5-Oxo-eicosanoids are potent eosinophil chemotactic factors. Functional characterization and structural requirements

Baseline Elevations of Leukotriene Metabolites and Altered Plasmalogens Are Prognostic Biomarkers of Plaque Progression in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is associated with an increased incidence of acute and chronic cardiovascular disease as compared to the general population. This study uses a comprehensive metabolomic screen of baseline sera from lupus patients to identify metabolites that predict future carotid plaque progression, following 8–9 years of follow-up. Nine patients had SLE without plaque progression, 8 had SLE and went on to develop atherosclerotic plaques (SLE^PP), and 8 patients were controls who did not have SLE. The arachidonic acid pathway metabolites, leukotriene B4 (LTB4) and 5-hydroxyeicosatetraenoic acid (5-HETE), and the oxidized lipids 9/13-hydroxyoctodecadienoic acid (HODE) were found to be significantly altered (p < 0.05 and fold-change >2) in SLE^PP patients compared to SLE patients without plaque progression. SLE^PP patients also exhibited significantly altered levels of branched chain amino acid (BCAA) metabolites and plasmalogens compared to the non-SLE controls. Taken together with the rich literature on these metabolites, these findings suggest that the identified metabolites may not only be prognostic of cardiovascular disease development in SLE patients, but they may also be active drivers of atheroma formation. Early identification of these high risk SLE patients may help institute preventive measures early in the disease course.

The role of 15 lipoxygenase 1 in asthma comes into focus

IL-4– and IL-13–driven epithelial cell expression of 15 lipoxygenase 1 (15LO1) is a consistent feature of eosinophil-dominated asthma known as type 2–high (T2-high) asthma. The abundant soluble products of arachidonic acid (AA) metabolized by 15LO1 reflect a high level of enzymatic activity in asthma and chronic rhinosinusitis. However, the precise role of 15LO1 and its products in disease pathogenesis remains enigmatic. In this issue of the JCI, Nagasaki and colleagues demonstrate a role for 15LO1 in controlling redox balance and epithelial homeostasis in T2-high asthma by metabolizing AA that is esterified to membrane phospholipids. The findings may pave the way toward the development of 15LO1 inhibitors as asthma treatments.

Targeting the OXE receptor as a potential novel therapy for asthma

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is an arachidonic acid metabolite formed by oxidation of the 5-lipoxygenase (5-LO) product 5S-hydroxy-6,8,11,14-eicosatetraenoic acid (5S-HETE) by the NADP+-dependent enzyme 5-hydroxyeicosanoid dehydrogenase. It is the only 5-LO product with appreciable chemoattractant activity for human eosinophils. Its actions are mediated by the selective OXE receptor, which is highly expressed on eosinophils, basophils, neutrophils and monocytes. Orthologs of the OXER1 gene, which encodes this receptor, are found in many species except for rodents. Intradermal injection of 5-oxo-ETE into humans and monkeys elicits eosinophil infiltration into the skin, raising the possibility that it may play a pathophysiological role in eosinophilic diseases. To investigate this and possibly identify a novel therapy we sought to prepare synthetic antagonists that could selectively block the OXE receptor. We synthesized a series of indole-based compounds bearing substituents that mimic the regions of 5-oxo-ETE that are required for biological activity, which we modified to reduce metabolism. The most potent of these OXE receptor antagonists is S-Y048, which is a potent inhibitor of 5-oxo-ETE-induced calcium mobilization (IC50, 20 pM) and has a long half-life following oral administration. S-Y048 inhibited allergen-induced eosinophil infiltration into the skin of rhesus monkeys that had been experimentally sensitized to house dust mite and inhibited pulmonary inflammation resulting from challenge with aerosolized allergen. These data provide the first evidence for a pathophysiological role for 5-oxo-ETE in mammals and suggest that potent and selective OXE receptor antagonists such as S-Y048 may be useful therapeutic agents in asthma and other eosinophilic diseases.

Novel highly potent OXE receptor antagonists with prolonged plasma lifetimes that are converted to active metabolites in vivo in monkeys

BACKGROUND AND PURPOSE

The 5-lipoxygenase product 5-oxo-6E,8Z,11Z,14Z-eicosatetraenoic acid (5-oxo-ETE), acting through the OXE receptor, is a potent eosinophil chemoattractant that may be an important proinflammatory mediator in eosinophilic diseases such as asthma. We previously identified a series of indole-based OXE receptor antagonists that rapidly appear in the blood following oral administration but have limited lifetimes. The objective of this study was to increase the potency and plasma half-lives of these compounds and thereby identify the optimal candidate for future preclinical studies in monkeys, as rodents do not have an OXE receptor orthologue.

EXPERIMENTAL APPROACH

We synthesized a series of substituted phenylalkyl indoles and compared their antagonist potencies, pharmacokinetics, and metabolism to those of our earlier compounds. The potencies of some of their metabolites were also investigated.

KEY RESULTS

Among the compounds tested, the S-enantiomer of the m-chlorophenyl compound (S-Y048) was the most potent, with an pIC50 of about 10.8 for inhibition of 5-oxo-ETE-induced calcium mobilization in human neutrophils. When administered orally to cynomolgus monkeys, S-Y048 rapidly appeared in the blood and had a half-life in plasma of over 7 hr, considerably longer than any of the other OXE analogues tested. A major hydroxylated metabolite, with a potency close to that of its precursor, was identified in plasma.

CONCLUSION AND IMPLICATIONS

Because of its highly potent antagonist activity and its long lifetime in vivo, S-Y048 may be a useful anti-inflammatory agent for the treatment of eosinophilic diseases such as asthma, allergic rhinitis, and atopic dermatitis.

Synthesis, molecular modelling studies and biological evaluation of new oxoeicosanoid receptor 1 agonists

The oxoeicosanoid receptor 1 (OXER1) is a member of the G-protein coupled receptors (GPCR) family, and is involved in inflammatory processes and oncogenesis. As such it is an attractive target for pharmacological intervention. The present study aimed to shed light on the molecular fundaments of OXER1 modulation using chemical probes structurally related to the natural agonist 5-oxo-ETE. In a first step, 5-oxo-ETE and its closely related derivatives (5-oxo-EPE and 4-oxo-DHA) were obtained by conducting concise and high-yielding syntheses. The biological activity of obtained compounds was assessed in terms of potency (EC₅₀) and efficacy (E_max) for arrestin recruitment. Finally, molecular modelling and simulation were used to explore binding characteristics of 5-oxo-ETE and derivatives with the aim to rationalize biological activity. Our data suggest that the tested 5-oxo-ETE derivatives (i) insert quickly into the membrane, (ii) access the receptor via transmembrane helices (TMs) 5 and 6 from the membrane side and (iii) drive potency and efficacy by differential interaction with TM5 and 7. Most importantly, we found that the methyl ester of 5-oxo-ETE (1a) showed even a higher maximum response than the natural agonist (1). In contrast, shifting the 5-oxo group into position 4 results in inactive compounds (4-oxo DHA compounds (3) and (3a)). All in all, our study provides relevant structural data that help understanding better OXER1 functionality and its modulation. The structural information presented herein will be useful for designing new lead compounds with desired signalling profiles.

5-Oxo-ETE from Nasal Epithelial Cells Upregulates Eosinophil Cation Protein by Eosinophils in Nasal Polyps in vitro

BACKGROUND

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a potent eosinophil chemoattractant and activator that is synthesized not only in inflammatory cells but also in bronchial epithelial cells. The purpose of this study is to clarify whether 5-oxo-ETE can promote the production of eosinophil cation protein (ECP) by eosinophils in nasal polyps (NP) in vitro, and whether normal nasal epithelial cells can produce this lipid mediator in response to oxidative stress.

MATERIALS AND METHODS

Nasal biopsy samples were obtained from normal subjects or subjects with chronic rhinosinusitis with NP. The infiltration of eosinophil in NP was detected and cultured. After that, concentrations of ECP in eosinophil and NP cultures were evaluated after the treatment of 5-oxo-ETE or 5-oxo-ETE + its receptor (OXER) antagonist, pertussis toxin (PT). Then we studied the synthesis of 5-oxo-ETE after H2O2 stimulation by normal nasal epithelial cells and by epithelial cells of NP alone in the cultures, and also determined the OXER expression in NP.

RESULTS

The number of infiltrative eosinophils in NP was increased. The ECP levels in eosinophil and NP cultures were enhanced after the administration of 5-oxo-ETE, and decreased by the PT treatment. 5-Oxo-ETE was upregulated in the cultures of nasal epithelial cells in the presence of H2O2 and of NP epithelial cells alone. The OXER was expressed in inflammatory cells, and not in epithelial cells.

CONCLUSION

5-Oxo-ETE produced by nasal epithelial cells may play a role in the formation and development of NP.

In vivo α-hydroxylation of a 2-alkylindole antagonist of the OXE receptor for the eosinophil chemoattractant 5-oxo-6,8,11,14-eicosatetraenoic acid in monkeys

We have developed a selective indole antagonist (230) targeting the OXE receptor for the potent eosinophil chemoattractant 5-oxo-ETE (5-oxo-6,8,11,14-eicosatetraenoic acid), that may be useful for the treatment of eosinophilic diseases such as asthma. In previous studies we identified ω2-oxidation of the hexyl side chain of racemic 230 as a major metabolic route in monkeys, but also obtained evidence for another pathway that appeared to involve hydroxylation of the hexyl side chain close to the indole. The present study was designed to investigate the metabolism of the active S-enantiomer of 230 (S230) and to identify the novel hydroxy metabolite and its chirality. Following oral administration, S230 rapidly appeared in the blood along with metabolites formed by a novel and highly stereospecific α-hydroxylation pathway, resulting in the formation of αS-hydroxy-S230. The chirality of α-hydroxy-S230 was determined by the total synthesis of the relevant diastereomers. Of the four possible diastereomers of α-hydroxy-230 only αS-hydroxy-S230 has significant OXE receptor antagonist activity and only this diastereomer was found in significant amounts in blood following oral administration of S230. Other novel metabolites of S230 identified in plasma by LC-MS/MS were αS,ω2-dihydroxy-S230 and glucuronides of S230 and ω2-hydroxy-S230. Thus the alkyl side chain of S230, which is essential for its antagonist activity, is also the major target of the metabolic enzymes that terminate its antagonist activity. Modification of this side chain might result in the development of related antagonists with improved metabolic stability and efficacy.

Eosinophil transendothelial migration induced by the bronchoalveolar lavage fluid of acute eosinophilic pneumonia

BACKGROUND AND OBJECTIVE

Acute eosinophilic pneumonia (AEP) is characterized by a massive pulmonary infiltration of eosinophils. Mechanisms regulating the selective accumulation of eosinophils in AEP have not been fully established. The objective of this study was to evaluate the mechanisms of eosinophil accumulation in alveolar spaces through examination of bronchoalveolar lavage fluid (BALF) from AEP patients (AEP-BALF).

METHODS

Eosinophils were isolated from the blood of healthy subjects and were placed on a human pulmonary microvascular endothelial cell monolayer cultured on Transwell filters (Coster, Cambridge, MA, USA). A saline control solution or BALF from patients with AEP, sarcoidosis or hypersensitivity pneumonitis was applied to the lower compartment, and the transendothelial migration of the eosinophils was evaluated. The concentrations of cytokines and chemokines in BALF were also measured.

RESULTS

Transmigration of eosinophils across endothelial cells was only induced by the AEP-BALF. This transmigration was blocked by anti-β₂ integrin mAb. The concentrations of eotaxin-2 and monocyte chemotactic protein (MCP)-4, which are CC chemokine receptor (CCR) 3 ligands, were elevated in the AEP-BALF, and anti-CCR3 mAb or anti-MCP-4 mAb inhibited the AEP-BALF-induced transmigration of eosinophils. Furthermore, the concentration of leukotriene (LT) B₄ was increased in the AEP-BALF, and an LTB₄ receptor antagonist partially suppressed the AEP-BALF-induced transmigration of eosinophils.

CONCLUSION

These findings suggest that CCR3 ligands including eotaxin-2 and MCP-4, and LTB₄ play a role in the accumulation of eosinophils in AEP.

Cross-Talk between Cancer Cells and the Tumour Microenvironment: The Role of the 5-Lipoxygenase Pathway

5-lipoxygenase is an enzyme responsible for the synthesis of a range of bioactive lipids signalling molecules known collectively as eicosanoids. 5-lipoxygenase metabolites such as 5-hydroxyeicosatetraenoic acid (5-HETE) and a number of leukotrienes are mostly derived from arachidonic acid and have been shown to be lipid mediators of inflammation in different pathological states including cancer. Upregulated 5-lipoxygenase expression and metabolite production is found in a number of cancer types and has been shown to be associated with increased tumorigenesis. 5-lipoxygenase activity is present in a number of diverse cell types of the immune system and connective tissue. In this review, we discuss potential routes through which cancer cells may utilise the 5-lipoxygenase pathway to interact with the tumour microenvironment during the development and progression of a tumour. Furthermore, immune-derived 5-lipoxygenase signalling can drive both pro- and anti-tumour effects depending on the immune cell subtype and an overview of evidence for these opposing effects is presented.

Biosynthesis and actions of 5-oxoeicosatetraenoic acid (5-oxo-ETE) on feline granulocytes

The 5-lipoxygenase product 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is the most powerful human eosinophil chemoattractant among lipid mediators and could play a major pathophysiological role in eosinophilic diseases such as asthma. Its actions are mediated by the OXE receptor, orthologs of which are found in many species from humans to fish, but not rodents. The unavailability of rodent models to examine the pathophysiological roles of 5-oxo-ETE and the OXE receptor has substantially hampered progress in this area. As an alternative, we have explored the possibility that the cat could serve as an appropriate animal model to investigate the role of 5-oxo-ETE. We found that feline peripheral blood leukocytes synthesize 5-oxo-ETE and that physiologically relevant levels of 5-oxo-ETE are present in bronchoalveolar lavage fluid from cats with experimentally induced asthma. 5-Oxo-ETE (EC50, 0.7nM) is a much more potent activator of actin polymerization in feline eosinophils than various other eicosanoids, including leukotriene (LT) B4 and prostaglandin D2. 5-Oxo-ETE and LTB4 induce feline leukocyte migration to similar extents at low concentrations (1nM), but at higher concentrations the response to 5-oxo-ETE is much greater. Although high concentrations of selective human OXE receptor antagonists blocked 5-oxo-ETE-induced actin polymerization in feline granulocytes, their potencies were about 200 times lower than for human granulocytes. We conclude that feline leukocytes synthesize and respond to 5-oxo-ETE, which could potentially play an important role in feline asthma, a common condition in this species. The cat could serve as a useful animal model to investigate the pathophysiological role of 5-oxo-ETE.

Biosynthesis, biological effects, and receptors of hydroxyeicosatetraenoic acids (HETEs) and oxoeicosatetraenoic acids (oxo-ETEs) derived from arachidonic acid

Arachidonic acid can be oxygenated by a variety of different enzymes, including lipoxygenases, cyclooxygenases, and cytochrome P450s, and can be converted to a complex mixture of oxygenated products as a result of lipid peroxidation. The initial products in these reactions are hydroperoxyeicosatetraenoic acids (HpETEs) and hydroxyeicosatetraenoic acids (HETEs). Oxoeicosatetraenoic acids (oxo-ETEs) can be formed by the actions of various dehydrogenases on HETEs or by dehydration of HpETEs. Although a large number of different HETEs and oxo-ETEs have been identified, this review will focus principally on 5-oxo-ETE, 5S-HETE, 12S-HETE, and 15S-HETE. Other related arachidonic acid metabolites will also be discussed in less detail. 5-Oxo-ETE is synthesized by oxidation of the 5-lipoxygenase product 5S-HETE by the selective enzyme, 5-hydroxyeicosanoid dehydrogenase. It actions are mediated by the selective OXE receptor, which is highly expressed on eosinophils, suggesting that it may be important in eosinophilic diseases such as asthma. 5-Oxo-ETE also appears to stimulate tumor cell proliferation and may also be involved in cancer. Highly selective and potent OXE receptor antagonists have recently become available and could help to clarify its pathophysiological role. The 12-lipoxygenase product 12S-HETE acts by the GPR31 receptor and promotes tumor cell proliferation and metastasis and could therefore be a promising target in cancer therapy. It may also be involved as a proinflammatory mediator in diabetes. In contrast, 15S-HETE may have a protective effect in cancer. In addition to GPCRs, higher concentration of HETEs and oxo-ETEs can activate peroxisome proliferator-activated receptors (PPARs) and could potentially regulate a variety of processes by this mechanism. This article is part of a Special Issue entitled "Oxygenated metabolism of PUFA: analysis and biological relevance".

Update on leukotriene, lipoxin and oxoeicosanoid receptors: IUPHAR Review 7

The endogenous ligands for the LT, lipoxin (LX) and oxoeicosanoid receptors are bioactive products produced by the action of the lipoxygenase family of enzymes. The LT receptors BLT1 and BLT2 , are activated by LTB4 and the CysLT1 and CysLT2 receptors are activated by the cysteinyl-LTs, whereas oxoeicosanoids exert their action through the OXE receptor. In contrast to these pro-inflammatory mediators, LXA4 transduces responses associated with the resolution of inflammation through the receptor FPR2/ALX (ALX/FPR2). The aim of the present review is to give a state of the field on these receptors, with focus on recent important findings. For example, BLT1 receptor signalling in cancer and the dual role of the BLT2 receptor in pro- and anti-inflammatory actions have added more complexity to lipid mediator signalling. Furthermore, a cross-talk between the CysLT and P2Y receptor systems has been described, and also the presence of novel receptors for cysteinyl-LTs, such as GPR17 and GPR99. Finally, lipoxygenase metabolites derived from ω-3 essential polyunsaturated acids, the resolvins, activate the receptors GPR32 and ChemR23. In conclusion, the receptors for the lipoxygenase products make up a sophisticated and tightly controlled system of endogenous pro- and anti-inflammatory signalling in physiology and pathology.

Regulation of 5-oxo-ETE synthesis by nitric oxide in human polymorphonuclear leucocytes upon their interaction with zymosan and Salmonella typhimurium

In the present study we have presented data on the regulation of LT (leukotriene) and 5-oxo-ETE (5-oxo-6,8,11,14-eicosatetraenoic acid) syntheses in human neutrophils upon interaction with OZ (opsonized zymosan) or Salmonella typhimurium. Priming of neutrophils with PMA (phorbol 12-myristate 13-acetate) and LPS (lipopolysaccharide) elicits 5-oxo-ETE formation in neutrophils exposed to OZ, and the addition of AA (arachidonic acid) significantly increases 5-oxo-ETE synthesis. We found that NO (nitric oxide)-releasing compounds induce 5-oxo-ETE synthesis in neutrophils treated with OZ or S. typhimurium. Exposure of neutrophils to zymosan or bacteria in the presence of the NO donor DEA NONOate (1,1-diethyl-2-hydroxy-2-nitroso-hydrazine sodium) considerably increased the conversion of endogenously formed 5-HETE (5S-hydroxy-6,8,11,14-eicosatetraenoic acid) to 5-oxo-ETE. To our knowledge, this study is the first to demonstrate that NO is a potent regulator of 5-oxo-ETE synthesis in human polymorphonuclear leucocytes exposed to Salmonella typhimurium and zymosan.

Nitric oxide significantly increased 5-oxo-ETE formation in neutrophils. 5-oxo-ETE is a key 5-lipoxygenase metabolite in human polymorphonuclear leucocytes exposed to NO upon interaction with opsonized zymosan or Salmonella typhimurium.

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.

The eosinophil chemoattractant 5-oxo-ETE and the OXE receptor

5-Oxo-ETE (5-oxo-6,8,11,14-eicosatetraenoic acid) is formed from the 5-lipoxygenase product 5-HETE (5S-hydroxy-6,8,11,14-eicosatetraenoic acid) by 5-hydroxyeicosanoid dehydrogenase (5-HEDH). The cofactor NADP(+) is a limiting factor in the synthesis of 5-oxo-ETE because of its low concentrations in unperturbed cells. Activation of the respiratory burst in phagocytic cells, oxidative stress, and cell death all dramatically elevate both intracellular NADP(+) levels and 5-oxo-ETE synthesis. 5-HEDH is widely expressed in inflammatory, structural, and tumor cells. Cells devoid of 5-lipoxygenase can synthesize 5-oxo-ETE by transcellular biosynthesis using inflammatory cell-derived 5-HETE. 5-Oxo-ETE is a chemoattractant for neutrophils, monocytes, and basophils and promotes the proliferation of tumor cells. However, its primary target appears to be the eosinophil, for which it is a highly potent chemoattractant. The actions of 5-oxo-ETE are mediated by the highly selective OXE receptor, which signals by activating various second messenger pathways through the release of the βγ-dimer from Gi/o proteins to which it is coupled. Because of its potent effects on eosinophils, 5-oxo-ETE may be an important mediator in asthma, and, because of its proliferative effects, may also contribute to tumor progression. Selective OXE receptor antagonists, which are currently under development, could be useful therapeutic agents in asthma and other allergic diseases.

5-Oxo-ETE receptor antagonists

5-Oxo-ETE is the most powerful eosinophil chemoattractant among lipid mediators. Eosinophil infiltration into the lungs of asthmatics may be responsible for the late phase of inflammatory asthma. We have designed and synthesized a 5-oxo-ETE receptor antagonist, the purpose of which is to prevent eosinophil migration to the lung during an asthma attack and thereby reduce asthma symptoms.

C20-trifluoro-5-oxo-ETE: a metabolically stable 5-oxo-ETE derivative

The total synthesis of C(20)-trifluoro-6(E),8(Z),11(Z),14(Z) 5-oxo-ETE is reported. This compound was designed as an ω-oxidation-resistant analog of 5-oxo-ETE that would be resistant to metabolism. The trifluoro derivative of 5-oxo-ETE stimulated calcium mobilization in neutrophils and desensitized these cells to subsequent exposure to 5-oxo-ETE.

5-oxo-15-HETE: total synthesis and bioactivity

The first total synthesis of 6(E),8(Z),11(Z),13(E) 5-oxo-15-HETE 4 was accomplished. The synthetic material was evaluated with calcium mobilization assay and compared with 5-oxo-ETE the natural ligand for the OXE receptor.

Phytoceuticals: the new 'physic garden' for asthma and chronic obstructive pulmonary disease

Phytoceuticals (non-nutritional but beneficial plant chemicals) merit investigation as pharmacotherapy for asthma and chronic obstructive pulmonary disease (COPD). Although asthma is mostly treated adequately, COPD is not. Thus, there is a need for new drugs with improved therapeutic benefit, especially in COPD. Recent interest in herbal remedies has redirected attention towards plants as sources of improved treatments for lung disease. Phytoceuticals from a variety of plants and plant products, including butterbur, English ivy, apples, chocolate, green tea and red wine, demonstrate broad-spectrum pharmacotherapeutic activities that could be exploited in the clinic. Well-designed clinical trials are required to determine whether these beneficial activities are reproduced in patients, with the prospect that phytoceuticals are the new physic garden for asthma and COPD.

5-Oxo-ETE and the OXE receptor

5-Oxo-ETE is a product of the 5-lipoxygenase pathway that is formed by the oxidation of 5-HETE by 5-hydroxyeicosanoid dehydrogenase (5-HEDH). 5-HEDH is a microsomal NADP(+)-dependent enzyme that is highly selective for 5-HETE. 5-Oxo-ETE synthesis is regulated by intracellular NADP(+) levels and is dramatically increased under conditions that favor oxidation of NADPH to NADP(+) such as oxidative stress and the respiratory burst in phagocytic cells. 5-Oxo-ETE is a potent chemoattractant for eosinophils and has similar effects on neutrophils, basophils and monocytes. It elicits infiltration of eosinophils and, to a lesser extent, neutrophils into the skin after intradermal injection in humans. It also promotes the survival of tumor cells and has been shown to block the induction of apoptosis by 5-LO inhibitors. 5-Oxo-ETE acts by the G(i/o)-coupled OXE receptor, which was also known as TG1019, R527 and hGPCR48. Although the pathophysiological role of 5-oxo-ETE is not well understood, it may play important roles in asthma and allergic diseases, cancer, and cardiovascular disease. The availability of a selective antagonist would help to clarify the role of 5-oxo-ETE and may be of therapeutic benefit.

Aromatic D-amino acids act as chemoattractant factors for human leukocytes through a G protein-coupled receptor, GPR109B

GPR109B (HM74) is a putative G protein-coupled receptor (GPCR) whose cognate ligands have yet to be characterized. GPR109B shows a high degree of sequence similarity to GPR109A, another GPCR that was identified as a high-affinity nicotinic acid (niacin) receptor. However, the affinity of nicotinic acid to GPR109B is very low. In this study, we found that certain aromatic D-amino acids, including D-phenylalanine, D-tryptophan, and the metabolite of the latter, D-kynurenine, decreased the activity of adenylate cyclase in cells transfected with GPR109B cDNA through activation of pertussis toxin (PTX)-sensitive G proteins. These D-amino acids also elicited a transient rise of intracellular Ca(2+) level in cells expressing GPR109B in a PTX-sensitive manner. In contrast, these D-amino acids did not show any effects on cells expressing GPR109A. We found that the GPR109B mRNA is abundantly expressed in human neutrophils. D-phenylalanine and D-tryptophan induced a transient increase of intracellular Ca(2+) level and a reduction of cAMP levels in human neutrophils. Furthermore, knockdown of GPR109B by RNA interference inhibited the D-amino acids-induced decrease of cellular cAMP levels in human neutrophils. These D-amino acids induced chemotactic activity of freshly prepared human neutrophils. We also found that D-phenylalanine and D-tryptophan induced chemotactic responses in Jurkat cells transfected with the GPR109B cDNA but not in mock-transfected Jurkat cells. These results suggest that these aromatic D-amino acids elicit a chemotactic response in human neutrophils via activation of GPR109B.

Relaxing effects of 5-oxo-ETE on human bronchi involve BKCa channel activation

The present study investigated the ability of 5-oxo-EicosaTetraEnoic acid (5-oxo-ETE) for modulating airway smooth muscle (ASM) tone in human bronchi. 5-Oxo-ETE induced a concentration-dependent relaxing effect on human bronchi pre-contracted with methacholine (MCh) and arachidonic acid (AA). This relaxing response was highly sensitive to Iberiotoxin (IbTx), a large conducting Ca(2+)-activated K(+) channel (BK(Ca)) inhibitor. Furthermore, microelectrode measurements revealed that 5-oxo-ETE (0.1-10 microM) hyperpolarizes the membrane potential of human bronchial ASM cells. These hyperpolarizing effects were also inhibited in the presence of 10nM IbTx. Lastly, 5-oxo-ETE was shown to directly activate reconstituted BK(Ca) channels derived from human airway smooth muscles. In summary, the 5-oxo-ETE eicosanoid activates a specific K(+) conductance, involved in membrane hyperpolarization, which in turn reduces Ca(2+) entry and facilitates relaxation of smooth muscle cells.

Airway epithelial cells synthesize the lipid mediator 5-oxo-ETE in response to oxidative stress

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a potent eosinophil chemoattractant that is synthesized from the 5-lipoxygenase product 5S-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) by the NADP+-dependent enzyme 5-hydroxyeicosanoid dehydrogenase (5-HEDH), previously reported only in inflammatory cells. Because of their critical location at the interface of the lung with the external environment, we sought to determine whether epithelial cells could also synthesize this substance. We found that HEp-2, T84, A549, and BEAS-2B cells all synthesize 5-oxo-ETE from 5-HETE in amounts comparable to leukocytes. The epithelial dehydrogenase is localized in the microsomal fraction, requires NADP+, and is selective for the S-isomer of 5-HETE, suggesting that it is identical to leukocyte 5-HEDH. Normal human bronchial epithelial cells have an even greater capacity to synthesize 5-oxo-ETE. H2O2 dramatically stimulates its synthesis in association with increased levels of intracellular GSSG and NADP+. These responses were all blocked by removal of GSH/GSSG with N-ethylmaleimide, suggesting that H2O2 stimulates 5-oxo-ETE synthesis by raising NADP+ levels through activation of the GSH redox cycle. Airway smooth muscle cells can also synthesize 5-oxo-ETE, but to a lesser extent. These results suggest that epithelial cells may be a major source of 5-oxo-ETE under conditions of oxidative stress, which may contribute to eosinophil infiltration in allergic diseases.

Metabolism of 5-hydroxy-6,8,11,14-eicosatetraenoic acid by human endothelial cells

There is increasing evidence that proinflammatory products of the 5-lipoxygenase pathway play an important role in cardiovascular disease. In the present study, we found that human endothelial cells rapidly oxidize the 5-lipoxygenase product 5S-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) to 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), a potent chemoattractant for myeloid cells. 5-Oxo-ETE synthesis is strongly stimulated by oxidative stress. This effect is enhanced following inhibition of the pentose phosphate pathway with dehydroepiandrosterone and is mimicked by diamide, which oxidizes intracellular GSH to GSSG. Conversely, it is blocked by depletion of intracellular GSH/GSSG. The kinetics of H2O2-induced 5-oxo-ETE synthesis by endothelial cells correlate well with changes in the intracellular levels of GSSG and NADP+. These results suggest that exposure of the endothelium to oxidative stress and inflammation could result in the synthesis of 5-oxo-ETE, which could then induce the infiltration of inflammatory cells into the tissue.

Hierarchy of eosinophil chemoattractants: role of p38 mitogen-activated protein kinase

Several chemoattractants can regulate the recruitment of eosinophils to sites of inflammation, but the hierarchy among them is unknown. We observed here that eosinophil chemotaxis towards eotaxin or 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) was amplified up to sixfold in the presence of prostaglandin (PG) D2. This effect was only seen in eosinophils, and not in neutrophils or basophils. Pretreatment with the chemoattractant receptor-homologous molecule expressed on TH2 cells (CRTH2) antagonist ramatroban prevented the PGD2 enhancement of eosinophil migrations. In contrast, eotaxin or 5-oxo-ETE inhibited the migration of eosinophils towards PGD2. 5-oxo-ETE enhanced the chemotaxis to eotaxin, while eotaxin had no effect on 5-oxo-ETE-induced migration. 5-oxo-ETE induced the phosphorylation of p38 mitogen-activated protein kinase, and inhibition of p38 mitogen-activated protein kinase by SB-202190 converted the effect of 5-oxo-ETE on the chemotaxis to PGD2 from inhibition to enhancement. The presence of blood or plasma markedly decreased the sensitivity of eosinophils to eotaxin or 5-oxo-ETE, while responses to PGD2 were unaltered. In conclusion, PGD2 might be an initial chemoattractant, since it maintains its potency in the circulation and augments the responsiveness of eosinophils to other chemoattractants. In contrast, eotaxin seems to be an end-point chemoattractant, since it has reduced efficacy in blood and is capable of down-modulating eosinophil responsiveness to other chemoattractants.

Chemotaxis of human peripheral blood eosinophils to 2-arachidonoylglycerol: comparison with other eosinophil chemoattractants

BACKGROUND

2-Arachidonoylglycerol (2-AG), an endogenous ligand for the cannabinoid receptors (CB1 and CB2), has been shown to exhibit a variety of cannabimimetic activities in vitro and in vivo. Recently, we found that human eosinophilic leukemia EoL-1 cells and human peripheral blood eosinophils express the CB2 receptor. We also found that 2-AG induces the migration of these cells in a CB2 receptor-dependent manner. In this study, we investigated whether the 2-AG-induced migration of human eosinophils is due to chemotaxis or chemokinesis. We also compared the ability of 2-AG to induce the migration of eosinophils with those of other eosinophil chemoattractants.

METHODS

Eosinophils were separated from the peripheral blood of healthy donors. The migration of eosinophils to various stimulants was examined using Transwell inserts. In view of the fact that 2-AG is rapidly metabolized by cells, we employed 2-AG ether, an ether-linked nonhydrolyzable analog of 2-AG, instead of 2-AG to determine whether the 2-AG-induced migration is due to chemotaxis or chemokinesis.

RESULTS

2-AG ether induced the migration of human eosinophils, like 2-AG. The 2-AG ether-induced migration was reduced by the coincubation of eosinophils with 2-AG ether in the upper compartment of the Transwell inserts, indicating that the migration is attributable to chemotaxis. The concentration of 2-AG required to induce the eosinophil migration appears to be pathophysiologically relevant, although the order of the pharmacologically effective concentration of 2-AG was approximately ten times lower than those of platelet-activating factor, RANTES and eotaxin.

CONCLUSION

These results strongly suggest that 2-AG is involved in the infiltration of eosinophils during allergic inflammation.

5-Oxo-Eicosatetraenoic Acid-Induced Chemotaxis: Identification of a Responsible Receptor hGPCR48 and Negative Regulation by G Protein G12/13

While screening genes encoding G protein-coupled receptors (GPCRs) in the human genome, we and other groups have identified a GPCR named hGPCR48 as a high affinity receptor for 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), which is arachidonic acid metabolite and an endogenous chemoattractant for granulocytes. Using Chinese hamster ovary (CHO) cells stably expressing hGPCR48, we show here that activation of the receptor causes the chemotaxis of the cells toward 5-oxo-ETE. We also show that the chemotaxis of human granulocytes toward 5-oxo-ETE is inhibited by pretreatment with anti-hGPCR48 antibodies, indicating that hGPCR48 is an endogenous receptor responsible for chemotaxis of granulocytes toward 5-oxo-ETE. In addition, we show that the chemotaxis of CHO cells expressing hGPCR48 is suppressed by pretreatment with pertussis toxin, and enhanced by overexpression of the carboxy terminal peptides of Galpha (12/13) subunits or a regulator of the G protein signaling domain of p115RhoGEF, both of which are known to suppress G(12/13)-dependent signaling pathways. These results indicate that hGPCR48 couples with G(i/o) and G(12/13) proteins, which then initiate or attenuate the chemotaxis of the cells toward 5-oxo-ETE, respectively.

High expression of eosinophil chemoattractant ecalectin/galectin-9 in drug-induced liver injury

BACKGROUND

Ecalectin/galectin-9 (ECL/GL9) is an eosinophil chemoattractant isolated from T lymphocytes. Drug-induced liver injury (DILI), often caused by an allergic mechanism, is occasionally accompanied by eosinophilic infiltration. In this study, we intended to determine whether DILI can induce augmentation of ECL/GL9 expression. Further, we investigated whether this augmentation is associated with tissue eosinophilia.

METHODS

We examined the expression of ECL/GL9 in biopsy specimens of DILI using the immunohistochemical technique. A rabbit anti-ECL/GL9 antibody was produced by immunizing rabbits with synthetic peptide corresponding to a molecular epitope of ECL/GL9. Thereafter, immunohistochemical staining with the use of this antibody was performed on 16 DILI needle biopsy specimens, and on biopsy specimens of chronic viral hepatitis, liver cirrhosis, and normal liver tissues as controls.

RESULTS

In all cases of DILI specimens, but not in control liver specimens, a clear positive staining for ECL/GL9 was observed. Such positive staining was noted on Kupffer cells, fibroblasts, and histiocytes, but not on lymphocytes or hepatocytes. However, the intensity of immunolabeling did not correlate with the extent of eosinophile leukocyte infiltration.

CONCLUSION

High expression of ECL/GL9 is suggested to be a specific finding of DILI. However, tissue eosinophilia in DILI cannot be explained by the augmentation of ECL/GL9 expression.

5-Oxo-6,8,11,14-eicosatetraenoic acid is a potent chemoattractant for human basophils

BACKGROUND

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a chemoattractant for eosinophils and neutrophils, and the messenger RNA for its receptor, the oxo-eicosatetraenoic acid receptor (OXE), has been detected in several tissues.

OBJECTIVES

This study aimed at clarifying the role of 5-oxo-ETE in the regulation of basophil function.

METHODS

Basophil responses were determined in assays of flow-cytometric shape change, Ca(2+) flux, chemotaxis, and histamine release. Messenger RNA for OXE was detected by real-time PCR.

RESULTS

We observed that human eosinophils were 3 to 10 times more sensitive to 5-oxo-ETE than neutrophils in flow-cytometric shape change and Ca(2+) flux assays, as estimated from the half-maximal responses of the cells. Basophils responded to 5-oxo-ETE in the shape change assay with a sensitivity similar to that of eosinophils. 5-Oxo-ETE was a weak inducer of Ca(2+) flux in basophils and did not cause histamine release but was a highly effective chemoattractant for basophils in the low nanomolar concentration range in a pertussis toxin-sensitive manner. In agreement with these functional studies, the messenger RNA for the 5-oxo-ETE receptor, OXE, was detectable in basophils as in monocytes, eosinophils, and neutrophils, but not in fibroblasts. Specimens from sinus mucosa, tonsils, and adenoids also contained detectable levels of messenger RNA for OXE.

CONCLUSION

Our data suggest that 5-oxo-ETE is potentially involved in the regulation of basophil recruitment and might hence be a useful therapeutic target in atopic disease.

The Eotaxin Chemokines and CCR3 Are Fundamental Regulators of Allergen-Induced Pulmonary Eosinophilia

The eotaxin chemokines have been implicated in allergen-induced eosinophil responses in the lung. However, the individual and combined contribution of each of the individual eotaxins is not well defined. We aimed to examine the consequences of genetically ablating eotaxin-1 or eotaxin-2 alone, eotaxin-1 and eotaxin-2 together, and CCR3. Mice carrying targeted deletions of these individual or combined genes were subjected to an OVA-induced experimental asthma model. Analysis of airway (luminal) eosinophilia revealed a dominant role for eotaxin-2 and a synergistic reduction in eotaxin-1/2 double-deficient (DKO) and CCR3-deficient mice. Examination of pulmonary tissue eosinophilia revealed a modest role for individually ablated eotaxin-1 or eotaxin-2. However, eotaxin-1/2 DKO mice had a marked decrease in tissue eosinophilia approaching the low levels seen in CCR3-deficient mice. Notably, the organized accumulation of eosinophils in the peribronchial and perivascular regions of allergen-challenged wild-type mice was lost in eotaxin-1/2 DKO and CCR3-deficient mice. Mechanistic analysis revealed distinct expression of eotaxin-2 in bronchoalveolar lavage fluid cells consistent with macrophages. Taken together, these results provide definitive evidence for a fundamental role of the eotaxin/CCR3 pathway in eosinophil recruitment in experimental asthma. These results imply that successful blockade of Ag-induced pulmonary eosinophilia will require antagonism of multiple CCR3 ligands.

5-Lipoxygenase products regulate basophil functions: 5-Oxo-ETE elicits migration, and leukotriene B4 induces degranulation

BACKGROUND

5-Lipoxygenase (5-LO) products have been strongly implicated in the pathogenesis of allergic diseases. In addition to their physiologic effects on residential cells, 5-LO products are capable of stimulating various eosinophil functions. However, little is known regarding the effects of 5-LO products on basophil functions.

OBJECTIVE

This study was designed to elucidate the effects of the main 5-LO products (ie, leukotriene [LT] B(4), LTD(4), and 5-oxo-6,8,11,14-eicosatetraenoic acid [5-oxo-ETE]), as well as their receptor expression on human basophils.

METHODS

We studied the effects of 5-LO products on Ca(2+) mobilization, migration, CD 11b expression, and degranulation of human basophils. Expression of the receptors for LTC(4)/D(4)/E(4) (cysteinyl leukotriene 1 [CysLT(1)] and CysLT(2)), LTB4 (BLT(1) and BLT(2)), and 5-oxo-ETE (oxoeicosanoid [OXE]) was assessed by means of real-time PCR and flow cytometry.

RESULTS

At the mRNA level, basophils strongly expressed OXE and predominantly expressed CysLT(1) and BLT(2). The expression level of OXE mRNA in basophils was approximately 20-fold higher than in neutrophils and similar to that in eosinophils. At the protein level, basophils expressed CysLT(1), CysLT(2), BLT(1), and OXE, but not BLT(2). All products elicited a transient increase of cytosolic calcium, with the order of magnitude being LTB(4)>5-oxo-ETE>LTD(4). 5-Oxo-ETE induced a strong basophil migratory response that was almost equivalent to that of prostaglandin D(2). LTB(4) elicited significant degranulation of IL-3-primed basophils. In contrast, no functional significance was observed for LTD(4).

CONCLUSION

Among 5-LO products, 5-oxo-ETE induces a potent basophil migratory response, and LTB(4) elicits degranulation under certain conditions. Our results strongly suggest that 5-oxo-ETE might afford opportunities for therapeutic targeting in allergic inflammation.

TG1019/OXE, a Gαi/o-protein-coupled receptor, mediates 5-oxo-eicosatetraenoic acid-induced chemotaxis

We have previously identified a Galpha(i/o)-protein-coupled receptor (TG1019/OXE) using 5-oxo-6E,8Z,11Z,14Z-eicosatetraenoic acid (5-oxo-ETE) as its ligand. We investigated signal transduction from TG1019 following stimulation with 5-oxo-ETE and role of TG1019 in 5-oxo-ETE-induced chemotaxis, using Chinese hamster ovary cells expressing TG1019 (CHO/TG1019 cells). 5-Oxo-ETE induced intracellular calcium mobilization and rapid activation of MEK/ERK and PI3K/Akt pathways in CHO/TG1019 cells. CHO/TG1019 cells stimulated with 5-oxo-ETE and other eicosanoids exhibited chemotaxis with efficacies related to agonistic activity of each eicosanoid for TG1019. Pretreatment of the cells with pertussis toxin, a phospholipase C (PLC) inhibitor (U73122) or a PI3K inhibitor (LY294002), markedly suppressed 5-oxo-ETE-induced chemotaxis, whereas pretreatment with a MEK inhibitor (PD98059) had no significant effect on the chemotaxis. Our results show that TG1019 mediates 5-oxo-ETE-induced chemotaxis and that signals from TG1019 are transduced via Galpha(i/o) protein to PLC/calcium mobilization, MEK/ERK, and PI3K/Akt, among which PLC and PI3K would play important roles in the chemotaxis.

2-arachidonoylglycerol, an endogenous cannabinoid receptor ligand, induces the migration of EoL-1 human eosinophilic leukemia cells and human peripheral blood eosinophils

2-arachidonoylglycerol (2-AG) is an endogenous cannabinoid receptor ligand. To date, two types of cannabinoid receptors have been identified: the CB1 receptor, abundantly expressed in the brain, and the CB2 receptor, expressed in various lymphoid tissues such as the spleen. The CB1 receptor has been assumed to play an important role in the regulation of synaptic transmission, whereas the physiological roles of the CB2 receptor remain obscure. In this study, we examined whether the CB2 receptor is present in human eosinophils and found that the CB2 receptor is expressed in human peripheral blood eosinophils. In contrast, human neutrophils do not contain a significant amount of the CB2 receptor. We then examined the effect of 2-AG on the motility of eosinophils. We found that 2-AG induces the migration of human eosinophilic leukemia EoL-1 cells. The migration evoked by 2-AG was abolished in the presence of SR144528, a CB2 receptor antagonist, or by pretreatment of the cells with pertussis toxin, suggesting that the CB2 receptor and Gi/o are involved in the 2-AG-induced migration. The migration of EoL-1 cells induced by 2-AG was suggested to be a result of chemotaxis. In contrast to 2-AG, neither anandamide nor free arachidonic acid elicited the migration. Finally, we examined the effect of 2-AG on human peripheral blood eosinophils and neutrophils and found that 2-AG induces migration of eosinophils but not neutrophils. These results suggest that the CB2 receptor and its endogenous ligand 2-AG may be closely involved in allergic inflammation accompanied by the infiltration of eosinophils.

International Union of Pharmacology XLIV. Nomenclature for the Oxoeicosanoid Receptor

Oxoeicosanoids are a family of biologically active arachidonic acid derivatives that have been intimately linked with cellular migration. These metabolites are not only potent chemotaxins but also elicit oxygen radical production as well as induce secretory events in different cells. The most potent native ligand reported is 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), and the cell membrane receptor activated has now been cloned. This receptor is distinct from those receptors activated by either the prostaglandins or the leukotrienes. The purpose of this review is to briefly summarize the molecular evidence and highlight the significance of this receptor. In addition, an official nomenclature for this oxoeicosanoid receptor is proposed.

Identification of surrogate ligands for orphan G protein-coupled receptors

We prepared fusion proteins with an alpha subunit of G protein Gi (Gi1alpha) of 26 orphan G protein-coupled receptors (GPCRs) and with Gsalpha of 10 orphan GPCRs, most of which had been identified from the human genome previously [FEBS Lett 520 (2002) 97]. Ligands for these fusion proteins were screened from a library consisting of approximately 1000 authentic compounds by measuring their effect on [35S]GTPgammaS binding to membrane preparations of insect Sf9 cells expressing these fusion proteins. Eleven compounds were found to act as surrogate agonists for a GPCR-Gsalpha and four GPCR-Gialpha fusion proteins, a compound as an inverse agonist for two GPCR-Gsalpha fusion proteins, and a compound as an endogenous agonist for a GPCR-Gialpha fusion protein.

Biosynthesis of 5-oxo-6,8,11,14-eicosatetraenoic acid from 5-hydroperoxyeicosatetraenoic acid in the murine macrophage

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a metabolite of arachidonic acid shown to possess important biological activities within different cell types. In the neutrophil, a specific NADP(+)-dependent dehydrogenase utilizes 5-lipoxygenase-derived 5-hydroxy-6,8,11,14-eicosatetraenoic acid (5(S)-HETE) as the required substrate. In the present study, 5-hydroperoxy-6,8,11,14-eicosatetraenoic acid (5-HpETE), rather than 5-HETE, was found to be the biosynthetic precursor of 5-oxo-ETE in the murine macrophage. The macrophage was not able to convert 5-HETE into 5-oxo-ETE even when preincubated with phorbol ester or with other lipid hydroperoxides. The factor responsible for the conversion of 5-HpETE into 5-oxo-ETE was found predominantly in the cytosolic fraction of the macrophage, with an approximate molecular weight of 50,000-60,000, as assessed by size exclusion chromatography. Formation of 5-oxo-ETE was rapid and the catalytic protein was found to have an apparent K(m) of 5.3 microM for the eicosanoid. Furthermore, the protein could efficiently utilize 5(R,S)-HpETE as substrate and was heat and protease labile. This novel pathway of 5-oxo-ETE biosynthesis in the murine macrophage was consistent with reduction of a 5-hydroperoxy group to an intermediate alkoxy radical that could be subsequently oxidized to the 5-oxo product. Such a mechanism would enable racemic 5-HpETE, derived from free radical oxidation of arachidonic acid, to be efficiently converted into this potent chemotactic eicosanoid.

Expression and characterization of a 5-oxo-6E,8Z,11Z,14Z-eicosatetraenoic acid receptor highly expressed on human eosinophils and neutrophils

Using a bioinformatics approach, we have isolated a novel G-protein-coupled receptor (GPCR), R527, and have demonstrated that this receptor shows no significant homology to previously deorphanized GPCRs. Quantitative reverse transcription-polymerase chain reaction analysis of the expression of GPCR R527 indicated a very high level of mRNA expression in eosinophils, with high expression also detected in neutrophils and lung macrophages. Stable cell lines were generated expressing this receptor together with the G-protein alpha-subunit G alpha(16). These cells were used to screen an agonist collection in a calcium mobilization assay and 5-oxo-6E,8Z,11Z,14Z-eicosatetraenoic acid (5-oxo-ETE) was identified as a putative ligand. 5(S)-hydroxyperoxy-6E,8Z,11Z,14Z-eicosatetraenoic acid was also shown to activate the receptor, whereas the leukotrienes LTB(4), LTC(4), LTD(4), and LTE(4) failed to elicit a response. In cAMP assays, pertussis toxin reversed the inhibitory effects of 5-oxo-ETE on cAMP production, indicating that the receptor is G alpha(i)-coupled. The GPCR R527 shows pharmacological properties similar to those of the previously described 5-oxo-ETE receptor expressed on eosinophils, neutrophils, and monocytes. These cell types show chemotactic responses to 5-oxo-ETE, and this eicosanoid has been proposed to play a key role in the inflammatory response. The molecular identification of a receptor binding 5-oxo-ETE will expand our understanding of the physiological role of this mediator and may provide new therapeutic opportunities.

Identification of a novel human eicosanoid receptor coupled to G(i/o)

We have conducted an in silico data base search for and cloned a novel G-protein-coupled receptor (GPCR) named TG1019. Dot and Northern blotting analyses showed that transcripts of the novel GPCR were expressed in various tissues except brain, and the expression was more intense in liver, kidney, peripheral leukocyte, lung, and spleen than in other tissues. By GTP gamma S binding assay using the TG1019-G alpha(i1)-protein fusion expressed in insect cells, eicosanoids, and polyunsaturated fatty acids such as 5-oxo-6E,8Z,11Z,14Z-eicosatetraenoic acid (5-oxo-ETE), 5(S)-hydroperoxy-6E,8Z, 11Z,14Z-eicosatetraenoic acid, and arachidonic acid were identified to exhibit agonistic activities against TG1019. 5-oxo-ETE was the most potent to enhance the specific binding by 6-fold at a maximum effect dose of submicromolar to micromolar order with an ED(50) value of 5.7 nM. Conversely, polyunsaturated fatty acids such as docosahexaenoic acid and eicosapentaenoic acid showed antagonistic activities against TG1019. In Chinese hamster ovary cells transiently expressing TG1019, the forskolin-stimulated production of cAMP was inhibited up to approximately 70% by 5-oxo-ETE, with an IC(50) value of 33 nM. This inhibition was sensitive to pretreatment of the cells with pertussis toxin.

Calcium-independent phospholipase A(2) is required for human monocyte chemotaxis to monocyte chemoattractant protein 1

Monocyte chemoattractant protein 1 (MCP-1) has an important influence on monocyte migration into sites of inflammation. Our understanding of the signal transduction pathways involved in the response of monocytes to MCP-1 is quite limited yet potentially significant for understanding and manipulating the inflammatory response. Prior studies have demonstrated a crucial regulatory role for cytosolic phospholipase A(2) (cPLA(2)) in monocyte chemotaxis to MCP-1. In these studies we investigated the role for another PLA(2), calcium-independent PLA(2) (iPLA(2)) in comparison to cPLA(2). Pharmacological inhibitors of PLA(2) were found to substantially inhibit chemotaxis. Using antisense oligodeoxyribonucleotide treatment we found that iPLA(2) expression is required for monocyte migration to MCP-1. Complete blocking of the chemotactic response was observed with inhibition of either iPLA(2) or cPLA(2) expression by their respective antisense oligodeoxyribonucleotide. In reconstitution experiments, lysophosphatidic acid completely restored MCP-1-stimulated migration in iPLA(2)-deficient monocytes, whereas lysophosphatidic acid was without effect in restoring migration in cPLA(2)-deficient monocytes. To the contrary, arachidonic acid fully restored migration of cPLA(2)-deficient monocytes while having no effect on the iPLA(2)-deficient monocytes. Additional studies revealed that neither enzyme appears to be upstream of the other indicating that iPLA(2) and cPLA(2) represent parallel regulatory pathways. These data demonstrate novel and distinct roles for these two phospholipases in this critical step in inflammation.

Quantitative analysis of 5-oxo-6,8,11,14-eicosatetraenoic acid by electrospray mass spectrometry using a deuterium-labeled internal standard

5-Oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE), a metabolite of arachidonic acid formed by the 5-lipoxygenase pathway, is a potent eosinophil chemoattractant that may be an important mediator in asthma. To further investigate the physiological and pathological roles of 5-oxo-ETE we have developed a mass spectrometric assay employing a tetradeuterated analog (5-oxo-[11,12,14,15-(2)H]ETE) as an internal standard. Collision-induced dissociation of the quasimolecular anion of 5-oxo-[11,12,14,15-(2)H]ETE (m/z 321) resulted in the formation of a major ion at m/z 207 that retained all four deuterium atoms. Measurement of the ratio of ions at m/z 203 (endogenous 5-oxo-ETE) and m/z 207 permitted quantitation of this compound by liquid chromatography-mass spectrometry-mass spectrometry using multiple reaction monitoring. The resulting assay was highly sensitive (< or =20 pg/sample) and selective, enabling detection of the amount of 5-oxo-ETE produced by as few as 10,000 neutrophils. This assay should permit measurement of 5-oxo-ETE in biological fluids, enabling evaluation of its role in asthma and other inflammatory diseases.

Identification and Quantitation of Unique Fatty Acid Oxidation Products in Human Atherosclerotic Plaque Using High-Performance Liquid Chromatography

Oxidation of lipoproteins, particularly low-density lipoprotein, is thought to play a major role in the development of atherosclerosis. We set out to identify and quantitate the major fatty acid oxidation products in human atherosclerotic plaque obtained from individuals undergoing carotid endarterectomy. Oxidized lipids were extracted from plaque homogenate under conditions to prevent artifactual oxidation. Identification and quantitation was performed using HPLC and GC-MS. High levels of hydroxyoctadecanoic acids (0.51 +/- 0.17 ng/microg of linoleic acid), 15-hydroxyeicosatetranoic acid (HETE) (0.66 +/- 0.24 ng/microg of arachidonic acid), and 11-HETE (0.84 +/- 0.24 ng/microg of arachidonic acid) were detected in all atherosclerotic plaques (n = 10). Low levels of 9-oxo-octadecanoic acid (oxoODE) (0.04 +/- 0.01 ng/microg of linoleic acid), were present in all samples, while 13-oxoODE (0.01 +/- 0.008 ng/microg of linoleic acid) was present in only 4 of the 10 plaque samples. Of interest was the identification of two previously unidentified compounds in atherosclerotic plaque, 11-oxo-eicosatetranoic acid in 9 of the 10 samples and 5,6-dihydroxyeicosatetranoic acid in 3 samples. Chiral analysis revealed that all the major compounds identified in this study are of a nonenzymatic origin. This study is the first to provide a convenient HPLC method to quantify all the products of both linoleic acid and arachidonic acid oxidation in human atherosclerotic plaque. The quantitation of lipid peroxidation products in plaque may be important given the potential biological activity of these compounds and their possible relationship to plaque pathogenesis and instability.

Characterization of synthetic C3a analog peptides on human eosinophils in comparison to the native complement component C3a

The C3a anaphylatoxin is a potent proinflammatory mediator derived from the complement system inducing biologic effects of human eosinophils like Ca2+ transients and the activation of the respiratory burst. These findings support an important role for C3a in diseases typically associated with a peripheral blood or tissue eosinophilia. Synthetic human C3a analogue peptides with variations at the C-terminal effector domain have been evaluated with respect to their binding affinity and signaling potency on human eosinophils. Flow cytometrical analysis and RT-PCR revealed that the C3a receptor is constitutively expressed on human eosinophils. Peptides bearing an N-terminal 9-fluorenylmethoxycarbonyl and the 6-aminohexanoyl motif were the most powerful peptides tested. Amino acid replacements in the conserved C-terminal pentapeptide decreased binding affinity and functional potency substantially. In addition, synthetic C3a analogue peptides induced C3aR internalization, led to transient changes of intracellular Ca2+ concentration, and did release reactive oxygen species in human eosinophils indicating the in vivo relevance of C3a-related sequences. The tripeptide LAR was found to be essential for C3a receptor binding on human eosinophils. Moreover, the putative binding motif of C3a anaphylatoxin is also crucial for the induction of biologic effects in the human system such as changes of intracellular Ca2+ concentration and the release of reactive oxygen species. This study demonstrates that the carboxyl terminus is important for the interaction with the C3aR and the biologic potency of C3a anaphylatoxin in the human system and plays a key role in the activation process of human eosinophils.

The coupling of 5-oxo-eicosanoid receptors to heterotrimeric G proteins

5-Oxo-eicosatetraenoic acid (5-oxoETE) stimulated human neutrophil (PMN) and eosinophil chemotaxis, PMN hexose uptake, and PMN membrane GTP/GDP exchange. Pertussis toxin (PT), a blocker of heterotrimeric G proteins (GP), completely inhibited these responses, but proved far less effective on the same responses when elicited by leukotriene B4, C5a, FMLP, platelet-activating factor, IL-8, or RANTES chemotactic factors. 5-OxoETE also specifically bound to the membrane preparations that conducted GTP/GDP exchange. This binding was down-regulated by GTPgammaS, but not ADPgammaS, and displaced by 5-oxoETE analogues, but not by leukotriene B4, lipoxin A4, or lipoxin B4. Finally, PMN expressed PT-sensitive GP alphaiota2 and PT-resistant GP alphaq/11- and alpha13-chains; eosinophils expressed only alphai2 and alphaq/11. We conclude that 5-oxoETE activates granulocytes through a unique receptor that couples preferentially to PT-sensitive GP. The strict dependency of this putative receptor on PT-sensitive GP may underlie the limited actions of 5-oxoETE, compared with other CF, and help clarify the complex relations between receptors, GP, cell signals, and cell responses.

LTA(4)-derived 5-oxo-eicosatetraenoic acid: pH-dependent formation and interaction with the LTB(4) receptor of human polymorphonuclear leukocytes

5-oxo-(7E,9E,11Z,14Z)-eicosatetraenoic acid (5-oxo-ETE) has been identified as a non-enzymatic hydrolysis product of leukotriene A(4) (LTA(4)) in addition to 5,12-dihydroxy-(6E,8E,10E, 14Z)-eicosatetraenoic acids (5,12-diHETEs) and 5,6-dihydroxy-(7E,9E, 11Z,14Z)-eicosatetraenoic acids (5,6-diHETEs). The amount of 5-oxo-ETE detected in the mixture of the hydrolysis products of LTA(4) was found to be pH-dependent. After incubation of LTA(4) in aqueous medium, the ratio of 5-oxo-ETE to 5,12-diHETE was 1:6 at pH 7.5, and 1:1 at pH 9.5. 5-Oxo-ETE was isolated from the alkaline hydrolysis products of LTA(4) in order to evaluate its effects on human polymorphonuclear (PMN) leukocytes. 5-Oxo-ETE induced a rapid and dose-dependent mobilization of calcium in PMN leukocytes with an EC(50) of 250 nM, as compared to values of 3.5 nM for leukotriene B(4) (LTB(4)500 nM for 5(S)-hydroxy-(6E,8Z,11Z,14Z)-eicosatetraenoic acid (5-HETE). Pretreatment of the cells with LTB(4) totally abolished the calcium response induced by 5-oxo-ETE. In contrast, the preincubation with 5-oxo-ETE did not affect the calcium mobilization induced by LTB(4). The calcium response induced by 5-oxo-ETE was totally inhibited by the specific LTB(4) receptor antagonist LY223982. These data demonstrate that 5-oxo-ETE can induce calcium mobilization in PMN leukocyte via the LTB(4) receptor in contrast to the closely related analog 5-oxo-(6E,8Z,11Z, 14Z)-eicosatetraenoic acid which is known to activate human neutrophils by a mechanism independent of the receptor for LTB(4).

The role of chemokines in cutaneous allergic inflammation

Eosinophils are the major effector cells that kill helminthic parasites and are - for unknown reasons present in the dermal part of atopic skin. This review summarizes our knowledge on the chemotactic factors involved in eosinophil tissue recruitment, focusing on the role of eosinophil-chemotactic chemokines. It is the current view that the chemokines RANTES and eotaxin represent the most important eosinophil-attracting chemokines. The inducibility of eotaxin in dermal fibroblasts only upon stimulation with Th2-cytokines IL-4 and IL-13 may explain why eosinophils appear only in the dermis and why the presence of Th2-cytokines is always linked with tissue eosinophilia.

Biological Inactivation of 5-oxo-6,8,11,14-Eicosatetraenoic Acid by Human Platelets

Neutrophil-derived 5-oxo-6,8,11,14-eicosatetraenoic acid (5-oxo-ETE) is a potent activator of neutrophils and eosinophils. In the present study we examined the biosynthesis and metabolism of this substance by platelets. Although platelets contain an abundant amount of 5-hydroxyeicosanoid dehydrogenase, the enzyme responsible for the formation of 5-oxo-ETE, they synthesize only very small amounts of this substance from exogenous 5-hydroxyeicosatetraenoic acid (5-HETE) unless endogenous NADPH is converted to NADP+ by addition of phenazine methosulfate. Similarly, relatively small amounts of 5-oxo-ETE were formed by A23187-stimulated mixtures of platelets and neutrophils, which instead formed substantial amounts of two 12-hydroxy metabolites of this substance, 5-oxo-12-HETE and 8-trans-5-oxo-12-HETE, which were identified by comparison with authentic chemically synthesized compounds. These metabolites were also formed from 5-oxo-ETE by platelets stimulated with thrombin or A23187. In contrast, unstimulated platelets converted 5-oxo-ETE principally to 5-HETE. Neither 5-oxo-12-HETE nor 8-trans-5-oxo-12-HETE had appreciable effects on neutrophil calcium levels or platelet aggregation at concentrations as high as 10 μmol/L, but both blocked 5-oxo-ETE–induced calcium mobilization in neutrophils with IC50 values of 0.5 and 2.5 μmol/L, respectively. We conclude that platelets can biologically inactivate 5-oxo-ETE. Unstimulated platelets convert 5-oxo-ETE to 5-HETE, with a 99% loss of biological potency, whereas stimulated platelets convert this substance to 12-hydroxy metabolites, which possess antagonist properties.