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

Advancements in diabetic kidney disease management: integrating innovative therapies and targeted drug development

Diabetic kidney disease (DKD) is a leading cause of chronic kidney disease and affects approximately 40% of individuals with diabetes . Cases of DKD continue to rise globally as the prevalence of diabetes mellitus increases, with an estimated 415 million people living with diabetes in 2015 and a projected 642 million by 2040. DKD is associated with significant morbidity and mortality, representing 34% and 36% of all chronic kidney disease deaths in men and women, respectively. Common comorbidities including hypertension and ageing-related nephron loss further complicate disease diagnosis and progression. The progression of DKD involves several mechanisms including glomerular endothelial cell dysfunction, inflammation, and fibrosis. Targeting these mechanisms has formed the basis of several therapeutic agents. Renin-angiotensin-aldosterone system (RAAS) blockers, specifically angiotensin receptor blockers (ARBs), demonstrate significant reductions in macroalbuminuria. Sodium-glucose transporter type 2 (SGLT-2) inhibitors demonstrate kidney protection independent of diabetes control while also decreasing the incidence of cardiovascular events. Emerging agents including glucagon-like peptide 1 (GLP-1) agonists, anti-inflammatory agents like bardoxolone, and mineralocorticoid receptor antagonists show promise in mitigating DKD progression. Many novel therapies including monoclonal antibodies CSL346, lixudebart, and tozorakimab; mesenchymal stem/stromal cell infusion; and cannabinoid-1 receptor inverse agonism via INV-202 are currently in clinical trials and present opportunities for further drug development.

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

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

Structural diversity of leukotriene G-protein coupled receptors

Dihydroxy acid leukotriene (LTB4) and cysteinyl leukotrienes (LTC4, LTD4, and LTE4) are inflammatory mediators derived from arachidonic acid via the 5-lipoxygenase pathway. While structurally similar, these two types of leukotrienes (LTs) exert their functions through interactions with two distinct G protein-coupled receptor (GPCR) families, BLT and CysLT receptors, which share low sequence similarity and belong to phylogenetically divergent GPCR groups. Selective antagonism of LT receptors has been proposed as a promising strategy for the treatment of many inflammation-related diseases including asthma and chronic obstructive pulmonary disease, rheumatoid arthritis, cystic fibrosis, diabetes, and several types of cancer. Selective CysLT1R antagonists are currently used as antiasthmatic drugs, however, there are no approved drugs targeting CysLT2 and BLT receptors. In this review, we highlight recently published structures of BLT1R and CysLTRs revealing unique structural features of the two receptor families. X-ray and cryo-EM data shed light on their overall conformations, differences in functional motifs involved in receptor activation, and details of the ligand-binding pockets. An unexpected binding mode of the selective antagonist BIIL260 in the BLT1R structure makes it the first example of a compound targeting the sodium-binding site of GPCRs and suggests a novel strategy for the receptor activity modulation. Taken together, these recent structural data reveal dramatic differences in the molecular architecture of the two LT receptor families and pave the way to new therapeutic strategies of selective targeting individual receptors with novel tool compounds obtained by the structure-based drug design approach.

Development of bile acid activated receptors hybrid molecules for the treatment of inflammatory and metabolic disorders

The farnesoid-x-receptor (FXR) and the G protein bile acid activated receptor (GPBAR)1 are two bile acid activated receptors highly expressed in entero-hepatic, immune, adipose and cardiovascular tissues. FXR and GPBAR1 are clinically validated targets in the treatment of metabolic disorders and FXR agonists are currently trialled in patients with non-alcoholic steato-hepatitis (NASH). Results of these trials, however, have raised concerns over safety and efficacy of selective FXR ligands suggesting that the development of novel agent designed to impact on multiple targets might have utility in the treatment of complex, multigenic, disorders. Harnessing on FXR and GPBAR1 agonists, several novel hybrid molecules have been developed, including dual FXR and GPBAR1 agonists and antagonists, while exploiting the flexibility of FXR agonists toward other nuclear receptors, dual FXR and peroxisome proliferators-activated receptors (PPARs) and liver-X-receptors (LXRs) and Pregnane-X-receptor (PXR) agonists have been reported. In addition, modifications of FXR agonists has led to the discovery of dual FXR agonists and fatty acid binding protein (FABP)1 and Leukotriene B4 hydrolase (LTB4H) inhibitors. The GPBAR1 binding site has also proven flexible to accommodate hybrid molecules functioning as GPBAR1 agonist and cysteinyl leukotriene receptor (CYSLTR)1 antagonists, as well as dual GPBAR1 agonists and retinoid-related orphan receptor (ROR)γt antagonists, dual GPBAR1 agonist and LXR antagonists and dual GPBAR1 agonists endowed with inhibitory activity on dipeptidyl peptidase 4 (DPP4). In this review we have revised the current landscape of FXR and GPBAR1 based hybrid agents focusing on their utility in the treatment of metabolic associated liver disorders.

Leukotrienes vs. Montelukast—Activity, Metabolism, and Toxicity Hints for Repurposing

Increasing environmental distress is associated with a growing asthma incidence; no treatments are available but montelukast (MTK)—an antagonist of the cysteinyl leukotrienes receptor 1—is widely used in the management of symptoms among adults and children. Recently, new molecular targets have been identified and MTK has been proposed for repurposing in other therapeutic applications, with several ongoing clinical trials. The proposed applications include neuroinflammation control, which could be explored in some neurodegenerative disorders, such as Alzheimer’s and Parkinson’s diseases (AD and PD). However, this drug has been associated with an increasing number of reported neuropsychiatric adverse drug reactions (ADRs). Besides, and despite being on the market since 1998, MTK metabolism is still poorly understood and the mechanisms underlying neuropsychiatric ADRs remain unknown. We review the role of MTK as a modulator of leukotriene pathways and systematize the current knowledge about MTK metabolism. Known toxic effects of MTK are discussed, and repurposing applications are presented comprehensively, with a focus on AD and PD.

Discovery of a Potent and Orally Active Dual GPBAR1/CysLT1R Modulator for the Treatment of Metabolic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) are two highly prevalent human diseases caused by excessive fat deposition in the liver. Although multiple approaches have been suggested, NAFLD/NASH remains an unmet clinical need. Here, we report the discovery of a novel class of hybrid molecules designed to function as cysteinyl leukotriene receptor 1 (CysLT₁R) antagonists and G protein bile acid receptor 1 (GPBAR1/TGR5) agonists for the treatment of NAFLD/NASH. The most potent of these compounds generated by harnessing the scaffold of the previously described CystLT₁R antagonists showed efficacy in reversing liver histopathology features in a preclinical model of NASH, reshaping the liver transcriptome and the lipid and energy metabolism in the liver and adipose tissues. In summary, the present study described a novel orally active dual CysLT₁R antagonist/GPBAR1 agonist that effectively protects against the development of NAFLD/NASH, showing promise for further development.

Effects of non-steroidal anti-inflammatory drugs and other eicosanoid pathway modifiers on antiviral and allergic responses: EAACI task force on eicosanoids consensus report in times of COVID-19

Non‐steroidal anti‐inflammatory drugs (NSAIDs) and other eicosanoid pathway modifiers are among the most ubiquitously used medications in the general population. Their broad anti‐inflammatory, antipyretic, and analgesic effects are applied against symptoms of respiratory infections, including SARS‐CoV‐2, as well as in other acute and chronic inflammatory diseases that often coexist with allergy and asthma. However, the current pandemic of COVID‐19 also revealed the gaps in our understanding of their mechanism of action, selectivity, and interactions not only during viral infections and inflammation, but also in asthma exacerbations, uncontrolled allergic inflammation, and NSAIDs‐exacerbated respiratory disease (NERD). In this context, the consensus report summarizes currently available knowledge, novel discoveries, and controversies regarding the use of NSAIDs in COVID‐19, and the role of NSAIDs in asthma and viral asthma exacerbations. We also describe here novel mechanisms of action of leukotriene receptor antagonists (LTRAs), outline how to predict responses to LTRA therapy and discuss a potential role of LTRA therapy in COVID‐19 treatment. Moreover, we discuss interactions of novel T2 biologicals and other eicosanoid pathway modifiers on the horizon, such as prostaglandin D2 antagonists and cannabinoids, with eicosanoid pathways, in context of viral infections and exacerbations of asthma and allergic diseases. Finally, we identify and summarize the major knowledge gaps and unmet needs in current eicosanoid research.

Structural Basis for Developing Multitarget Compounds Acting on Cysteinyl Leukotriene Receptor 1 and G-Protein-Coupled Bile Acid Receptor 1

G-protein-coupled receptors (GPCRs) are the molecular target of 40% of marketed drugs and the most investigated structures to develop novel therapeutics. Different members of the GPCRs superfamily can modulate the same cellular process acting on diverse pathways, thus representing an attractive opportunity to achieve multitarget drugs with synergic pharmacological effects. Here, we present a series of compounds with dual activity toward cysteinyl leukotriene receptor 1 (CysLT₁R) and G-protein-coupled bile acid receptor 1 (GPBAR1). They are derivatives of REV5901─the first reported dual compound─with therapeutic potential in the treatment of colitis and other inflammatory processes. We report the binding mode of the most active compounds in the two GPCRs, revealing unprecedented structural basis for future drug design studies, including the presence of a polar group opportunely spaced from an aromatic ring in the ligand to interact with Arg79^2.60 of CysLT₁R and achieve dual activity.

Biologically active lipids in the regulation of lymphangiogenesis in disease states

Lymphatic vessels have crucial roles in the regulation of interstitial fluids, immune surveillance, and the absorption of dietary fat in the intestine. Lymphatic function is also closely related to the pathogenesis of various disease states such as inflammation, lymphedema, endometriosis, liver dysfunction, and tumor metastasis. Lymphangiogenesis, the formation of new lymphatic vessels from pre-existing lymphatic vessels, is a critical determinant in the above conditions. Although the effect of growth factors on lymphangiogenesis is well-characterized, and biologically active lipids are known to affect smooth muscle contractility and vasoaction, there is accumulating evidence that biologically active lipids are also important inducers of growth factors and cytokines that regulate lymphangiogenesis. This review discusses recent advances in our understanding of biologically active lipids, including arachidonic acid metabolites, sphingosine 1-phosphate, and lysophosphatidic acid, as regulators of lymphangiogenesis, and the emerging importance of the lymphangiogenesis as a therapeutic target.

Eicosanoid receptors as therapeutic targets for asthma

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

A review of non-prostanoid, eicosanoid receptors: expression, characterization, regulation, and mechanism of action

Eicosanoid signaling controls a wide range of biological processes from blood pressure homeostasis to inflammation and resolution thereof to the perception of pain and to cell survival itself. Disruption of normal eicosanoid signaling is implicated in numerous disease states. Eicosanoid signaling is facilitated by G-protein-coupled, eicosanoid-specific receptors and the array of associated G-proteins. This review focuses on the expression, characterization, regulation, and mechanism of action of non-prostanoid, eicosanoid receptors.

Metabolism pathways of arachidonic acids: mechanisms and potential therapeutic targets

The arachidonic acid (AA) pathway plays a key role in cardiovascular biology, carcinogenesis, and many inflammatory diseases, such as asthma, arthritis, etc. Esterified AA on the inner surface of the cell membrane is hydrolyzed to its free form by phospholipase A2 (PLA2), which is in turn further metabolized by cyclooxygenases (COXs) and lipoxygenases (LOXs) and cytochrome P450 (CYP) enzymes to a spectrum of bioactive mediators that includes prostanoids, leukotrienes (LTs), epoxyeicosatrienoic acids (EETs), dihydroxyeicosatetraenoic acid (diHETEs), eicosatetraenoic acids (ETEs), and lipoxins (LXs). Many of the latter mediators are considered to be novel preventive and therapeutic targets for cardiovascular diseases (CVD), cancers, and inflammatory diseases. This review sets out to summarize the physiological and pathophysiological importance of the AA metabolizing pathways and outline the molecular mechanisms underlying the actions of AA related to its three main metabolic pathways in CVD and cancer progression will provide valuable insight for developing new therapeutic drugs for CVD and anti-cancer agents such as inhibitors of EETs or 2J2. Thus, we herein present a synopsis of AA metabolism in human health, cardiovascular and cancer biology, and the signaling pathways involved in these processes. To explore the role of the AA metabolism and potential therapies, we also introduce the current newly clinical studies targeting AA metabolisms in the different disease conditions.

Cytochrome P450 derived epoxidized fatty acids as a therapeutic tool against neuroinflammatory diseases

Cytochrome P450 (CYP) metabolism of arachidonic acid (ARA) produces epoxy fatty acids (EpFAs) such as epoxyeicosatrienoic acids (EETs) that are known to exert protective effects in inflammatory disorders. Endogenous EpFAs are further metabolized into corresponding diols by the soluble epoxide hydrolase (sEH). Through inhibition of sEH, many studies have demonstrated the cardioprotective and renoprotective effects of EpFAs; however, the role of sEH inhibition in modulating the pathogenesis of neuroinflammatory disorders is less well described. In this review, we discuss the current knowledge surrounding the effects of sEH inhibition and EpFA action in neuroinflammatory disorders such as Parkinson's Disease (PD), stroke, depression, epilepsy, and Alzheimer's Disease (AD), as well as the potential mechanisms that underlie the therapeutic effects of sEH inhibition.

Nasal Polyposis and Aspirin-Exacerbated Respiratory Disease

Aspirin-exacerbated respiratory disease (AERD) is characterized by eosinophilic chronic rhinosinusitis with nasal polyps, asthma, and upper-/lower-respiratory tract reactions to nonsteroidal antiinflammatory drugs. Persistent, severe disease, anosmia, and alcohol sensitivity is typical. AERD is mediated by multiple pathways, including aberrant arachidonic acid metabolism leading to elevated leukotriene E4 and decreased prostaglandin E2. Mast cell mediators (prostaglandin D2) and unique properties of eosinophils and type 2 innate lymphoid cells, along with receptor-mediated signaling, also contribute to AERD pathogenesis. Pharmacologic therapies are a cornerstone of AERD treatment and include leukotriene modifiers, corticosteroids, biologics, and aspirin.

Dual Farnesoid X Receptor/Soluble Epoxide Hydrolase Modulators Derived from Zafirlukast

The nuclear farnesoid X receptor (FXR) and the enzyme soluble epoxide hydrolase (sEH) are validated molecular targets to treat metabolic disorders such as non-alcoholic steatohepatitis (NASH). Their simultaneous modulation in vivo has demonstrated a triad of anti-NASH effects and thus may generate synergistic efficacy. Here we report dual FXR activators/sEH inhibitors derived from the anti-asthma drug Zafirlukast. Systematic structural optimization of the scaffold has produced favorable dual potency on FXR and sEH while depleting the original cysteinyl leukotriene receptor antagonism of the lead drug. The resulting polypharmacological activity profile holds promise in the treatment of liver-related metabolic diseases.

Computer-Assisted Selective Optimization of Side-Activities-from Cinalukast to a PPARα Modulator

Automated computational analogue design and scoring can speed up hit-to-lead optimization and appears particularly promising in selective optimization of side-activities (SOSA) where possible analogue diversity is confined. Probing this concept, we employed the cysteinyl leukotriene receptor 1 (CysLT₁ R) antagonist cinalukast as lead for which we discovered peroxisome proliferator-activated receptor α (PPARα) modulatory activity. We automatically generated a virtual library of close analogues and classified these roughly 8000 compounds for PPARα agonism and CysLT₁ R antagonism using automated affinity scoring and machine learning. A computationally preferred analogue for SOSA was synthesized, and in vitro characterization indeed revealed a marked activity shift toward enhanced PPARα activation and diminished CysLT₁ R antagonism. Thereby, this prospective application study highlights the potential of automating SOSA.

IL-33 Upregulates Cysteinyl Leukotriene Receptor Type 1 Expression in Human Peripheral Blood CD4+ T Lymphocytes

IL-33 and cysteinyl leukotrienes (cysLTs) are key components of asthma pathogenesis, and both contribute to the initiation and maintenance of the type 2 inflammatory environment. However, little is known about the potential interactions between the two mediators. In this work, we aimed at studying the regulation of expression of the cysLT receptors CysLT1 and CysLT2 by IL-33 in human PBLs. Our results show that the IL-33/ST2L axis increases CysLT1 but not CysLT2 expression in a concentration- and time-dependent manner in PBLs. IL-33-induced CysLT1 upregulation was observed at the protein but not at the mRNA level and was accompanied by an increase in LTD₄-induced calcium mobilization and migration of CD4⁺ T lymphocytes. We also show that purified naive CD4⁺ T lymphocytes expressed ST2L and responded to IL-33 in the absence of Ag or TCR stimulation, suggesting a mechanism independent of Ag presentation. These results contribute to expanding our knowledge in the field of IL-33 by proposing a new mode of action of the cytokine on T cells and by extending its role to the regulation of naive T cell trafficking, therefore reinforcing its interest as a potential therapeutic target for the treatment of asthma.

Zafirlukast promotes insulin secretion by increasing calcium influx through L-type calcium channels

The zafirlukast has been reported to be anti-inflammatory and widely used to alleviate the symptoms of asthma. However, its influence on insulin secretion in pancreatic β-cells has not been investigated. Herein, we examined the effects of zafirlukast on insulin secretion and the potential underlying mechanisms. Among the cysteinyl leukotriene receptor 1 antagonists, zafirlukast, pranlukast, and montelukast, only zafirlukast enhanced insulin secretion in a concentration-dependent manner in both low and high glucose conditions and elevated the level of [Ca²⁺ ]_i , further activating Ca²⁺ /calmodulin-dependent protein kinase II (CaMKII), protein kinase B (AKT), and extracellular signal-regulated kinase (ERK) signaling. These effects were nearly abolished by the L-type Ca²⁺ channel antagonist nifedipine, while treatment with thapsigargin, a sarco/endoplasmic reticulum Ca²⁺ ATPase inhibitor, did not have the same effect, suggesting that zafirlukast primarily induces the entry of extracellular Ca²⁺ rather than intracellular Ca²⁺ from the endoplasmic reticulum. Zafirlukast treatment resulting in a significant drop in glucose levels and increased insulin secretion in C57BL/6J mice. These findings will contribute to an improved understanding of the side effects of zafirlukast and potential candidate for a therapeutic intervention in diabetes.

Leukotriene receptors as potential therapeutic targets

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

Role of lipid mediators and control of lymphocyte responses in type 2 immunopathology

Type 2 immunopathology is a cardinal feature of allergic diseases and involves cooperation between adaptive immunity and innate effector responses. Virtually all cell types relevant to this pathology generate leukotriene and/or prostaglandin mediators that derive from arachidonic acid, express receptors for such mediators, or both. Recent studies highlight prominent functions for these mediators in communication between the innate and adaptive immune systems, as well as amplification or suppression of type 2 effector responses. This review focuses on recent advances and insights, and highlights existing and potential therapeutic applications of drugs that target these mediators or their receptors, with a special emphasis on their regulation of the innate and adaptive lymphocytes relevant to type 2 immunopathology.

Role of the Cysteinyl Leukotrienes in the Pathogenesis and Progression of Cardiovascular Diseases

Cysteinyl leukotrienes (CysLTs) are potent lipid inflammatory mediators synthesized from arachidonic acid, through the 5-lipoxygenase (5-LO) pathway. Owing to their properties, CysLTs play a crucial role in the pathogenesis of inflammation; therefore, CysLT modifiers as synthesis inhibitors or receptor antagonists, central in asthma management, may become a potential target for the treatment of other inflammatory diseases such as the cardiovascular disorders. 5-LO pathway activation and increased expression of its mediators and receptors are found in cardiovascular diseases. Moreover, the cardioprotective effects observed by using CysLT modifiers are promising and contribute to elucidate the link between CysLTs and cardiovascular disease. The aim of this review is to summarize the state of present research about the role of the CysLTs in the pathogenesis and progression of atherosclerosis and myocardial infarction.

Cysteinyl Leukotrienes as Potential Pharmacological Targets for Cerebral Diseases

Cysteinyl leukotrienes (CysLTs) are potent lipid mediators widely known for their actions in asthma and in allergic rhinitis. Accumulating data highlights their involvement in a broader range of inflammation-associated diseases such as cancer, atopic dermatitis, rheumatoid arthritis, and cardiovascular diseases. The reported elevated levels of CysLTs in acute and chronic brain lesions, the association between the genetic polymorphisms in the LTs biosynthesis pathways and the risk of cerebral pathological events, and the evidence from animal models link also CysLTs and brain diseases. This review will give an overview of how far research has gone into the evaluation of the role of CysLTs in the most prevalent neurodegenerative disorders (ischemia, Alzheimer's and Parkinson's diseases, multiple sclerosis/experimental autoimmune encephalomyelitis, and epilepsy) in order to understand the underlying mechanism by which they might be central in the disease progression.

Opportunities and Challenges for Fatty Acid Mimetics in Drug Discovery

Fatty acids beyond their role as an endogenous energy source and storage are increasingly considered as signaling molecules regulating various physiological effects in metabolism and inflammation. Accordingly, the molecular targets involved in formation and physiological activities of fatty acids hold significant therapeutic potential. A number of these fatty acid targets are addressed by some of the oldest and most widely used drugs such as cyclooxygenase inhibiting NSAIDs, whereas others remain unexploited. Compounds orthosterically binding to proteins that endogenously bind fatty acids are considered as fatty acid mimetics. On the basis of their structural resemblance, fatty acid mimetics constitute a family of bioactive compounds showing specific binding thermodynamics and following similar pharmacokinetic mechanisms. This perspective systematically evaluates targets for fatty acid mimetics, investigates their common structural characteristics, and highlights demands in their discovery and design. In summary, fatty acid mimetics share particularly favorable characteristics justifying the conclusion that their therapeutic potential vastly outweighs the challenges in their design.

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

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

CysLT1R downregulation reverses intracerebroventricular streptozotocin-induced memory impairment via modulation of neuroinflammation in mice

Our previous studies showed that cysteinyl leukotrienes receptor 1 (CysLT₁R) is upregulated in amyloid-β (Aβ)-induced neurotoxicity and that administration of CysLT₁R antagonists such as pranlukast or montelukast can ameliorate memory impairment in mice. In the current study, we sought to explore the role of CysLT₁R in intracerebroventricular streptozotocin (STZ-ICV)-induced mouse model of memory impairment and neuroinflammation through shRNA-mediated knockdown of CysLT₁R and also its pharmacological blockade by pranlukast. ICR mice were infused with STZ (3.0mg/kg) by a single bilateral stereotaxic ICV microinjection followed by administration of CysLT₁R-shRNA (intra-hippocampal) or pranlukast (intragastric, IG). After 21days, a set of behavioral and biochemical tests were performed in order to assess the degree of memory impairment and neuroinflammation in mice. STZ-infused mice spent less time in the target quadrant of Morris water maze test and took more time to find the shock-free arm in modified Y-maze test, which were rescued in the CysLT₁R-knockdowned or pranlukast-treated mice. STZ-induced memory impairment was also accompanied by an elevated level of hippocampal CysLT₁R, microglial activation, increased IL-1β, and TNF-α. Such elevation of these factors was found to be mediated through the classical NF-κB pathway and administration of CysLT₁R-shRNA or pranlukast for 21days reversed all these parameters, suggesting a role of CysLT₁R in STZ-induced memory deficit and neuroinflammation.

Cysteinyl Leukotrienes and Their Receptors: Emerging Therapeutic Targets in Central Nervous System Disorders

Cysteinyl leukotrienes are a group of the inflammatory lipid molecules well known as mediators of inflammatory signaling in the allergic diseases. Although they are traditionally known for their role in allergic asthma, allergic rhinitis, and others, recent advances in the field of biomedical research highlighted the role of these inflammatory mediators in a broader range of diseases such as in the inflammation associated with the central nervous system (CNS) disorders, vascular inflammation (atherosclerotic), and in cancer. Among the CNS diseases, they, along with their synthesis precursor enzyme 5-lipoxygenase and their receptors, have been shown to be associated with brain injury, Multiple sclerosis, Alzheimer's disease, Parkinson's disease, brain ischemia, epilepsy, and others. However, a lot more remains elusive as the research in these areas is emerging and only a little has been discovered. Herein, through this review, we first provided a general up-to-date information on the synthesis pathway and the receptors for the molecules. Next, we summarized the current findings on their role in the brain disorders, with an insight given to the future perspectives.

Pulmonary epithelial cancer cells and their exosomes metabolize myeloid cell-derived leukotriene C4 to leukotriene D4

Leukotrienes (LTs) play major roles in lung immune responses, and LTD4 is the most potent agonist for cysteinyl LT1, leading to bronchoconstriction and tissue remodeling. Here, we studied LT crosstalk between myeloid cells and pulmonary epithelial cells. Monocytic cells (Mono Mac 6 cell line, primary dendritic cells) and eosinophils produced primarily LTC4 In coincubations of these myeloid cells and epithelial cells, LTD4 became a prominent product. LTC4 released from the myeloid cells was further transformed by the epithelial cells in a transcellular manner. Formation of LTD4 was rapid when catalyzed by γ-glutamyl transpeptidase (GGT)1 in the A549 epithelial lung cancer cell line, but considerably slower when catalyzed by GGT5 in primary bronchial epithelial cells. When A549 cells were cultured in the presence of IL-1β, GGT1 expression increased about 2-fold. Also exosomes from A549 cells contained GGT1 and augmented LTD4 formation. Serine-borate complex (SBC), an inhibitor of GGT, inhibited conversion of LTC4 to LTD4 Unexpectedly, SBC also upregulated translocation of 5-lipoxygenase (LO) to the nucleus in Mono Mac 6 cells, and 5-LO activity. Our results demonstrate an active role for epithelial cells in biosynthesis of LTD4, which may be of particular relevance in the lung.

Expression of inflammation/pain-related genes in the dorsal root ganglion following disc puncture in rats

PURPOSE

To determine the expression of inflammation- and pain-related genes at days 1 and 3 in the dorsal root ganglion (DRG) of rats with or without disc puncture, using real-time quantitative polymerase chain reaction (RT-qPCR) with the TaqMan low-density array (TLDA).

METHODS

53 female Sprague-Dawley rats were used. The left facet joint between L4 and L5 was removed, and the DRG and intervertebral disc between the vertebrae were exposed. The L4-5 intervertebral disc was punctured using a 0.4-mm diameter injection needle (disc puncture group) or left unpunctured (sham group). After one or 3 days, the 53 DRGs were harvested, frozen, and assessed for expression of inflammation-related genes. Total RNA was isolated from the DRGs. Expression of 119 genes related to inflammation and pain in the DRG after disc puncture were analysed using RT-qPCR with the TLDA.

RESULTS

Of the 95 inflammation-related genes, 78 genes were reliably detected. Two genes were significantly up-regulated: cysteinyl leukotriene receptor 1 (CYSLTR1) at day 3 and interleukin 2 receptor gamma (IL2RG) at day 1, and one gene was significantly down-regulated: phospholipase C beta 3 (PLCB3) at day 1. Of the 24 pain-related genes, 18 genes were reliably detected. Two genes were significantly up-regulated: nitric oxide synthase 1 (NOS1) at days 1 and 3 and 5-HT2A receptor (HTR2A) at day 1.

CONCLUSION

Disc puncture may elicit changes in the expression of a variety of genes. Gene expression profiling is a useful tool for detecting new potential pharmaceutical targets for spinal pain syndromes.

Cellular signalling of cysteinyl leukotriene type 1 receptor variants CysLT₁-G300S and CysLT₁-I206S

Cysteinyl-leukotrienes are pro-inflammatory lipid mediators, involved in allergic asthma, that bind the G-protein-coupled receptors CysLT1, CysLT2 and GPR99. A polymorphism in one of these receptors, CysLT1-G300S was strongly associated with atopy, whereas the CysLT1-I206S polymorphism was not. In the present work, our aim was to characterize these two variants by studying their cellular signalling. Cell surface expression of mutant receptors in transfected HEK-293 cells was comparable to that of the wild-type receptor. Compared to CysLT1-WT, production of inositol phosphates as well as IL-8 and IL-13 promoter transactivation in response to either LTD4 or LTC4 was significantly increased in CysLT1-G300S-transfected cells. Moreover, LTD4-induced phosphorylation of the signalling effector Erk, but not p38, p65 or c-Jun was higher in CysLT1-G300S-transfected cells. On the other hand, the variant CysLT1-I206S did not show a significant difference in its signal transduction compared to the wild-type receptor. Taken together, our results indicate that the variant CysLT1-G300S can induce a greater signal than the CysLT1-WT receptor, a feature that may be relevant to its association with atopy.

Pharmacological inhibition of eicosanoids and platelet-activating factor signaling impairs zymosan-induced release of IL-23 by dendritic cells

The engagement of the receptors for fungal patterns induces the expression of cytokines, the release of arachidonic acid, and the production of PGE2 in human dendritic cells (DC), but few data are available about other lipid mediators that may modulate DC function. The combined antagonism of leukotriene (LT) B4, cysteinyl-LT, and platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) inhibited IL23A mRNA expression in response to the fungal surrogate zymosan and to a lower extent TNFA (tumor necrosis factor-α) and CSF2 (granulocyte macrophage colony-stimulating factor) mRNA. The combination of lipid mediators and the lipid extract of zymosan-conditioned medium increased the induction of IL23A by LPS (bacterial lipopolysaccharide), thus suggesting that unlike LPS, zymosan elicits the production of mediators at a concentration enough for optimal response. Zymosan induced the release of LTB4, LTE4, 12-hydroxyeicosatetraenoic acid (12-HETE), and PAF C16:0. DC showed a high expression and detectable Ser663 phosphorylation of 5-lipoxygenase in response to zymosan, and a high expression and activity of LPCAT1/2 (lysophosphatidylcholine acyltransferase 1 and 2), the enzymes that incorporate acetate from acetyl-CoA into choline-containing lysophospholipids to produce PAF. Pharmacological modulation of the arachidonic acid cascade and the PAF receptor inhibited the binding of P-71Thr-ATF2 (activating transcription factor 2) to the IL23A promoter, thus mirroring their effects on the expression of IL23A mRNA and IL-23 protein. These results indicate that LTB4, cysteinyl-LT, and PAF, acting through their cognate G protein-coupled receptors, contribute to the phosphorylation of ATF2 and play a central role in IL23A promoter trans-activation and the cytokine signature induced by fungal patterns.

Enhanced cysteinyl-leukotriene type 1 receptor expression in T cells from house dust mite-allergic individuals following stimulation with Der p

In order to determine the potential for allergen to modulate T cell expression of the CysLT₁ receptor and responsiveness to leukotrienes, peripheral blood mononuclear cells from house dust mite-allergic or nonallergic individuals were incubated with D. pteronyssinus allergen (Der p). Baseline CysLT₁ expression was similar in both groups of donors, but Der p significantly enhanced CysLT₁ expression in CD4⁺ and CD8⁺ T cells of only allergic individuals and induced enhanced responsiveness of CD4⁺ T cells to LTD₄ in terms of calcium mobilisation. This effect was prevented by the CysLT₁ antagonist MK571. Der p also induced IL-4 and IL-10 production, and neutralizing antibody to IL-4 prevented both the enhanced CysLT₁ expression and the enhanced responsiveness of T cells to LTD₄ induced by Der p. In allergic individuals, Der p also induced T cell proliferation and a Th2-biased phenotype. Our data suggest that, in allergen-sensitized individuals, exposure to allergen can enhance T cell expression of CysLT₁ receptors through a mechanism involving IL-4 production. This, in turn, would induce CD4⁺ T cell responsiveness to cysteinyl-leukotrienes and Th2 cell activation.

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

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

Prostaglandin D₂: a dominant mediator of aspirin-exacerbated respiratory disease

BACKGROUND

Aspirin desensitization followed by high-dose aspirin therapy is routinely performed for patients with aspirin-exacerbated respiratory disease (AERD). Little is known about the contributions of mediators other than cysteinyl leukotrienes to aspirin reactions and to the therapeutic benefit of high-dose aspirin therapy.

OBJECTIVE

We investigated differences in urinary eicosanoid metabolite levels and blood eosinophil counts in patients with AERD who tolerate and those who fail aspirin desensitization and also in patients with AERD who were successfully treated with high-dose aspirin therapy.

METHODS

Twenty-nine patients with AERD were stratified into those who tolerated aspirin desensitization (group I) and those who did not (group II). Urine was analyzed for eicosanoid metabolites at baseline, during aspirin reactions, and during high-dose aspirin therapy. Blood was analyzed for cell differentials at baseline and during aspirin therapy.

RESULTS

Basal prostaglandin D2 metabolite (PGD-M; 13.6 ± 2.7 vs 7.0 ± 0.8 pmol/mg creatinine [Cr], P < .05) and thromboxane metabolite (TX-M; 1.4 ± 0.3 vs 0.9 ± 0.1 pmol/mg Cr, P < .01) levels were higher in group II than in group I. During aspirin reactions, PGD-M levels remained unchanged, whereas TX-M levels (0.7 ± 0.1 pmol/mg Cr, P = .07) tended to decrease in group I. In contrast, PGD-M levels increased dramatically in group II (61.3 ± 19.9 pmol/mg Cr, P < .05), whereas TX-M levels did not change. The decrease in FEV1 inversely correlated with basal urinary levels of both leukotriene E4 and PGD-M. Blood eosinophil and basophil levels increased and urinary PGD-M levels (2.2 ± 0.8 pmol/mg Cr, P < .001) decreased on 2 months of high-dose aspirin therapy in group I.

CONCLUSION

Failure to tolerate aspirin desensitization in a subset of patients with AERD is associated with prostaglandin D2 overproduction. The increase in blood eosinophil and basophil counts during high-dose aspirin therapy might reflect the functional consequences of decreased prostaglandin D2 release and the therapeutic benefit of aspirin.

The role of leukotrienes in allergic diseases

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

Evolutionary aspects of lipoxygenases and genetic diversity of human leukotriene signaling

Leukotrienes are pro-inflammatory lipid mediators, which are biosynthesized via the lipoxygenase pathway of the arachidonic acid cascade. Lipoxygenases form a family of lipid peroxidizing enzymes and human lipoxygenase isoforms have been implicated in the pathogenesis of inflammatory, hyperproliferative (cancer) and neurodegenerative diseases. Lipoxygenases are not restricted to humans but also occur in a large number of pro- and eucaryotic organisms. Lipoxygenase-like sequences have been identified in the three domains of life (bacteria, archaea, eucarya) but because of lacking functional data the occurrence of catalytically active lipoxygenases in archaea still remains an open question. Although the physiological and/or pathophysiological functions of various lipoxygenase isoforms have been studied throughout the last three decades there is no unifying concept for the biological importance of these enzymes. In this review we are summarizing the current knowledge on the distribution of lipoxygenases in living single and multicellular organisms with particular emphasis to higher vertebrates and will also focus on the genetic diversity of enzymes and receptors involved in human leukotriene signaling.

Caveolin-1 alters the pattern of cytoplasmic Ca2+ oscillations and Ca2+-dependent gene expression by enhancing leukotriene receptor desensitization

Cytoplasmic Ca²⁺ oscillations constitute a widespread signaling mode and are often generated in response to stimulation of G protein-coupled receptors that activate phospholipase C. In mast cells, repetitive Ca²⁺ oscillations can be evoked by modest activation of cysteinyl leukotriene type I receptors by the physiological trigger, leukotriene C₄. The Ca²⁺ oscillations arise from regenerative Ca²⁺ release from inositol 1,4,5-trisphosphate-sensitive stores followed by Ca²⁺ entry through store-operated Ca²⁺ channels, and the latter selectively activate the Ca²⁺-dependent transcription factor NFAT. The cysteinyl leukotriene type I receptors desensitize through negative feedback by protein kinase C, which terminates the oscillatory Ca²⁺ response. Here, we show that the scaffolding protein caveolin-1 has a profound effect on receptor-driven Ca²⁺ signals and downstream gene expression. Overexpression of caveolin-1 increased receptor-phospholipase C coupling, resulting in initially larger Ca²⁺ release transients of longer duration but which then ran down quickly. NFAT-activated gene expression, triggered in response to the Ca²⁺ signal, was also reduced by caveolin-1. Mutagenesis studies revealed that these effects required a functional scaffolding domain within caveolin-1. Mechanistically, the increase in Ca²⁺ release in the presence of caveolin-1 activated protein kinase C, which accelerated homologous desensitization of the leukotriene receptor and thereby terminated the oscillatory Ca²⁺ response. Our results reveal that caveolin-1 is a bimodal regulator of receptor-dependent Ca²⁺ signaling, which fine-tunes the spatial and temporal profile of the Ca²⁺ rise and thereby its ability to activate the NFAT pathway.

The Concise Guide to PHARMACOLOGY 2013/14: G protein-coupled receptors

The Concise Guide to PHARMACOLOGY 2013/14 provides concise overviews of the key properties of over 2000 human drug targets with their pharmacology, plus links to an open access knowledgebase of drug targets and their ligands (www.guidetopharmacology.org), which provides more detailed views of target and ligand properties. The full contents can be found at http://onlinelibrary.wiley.com/doi/10.1111/bph.12444/full. G protein-coupled receptors are one of the seven major pharmacological targets into which the Guide is divided, with the others being G protein-coupled receptors, ligand-gated ion channels, ion channels, catalytic receptors, nuclear hormone receptors, transporters and enzymes. These are presented with nomenclature guidance and summary information on the best available pharmacological tools, alongside key references and suggestions for further reading. A new landscape format has easy to use tables comparing related targets. It is a condensed version of material contemporary to late 2013, which is presented in greater detail and constantly updated on the website www.guidetopharmacology.org, superseding data presented in previous Guides to Receptors and Channels. It is produced in conjunction with NC-IUPHAR and provides the official IUPHAR classification and nomenclature for human drug targets, where appropriate. It consolidates information previously curated and displayed separately in IUPHAR-DB and the Guide to Receptors and Channels, providing a permanent, citable, point-in-time record that will survive database updates.

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.

The role of leukotrienes in immunopathogenesis of rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disorder of joints for which there is no strict cure. However, conventional medications can reduce inflammation, relieve pain, and slow joint damage. Leukotrienes are a family of paracrine agents derived from oxidative metabolism of arachidonic acid. Synthesis of lipid mediators and subsequent induction of receptor activity are tightly regulated under normal physiological conditions, so that enzyme and/or receptor dysfunction can lead to a variety of clinical signs and symptoms of disease, such as local pain and tissue edema. In these tissues, immunocompetent cells accumulate at the site of injury, contributing to tissue damage and perpetuation of the disease process. Leukotrienes (often leukotriene B4) as potent chemotactic agents can provoke most signs and symptoms in rheumatoid arthritis by initiating, coordinating, sustaining, and amplifying the inflammatory response, through recruitment of leukocytes. A number of studies have reported that pharmacological modulation in this field can significantly attenuate clinical manifestations associated with different inflammatory pathologies.

Eosinophil recruitment and activation: the role of lipid mediators

Eosinophils are effector cells that migrate toward several mediators released at inflammatory sites to perform their multiple functions. The mechanisms driving eosinophil selective accumulation in sites of allergic inflammation are well-established and involve several steps controlled by adhesion molecules, priming agents, chemotactic, and surviving factors. Even though the majority of studies focused on role of protein mediators like IL-5 and eotaxins, lipid mediators also participate in eosinophil recruitment and activation. Among the lipid mediators with distinguish eosinophil recruitment and activation capabilities are platelet activating factor and the eicosanoids, including leukotriene B₄, cysteinyl leukotrienes, and prostaglandin D₂. In this review, we focused on the role of these four lipid mediators in eosinophil recruitment and activation, since they are recognized as key mediators of eosinophilic inflammatory responses.

G protein-coupled receptor crosstalk and signaling in hematopoietic stem and progenitor cells

A variety of G protein-coupled receptors (GPCRs) is expressed in hematopoietic stem and progenitor cells (HPCs), including the chemokine receptor CXCR4, the leukotriene receptor CysLT1, the sphingosine 1-phosphate receptor S1P1, the cannabinoid receptor CB2, and the complement receptor C3aR. While the role of CXCR4 in stem cell homing is largely established, the function of the other GPCRs expressed in HPCs is only partially understood. CXCR4 and CysLT1 inhibit their own activation after ligand binding (homologous desensitization). Stimulation of S1P1 or C3aR has been shown to activate CXCR4 in HPCs that may sensitize CXCR4-dependent stem cell homing. In contrast, activation of CXCR4 results in a loss of CysLT1 function, which is most likely mediated by protein kinase C (PKC) signaling (heterologous desensitization) and could explain the ineffectiveness of CysLT1 antagonists to mobilize HPCs in vivo. Further characterization of GPCR crosstalk will allow a better understanding of HPC trafficking.

Tyrosine urea muscarinic acetylcholine receptor antagonists: achiral quaternary ammonium groups

Tyrosine ureas had been identified as potent muscarinic receptor antagonists with promising in vivo activity. Controlling the stereochemistry of the chiral quaternary ammonium center had proved to be a serious issue for this series, however. Herein we describe the preparation and SAR of tyrosine urea antagonists containing achiral quaternary ammonium centers. The most successful such moiety was the 2-methylimidazo[2,1-b][1,3]thiazol-7-ium group which yielded highly potent antagonists with long duration of action in an inhaled animal model of bronchoconstriction.