were incubated with [3H]-pranlukast for autoradiography. Nonspecific binding was determined by adding unlabelled pranlukast.

RESULTS

Autoradiograms indicated [3H]-pranlukast densely labeled on the interstitial cells. Blood vessels were sparsely labeled. There was no specific labeling in the submucosal glands or epithelium. These results support our previous report from in situ hybridization and immunohistochemistry of CysLT1 receptor.

Pharmacogenomics and the future of drug therapy

With the completion of the human genome project, many investigators are striving to translate the resulting wealth of new information into new and improved clinical practices. Pharmacogenomics represents one of the most promising of these applications for adult- and pediatric-based therapies. This article provides a historical perspective, but most importantly, uses this background to illustrate important principles of the field. The application of pharmacogenomics to asthma therapy is presented as an example of the current status of pharmacogenomics as it is being applied to an important pediatric health problem. Finally, a discussion of future promises and challenges to the application of pharmacogenomics is presented, including economic and ethical issues.

Characterization of the human patatin-like phospholipase family

Several publications have described biological roles for human patatin-like phospholipases (PNPLAs) in the regulation of adipocyte differentiation. Here, we report on the characterization and expression profiling of 10 human PNPLAs. A variety of bioinformatics approaches were used to identify and characterize all PNPLAs encoded by the human genome. The genes described represent a divergent family, most with a highly conserved ortholog in several mammalian species. In silico characterization predicts that two of the genes function as integral membrane proteins and are regulated by cAMP/cGMP. A structurally guided protein alignment of the patatin-like domain identifies a number of conserved residues in all family members. Quantitative PCR was used to determine the expression profile of each family member. Affymetrix-based profiling of a human preadipocyte cell line identified several members that are differentially regulated during cell differentiation. Cumulative data suggest that patatin-like genes normally expressed at very low levels are induced in response to environmental signals. Given the observed conservation of the patatin fold and lipase motif in all human PNPLAs, a single nomenclature to describe the PNPLA family is proposed.

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.

Increased expression of cysteinyl leukotriene receptor-1 in the brain mediates neuronal damage and astrogliosis after focal cerebral ischemia in rats

Cysteinyl leukotrienes are potent pro-inflammatory mediators. Cysteinyl leukotriene receptor 1 is one of the two cysteinyl leukotriene receptors cloned. We recently reported that cysteinyl leukotriene receptor 1 antagonists protected against cerebral ischemic injury, and an inducible expression of cysteinyl leukotriene receptor 1 was found in neuron- and glial-appearing cells after traumatic injury in human brain. To determine the role of cysteinyl leukotriene receptor 1 in ischemic brain injury, we investigated the temporal and spatial profile of cysteinyl leukotriene receptor 1 expression in rat brain from 3 h to 14 days after 30 min of middle cerebral artery occlusion, and observed the effect of pranlukast, a cysteinyl leukotriene receptor 1 antagonist, on the ischemic injury. We found that cysteinyl leukotriene receptor 1 mRNA expression was up-regulated in the ischemic core both 3-12 h and 7-14 days, and in the boundary zone 7-14 days after reperfusion. In the ischemic core, cysteinyl leukotriene receptor 1 was primarily localized in neurons 24 h, and in macrophage/microglia 14 days after reperfusion; while in the boundary zone it was localized in proliferated astrocytes 14 days after reperfusion. Pranlukast attenuated neurological deficits, reduced infarct volume and ameliorated neuron loss in the ischemic core 24 h after reperfusion; it reduced infarct volume, ameliorated neuron loss and inhibited astrocyte proliferation in the boundary zone 14 days after reperfusion. Thus, we conclude that cysteinyl leukotriene receptor 1 mediates acute neuronal damage and subacute/chronic astrogliosis after focal cerebral ischemia.

Toll-like receptor agonists differentially regulate cysteinyl-leukotriene receptor 1 expression and function in human dendritic cells

BACKGROUND

Dendritic cells (DCs) acquire, during their maturation, the expression of the chemokine receptor CCR7 and the ability to migrate to lymph nodes in response to CC chemokine ligand 19 (CCL19). This migration is impaired in mice lacking the leukotriene (LT) C4 transporter and restored by addition of exogenous LTC4.

OBJECTIVE

To define the role of LT in human DC function, we studied the expression and function of the cysteinyl-leukotriene (CysLT) receptors during DC differentiation from monocytes and subsequent maturation.

METHODS

Receptor expression was measured by flow cytometry and real-time PCR. Responsiveness to LTD4 stimulation was assessed by calcium flux and chemotaxis.

RESULTS

Maturation of DC with LPS, a classic Toll-like receptor 4 agonist, reduced CysLT receptor 1 (CysLT1) expression by 50%, whereas CysLT receptor 2 expression was increased. In contrast, the Toll-like receptor 3 agonist poly inosinic and cytidylic acid (polyI:C) had no effect on receptor expression. Downregulation of CysLT1 expression by LPS could not be mimicked by TNF-alpha alone or in combination with IL-1beta or IL-6. It was, however, prevented by inhibitors of COX and could be reproduced by a combination of TNF-alpha and prostaglandin E2. Immature DCs and DCs matured with polyI:C, but not with LPS, responded to LTD4 with a robust cytosolic calcium flux, which was prevented by the CysLT1 antagonist montelukast. LTD4 induced DC chemotaxis and enhanced DC migration in response to CCL19 in DCs matured with polyI:C, but only weakly in DCs matured with LPS.

CONCLUSION

Our data suggest that human DCs may differentially respond to leukotriene, depending on their maturational stimuli.

CLINICAL IMPLICATIONS

Our study demonstrates that some microbial agents can reduce the migration of dendritic cells in response to leukotrienes, with potential for differential involvement of these cells in allergic inflammation.

Interactions between leukotriene C4 and interleukin 13 signaling pathways in a mouse model of airway disease

CONTEXT

During an asthmatic episode, leukotriene C4 (LTC4) and interleukin 13 (IL-13) are released into the airways and are thought to be central mediators of the asthmatic response. However, little is known about how these molecules interact or affect each other's signaling pathway.

OBJECTIVE

To determine if the LTC4 and IL-13 signaling pathways interact with each other's pathways.

DESIGN

We examined airway responsiveness, cysteinyl LTs (Cys-LTs), and Cys-LT and IL-13 receptor transcript levels in wild-type mice and in mice that were deficient in gamma-glutamyl leukotrienase (an enzyme that converts LTC4 to LTD4), STAT6 (signal transducer and activator of transcription 6 [a critical molecule in IL-13 signaling]), and IL-4Ralpha (a subunit of the IL-13 receptor).

RESULTS

Wild-type (C57BL/129SvEv) and gamma-glutamyl leukotrienase-deficient mice showed increased airway responsiveness after intranasal instillation of IL-13; similar results were observed after intranasal instillation of IL-13 or LTC4 in a second wild-type strain (BALB/c). Interleukin 13 treatment reduced levels of Cys-LTs in bronchoalveolar lavage fluid. This change was unaccompanied by changes in other arachidonic acid metabolites or in RNA transcript levels of enzymes associated with Cys-LT synthesis. Interleukin 13 treatment also increased transcript levels of the Cys-LT 1 and Cys-LT 2 receptors, while LTC4 increased transcript levels of the alpha1 chain of the IL-13 receptor. Furthermore, IL-4Ralpha-deficient mice had increased airway responsiveness to LTC4 but not to IL-13, whereas STAT6-deficient mice failed to respond to either agonist.

CONCLUSIONS

These findings indicate that LTC4 and IL-13 are dependent on or signal through STAT6 to increase airway responsiveness and that both agonists regulate expression of each other's receptors.

Montelukast in pediatric asthma management

Leukotriene modifiers (receptor antagonist and biosynthesis inhibitor) represent the first mediator specific therapeutic option for asthma. Montelukast, a leukotriene receptor antagonist is the only such agent approved for use in pediatric patients. Montelukast modifies action of leukotrienes, which are the most potent bronchoconstrictors, by blocking Cysteinyl leukotriene receptors. Systemic drug like mountelukast can reach lower airways and improves the peripheral functions which play a crucial role in the evolution of asthma. Review of existing literature showed that montelukast compared to placebo has proven clinical efficacy in better control of day time asthma symptoms, percentage of symptom free days, need for rescue drugs and improvement in FEV 1. Studies also demonstrated improvement in airway inflammation as indicated by reduction in fractional exhaled nitric oxide, a marker of inflammation. Studies comparing low dose inhaled corticosteroids (ICS) with montelukast are limited in children and conclude that it is not superior to ICS. For moderate to severe persistent asthma, montelukast has been compared with long acting beta agonists (LABA) as an add-on therapy to ICS, montelukast was less efficacious and less cost-effective. It has beneficial effects in exercise induced asthma and aspirin-sensitive asthma. Montelukast has onset of action within one hour. Patient satisfaction and compliance was better with montelukast than inhaled anti-inflammatory agents due to oral, once a day administration. The recommended doses of montelukast in asthma are- children 1-5 years: 4 mg chewable tablet, children 6-14 years: 5mg chewable tablet,

ADULTS

10mg tablet; administered once daily. The drug is well tolerated. Based on the presently available data montelukast may be an alternative treatment for mild persistent asthma as monotherapy where ICS cannot be administered. It is also an alternative to LABA as an add-on therapy to ICS for moderate to severe persistent asthma. The other indications for use of montelukast include: allergic rhinitis, exercise induced bronchoconstriction and aspirin-induced asthma.

Pranlukast reduces neutrophil but not macrophage/microglial accumulation in brain after focal cerebral ischemia in mice

AIM

To determine whether pranlukast, a cysteinyl leukotriene receptor-1 antagonist, exerts an anti-inflammatory effect on focal cerebral ischemia in mice.

METHODS

Focal cerebral ischemia in mice was induced by permanent middle cerebral artery occlusion (MCAO). In addition to neurological deficits, infarct volume, degenerated neurons and endogenous IgG exudation, we detected accumulation of neutrophils and macrophage/microglia in the ischemic brain tissue 72 h after MCAO. Pranlukast was ip injected 30 min before and after MCAO.

RESULTS

Pranlukast significantly attenuated neurological deficits, infarct volume, neuron degeneration and IgG exudation. Importantly, pranlukast (0.01 and 0.1 mg/kg) inhibited myeloperoxidase-positive neutrophil, but not CD11b-positive macrophage/microglial accumulation in the ischemic cortical tissue.

CONCLUSION

Pranlukast exerts an anti-inflammatory effect on focal cerebral ischemia in the subacute phase that is limited to neutrophil recruitment through the disrupted blood-brain barrier.

Functional characterization of human cysteinyl leukotriene 1 receptor gene structure

The 5-lipoxygenase pathway has been strongly implicated in the pathogenesis of chronic inflammatory disorders, such as bronchial asthma and atherosclerosis. Cysteinyl leukotrienes (cysLTs), 5-lipoxygenase pathway products, are recognized now not only as important factors in asthmatic inflammation, but also as mediators of cell trafficking and innate immune responses. To study a role of cysLTs in inflammatory reactions we have characterized the gene structure of human cysteinyl leukotriene receptor type I (cysLT(1)R). The cysLT(1)R gene consists of 5 exons that are variably spliced and a single promoter region with multiple transcription start sites. Four different cysLT(1)R transcripts were identified. RT-PCR showed dominant and wide expression of the transcript I, containing exons 1, 4, and 5, with the strongest presence in blood leukocytes, spleen, thymus, lung, and heart. The expression of cysLT(1)R is functionally regulated at the transcriptional level by IL-4 through a STAT6 response element localized to the proximal cysLT(1)R promoter region. IL-4 stimulation increased cysLT(1)R mRNA (real-time PCR) and surface protein expression (flow cytometry) in a time-dependent fashion. CysLTs (LTD(4) and LTC(4)) induced an increased production of a potent monocyte chemoattractant CCL2 (MCP-1) in IL-4-primed THP-1 cells in a dose-dependent manner. This effect was effectively inhibited by the cysLT(1)R-selective antagonist MK571 in a dose-dependent manner and only partially by a nonselective cysLT(1)R/cysLT(2)R inhibitor BAY-u9773, implying a cysLT(1)R-mediated mechanism. Thus, cysLTs signaling through cysLT(1)R might contribute to inflammatory reactions by cooperating with IL-4 in enhanced CCL2 production in human monocytic cells.

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.

CysLT1 leukotriene receptor antagonists inhibit the effects of nucleotides acting at P2Y receptors

Montelukast and pranlukast are orally active leukotriene receptor antagonists selective for the CysLT1 receptor. Conversely, the hP2Y(1,2,4,6,11,12,13,14) receptors represent a large family of GPCRs responding to either adenine or uracil nucleotides, or to sugar-nucleotides. Montelukast and pranlukast were found to inhibit nucleotide-induced calcium mobilization in a human monocyte-macrophage like cell line, DMSO-differentiated U937 (dU937). Montelukast and pranlukast inhibited the effects of UTP with IC50 values of 7.7 and 4.3 microM, respectively, and inhibited the effects of UDP with IC50 values of 4.5 and 1.6 microM, respectively, in an insurmountable manner. Furthermore, ligand binding studies using [3H]LTD4 excluded the possibility of orthosteric nucleotide binding to the CysLT1 receptor. dU937 cells were shown to express P2Y2, P2Y4, P2Y6, P2Y11, P2Y13 and P2Y14 receptors. Therefore, these antagonists were studied functionally in a heterologous expression system for the human P2Y receptors. In 1321N1 astrocytoma cells stably expressing human P2Y(1,2,4,6) receptors, CysLT1 antagonists inhibited both the P2Y agonist-induced activation of phospholipase C and intracellular Ca2+ mobilization. IC50 values at P2Y1 and P2Y6 receptors were <1 microM. In control astrocytoma cells expressing an endogenous M3 muscarinic receptor, 10 microM montelukast had no effect on the carbachol-induced rise in intracellular Ca2+. These data demonstrated that CysLT1 receptor antagonists interact functionally with signaling pathways of P2Y receptors, and this should foster the study of possible implications for the clinical use of these compounds in asthma or in other inflammatory conditions.

Identification of endogenous surrogate ligands for human P2Y12 receptors by in silico and in vitro methods

Endogenous ligands acting on a human P2Y12 receptor, one of the G-protein coupled receptors, were searched by in silico screening against our own database, which contains more than 500 animal metabolites. The in silico screening using the docking software AutoDock resulted in selection of cysteinylleukotrienes (CysLTs) and 5-phosphoribosyl 1-pyrophosphate (PRPP), with high free energy changes, in addition to the known P2Y12 ligands such as 2MeSADP and ADP. These candidates were subjected to an in vitro Ca2+ assay using the CHO cells stably expressing P2Y12-G16alpha fusion proteins. We found that CysLTE4 and PRPP acted on the P2Y12 receptor as agonists with the EC50 values of 1.3 and 7.8 nM, respectively. Furthermore, we analyzed the phylogenetic relationship of the P2Y, P2Y-like, and CysLT receptors based on sequence alignment followed by evolutionary analyses. The analyses showed that the P2Y12, P2Y13, P2Y14, GPR87, CysLT-1, and CysLT-2 receptors formed a P2Y-related receptor subfamily with common sequence motifs in the transmembrane regions.

Pranlukast, a cysteinyl leukotriene receptor-1 antagonist, protects against chronic ischemic brain injury and inhibits the glial scar formation in mice

We have recently reported the neuroprotective effect of pranlukast (ONO-1078), a cysteinyl leukotriene receptor-1 (CysLT1) antagonist, on cerebral ischemia in rats and mice. In this study, we further determined whether the effect of pranlukast is long lasting and related to the formation of a glial scar in cerebral ischemic mice. Focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO). After ischemia, pranlukast (0.1 mg/kg) was injected intraperitoneally for 5 consecutive days. Neurological deficits and sensorimotor function were determined during 70 days after ischemia. Brain lesion and glial scar formation were detected at the end of the experiment. Pranlukast did not reduce mortality, but significantly improved neurological deficits and promoted sensorimotor recovery during 70 days. At the end of the experiment, pranlukast significantly reduced lesion volume, and increased neuron densities in the cortex and hippocampal CA1 region in the ischemic hemispheres. Importantly, pranlukast also remarkably reduced the thickness of a scar wall in the ischemic hemispheres. These findings indicate that pranlukast has a long-lasting protective effect on focal cerebral ischemia in mice, and inhibit the ischemia-induced glial scar formation, providing further evidence of the therapeutic potential of pranlukast in the treatment of ischemic stroke.

Distribution of cysteinyl leukotriene receptor 2 in human traumatic brain injury and brain tumors

AIM

To determine the distribution of cysteinyl leukotriene receptor 2 (CysLT2), one of the cysteinyl leukotriene receptors, in human brains with traumatic injury and tumors.

METHODS

Brain specimens were obtained from patients who underwent brain surgery. CysLT2 in brain tissues was examined using immunohistochemical analysis.

RESULTS

CysLT2 was expressed in the smooth muscle cells (not in the endothelial cells) of arteries and veins. CysLT2 was also expressed in the granulocytes in both vessels and in the brain parenchyma. In addition, CysLT2 was detected in neuron- and glial-appearing cells in either the late stages of traumatic injury or in the area surrounding the tumors. Microvessels regenerated 8 d after trauma and CysLT2 expression was recorded in their endothelial cells.

CONCLUSION

CysLT2 is distributed in vascular smooth muscle cells and granulocytes, and brain trauma and tumor can induce its expression in vascular endothelial cells and in a number of other cells.

Free fatty acids inhibit serum deprivation-induced apoptosis through GPR120 in a murine enteroendocrine cell line STC-1

Free fatty acids (FFAs) provide an important energy source and also act as signaling molecules. FFAs are known to exert a variety of physiological responses via their G protein-coupled receptors (GPCRs), such as the GPR40 family. Recently, we identified a novel FFA receptor, GPR120, that promotes secretion of glucagon-like peptide-1 (Hirasawa, A., Tsumaya, K., Awaji, T., Katsuma, S., Adachi, T., Yamada, M., Sugimoto, Y., Miyazaki, S., and Tsujimoto, G. (2005) Nat. Med. 11, 90-94). Here we showed that FFAs inhibit serum deprivation-induced apoptosis of murine enteroendocrine STC-1 cells, which express two types of GPCRs, GPR120 and GPR40, for unsaturated long chain FFA. We first found that linolenic acid potently activated ERK and Akt/protein kinase B (Akt) in STC-1 cells. ERK kinase inhibitors significantly reduced the anti-apoptotic effects of linolenic acid. Inhibitors for phosphatidylinositol 3-kinase (PI3K), a major target of which is Akt, significantly reduced the anti-apoptotic effects. Transfection of STC-1 cells with the dominant-negative form of Akt also inhibited the anti-apoptotic effect. These results suggested that the activation of ERK and PI3K-Akt pathways is required for FFA-induced anti-apoptotic effects on STC-1 cells. Transient transfection of STC-1 cells with GPR120 cDNA, but not GPR40 cDNA, enhanced inhibition of caspase-3 activation. RNA interference experiments showed that reduced expression of GPR120, but not GPR40, resulted in reduced ERK activation and reduced effects of FFAs on caspase-3 inhibition. Collectively, these results demonstrated that FFAs promote the activation of ERK and PI3K-Akt pathways mainly via GPR120, leading to the anti-apoptotic effect of STC-1 cells.

A coding polymorphism in the CYSLT2 receptor with reduced affinity to LTD4 is associated with asthma

BACKGROUND

Cysteinyl leukotrienes (CYSLTR) are potent biological mediators in the pathophysiology of asthma for which two receptors have been characterized, CYSLTR1 and CYSLTR2. The leukotriene modifying agents currently used to control bronchoconstriction and inflammation in asthmatic patients are CYSLTR1-specific leukotriene receptor antagonists. In this report, we investigated a possible role for therapeutic modulation of CYSLTR2 in asthma by investigating genetic association with asthma and further characterization of the pharmacology of a coding polymorphism.

METHODS

The association of CYSLTR2 polymorphisms with asthma was assessed by transmission disequilibrium test in two family-based collections (359 families from Denmark and Minnesota, USA and 384 families from the Genetics of Asthma International Network).

RESULTS

A significant association of the coding polymorphism, 601A>G, with asthma was observed (P = 0.003). We replicated these findings in a collection of 384 families from the Genetics of Asthma International Network (P = 0.04). The G allele is significantly under-transmitted to asthmatics, indicating a possible role for this receptor in resistance to asthma. The potency of cysteinyl leukotrienes at the wild-type CYSLTR2 and the coding polymorphism 601A>G were assessed using a calcium mobilization assay. The potency of LTC4 and LTE4 was similar for both forms of the receptor and LTB4 was inactive, however, LTD4 was approximately five-fold less potent on 601A>G compared to wild-type CYSLTR2.

CONCLUSIONS

Since 601A>G alters the potency of LTD4 and this variant allele may be associated with resistance to asthma, it is possible that modulation of the CYSLTR2 may be useful in asthma pharmacotherapy.

Oleate promotes the proliferation of breast cancer cells via the G protein-coupled receptor GPR40

Evidence from epidemiological studies and animal models suggests a link between high levels of dietary fat intake and risk of breast cancer. In addition, obesity, in which circulating lipids are elevated, is associated with increased risk of various cancers. Relative to this point, we previously showed that oleate stimulates the proliferation of breast cancer cells and that phosphatidylinositol 3-kinase plays a role in this process. Nonetheless, questions remain regarding the precise mechanism(s) by which oleate promotes breast cancer cell growth. Pharmacological inhibitors of the GTP-binding proteins G(i)/G(o), phospholipase C, Src, and mitogenic-extracellular signal-regulated kinase 1/2 (MEK 1/2) decreased oleate-induced [3H]thymidine incorporation in the breast cancer cell line MDA-MB-231. In addition, oleate caused a rapid and transient rise in cytosolic Ca2+ and an increase in protein kinase B phosphorylation. Overexpressing in these cells the G protein-coupled receptor GPR40, a fatty acid receptor, amplified oleate-induced proliferation, whereas silencing the GPR40 gene using RNA interference decreased it. Overexpressing GPR40 in T47D and MCF-7 breast cancer cells that are poorly responsive to oleate allowed a robust proliferative action of oleate. The data indicate that the phospholipase C, MEK 1/2, Src, and phosphatidylinositol 3-kinase/protein kinase B signaling pathways are implicated in the proliferative signal induced by oleate and that these effects are mediated at least in part via the G protein-coupled receptor GPR40. The results suggest that GPR40 is implicated in the control of breast cancer cell growth by fatty acids and that GPR40 may provide a link between fat and cancer.

Treatment of chronic cough in children with montelukast,a leukotriene receptor antagonist

Twenty-two children (13 boys and 9 girls) with chronic cough were treated with the leukotriene receptor antagonist montelukast (Singulair tbl. 5 mg) administered once daily for four weeks. In 14 children (68%), the cough ceased during the third week of treatment. Children responding to montelukast were found to have higher blood levels of eosinophil cationic protein (S-ECP) in the pretreatment blood sample than children with no response (responders 14.88+/-2.651 microg/l versus nonresponders 6.62+/-0.948 microg/l; p<0.01). Blood S-ECP levels remained higher also in the post-treatment blood sample in responders (10.55+/-1.631 microg/l) compared to nonresponders (6.13+/-0.937 microg/l; p<0.05). The difference is statistically significant. There were also differences in absolute eosinophil blood count and IgE blood levels between the two groups in the pretreatment blood sample. Using 24-hour pH-metry, two children not responding to therapy were subsequently diagnosed to have gastroesophageal reflux. Judging from the results, one might deduct that patients with chronic cough who have increased levels of serum ECP and absolute eosinophil blood counts are likely to benefit from treatment with montelukast.

Cysteinyl-leukotrienes are released from astrocytes and increase astrocyte proliferation and glial fibrillary acidic protein via cys-LT1 receptors and mitogen-activated protein kinase pathway

Cysteinyl-leukotrienes (cys-LTs), potent mediators in inflammatory diseases, are produced by nervous tissue, but their cellular source and role in the brain are not very well known. In this report we have demonstrated that rat cultured astrocytes express the enzymes (5'-lipoxygenase and LTC(4) synthase) required for cys-LT production, and release cys-LTs in resting condition and, to a greater extent, in response to calcium ionophore A23187, 1 h combined oxygen-glucose deprivation or 2-methyl-thioATP, a selective P2Y(1)/ATP receptor agonist. MK-886, a LT synthesis inhibitor, prevented basal and evoked cys-LT release. In addition, 2-methyl-thioATP-induced cys-LT release was abolished by suramin, a P2 receptor antagonist, or by inhibitors of ATP binding cassette proteins involved in cys-LT release. We also showed that astrocytes express cys-LT(1) and not cys-LT(2) receptors. The stimulation of these receptors by LTD(4) activated the mitogen-activated protein kinase (MAPK) pathway. This effect was: (i) insensitive to inhibitors of receptor-coupled Gi protein (pertussis toxin) or tyrosine kinase receptors (genistein); (ii) abolished by MK-571, a cys-LT(1) selective receptor antagonist, or PD98059, a MAPK inhibitor; (iii) reduced by inhibitors of calcium/calmodulin-dependent kinase II (KN-93), Ca(2+)-dependent and -independent (GF102903X) or Ca(2+)-dependent (Gö6976) protein kinase C isoforms. LTD(4) also increased astrocyte proliferation and glial fibrillary acidic protein content, which are considered hallmarks of reactive astrogliosis. Both effects were counteracted by cell pretreatment with MK-571 or PD98059. Thus, cys-LTs released from astrocytes might play an autocrine role in the induction of reactive astrogliosis that, in brain injuries, contributes to the formation of a reparative glial scar.

Regulation of cysteinyl leukotriene type 1 receptor internalization and signaling

Cysteinyl leukotrienes activate the cysteinyl leukotriene type 1 receptor (CysLT1R) to regulate numerous cell functions important in inflammatory processes and diseases such as asthma. Despite its physiologic importance, no studies to date have examined the regulation of CysLT1R signaling or trafficking. We have established model systems for analyzing recombinant human CysLT1R and found regulation of internalization and signaling of the CysLT1R to be unique among G protein-coupled receptors. Rapid and profound LTD4-stimulated internalization was observed for the wild type (WT) CysLT1R, whereas a C-terminal truncation mutant exhibited impaired internalization yet signaled robustly, suggesting a region within amino acids 310-321 as critical to internalization. Although overexpression of WT arrestins significantly increased WT CysLT1R internalization, expression of dominant-negative arrestins had minimal effects, and WT CysLT1R internalized in murine embryonic fibroblasts lacking both arrestin-2 and arrestin-3, suggesting that arrestins are not the primary physiologic regulators of CysLT1Rs. Instead, pharmacologic inhibition of protein kinase C (PKC) was shown to profoundly inhibit CysLT1R internalization while greatly increasing both phosphoinositide (PI) production and calcium mobilization stimulated by LTD4 yet had almost no effect on H1 histamine receptor internalization or signaling. Moreover, mutation of putative PKC phosphorylation sites within the CysLT1R C-tail (CysLT1RS(313-316)A) reduced receptor internalization, increased PI production and calcium mobilization by LTD4, and significantly attenuated the effects of PKC inhibition. These findings characterized the CysLT1R as the first G protein-coupled receptor identified to date in which PKC is the principal regulator of both rapid agonist-dependent internalization and rapid agonist-dependent desensitization.

Montelukast, a Cysteinyl Leukotriene Receptor-1 Antagonist, Dose- and Time-Dependently Protects against Focal Cerebral Ischemia in Mice

Our previous studies showed that cysteinyl leukotriene receptor-1 (CysLT1) antagonist pranlukast has a neuroprotective effect on cerebral ischemia in rats and mice. However, whether the neuroprotective effect of pranlukast is its special action or a common action of CysLT1 receptor antagonists remains to be clarified. This study was performed to determine whether montelukast, another CysLT1 receptor antagonist, has the neuroprotective effect on focal cerebral ischemia in mice, and to observe its dose- and time-dependent properties. Permanent focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO). Montelukast was injected intraperitoneally either as multiple doses (once a day for 3 days and 30 min before MCAO) or as a single dose (at 30 min before, 30 min after, or 1 h after MCAO), respectively, and pranlukast and edaravone were used as controls. The neurological deficits, infarct volumes, brain edema, neuron density, and Evans blue extravasation in the brain were determined 24 h after MCAO. Pretreatments with multiple doses or a single dose of montelukast (0.1 and 1.0 mg/kg) before MCAO significantly attenuated all the ischemic insults. Post-treatment with a single dose of montelukast (0.1 and 1.0 mg/kg) at 30 min after MCAO also significantly decreased brain edema and infarct volume, but not neurological deficits. However, post-treatment with a single dose of montelukast at 1 h after MCAO had no significant effect. Pranlukast showed the same effects as montelukast, but edaravone attenuated the ischemic insults only with multiple doses before MCAO. Thus, montelukast has a dose- and time-dependent neuroprotective effect on permanent focal cerebral ischemia in mice, with an effective dose range of 0.1-1.0 mg/kg and a therapeutic window of 30 min. These findings further support the therapeutic potential of CysLT1 receptor antagonists in the treatment of cerebral ischemia at earlier phases.

Directed Vascular Expression of Human Cysteinyl Leukotriene 2 Receptor Modulates Endothelial Permeability and Systemic Blood Pressure

Background— The proinflammatory and vascular actions of cysteinyl leukotrienes (CysLTs) are mediated by 2 receptors: cysteinyl leukotriene 1 receptor (CysLT 1 R) and cysteinyl leukotriene 2 receptor (CysLT 2 R). However, the distinct contribution of CysLT 2 R to the vascular actions of CysLTs has not been addressed.

Methods and Results— We generated an endothelial cell–specific human CysLT 2 R (EC-hCysLT 2 R) transgenic (TG) mouse model using the Tie2 promoter/enhancer. Strong expression of hCysLT 2 R in TG lung and endothelial cells, detected by real-time polymerase chain reaction, markedly enhanced CysLT-stimulated intracellular calcium mobilization compared with endogenous expression in cells from nontransgenic mice. The permeability response to exogenous LTC 4 and to endogenous CysLTs evoked by passive cutaneous anaphylaxis was augmented in TG mice. The rapid, systemic pressor response to intravenous LTC 4 was also diminished in TG mice coincidentally with augmented production of nitric oxide.

Conclusions— The development of EC-hCysLT 2 R mice has permitted detection of distinct vascular effects of CysLTs, which can be mediated via the CysLT 2 R in vivo.

The quest for new cysteinyl-leukotriene and lipoxin receptors: recent clues

The metabolism of arachidonic acid via the 5-lipoxygenase enzymatic pathway leads to the formation of the cysteinyl-leukotrienes and lipoxins, which have been implicated in several inflammatory reactions. While these lipid mediators are responsible for a variety of effects, their actions occur through the activation of 3 specific types of cloned receptors (i.e., CysLT(1), CysLT(2), and ALX). Although receptor activation can explain several biological actions associated with the mediators, there is some evidence to suggest that not all responses fit the well-known characteristics of these cloned receptors. Other receptor subtypes may also exist. Interestingly, the indirect evidence for support of this observation is principally derived from work performed on either blood elements and/or vascular smooth muscle. Because the initiating events associated with inflammation are essentially of vascular origin, further work at the molecular level may be necessary to confirm the data, which do not fit the well-known CysLT and ALX receptor profiles.

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.

Expression of cysteinyl leukotriene receptor 1 in human traumatic brain injury and brain tumors

Cysteinyl leukotrienes (CysLTs) are potent proinflammatory mediators. CysLT receptor 1 (CysLT(1)) is one of the two CysLT receptors that has been cloned. Although the expression of CysLT(1) in the brain has been demonstrated by Northern blot and RT-PCR analyses, the location of CysLT(1) in the brain remains unknown. The objective of this study was to examine the distribution of CysLT(1) by immunohistochemical analysis in human brains with traumatic injury or tumors. CysLT(1) was expressed intensely in the microvascular endothelial cells in both normal and abnormal conditions. At 8 days after traumatic injury, microvascular regeneration was found and all of the endothelial cells highly expressed CysLT(1). In gray and white matters of the normal regions of the brain, CysLT(1) was expressed weekly or not at all. However, the CysLT(1) expression increased in the neuron- and glial-appearing cells in gray and white matters after traumatic brain injury. CysLT(1) was also detected in astrocytoma, ganglioglioma and metastatic adenocarcinoma, and the expression in the neuron- and glial-appearing cells around brain tumors increased robustly.

A cysteinyl leukotriene 2 receptor variant is associated with atopy in the population of Tristan da Cunha

The clinical heterogeneity of asthma suggests that the contribution of genetic variability in candidate gene loci to well-defined phenotypes, such as atopy, may be examined to identify appropriate genetic risk factors for asthma. The gene encoding the cysteinyl leukotriene 2 (CysLT2) receptor has been implicated in atopy since it is localized to a region of chromosome 13q14 that has been linked to atopy in several populations and the cysteinyl leukotrienes are known to activate eosinophils and mast cells in atopy. Accordingly, we analysed the contribution of CysLT2 receptor gene variation to atopy in the inhabitants of Tristan da Cunha, a population characterized by both a founder effect and a 47% prevalence of atopy. Single-stranded conformational polymorphism analysis revealed four variants. Among these, the M201V [corrected] variant was activated with four-fold less potency by leukotriene D4 (LTD4) in a calcium flux assay. The CysLT2 receptor partial agonist, BAY u9773, also showed four-fold lower potency on the M201V [corrected] variant. The M201V [corrected] mutation is located within the extracellular region of the fifth transmembrane spanning domain of CysLT2 receptor, a position that may alter ligand binding and effector signalling. The novel M201V [corrected] CysLT2 receptor variant was associated with atopy (21%) on Tristan da Cunha compared with those who were non-atopic (7%) (Fisher's exact test, P=0.0016) in a manner that was independent of asthma (two-way ANOVA, P=0.0015). This represents the first association of a coding mutation in the CysLT2 receptor gene, located on chromosome 13q14, with the atopic phenotype found in the Tristan da Cunha population.

Role of leukotrienes on hepatic ischemia/reperfusion injury in rats

BACKGROUND

Leukotrienes (LT), composed of cysteinyl LT (cLT; LTC(4), LTD(4), and LTE(4)) and LTB(4), are potent lipid mediators enhancing the vascular permeability and recruitment of neutrophils, which are common features of hepatic ischemia/reperfusion (I/R) injury. The aim of this study was to investigate whether LT can mediate the liver and lung injuries following hepatic I/R.

MATERIALS AND METHODS

Sprague-Dawley rats were subjected to 90 min of partial hepatic ischemia followed by 3, 12, and 24 h of reperfusion. In the hepatic and pulmonary tissues, LT content and the mRNA expression of LT-synthesis enzymes, 5-lypoxygenase (5-LO), LTC(4) synthase (LTC(4)-S), and LTA(4) hydrolase (LTA(4)-H) were measured. Tissue injuries were assessed by plasma ALT, histological examination, and wet-to-dry tissue weight ratios.

RESULTS

The cLT content in the hepatic tissue after 12 and 24 h reperfusion was increased 4- to 5-fold compared to controls and this was accompanied by the enhancement of hepatic edema and plasma ALT elevation. There were no significant changes in the mRNA expression of LT-synthesis enzymes in both tissues. LTB(4) levels were not increased despite a significant neutrophil infiltration in both tissues.

CONCLUSIONS

These data suggest that cLT are generated in the liver during the reperfusion period and may contribute to the development of hepatic edema and exert cytotoxicity. Factors other than LTB(4) may contribute to neutrophil infiltration.

Cysteinyl leukotrienes regulate dendritic cell functions in a murine model of asthma

Dendritic cells (DCs) act as APCs in the airway and play a critical role in allergy. Cysteinyl leukotrienes (cysLTs) synthesized from arachidonic acid are primary mediators of immediate asthmatic reaction. The aim of this study was to investigate the effects of cysLTs on Dermatophagoides farinae (Der f)-pulsed mouse myeloid DCs in inducing allergic airway inflammation in vitro and in vivo. Control DC (medium-pulsed), Der f-pulsed DC, cysLT-pulsed DC, Der f- and cysLT-pulsed DC, and Der f-pulsed and cysLT receptor antagonist (LTRA)-treated DC were prepared from murine bone marrow, and the production of cytokines ws compared. Subsequently, these DCs were intranasally instilled into another group of naive mice, followed by intranasal Der f challenge to induce allergic airway inflammation in vivo. Der f-pulsed DC produced significantly higher amounts of IL-10 and IL-12 compared with control DC. Der f- and cysLT-pulsed DC further increased IL-10 production compared with Der f-pulsed DC. In contrast, treatment of Der f-pulsed DC with LTRA increased IL-12 and decreased IL-10. Intranasal instillation of Der f-pulsed DC resulted in airway eosinophilia associated with a significant rise in IL-5 levels in the airway compared with control DC. Pulmonary eosinophilia and excess IL-5 were further enhanced in Der f- and cysLT-pulsed DC-harboring mice. In contrast, Der f-pulsed and LTRA-treated DC significantly inhibited airway eosinophilia, reduced IL-5, and increased IFN-gamma in the airway. Our results suggest that cysLTs play an important role in the development of allergic airway inflammation by regulating the immunomodulatory functions of DCs.