Cysteinyl leukotriene receptors

Neuromodulatory Effects of Leukotriene receptor antagonists: A comprehensive review

Cysteinyl leukotrienes (CysLTs) are central to the pathophysiology of asthma and various inflammatory disorders. Leukotriene receptor antagonists (LTRAs) effectively treat respiratory conditions by targeting cysteinyl leukotriene receptors, CysLT1 and CysLT2 subtypes. This review explores the multifaceted effects of LTs, extending beyond bronchoconstriction. CysLT receptors are not only present in the respiratory system but are also crucial in neuronal signaling pathways. LTRAs modulate these receptors, influencing downstream signaling, calcium levels, inflammation, and oxidative stress (OS) within neurons hinting at broader implications. Recent studies identify novel molecular targets, sparking interest in repurposing LTRAs for therapeutic use. Clinical trials are investigating their potential in neuroinflammation control, particularly in Alzheimer's disease (AD) and Parkinson's diseases (PD). However, montelukast, a long-standing LTRA since 1998, raises concerns due to neuropsychiatric adverse drug reactions (ADRs). Despite widespread use, understanding montelukast's metabolism and underlying ADR mechanisms remains limited. This review comprehensively examines LTRAs' diverse biological effects, emphasizing non-bronchoconstrictive activities. It also analyses plausible mechanisms behind LTRAs' neuronal effects, offering insights into their potential as neurodegenerative disease modulators. The aim is to inform clinicians, researchers, and pharmaceutical developers about LTRAs' expanding roles, particularly in neuroinflammation control and their promising repurposing for neurodegenerative disease management.

Design, synthesis, and pharmacological evaluation of indazole carboxamides of N-substituted pyrrole derivatives as soybean lipoxygenase inhibitors

In this paper, we attempted to develop a novel class of compounds against lipoxygenase, a key enzyme in the biosynthesis of leukotrienes implicated in a series of inflammatory diseases. Given the absence of appropriate human 5-lipoxygenase crystallographic data, solved soybean lipoxygenase-1 and -3 structures were used as a template to generate an accurate pharmacophore model which was further used for virtual screening purposes. Eight compounds (1-8) have been derived from the in-house library consisting of N-substituted pyrroles conjugated with 5- or 6-indazole moieties through a carboxamide linker. This study led to the discovery of hit molecule 8 bearing a naphthyl group with the IC50 value of 22 μM according to soybean lipoxygenase in vitro assay. Isosteric replacement of naphthyl ring with quinoline moieties and reduction of carbonyl carboxamide group resulted in compounds 9-12 and 13, respectively. Compound 12 demonstrated the most promising enzyme inhibition. In addition, compounds 8 and 12 were found to reduce the carrageenan-induced paw edema in vivo by 52.6 and 49.8%, respectively. In view of the encouraging outcomes concerning their notable in vitro and in vivo anti-inflammatory activities, compounds 8 and 12 could be further optimized for the discovery of novel 5-lipoxygenase inhibitors in future. A structure-based 3D pharmacophore model was used in the virtual screening of in-house library to discover novel potential 5-lipoxygenase inhibitors.

Montelukast reduces grey matter abnormalities and functional deficits in a mouse model of inflammation-induced encephalopathy of prematurity

Encephalopathy of prematurity (EoP) affects approximately 30% of infants born < 32 weeks gestation and is highly associated with inflammation in the foetus. Here we evaluated the efficacy of montelukast, a cysteinyl leukotriene receptor antagonist widely used to treat asthma in children, to ameliorate peripheral and central inflammation, and subsequent grey matter neuropathology and behaviour deficits in a mouse model of EoP. Male CD-1 mice were treated with intraperitoneal (i.p.) saline or interleukin-1beta (IL-1β, 40 μg/kg, 5 μL/g body weight) from postnatal day (P)1-5 ± concomitant montelukast (1-30 mg/kg). Saline or montelukast treatment was continued for a further 5 days post-injury. Assessment of systemic and central inflammation and short-term neuropathology was performed from 4 h following treatment through to P10. Behavioural testing, MRI and neuropathological assessments were made on a second cohort of animals from P36 to 54. Montelukast was found to attenuate both peripheral and central inflammation, reducing the expression of pro-inflammatory molecules (IL-1β, IL-6, TNF) in the brain. Inflammation induced a reduction in parvalbumin-positive interneuron density in the cortex, which was normalised with high-dose montelukast. The lowest effective dose, 3 mg/kg, was able to improve anxiety and spatial learning deficits in this model of inflammatory injury, and alterations in cortical mean diffusivity were not present in animals that received this dose of montelukast. Repurposed montelukast administered early after preterm birth may, therefore, improve grey matter development and outcome in EoP.

Current knowledge of the implication of lipid mediators in psoriasis

The skin is an organ involved in several biological processes essential to the proper functioning of the organism. One of these essential biological functions of the skin is its barrier function, mediated notably by the lipids of the stratum corneum, and which prevents both penetration from external aggression, and transepidermal water loss. Bioactive lipid mediators derived from polyunsaturated fatty acids (PUFAs) constitute a complex bioactive lipid network greatly involved in skin homeostasis. Bioactive lipid mediators derived from n-3 and n-6 PUFAs have well-documented anti- and pro-inflammatory properties and are recognized as playing numerous and complex roles in the behavior of diverse skin diseases, including psoriasis. Psoriasis is an inflammatory autoimmune disease with many comorbidities and is associated with enhanced levels of pro-inflammatory lipid mediators. Studies have shown that a high intake of n-3 PUFAs can influence the development and progression of psoriasis, mainly by reducing the severity and frequency of psoriatic plaques. Herein, we provide an overview of the differential effects of n-3 and n-6 PUFA lipid mediators, including prostanoids, hydroxy-fatty acids, leukotrienes, specialized pro-resolving mediators, N-acylethanolamines, monoacylglycerols and endocannabinoids. This review summarizes current findings on lipid mediators playing a role in the skin and their potential as therapeutic targets for psoriatic patients.

Leukotrienes promote stem cell self-renewal and chemoresistance in acute myeloid leukemia

Acute myeloid leukemia (AML) is characterized by poor clinical outcomes due to high rates of relapse following standard-of-care induction chemotherapy. While many pathogenic drivers have been described in AML, our understanding of the molecular mechanisms mediating chemotherapy resistance remains poor. Therefore, we sought to identify resistance genes to induction therapy in AML and elucidated ALOX5 as a novel mediator of resistance to anthracycline-based therapy. ALOX5 is transcriptionally upregulated in AML patient blasts in comparison to normal hematopoietic stem/progenitor cells (HSPCs) and ALOX5 mRNA, and protein expression is increased in response to induction therapy. In vitro, and in vivo genetic, and pharmacologic perturbation studies confirm that ALOX5 positively regulates the leukemogenic potential of AML LSCs, and its loss does not significantly affect the function of normal HSPCs. ALOX5 mediates resistance to daunorubicin (DNR) and promotes AML cell survival and maintenance through its leukotriene (LT) synthetic capacity, specifically via modulating the synthesis of LTB4 and its binding to LTB receptor (BLTR). Our study reveals a previously unrecognized role of LTs in AML pathogenesis and chemoresistance, whereby inhibition of ALOX5 mediated LTB4 synthesis and function could be combined with standard chemotherapy, to enhance the overall therapeutic efficacy in AML.

Leukotriene D4 Upregulates Oxidized Low-Density Lipoprotein Receptor 1 and CD36 to Enhance Oxidized LDL Uptake and Phagocytosis in Macrophages Through Cysteinyl Leukotriene Receptor 1

Endothelial permeability, leukocyte attachment, and unregulated oxidized LDL (oxLDL) uptake by macrophages leading to the formation of foam cells are all vital in the initiation and progression of atherosclerosis. During inflammation, several inflammatory mediators regulate this process through the expression of distinct oxLDL binding cell surface receptors on macrophages. We have previously shown that Leukotriene D4 (LTD4) promotes endothelial dysfunction, increasing endothelial permeability and enhancing TNFα-mediated attachment of monocytes to endothelium, which hints at its possible role in atherosclerosis. Here we analyzed the effect of LTD4 on macrophage function. Macrophages mainly express CysLT1R and flux calcium in response to LTD4. Further, LTD4 potentiates phagocytosis in macrophages as revealed by the uptake of zymosan particles. Notably, LTD4 augmented macrophage phagocytosis and oxLDL uptake which is sensitive to MK-571 [Montelukast (MK)], a CysLT1R-specific antagonist. Mechanistically, LTD4 upregulated two receptors central to foam cell formation, oxidized low-density lipoprotein receptor-1 (OLR1/LOX-1), and CD36 in a time and dose-dependent manner. Finally, LTD4 enhanced the secretion of chemokines MCP-1 and MIP1β. Our results suggest that LTD4 contributes to atherosclerosis either through driving foam cell formation or recruitment of immune cells or both. CysLT1R antagonists are safely being used in the treatment of asthma, and the findings from the current study suggest that these can be re-purposed for the treatment of atherosclerosis.

Targeting Host Cellular Factors as a Strategy of Therapeutic Intervention for Herpesvirus Infections

Herpesviruses utilize various host factors to establish latent infection, survival, and spread disease in the host. These factors include host cellular machinery, host proteins, gene expression, multiple transcription factors, cellular signal pathways, immune cell activation, transcription factors, cytokines, angiogenesis, invasion, and factors promoting metastasis. The knowledge and understanding of host genes, protein products, and biochemical pathways lead to discovering safe and effective antivirals to prevent viral reactivation and spread infection. Here, we focus on the contribution of pro-inflammatory, anti-inflammatory, and resolution lipid metabolites of the arachidonic acid (AA) pathway in the lifecycle of herpesvirus infections. We discuss how various herpesviruses utilize these lipid pathways to their advantage and how we target them to combat herpesvirus infection. We also summarize recent development in anti-herpesvirus therapeutics and new strategies proposed or under clinical trials. These anti-herpesvirus therapeutics include inhibitors blocking viral life cycle events, engineered anticancer agents, epigenome influencing factors, immunomodulators, and therapeutic compounds from natural extracts.

Lipid metabolism in asthma: Immune regulation and potential therapeutic target

Asthma is a chronic inflammatory disease of the lungs that poses a considerable health and socioeconomic burden. Several risk factors work synergistically to affect the progression of asthma. Lipid metabolism, especially in distinct cells such as T cells, macrophages, granulocytes, and non-immune cells, plays an essential role in the pathogenesis of asthma, as lipids are potent signaling molecules that regulate a multitude of cellular response. In this review, we focused on the metabolic pathways of lipid molecules, especially fatty acids and their derivatives, and summarized their roles in various cells during the pathogenesis of asthma along with the current pharmacological agents targeting lipid metabolism.

A basophil-neuronal axis promotes itch

Itch is an evolutionarily conserved sensation that facilitates expulsion of pathogens and noxious stimuli from the skin. However, in organ failure, cancer, and chronic inflammatory disorders such as atopic dermatitis (AD), itch becomes chronic, intractable, and debilitating. In addition to chronic itch, patients often experience intense acute itch exacerbations. Recent discoveries have unearthed the neuroimmune circuitry of itch, leading to the development of anti-itch treatments. However, mechanisms underlying acute itch exacerbations remain overlooked. Herein, we identify that a large proportion of patients with AD harbor allergen-specific immunoglobulin E (IgE) and exhibit a propensity for acute itch flares. In mice, while allergen-provoked acute itch is mediated by the mast cell-histamine axis in steady state, AD-associated inflammation renders this pathway dispensable. Instead, a previously unrecognized basophil-leukotriene (LT) axis emerges as critical for acute itch flares. By probing fundamental itch mechanisms, our study highlights a basophil-neuronal circuit that may underlie a variety of neuroimmune processes.

Montelukast use over the past 20 years: monitoring of its effects and safety issues

Montelukast, a leukotriene receptor antagonist, was launched 20 years ago in Korea. It is recommended as an alternative treatment for asthma in children with mild persistent symptoms or as an add-on treatment to existing low-dose inhaled corticosteroids (ICSs) in children who require additional treatment. However, in the real-world setting, many doctors and patients prefer montelukast over ICSs despite their lower efficacy. Although montelukast is considered to be a safe drug, there are concerns regarding adverse drug reactions, including the rare occurrence of Churg-Strauss syndrome and, despite insufficient data, the possibility of neuropsychiatric events such as anxiety, depression, sleep disturbance, and suicidality. This review identified that montelukast has significantly contributed to asthma control over the past 20 years in Korea and has been critical for reducing asthma severity, especially early wheezing and disease control. Our findings suggest that the effects of montelukast treatment can be monitored by measuring serum eosinophilderived neurotoxin levels.

Serum metabolomic profiles reveal the impact of BuZangTongLuo formula on metabolic pathways in diabetic mice with hindlimb ischemia

ETHNOPHARMACOLOGICAL RELEVANCE

BuZangTongLuo Formula (BZTLF) was the decoction of eight traditional Chinese medicines including Astragalus membranaceus, Dioscorea opposita, Salvia miltiorrhiza, Scrophularia ningpoensis, Ophiopogon japonicus, Panax ginseng, Fritillariae cirrhosae and Whitmania pigra. This formula has been used as an effective remedy for treatment of diabetic ischemia clinically.

AIM OF THE STUDY

In previous study, we have reported the therapeutic effect of BZTLF on diabetic vascular dysfunction. However, it remains obscure about the role of metabolic pathways in BZTLF-initiated improvement on hindlimb ischemia.

MATERIALS AND METHODS

Diabetic mice with hindlimb ischemia were orally administrated with BZTLF by gavage. The serum samples were prepared for untargeted metabolomic analysis by ultra-performance liquid chromatography-mass spectrometer. The metabolic network was built by integrating metabolite data with the Gene Expression Omnibus (GEO) dataset (GSE3313). Further, quantitative PCR was used to confirm the key target genes.

RESULTS

BZTLF treatment remarkably led to the reversal of changed metabolite levels in serum of diabetic mice with hindlimb ischemia, which mainly derived from bacteria, plant and signaling molecules. Also, BZTLF reshaped the metabolic pathways, especially those responsible for metabolism of lipid, gluthanine and tryptophan. In addition, BZTLF led to the reduction of lysophosphatidic acids (LPAs) and increment of triglycerides (TGs) conjugation with non-saturated fatty acids in serum. BZTLF significantly restored the down-regulation of vascular endothelial growth factor receptor 2 (VEGFR2) and endothelial nitric oxide synthase (eNOS) or the up-regulation of interleukin 4-induced 1 (IL4I1) and cytochrome P450 family 1 subfamily B member 1 (CYP1B1) at mRNA level, which were key regulatory genes located in metabolic pathways of glutamate and tryptophan.

CONCLUSIONS

BZTLF improved hindlimb ischemia in diabetic mice by the positive regulation of metabolome changes in serum.

Identification of cysteinyl-leukotriene-receptor 1 antagonists as ligands for the bile acid receptor GPBAR1

The cysteinyl leukotrienes (CysLTs), i.e. LTC₄, LTD₄ and LTE₄, are a family of proinflammatory agents synthesized from the arachidonic acid. In target cells, these lipid mediators bind to the cysteinyl leukotriene receptors (CysLTR), a family of seven transmembrane G-protein coupled receptors. The CysLT₁R is a validated target for treatment of pulmonary diseases and several selective antagonists for this receptor, including montelukast, zafirlukast and pranlukast, have shown effective in the management of asthma. Nevertheless, others CysLT₁R antagonists, such as the alpha-pentyl-3-[2-quinolinylmethoxy] benzyl alcohol (REV5901), have been extensively characterized without reaching sufficient priority for clinical development. Since drug reposition is an efficient approach for maximizing investment in drug discovery, we have investigated whether CysLT₁R antagonists might exert off-target effects. In the report we demonstrate that REV5901 interacts with GPBAR1, a well characterized cell membrane receptor for secondary bile acids. REV5901 transactivates GPBAR1 in GPBAR1-transfected cells with an EC₅₀ of 2.5 µM and accommodates the GPBAR1 binding site as shown by in silico analysis. Exposure of macrophages to REV5901 abrogates the inflammatory response elicited by bacterial endotoxin in a GPBAR1-dependent manner. In vivo, in contrast to montelukast, REV5901 attenuates inflammation and immune dysfunction in rodent models of colitis. The beneficial effects exerted by REV5901 in these models were abrogated by GPBAR1 gene ablation, confirming that REV5901, a shelved CysLT₁R antagonist, is a GPBAR1 ligand. These data ground the basis for the development of novel hybrid ligands designed for simultaneous modulation of CysTL₁R and GPBAR1.

Omega-3 Polyunsaturated Fatty Acid Derived Lipid Mediators and their Application in Drug Discovery

Omega-3 (n-3) and omega-6 (n-6) polyunsaturated fatty acids (PUFAs) play crucial and often opposing regulatory roles in health and in pathological conditions. n-3 and n-6 PUFA undergo biotransformation to parallel series of lipid mediators that are potent modulators of many cellular processes. A wide range of biological actions have been attributed to lipid mediators derived from n-6 PUFA, and these mediators have served as lead compounds in the development of numerous clinically approved drugs, including latanoprost (Xalatan: Pfizer), which is listed on the WHO Model List of Essential Medicines. n-3 PUFA-derived mediators have received less attention, in part because early studies suggested that n-3 PUFA act simply as competitive substrates for biotransformation enzymes and decrease the formation of n-6 PUFA-derived lipid mediators. However, more recent studies suggest that n-3 PUFA-derived mediators are biologically important in their own right. It is now emerging that many n-3 PUFA-derived lipid mediators have potent and diverse activities that are distinct from their n-6 counterparts. These findings provide new opportunities for drug discovery. Herein, we review the biosynthesis of n-3 PUFA-derived lipid mediators and highlight their biological actions that may be exploited for drug development. Lastly, we provide examples of medicinal chemistry research that has utilized n-3 PUFA-derived lipid mediators as novel lead compounds in drug design.

Increased expression of CysLT2 receptors in the lung of asthmatic mice and role in allergic responses

Compared with CysLT₁ receptors, the functional role of CysLT₂ receptors in asthma has not been clarified. The purpose of this study was to determine 1) whether CysLT₂ receptors are expressed in the lung of mice and if expression increases in asthmatic mice, and 2) whether CysLT₂ receptors are involved in allergic leukocyte infiltration into the lung and in the development of airway remodeling in asthmatic mice. BALB/c mice were sensitized with ovalbumin (OVA) + Al(OH)₃, and intratracheally challenged with OVA 4 times. Lung tissue was isolated before and after the 4th OVA challenge for detection of CysLT₂ receptors by immunohistochemistry and flow cytometry. The effect of a CysLT₂ receptor antagonist BayCysLT₂RA on multiple antigen challenge-induced leukocyte infiltration into the lung and the development of airway remodeling was evaluated. Even in non-challenged mice, CysLT₂ receptors were expressed in bronchial smooth muscle. After multiple challenges, expression was also observed in leukocytes infiltrating into alveolar spaces. CysLT₂R⁺ leukocytes included alveolar macrophages, conventional dendritic cells, and eosinophils. BayCysLT₂RA significantly inhibited multiple antigen challenge-induced increases in eosinophils and mononuclear cells in the lung. The development of airway remodeling was tended to be suppressed by CysLT₂ receptor antagonist. In conclusion, CysLT₂ receptors were constitutively expressed in the lung, and expression was strengthened in asthmatic mice. Activation of CysLT₂ receptors was functionally involved in allergic leukocyte infiltration into the lung. The CysLT₂ receptor can be a molecular target for the development of new pharmacotherapies for asthma.

Dysregulated GPCR Signaling and Therapeutic Options in Uveal Melanoma

Uveal melanoma is the most common primary intraocular malignant tumor in adults and arises from the transformation of melanocytes in the uveal tract. Even after treatment of the primary tumor, up to 50% of patients succumb to metastatic disease. The liver is the predominant organ of metastasis. There is an important need to provide effective treatment options for advanced stage uveal melanoma. To provide the preclinical basis for new treatments, it is important to understand the molecular underpinnings of the disease. Recent genomic studies have shown that mutations within components of G protein-coupled receptor (GPCR) signaling are early events associated with approximately 98% of uveal melanomas.Implications: This review discusses the alterations in GPCR signaling components (GNAQ and GNA11), dysregulated GPCR signaling cascades, and viable targeted therapies with the intent to provide insight into new therapeutic strategies in uveal melanoma. Mol Cancer Res; 15(5); 501-6. ©2017 AACR.

Recurrent activating mutations of G-protein-coupled receptor CYSLTR2 in uveal melanoma

Uveal melanomas are molecularly distinct from cutaneous melanomas and lack mutations in BRAF, NRAS, KIT, and NF1. Instead, they are characterized by activating mutations in GNAQ and GNA11, two highly homologous α subunits of Gαq/11 heterotrimeric G proteins, and in PLCB4 (phospholipase C β4), the downstream effector of Gαq signaling. We analyzed genomics data from 136 uveal melanoma samples and found a recurrent mutation in CYSLTR2 (cysteinyl leukotriene receptor 2) encoding a p.Leu129Gln substitution in 4 of 9 samples that lacked mutations in GNAQ, GNA11, and PLCB4 but in 0 of 127 samples that harbored mutations in these genes. The Leu129Gln CysLT2R mutant protein constitutively activates endogenous Gαq and is unresponsive to stimulation by leukotriene. Expression of Leu129Gln CysLT2R in melanocytes enforces expression of a melanocyte-lineage signature, drives phorbol ester-independent growth in vitro, and promotes tumorigenesis in vivo. Our findings implicate CYSLTR2 as a uveal melanoma oncogene and highlight the critical role of Gαq signaling in uveal melanoma pathogenesis.

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.

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.

Cysteinyl leukotrienes regulate endothelial cell inflammatory and proliferative signals through CysLT₂ and CysLT₁ receptors

Cysteinyl leukotrienes (cys-LTs), LTC₄, LTD₄, LTE₄ are potent inflammatory lipid mediators that act through two distinct G-protein-coupled receptors, CysLT₁R and CysLT₂R. Although cys-LTs are shown to induce vascular leakage and atherosclerosis, the molecular mechanism by which cys-LTs modulate endothelial function is not known. Here, we show that cys-LTs (LTC₄ and LTD₄) induce robust calcium influx in human umbilical vein endothelial cells (HUVECs) through CysLT₂R, but not CysLT₁R. Further, cys-LT treatment induced endothelial cell (EC) contraction leading to monolayer disruption via CysLT₂R/Rho kinase dependent pathway. Furthermore, stimulation with cys-LTs potentiated TNFα-induced VCAM-1 expression and leukocyte recruitment to ECs through CysLT₂R. In contrast, we found that both LTC₄ and LTD₄ stimulated EC proliferation through CysLT₁R. Taken together, these results suggest that cys-LTs induce endothelial inflammation and proliferation via CysLT₂R/Rho kinase and CysLT₁R/Erk dependent pathways, respectively, which play critical role in the etiology of cardiovascular diseases such as atherosclerosis and myocardial infarction.

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.

Cysteinyl leukotriene receptors, old and new; implications for asthma

The cysteinyl leukotrienes (cys-LTs) are three structurally similar, but functionally distinct lipid mediators of inflammation. The parent cys-LT, LTC(4) , is synthesized by and released from mast cells, eosinophils, basophils, and macrophages, and is converted to the potent constrictor LTD(4) and the stable metabolite, LTE(4) . While only two cys-LT-selective receptors (CysLTRs) have been identified, cloned, and characterized, studies dating back three decades predicted the existence of at least three functional CysLTRs, each with a characteristic physiological function in airways and other tissues. The recent demonstration that mice lacking both known CysLTRs exhibit full (and in some instances, augmented) physiological responses to cys-LTs verifies the existence of unidentified CysLTRs. Moreover, the ability to manipulate receptor expression in both whole animal and cellular systems reveals that the functions of CysLTRs are controlled at multiple levels, including receptor-receptor interactions. Finally, studies in transgenic mice have uncovered a potentially major role for cys-LTs in controlling the induction of Th(2) responses to common allergens. This review focuses on these recent findings and their potential clinical implications.

5-Lipoxygenase mediates RANKL-induced osteoclast formation via the cysteinyl leukotriene receptor 1

5-Lipoxygenase (5-LO) catalyzes the formation of two major groups of leukotrienes, leukotriene B4 and cysteinyl leukotrienes (CysLTs), and it has been implicated as a promising drug target to treat various inflammatory diseases. However, its role in osteoclastogenesis has not been investigated. In this study, we used mouse bone marrow-derived macrophages (BMMs) to show that 5-LO inhibitor suppresses RANKL-induced osteoclast formation. Inhibition of 5-LO was associated with impaired activation of multiple signaling events downstream of RANK, including ERK and p38 phosphorylation, and IκB degradation, followed by a decrease in NFATc1 expression. Ectopic overexpression of a constitutively active form of NFATc1 partly rescued the antiosteoclastogenic effect of 5-LO inhibitor. The knockdown of 5-LO in BMMs also resulted in a significant reduction in RANKL-induced osteoclast formation, accompanied by decreased expression of NFATc1. Similar effects were shown with CysLT receptor (CysLTR)1/2 antagonist and small RNA for CysLTR1 in BMMs, indicating the involvement of CysLT and CysLTR1 in 5-LO-mediated osteoclastogenesis. Finally, 5-LO inhibitor suppressed LPS-induced osteoclast formation and bone loss in the in vivo mouse experiments, suggesting a potential therapeutic strategy for treating diseases involving bone destruction. Taken together, the results of this study demonstrate that 5-LO is a key mediator of RANKL-induced osteoclast formation and possibly a novel therapeutic target for bone-resorption diseases.

The G protein-coupled receptor CysLT1 mediates chemokine-like effects and prolongs survival in chronic lymphocytic leukemia

The G protein-coupled receptor (GPCR) CXCR4 is involved in bone marrow tropism and survival of chronic lymphocytic leukemia (CLL) cells. The function of the GPCRs cysteinyl leukotriene receptor 1 (CysLT1) and CysLT2 remains elusive. Here we demonstrate that in CLL and normal B lymphocytes, CysLT1 mRNA is consistently expressed, in contrast to low CysLT2 levels. Similar to the CXCR4 ligand CXCL12, the cysteinyl leukotriene (cysLT) LTD(4) induces calcium fluxes, actin polymerization, and chemotaxis. These effects are blocked by specific CysLT1 antagonists. Their inhibition by pertussis toxin suggests Giα/o protein involvement. Furthermore, CysLT1 mediates MAP-kinase phosphorylation, which implicates contribution of cysLT to survival. Indeed, CysLT1 antagonists induce apoptosis and reduce viability independent of Gαi/o protein signaling. Considering the production of cysLTs in the bone marrow, our data suggest that CysLT1 induces chemokine-like effects, supports accumulation and survival of CLL cells in the bone marrow and thus represents a potential treatment target.

Differential signaling of cysteinyl leukotrienes and a novel cysteinyl leukotriene receptor 2 (CysLT₂) agonist, N-methyl-leukotriene C₄, in calcium reporter and β arrestin assays

The cysteinyl leukotrienes (cysLTs) LTC₄, LTD₄, and LTE₄ are lipid mediators with physiological and pathophysiological functions. They exert their effects through G protein-coupled receptors (GPCRs), most notably via CysLT₁ and CysLT₂ receptor. The roles of the CysLT₂ receptor are beginning to emerge. Both LTC₄ and LTD₄ are potent agonists for the CysLT₂ receptor; however, LTC₄ is rapidly converted to LTD₄, which is also the main endogenous ligand for the CysLT₁ receptor. A selective and potent agonist at the CysLT₂ receptor would facilitate studies to discern between receptor subtypes. We show here that N-methyl LTC₄ (NMLTC₄), a metabolically stable LTC₄ mimetic, is a potent and selective CysLT₂ receptor agonist. Two expression systems were used to evaluate the functional activity of NMLTC₄ at human and/or mouse CysLT₁ and CysLT₂ receptors. Through the aequorin cell-based assay for calcium-coupled GPCRs, NMLTC₄ was almost equipotent to LTC₄ at CysLT₂ receptors but was the least efficacious at CysLT₂ receptors. In a β-galactosidase-β-arrestin complementation assay, the human (h) CysLT₂ receptor can couple with β-arrestin-2, and NMLTC₄ is slightly more potent for eliciting β-arrestin-2 binding compared with cysLTs. Furthermore, LTE₄ is nearly inactive in this assay compared with its weak partial agonist activity in the aequorin system. In a vascular leakage assay, NMLTC₄ is potent and active in mice overexpressing hCysLT₂ receptor in endothelium, whereas the response is abrogated in CysLT₂ receptor knockout mice. Therefore, NMLTC₄ is a potent subtype selective agonist for the CysLT₂ receptor in vitro and in vivo, and it will be useful to elucidate its biological roles.

Arachidonic acid promotes FAK activation and migration in MDA-MB-231 breast cancer cells

Arachidonic acid (AA) is a common dietary n-6 polyunsaturated fatty acid that is present in an esterified form in cell membrane phospholipids, and it might be present in the extracellular microenvironment. In particular, AA promotes MAPK activation and mediates the adhesion of MDA-MB-435 breast cancer cells to type IV collagen. However, the signal transduction pathways mediated by AA have not been studied in detail. Our results demonstrate that stimulation of MDA-MB-231 breast cancer cells with AA promotes an increase in the phoshorylation of Src and FAK, as revealed by site-specific antibodies that recognized the phosphorylation state of Src at Tyr-418, and of FAK at tyrosine-397 and in vitro kinase assays. In addition, AA also induces an increase in the migration of MDA-MB-231 cells. In contrast, AA does not induce phosphorylation of FAK and an increase in cell migration of non-tumorigenic epithelial cells MCF10A. Inhibition of Gi/Go proteins, LOX and Src activity prevent FAK activation and cell migration. In conclusion, our results demonstrate, for the first time, that Gi/Go proteins, LOX and Src play an important role in FAK activation and cell migration induced by AA in MDA-MB-231 breast cancer cells.

Cysteinyl leukotrienes are autocrine and paracrine regulators of fibrocyte function

Pulmonary fibrosis is characterized by the accumulation of fibroblasts and myofibroblasts. These cells may accumulate from three potential sources: the expansion of resident lung fibroblasts, the process of epithelial-mesenchymal transition, or the recruitment and differentiation of circulating mesenchymal precursors known as fibrocytes. We have previously demonstrated that fibrocytes participate in lung fibrogenesis following administration of FITC to mice. We now demonstrate that leukotriene-deficient 5-LO(-/-) mice are protected from FITC-induced fibrosis. Both murine and human fibrocytes express both cysteinyl leukotriene receptor (CysLT) 1 and CysLT2. In addition, fibrocytes are capable of producing CysLTs and can be regulated via the autocrine or paracrine secretion of these lipid mediators. Exogenous administration of leukotriene (LT) D(4), but not LTC(4) induces proliferation of both murine and human fibrocytes in a dose-dependent manner. Consistent with this result, CysLT1 receptor antagonists are able to block the mitogenic effects of exogenous LTD(4) on fibrocytes. Endogenous production of CysLTs contributes to basal fibrocyte proliferation, but does not alter fibrocyte responses to basic fibroblast growth factor. Although CysLTs can induce the migration of fibrocytes in vitro, they do not appear to be essential for fibrocyte recruitment to the lung in vivo, possibly due to compensatory chemokine-mediated recruitment signals. However, CysLTs do appear to regulate the proliferation of fibrocytes once they are recruited to the lung. These data provide mechanistic insight into the therapeutic benefit of leukotriene synthesis inhibitors and CysLT1 receptor antagonists in animal models of fibrosis.

Cysteinyl leukotrienes enhance tumour necrosis factor-alpha-induced matrix metalloproteinase-9 in human monocytes/macrophages

BACKGROUND

Matrix metalloproteinase-9 (MMP-9) is an important enzyme responsible for airway remodelling. Monocytes/macrophages have a cysteinyl leukotriene 1 (cysLT1) receptor, but its function is poorly understood.

OBJECTIVE

To elucidate the function of the cysLT1 receptor of human monocytes/macrophages in MMP-9 production.

METHODS

We examined the effect of cysLTs (LTC4, -D4 and -E4) on TNF-alpha-induced MMP-9 production in THP-1 cells, a human monocytic leukaemia cell line and peripheral blood CD14+ monocytes/macrophages. In addition, we examined the effect of pranlukast, a cysLT1 receptor antagonist, on the enhancement of TNF-alpha-induced MMP-9 production by cysLTs.

RESULTS

ELISA revealed that LTC4 and -D4, but not -E4, enhanced TNF-alpha-induced MMP-9 production in THP-1 cells and peripheral blood CD14+ monocytes/macrophages. Real-time polymerase chain reaction demonstrated that LTC4 and -D4, but not -E4, increased MMP-9 mRNA expression induced by TNF-alpha in THP-1 cells. Moreover, we demonstrated that pranlukast completely inhibited the enhancement of TNF-alpha-induced MMP-9 production by LTC4 and -D4 in THP-1 cells and peripheral blood CD14+ monocytes/macrophages.

CONCLUSION

LTC4 and -D4 enhanced the TNF-alpha-induced MMP-9 production via binding the cysLT1 receptor in human monocytes/macrophages. Pranlukast inhibited the enhancements by LTC4 and D4.

Biosynthesis and metabolism of leukotrienes

Leukotrienes are metabolites of arachidonic acid derived from the action of 5-LO (5-lipoxygenase). The immediate product of 5-LO is LTA4 (leukotriene A4), which is enzymatically converted into either LTB4 (leukotriene B4) by LTA4 hydrolase or LTC4 (leukotriene C4) by LTC4 synthase. The regulation of leukotriene production occurs at various levels, including expression of 5-LO, translocation of 5-LO to the perinuclear region and phosphorylation to either enhance or inhibit the activity of 5-LO. Several other proteins, including cPLA2α (cytosolic phospholipase A2α) and FLAP (5-LO-activating protein) also assemble at the perinuclear region before production of LTA4. LTC4 synthase is an integral membrane protein that is present at the nuclear envelope; however, LTA4 hydrolase remains cytosolic. Biologically active LTB4 is metabolized by ω-oxidation carried out by specific cytochrome P450s (CYP4F) followed by β-oxidation from the ω-carboxy position and after CoA ester formation. Other specific pathways of leukotriene metabolism include the 12-hydroxydehydrogenase/15-oxo-prostaglandin-13-reductase that forms a series of conjugated diene metabolites that have been observed to be excreted into human urine. Metabolism of LTC4 occurs by sequential peptide cleavage reactions involving a γ-glutamyl transpeptidase that forms LTD4 (leukotriene D4) and a membrane-bound dipeptidase that converts LTD4 into LTE4 (leukotriene E4) before ω-oxidation. These metabolic transformations of the primary leukotrienes are critical for termination of their biological activity, and defects in expression of participating enzymes may be involved in specific genetic disease.

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.

Gene expression of 5-, 12-, and 15-lipoxygenases and leukotriene receptors along the rat nephron

The arachidonate signaling pathways comprise prostanoids formed by cyclooxygenases, EETs, and HETEs formed by cytochrome P-450 (CYP) enzymes and HETEs and leukotrienes generated by lipoxygenases. Whereas the intrarenal localization of cyclooxygenases and of some CYP enzymes along the nephron has already been determined, the localization of lipoxygenases and leukotriene-forming enzymes together with leukotriene receptors in the kidney is less clear. This study therefore aimed to determine the expression of 5-, 12-, and 15-lipoxygenases as well as the leukotriene receptors along the rat nephron. The kidneys were dissected into cortex and outer and inner medulla, and the microdissected nephron segments were collected after a collagenase digestion. mRNA abundance was determined by RT-PCR and real-time PCR. 15-LOX mRNA showed a characteristic expression pattern along the distal nephron. 12-LOX mRNA was only found in the glomerulus. Similarly, 5-LOX mRNAs together with 5-LOX-activating protein mRNAs were expressed in the glomerulus and also in the vasa recta. The leukotriene A4 hydrolase was found in all nephron segments, whereas leukotriene C4 synthase mRNA could not be found in any nephron segment. The leukotriene receptor B4 and the cysteinyl leukotriene receptor type 1 were selectively expressed in the glomerulus, whereas cysteinyl receptor type 2 was not found in any nephron segment. Our data suggest that the glomerulus is a major source and target for 5- and 12-HETE and for leukotrienes. The collecting duct system, on the other hand, appears to be a major source of 15-HETE.

Cysteinyl leukotrienes induce monocyte chemoattractant protein 1 in human monocytes/macrophages

BACKGROUND

Monocytes/macrophages have a cysteinyl leukotriene 1 (CysLT1) receptor, but its function is poorly understood. Objective To elucidate the biological function of the CysLT1 receptor of human monocytes/macrophages.

METHODS

We examined the production of TNF-alpha, IL-1beta, IL-2, IL-4, IL-6, IL-8, IL-10, monocyte chemoattractant protein 1 (MCP-1), macrophage colony-stimulating factor (M-CSF), and eotaxin induced by CysLTs (leukotriene (LT)C4, -D4, and -E4) in THP-1 cells, a human monocytic leukaemia cell line, and peripheral blood CD14+ monocytes/macrophages. Moreover, we examined the effect of CysLTs on the expression of beta-chemokine receptor 2B (CCR2B) as the receptor of MCP-1 by Western blot analysis.

RESULTS

ELISA revealed that CysLTs induced MCP-1 in THP-1 cells and peripheral blood CD14+ monocytes/macrophages, but not other cytokines. PCR demonstrated that CysLTs increased MCP-1 mRNA expression in THP-1 cells, and Western blotting showed that CysLTs increased the expression of CCR2B in THP-1 cells. Moreover, we demonstrated that pranlukast, a CysLT1 receptor antagonist, blocked MCP-1 production by CysLTs in THP-1 cells almost completely, and partially inhibited MCP-1 release by CysLTs in peripheral blood CD14+ monocytes/macrophages and CCR2B expression by CysLTs in THP-1 cells.

CONCLUSION

CysLTs induce MCP-1 and increase CCR2B expression in human monocytes/macrophages.

Design, synthesis and bioactions of novel stable mimetics of lipoxins and aspirin-triggered lipoxins

The lipoxins (LX) are a class of potent endogenous oxygenated products that are enzymatically generated from arachidonic acid and have novel anti-inflammatory properties and promote resolution. Elucidation of the biochemical pathways involved in the metabolic inactivation of LX and the discovery of the aspirin-triggered lipoxins (ATL) provided the basis for the design and synthesis of stable analogs of LX and ATL. This special issue review describes the efforts that led to the design and synthesis of stable LX/ATL mimetics, which permitted the detailed elucidation of their novel biological roles, leading to the development of new anti-inflammatory agents that mimic their actions. These synthetic molecules provided the means to uncover the physiologic roles of both the LX and the ATL biosynthetic pathways which led to several unexpected discoveries. Among these findings is the involvement of polyisoprenyl phosphates (PIPP) in intracellular signaling mediated by presqualene diphosphate (PSDP), and the recognition of the novel roles of these lipid mediators in regulating cell trafficking during inflammation as well as in promoting resolution of inflammatory processes. These efforts also provided the basis for examining the potential therapeutic role of LX/ATL stable mimetics and led to the development of new analogs with improved pharmacokinetics that opened the way to potentially new approaches to treating human diseases.

Localization and upregulation of cysteinyl leukotriene-1 receptor in asthmatic bronchial mucosa

We have tested the hypothesis that the CysLT(1) receptor is expressed by a variety of bronchial mucosal immune cells and that the numbers of these cells increase in asthma, when stable and in exacerbations. We have applied in situ hybridization and immunohistochemistry to endobronchial biopsy tissue to identify and count inflammatory cells expressing CysLT(1) receptor mRNA and protein, respectively, and used double immunohistochemistry to identify the specific cell immunophenotypes expressing the receptor. Double-labeling demonstrated that bronchial mucosal eosinophils, neutrophils, mast cells, macrophages, B-lymphocytes, and plasma cells, but not T-lymphocytes, expressed the CysLT(1) receptor. The numbers of CysLT(1) receptor mRNA and protein positive inflammatory cells in nonsmoking, nonatopic control subjects without asthma were 13 and 16 mm(-2), respectively (median values; n = 15), and were significantly greater in stable asthma (50 and 43 mm(-2), respectively; n = 17; P < 0.001). Compared with stable asthma, there were further significant increases in subjects hospitalized for a severe exacerbation of their asthma (mRNA: median = 113 and protein: 156 mm(-2); n = 15; P < 0.002). For the combined data of both asthma subgroups, there were strong positive correlations between the increased numbers of CD45+ leukocytes and the greater numbers of cells expressing CysLT(1) receptor (mRNA: r = 0.60, P < 0.001; protein: r = 0.73, P < 0.0001). In conclusion, a variety of immunohistologically distinct inflammatory cells express the CysLT(1) receptor in the bronchial mucosa and both these and the total number of leukocytes increase in mild stable disease and increase further when there is a severe exacerbation of asthma.

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.

[Leukotriene-lipoxygenase pathway and drug discovery]

The first drugs affecting the leukotriene-lipoxygenase pathway, which have been introduced in clinical application, inhibit effects of slow reacting substance of anaphylaxis (SRS-A). Although, a 5-lipoxygenase inhibitor was first used in clinical practice as an anti-asthma drug, cysteinyl-leukotriene type 1 receptor (cysLT(1)R) antagonists are preferred as anti-asthma and anti-rhinitis drugs because they are almost as effective as the 5-lipoxygenase inhibitors but have fewer side effects. The cloning of genes related to lipoxygenase-leukotriene metabolism prompted us to try to elucidate the role of leukotrienes in various inflammations. There are at least two types of cysLTRs known: cysLT(1)R and cysLT(2)R. CysLT(1)R plays an important role in the pathophysiology of asthma; however, the role of the cysLT(2)R remains unknown. The abundant distribution of cysLT(2)R in heart and brain tissues suggests that cysLTs play an important role in the pathophysiology of ischemic heart diseases or arrhythmias and through this receptor (cysLT(2)R), psychoneurological disorders. The use of a selective cysLT(2)R antagonist may clarify these questions. Since the 5-lipoxygenase pathway is abundantly expressed in atherosclerotic lesions, and 12/15-lipoxygenase is able to oxygenate polyunsaturated fatty acid esterified in the membranous phospholipids, 5-lipoxygenase or 12/15-lipoxygenase inhibitors may prevent progression of atherosclerosis. In addition, it has been reported that 15-lipoxygenase participates in suppression of prostate cancer. In conclusion, the leukotriene-lipoxygenase metabolism may be involved in the pathophysiology of acute inflammatory to chronic progressive disorders. We think that more drugs modifying leukotriene-lipoxygenase metabolism will be introduced into clinical practice in the future.

Cysteinyl-leukotrienes receptor activation in brain inflammatory reactions and cerebral edema formation: a role for transcellular biosynthesis of cysteinyl-leukotrienes

We studied the effect of intravascular activation of human neutrophils on the synthesis of cysteinyl leukotrienes (cysLT) and the formation of cerebral edema in guinea-pig brains. Challenge with the chemotactic formylated tripeptide fMLP (0.1 microM) of neutrophil-perfused brain in vitro resulted in blood-brain barrier disruption associated with a significant increase of cysLT. Both events were completely prevented by neutrophil pretreatment with a specific 5-lipoxygenase (5-LO) inhibitor. Perfusion with the 5-LO metabolite leukotriene B4 (10 nM), together with neutrophils treated with the 5-LO inhibitor, did not restore the alteration in permeability observed upon perfusion with untreated and activated neutrophils. The dual cysLT1-cysLT2 receptor antagonist BAYu9773 was more potent and more effective than a selective cysLT1 antagonist in preventing the brain permeability alteration induced by neutrophil activation. RT-PCR showed significant expression of cysLT2 receptor mRNA in human umbilical vein endothelial cells. Intravital microscopy in mice showed that inhibition of leukotriene synthesis significantly reduced firm adhesion of neutrophils to cerebral vessels without affecting rolling. These data support the hypothesis that neutrophil and endothelial cells cooperate toward the local synthesis of cysLT within the brain vasculature and, acting via the cysLT2 receptor on endothelial cells, may represent a contributing pathogenic mechanism in the development of cerebral inflammation and edema.

Regulation of arachidonic acid availability for eicosanoid production

Mammalian cells have developed specific pathways for the incorporation, remodeling, and release of arachidonic acid. Acyltransferase and transacylase pathways function to regulate the levels of esterified arachidonic acid in specific phospholipid pools. There are several distinct, differentially regulated phospholipases A2in cells that mediate agonist-induced release of arachidonic acid. These pathways are important in controlling cellular levels of free arachidonic acid. Both arachidonic acid and its oxygenated metabolites are potent bioactive mediators that regulate a myriad of physiological and pathophysiological processes.Key words: phospholipase A2, arachidonic acid, eicosanoid, phospholipid.

Syntheses of 3-acetoacetylaminobenzo[b]furan derivatives having cysteinyl leukotriene 2 receptor antagonistic activity

Novel 3-acetoacetylaminobenzo[b]furan derivatives having a modified triene system at the 3-position were synthesized starting with 3-aminobenzo[b]furans. The enol isomers, 3-[(3-hydroxybut-2-enonyl)amino]benzo[b]furans (), of the 3-acetoacetylaminobenzo[b]furans were obtained as stable isomers owing to formation of a hydrogen bonding between the enol hydroxyl group and the amidocarbonyl group. The planarity of the C-2 substituent through the C-3 side chain suggested the existence of a modified conjugational triene system in the enol compound. Cysteinyl leukotriene 1 and 2 receptor antagonistic activities for these compounds were evaluated. 2-(4-Cyanobenzoyl or ethoxycarbonyl)-3-[(2-cyano-3-hydroxybut-2-enonyl)amino]benzo[b]furans (, ) were moderately active.

Stabilization of leukotriene A4 by epithelial fatty acid-binding protein in the rat basophilic leukemia cell

Leukotriene A(4) (LTA(4)) is a chemically unstable triene epoxide product of 5-lipoxygenase metabolism of arachidonic acid. Despite this chemical reactivity and its synthesis at the perinuclear membrane, LTA(4) is enzymatically converted into the cysteinyl leukotrienes and leukotriene B(4). Furthermore, LTA(4) participates in transcellular biosynthesis and is thus transferred between cells as an intact molecule. A cytosolic fatty acid-binding protein present in the rat basophilic leukemia cells was identified using mass spectrometry. This protein was determined to be the stabilizing factor present in the cell cytosol responsible for increasing the effective chemical half-life of LTA(4). Rat epithelial fatty acid-binding protein (E-FABP) was isolated using partial protein purification and immunoprecipitation. In-gel digestion with trypsin followed by peptide fingerprint analysis using matrix-assisted laser desorption ionization mass spectrometry and sequencing the major tryptic peptide obtained from liquid chromatography/mass spectrometry/mass spectrometry analysis identified E-FABP in the active fraction. Semi-quantitative Western blot analysis indicated that E-FABP in the cytosolic fraction of RBL-1 cells was present at approximately 1-3 pmol/10(6) cells. E-FABP (9 microm) was tested for its ability to stabilize LTA(4), and at 37 degrees C E-FABP was able to increase the half-life of LTA(4) from the previously reported half-life less than 3 s to a half-life of approximately 7 min. These results present a novel function for the well studied fatty acid-binding protein as a participant in leukotriene biosynthesis that permits LTA(4) to be available for further enzymatic processing in various cellular regions.

Eosinophils and cysteinyl leukotrienes

Eosinophils are the main source of the cysteinyl leukotrienes, LTC(4)/D(4)/E(4), which are lipid mediators that play major roles in the pathogenesis of asthma and other forms of allergic inflammation. Here, we review the mechanisms governing eosinophil LTC(4) synthesis, focusing on the distinct intracellular domains that regulate eicosanoid formation and function within eosinophils. Cysteinyl leukotrienes exert their actions by engaging specific receptors. As recently shown, eosinophils express CysLT1 and CysLT2, the only cloned receptors for cysteinyl leukotrienes. Therefore, here we also present some of the new findings regarding the paracrine/autocrine activation of these CysLT receptors on eosinophils, and discuss some data on novel intracrine effects of LTC(4) triggered by a putative third CysLT receptor expressed intracellularly within eosinophils.