Biosynthesis and biological activity of leukotriene B4

Redox processes are major regulators of leukotriene synthesis in neutrophils exposed to bacteria Salmonella typhimurium; the way to manipulate neutrophil swarming

Neutrophils play a primary role in protecting our body from pathogens. When confronted with invading bacteria, neutrophils begin to produce leukotriene B4, a potent chemoattractant that, in cooperation with the primary bacterial chemoattractant fMLP, stimulates the formation of swarms of neutrophils surrounding pathogens. Here we describe a complex redox regulation that either stimulates or inhibits fMLP-induced leukotriene synthesis in an experimental model of neutrophils interacting with Salmonella typhimurium. The scavenging of mitochondrial reactive oxygen species by mitochondria-targeted antioxidants MitoQ and SkQ1, as well as inhibition of their production by mitochondrial inhibitors, inhibit the synthesis of leukotrienes regardless of the cessation of oxidative phosphorylation. On the contrary, antioxidants N-acetylcysteine and sodium hydrosulfide promoting reductive shift in the reversible thiol-disulfide system stimulate the synthesis of leukotrienes. Diamide that oxidizes glutathione at high concentrations inhibits leukotriene synthesis, and the glutathione precursor S-adenosyl-L-methionine prevents this inhibition. Diamide-dependent inhibition is also prevented by diphenyleneiodonium, presumably through inhibition of NADPH oxidase and NADPH accumulation. Thus, during bacterial infection, maintaining the reduced state of glutathione in neutrophils plays a decisive role in the synthesis of leukotriene B4. Suppression of excess leukotriene synthesis is an effective strategy for treating various inflammatory pathologies. Our data suggest that the use of mitochondria-targeted antioxidants may be promising for this purpose, whereas known thiol-based antioxidants, such as N-acetylcysteine, may dangerously stimulate leukotriene synthesis by neutrophils during severe pathogenic infection.

The biosynthetic pathways of the protectins

Evidence for the biosynthetic pathways of the specialized pro-resolving mediator (SPM) protectin D1 (PD1) and its biochemical further local metabolism were presented during the 8th European Workshop on Lipid Mediators, organized June 29th-July 1st, 2022, in Stockholm, Sweden. Herein, we provide an extended and detailed discussion of these topics. PD1, one of 43 SPMs reported so far, exhibits very potent pro-resolution and anti-inflammatory bioactions. Many research groups worldwide have confirmed these and other interesting bioactions. The protectins constitute, together with the lipoxins, resolvins, and maresins, the four individual SPM families, which have received a great interest in basic biomedical research and drug discovery efforts.

Human Orphan Cytochrome P450 2U1 Catalyzes the ω-Hydroxylation of Leukotriene B4

Cytochrome P450 2U1 (CYP2U1) identified from the human genome remains poorly known since few data are presently available on its physiological function(s) and substrate(s) specificity. CYP2U1 mutations are associated with complicated forms of hereditary spastic paraplegia, alterations of mitochondrial architecture and bioenergetics. In order to better know the biological roles of CYP2U1, we used a bioinformatics approach. The analysis of the data invited us to focus on leukotriene B₄ (LTB₄), an important inflammatory mediator. Here, we show that CYP2U1 efficiently catalyzes the hydroxylation of LTB₄ predominantly on its ω-position. We also report docking experiments of LTB₄ in a 3D model of truncated CYP2U1 that are in agreement with this hydroxylation regioselectivity. The involvement of CYP2U1 in the metabolism of LTB₄ could have strong physiological consequences in cerebral pathologies including ischemic stroke because CYP2U1 is predominantly expressed in the brain.

Novel Unspecific Peroxygenase from Truncatella angustata Catalyzes the Synthesis of Bioactive Lipid Mediators

Lipid mediators, such as epoxidized or hydroxylated eicosanoids (EETs, HETEs) of arachidonic acid (AA), are important signaling molecules and play diverse roles at different physiological and pathophysiological levels. The EETs and HETEs formed by the cytochrome P450 enzymes are still not fully explored, but show interesting anti-inflammatory properties, which make them attractive as potential therapeutic target or even as therapeutic agents. Conventional methods of chemical synthesis require several steps and complex separation techniques and lead only to low yields. Using the newly discovered unspecific peroxygenase TanUPO from the ascomycetous fungus Truncatella angustata, 90% regioselective conversion of AA to 14,15-EET could be achieved. Selective conversion of AA to 18-HETE, 19-HETE as well as to 11,12-EET and 14,15-EET was also demonstrated with known peroxygenases, i.e., AaeUPO, CraUPO, MroUPO, MweUPO and CglUPO. The metabolites were confirmed by HPLC-ELSD, MS1 and MS2 spectrometry as well as by comparing their analytical data with authentic standards. Protein structure simulations of TanUPO provided insights into its substrate access channel and give an explanation for the selective oxyfunctionalization of AA. The present study expands the scope of UPOs as they can now be used for selective syntheses of AA metabolites that serve as reference material for diagnostics, for structure-function elucidation as well as for therapeutic and pharmacological purposes.

Lipid Metabolism Profiles in Rheumatic Diseases

Rheumatic diseases are a group of chronic autoimmune disorders that involve multiple organs or systems and have high mortality. The mechanisms of these diseases are still ill-defined, and targeted therapeutic strategies are still challenging for physicians. Recent research indicates that cell metabolism plays important roles in the pathogenesis of rheumatic diseases. In this review, we mainly focus on lipid metabolism profiles (dyslipidaemia, fatty acid metabolism) and mechanisms in rheumatic diseases and discuss potential clinical applications based on lipid metabolism profiles.

Treatment of Post-mastectomy Lymphedema with Herbal Medicine: An Innovative Pilot Study

Background

Lymphedema of the arms or legs is a difficult clinical problem yet devoid of effective treatment. Lymphedema is the result of obstructed lymphatic flow secondary to chronic infection, parasitic infestation, or postsurgical obstruction (eg, after axillary dissections). We arranged this clinical trial to investigate whether patients with limb lymphedema can benefit from a standard dose of Astragalus plus Paeoniae rubra to improve the symptomatology, functional capacity, and quality of life (QOL).

Method

The pilot study was designed as a self-control clinical trial. Patients with post-mastectomy lymphedema were recruited. A double-herb formulation (Astragalus, Paeoniae rubra) with standard dosage was administered orally in a powdered form, 6 times per week for 6 months. Outcome measurements included standard limb volume changes measured by water displacement method; handgrip strength; and QOL for limb lymphedema questionnaire (LYMQOL).

Results

There were no reported adverse effects or complications; there were no episodes of infection during the period of study. There was a tendency of limb volume reduction by 6 months, which, however, did not reach statistical significance. There was a significant improvement in appearance and symptom scores as was assessed with the LYMQOL questionnaire.

Conclusions

The oral herbal formula improved the symptomatology and QOL among the pilot group of patients with post-mastectomy lymphedema. Side effects were absent, and there was a trend of lymphedema reduction.

Leukotriene Involvement in the Insulin Receptor Pathway and Macrophage Profiles in Muscles from Type 1 Diabetic Mice

Type 1 diabetes (T1D) is a metabolic disease associated with systemic low-grade inflammation and macrophage reprogramming. There is evidence that this inflammation depends on the increased systemic levels of leukotriene (LT) B4 found in T1D mice, which shifts macrophages towards the proinflammatory (M1) phenotype. Although T1D can be corrected by insulin administration, over time T1D patients can develop insulin resistance that hinders glycemic control. Here, we sought to investigate the role of leukotrienes (LTs) in a metabolically active tissue such as muscle, focusing on the insulin signaling pathway and muscle-associated macrophage profiles. Type 1 diabetes was induced in the 129/SvE mouse strain by streptozotocin (STZ) in mice deficient in the enzyme responsible for LT synthesis (5LO^-/-) and the LT-sufficient wild type (WT). The response to insulin was evaluated by the insulin tolerance test (ITT), insulin concentration by ELISA, and Akt phosphorylation by western blotting. The gene expression levels of the insulin receptor and macrophage markers Stat1, MCP-1, Ym1, Arg1, and IL-6 were evaluated by qPCR, and that of IL-10 by ELISA. We observed that after administration of a single dose of insulin to diabetic mice, the reduction in glycemia was more pronounced in 5LO^-/- than in WT mice. When muscle homogenates were analyzed, diabetic 5LO^-/- mice showed a higher expression of the insulin receptor gene and higher Akt phosphorylation. Moreover, in muscle homogenates from diabetic 5LO^-/- mice, the expression of anti-inflammatory macrophage markers Ym1, Arg1, and IL-10 was increased, and the relative expression of the proinflammatory cytokine IL-6 was reduced compared with WT diabetic mice. These results suggest that LTs have an impact on the insulin receptor signaling pathway and modulate the inflammatory profile of muscle-resident macrophages from T1D mice.

Lipid Mediators in Inflammation

Lipids are potent signaling molecules that regulate a multitude of cellular responses, including cell growth and death and inflammation/infection, via receptor-mediated pathways. Derived from polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), each lipid displays unique properties, thus making their role in inflammation distinct from that of other lipids derived from the same PUFA. This diversity arises from their synthesis, which occurs via discrete enzymatic pathways and because they elicit responses via different receptors. This review will collate the bioactive lipid research to date and summarize the major pathways involved in their biosynthesis and role in inflammation. Specifically, lipids derived from AA (prostanoids, leukotrienes, 5-oxo-6,8,11,14-eicosatetraenoic acid, lipoxins, and epoxyeicosatrienoic acids), EPA (E-series resolvins), and DHA (D-series resolvins, protectins, and maresins) will be discussed herein.

Plant Natural Products Calycosin and Gallic Acid Synergistically Attenuate Neutrophil Infiltration and Subsequent Injury in Isoproterenol-Induced Myocardial Infarction: A Possible Role for Leukotriene B4 12-Hydroxydehydrogenase?

Leukotriene B4 12-hydroxydehydrogenase (LTB4DH) catalyzes the oxidation of proinflammatory LTB4 into less bioactive 12-oxo-LTB4. We recently discovered that LTB4DH was induced by two different natural products in combination. We previously isolated gallic acid from Radix Paeoniae through a bioactivity-guided fractionation procedure. The purpose of this study is to test the hypothesis that LTB4DH inducers may suppress neutrophil-mediated inflammation in myocardial infarction. We first isolated the active compound(s) from another plant, Radix Astragali, by the similar strategy. By evaluating LTB4DH induction, we identified calycosin and formononetin from Radix Astragali by HPLC-ESI-MS technique. We confirmed that gallic acid and commercial calycosin or formononetin could synergistically induce LTB4DH expression in HepG2 cells and human neutrophils. Moreover, calycosin and gallic acid attenuated the effects of LTB4 on the survival and chemotaxis of neutrophil cell culture. We further demonstrated that calycosin and gallic acid synergistically suppressed neutrophil infiltration and protected cardiac integrity in the isoproterenol-induced mice model of myocardial infarction. Calycosin and gallic acid dramatically suppressed isoproterenol-induced increase in myeloperoxidase (MPO) activity and malondialdehyde (MDA) level. Collectively, our results suggest that LTB4DH inducers (i.e., calycosin and gallic acid) may be a novel combined therapy for the treatment of neutrophil-mediated myocardial injury.

Impairment of neutrophil migration to remote inflammatory site during lung histoplasmosis

Histoplasma capsulatum (Hc) induces a pulmonary disease in which leukotrienes promote activation and recruitment of effectors cells. It is also well-recognized that leukotriene B₄ (LTB₄) and platelet-activating factor (PAF) induce leukocyte recruitment to inflammatory sites. We investigated the impact of pulmonary Hc infection on PMN migration to a remote inflammatory site. Our results show that pulmonary Hc infection impairs LTB₄- or PAF-stimulated PMN recruitment to air pouch. Yet, remote inflammation did not modify PMN numbers in the bronchoalveolar lavage fluid (BALF) of Hc-infected mice. Interestingly, the concomitant administration of PAF and LTB₄ receptor antagonists inhibited PMN recruitment to both BALF and the remote site, demonstrating cooperation between both mediators. Along that line, our results show that PAF-elicited PMN chemotaxis was abrogated in 5-lipoxygenase-deficient animals. These results suggest caution in the indiscriminate use of anti-inflammatory drugs during infectious diseases.

Red light as a 12-oxo-leukotriene B₄ antagonist: an explanation for the efficacy of intensive red light in the therapy of peripheral inflammatory diseases

To explain the successful treatment of various inflammatory diseases by using intensive red light, a non-linear theory is presented for the interaction of electric dipoles with light involving frequency doubling. It is applied to analyze the influence of light on organic molecules with permanent electric dipoles. The molecule 5-hydroxy-12-oxo-(5S,6Z,8E,10E,14Z)-6,8,10,14-eicosatetraenoic acid, 12-oxo-leukotriene B4 (12-Oxo-LTB4, an intermediate in the lipoxygenase-catalyzed path of arachidonic acid metabolism), is suspected to play a major role in the healing process, as, first, it plays a key role in the metabolism of leukotriene B4 (LTB4), which in many diseases acts as a source of inflammatory reactions; second, its dipole resonance is located at a wavelength of 316 nm, which can be excited by a 632 nm source through frequency doubling. From the structure of 12-Oxo-LTB4 and the knowledge of the partial charges of its 54 atoms, the equivalent values for dipole charges and dipole moment are derived. The power balance demonstrates that intensive red light with a power density of 0.4 W/cm2 transfers sufficient energy to 12-Oxo-LTB4 to render it biologically inactive. Hence, by generating a reactive high-energy leukotriene pathway intermediate, the law of mass action steers the chemical equilibrium to interrupt the inflammatory cascade.

Cooperative role of endogenous leucotrienes and platelet-activating factor in ischaemia-reperfusion-mediated tissue injury

Insufficient oxygen delivery to organs leads to tissue dysfunction and cell death. Reperfusion, although vital to organ survival, initiates an inflammatory response that may both aggravate local tissue injury and elicit remote organ damage. Polymorphonuclear neutrophil (PMN) trafficking to remote organs following ischaemia/reperfusion (I/R) is associated with the release of lipid mediators, including leucotriene (LT) B₄, cysteinyl-LTs (CysLTs) and platelet-activating factor (PAF). Yet, their potentially cooperative role in regulating I/R-mediated inflammation has not been thoroughly assessed. The present study aimed to determine the cooperative role of lipid mediators in regulating PMN migration, tissue oedema and injury using selective receptor antagonists in selected models of I/R and dermal inflammation. Our results show that rabbits, pre-treated orally with BIIL 284 and/or WEB 2086 and MK-0571, were protected from remote tissue injury following I/R or dermal inflammation in an additive or synergistic manner when the animals were pre-treated with two drugs concomitantly. The functional selectivity of the antagonists towards their respective agonists was assessed in vitro, showing that neither BIIL 284 nor WEB 2086 prevented the inflammatory response to IL-8, C5a and zymosan-activated plasma stimulation. However, these agonists elicited LTB₄ biosynthesis in isolated rabbit PMNs. Similarly, a cardioprotective effect of PAF and LTB₄ receptor antagonists was shown following myocardial I/R in mice. Taken together, these results underscore the intricate involvement of LTB₄ and PAF in each other’s responses and provide further evidence that targeting both LTs and PAF receptors provides a much stronger anti-inflammatory effect, regulating PMN migration and oedema formation.

Aspirin: a review of its neurobiological properties and therapeutic potential for mental illness

There is compelling evidence to support an aetiological role for inflammation, oxidative and nitrosative stress (O&NS), and mitochondrial dysfunction in the pathophysiology of major neuropsychiatric disorders, including depression, schizophrenia, bipolar disorder, and Alzheimer's disease (AD). These may represent new pathways for therapy. Aspirin is a non-steroidal anti-inflammatory drug that is an irreversible inhibitor of both cyclooxygenase (COX)-1 and COX-2, It stimulates endogenous production of anti-inflammatory regulatory 'braking signals', including lipoxins, which dampen the inflammatory response and reduce levels of inflammatory biomarkers, including C-reactive protein, tumor necrosis factor-α and interleukin (IL)--6, but not negative immunoregulatory cytokines, such as IL-4 and IL-10. Aspirin can reduce oxidative stress and protect against oxidative damage. Early evidence suggests there are beneficial effects of aspirin in preclinical and clinical studies in mood disorders and schizophrenia, and epidemiological data suggests that high-dose aspirin is associated with a reduced risk of AD. Aspirin, one of the oldest agents in medicine, is a potential new therapy for a range of neuropsychiatric disorders, and may provide proof-of-principle support for the role of inflammation and O&NS in the pathophysiology of this diverse group of disorders.

Activated LTB4 pathway in muscle tissue of patients with polymyositis or dermatomyositis

OBJECTIVE

To investigate the involvement of the leukotriene B4 (LTB4) pathway in polymyositis (PM) and dermatomyositis (DM) and the effect of immunosuppressive treatment on the LTB4 pathway.

METHODS

5-lipoxygenase (5-LO), 5-LO activating protein (FLAP) and LTB4 receptor-1 (BLT1) expression was analysed by immunohistochemistry in muscle tissue from patients with PM/DM before and after immunosuppressive treatment and from healthy individuals. In vivo LTB4 in thigh muscle was measured by microdialysis at rest and after acute exercise in another cohort of patients and healthy controls.

RESULTS

The number of 5-LO-positive cells and BLT1-positive capillaries was higher in patients with PM/DM than in healthy individuals. The number of FLAP-expressing cells divided the patients into two groups (high/low expression). Treatment reduced the number of FLAP-positive cells in the group with initial high levels, however the expression remained high compared with healthy individuals. The number of BLT1-positive cells was also reduced while staining for 5-LO was unchanged. An inverse correlation was observed between the number of 5-LO or FLAP-positive cells in muscle tissue and muscle performance. LTB4 could be detected in dialysate of muscle tissue in vivo in both patients and healthy controls and was significantly increased after exercise in patients.

CONCLUSION

The LTB4 pathway is upregulated in muscle tissue from patients with PM/DM and this upregulation correlated negatively to muscle performance, suggesting a role for LTB4 in myositis muscle weakness. The immunosuppressive treatment was insufficient on the LTB4 pathway and, for patients with high expression of FLAP, FLAP inhibitors may be considered as possible therapy.

Neutrophilic airways inflammation in lung cancer: the role of exhaled LTB-4 and IL-8

BACKGROUND

Recent advances in lung cancer biology presuppose its inflammatory origin. In this regard, LTB-4 and IL-8 are recognized to play a crucial role in neutrophil recruitment into airways during lung cancer.Notwithstanding the intriguing hypothesis, the exact role of neutrophilic inflammation in tumour biology remains complex and not completely known.The aim of this study was to give our contribution in this field by investigating LTB-4 and IL-8 in the breath condensate of NSCLC patients and verifying their role in cancer development and progression.

METHOD

We enrolled 50 NSCLC patients and 35 controls. LTB-4 and IL-8 concentrations were measured in the breath condensate and the blood of all the subjects under study using EIA kits. Thirty NSCLC patients and ten controls underwent induced sputum collection and analysis.

RESULTS

LTB-4 and IL-8 resulted higher in breath condensate and the blood of NSCLC patients compared to controls. Significantly higher concentrations were found as the cancer stages progressed. A positive correlation was observed between exhaled IL-8 and LTB-4 and the percentage of neutrophils in the induced sputum.

CONCLUSION

The high concentrations of exhaled LTB-4 and IL-8 showed the presence of a neutrophilic inflammation in the airways of NSCLC patients and gave a further support to the inflammatory signalling in lung cancer. These exhaled proteins could represent a suitable non-invasive marker in the diagnosis and monitoring of lung cancer.

Old and new generation lipid mediators in acute inflammation and resolution

Originally regarded as just membrane constituents and energy storing molecules, lipids are now recognised as potent signalling molecules that regulate a multitude of cellular responses via receptor-mediated pathways, including cell growth and death, and inflammation/infection. Derived from polyunsaturated fatty acids (PUFAs), such as arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), each lipid displays unique properties, thus making their role in inflammation distinct from that of other lipids derived from the same PUFA. The diversity of their actions arises because such metabolites are synthesised via discrete enzymatic pathways and because they elicit their response via different receptors. This review will collate the bioactive lipid research to date and summarise the findings in terms of the major pathways involved in their biosynthesis and their role in inflammation and its resolution. It will include lipids derived from AA (prostanoids, leukotrienes, 5-oxo-6,8,11,14-eicosatetraenoic acid, lipoxins and epoxyeicosatrienoic acids), EPA (E-series resolvins), and DHA (D-series resolvins, protectins and maresins).

Lipoxins: resolutionary road

The resolution of inflammation is an active process controlled by endogenous mediators with selective actions on neutrophils and monocytes. The initial phase of the acute inflammatory response is characterized by the production of pro-inflammatory mediators followed by a second phase in which lipid mediators with pro-resolution activities may be generated. The identification of these mediators has provided evidence for the dynamic regulation of the resolution of inflammation. Among these endogenous local mediators of resolution, lipoxins (LXs), lipid mediators typically formed during cell-cell interaction, were the first to be recognized. More recently, families of endogenous chemical mediators, termed resolvins and protectins, were discovered. LXs and aspirin-triggered LXs are considered to act as 'braking signals' in inflammation, limiting the trafficking of leukocytes to the inflammatory site. LXs are actively involved in the resolution of inflammation stimulating non-phlogistic phagocytosis of apoptotic cells by macrophages. Furthermore, LXs have emerged as potential anti-fibrotic mediators that may influence pro-fibrotic cytokines and matrix-associated gene expression in response to growth factors. Here, we provide a review and an update of the biosynthesis, metabolism and bioactions of LXs and LX analogues, and the recent studies on their therapeutic potential as promoters of resolution and fibro-suppressants.

Lipid mediators in innate immunity against tuberculosis: opposing roles of PGE2 and LXA4 in the induction of macrophage death

Virulent Mycobacterium tuberculosis (Mtb) induces a maladaptive cytolytic death modality, necrosis, which is advantageous for the pathogen. We report that necrosis of macrophages infected with the virulent Mtb strains H37Rv and Erdmann depends on predominant LXA(4) production that is part of the antiinflammatory and inflammation-resolving action induced by Mtb. Infection of macrophages with the avirulent H37Ra triggers production of high levels of the prostanoid PGE(2), which promotes protection against mitochondrial inner membrane perturbation and necrosis. In contrast to H37Ra infection, PGE(2) production is significantly reduced in H37Rv-infected macrophages. PGE(2) acts by engaging the PGE(2) receptor EP2, which induces cyclic AMP production and protein kinase A activation. To verify a role for PGE(2) in control of bacterial growth, we show that infection of prostaglandin E synthase (PGES)(-/-) macrophages in vitro with H37Rv resulted in significantly higher bacterial burden compared with wild-type macrophages. More importantly, PGES(-/-) mice harbor significantly higher Mtb lung burden 5 wk after low-dose aerosol infection with virulent Mtb. These in vitro and in vivo data indicate that PGE(2) plays a critical role in inhibition of Mtb replication.

Airway lipoxin A4 generation and lipoxin A4 receptor expression are decreased in severe asthma

RATIONALE

Airway inflammation is common in severe asthma despite antiinflammatory therapy with corticosteroids. Lipoxin A(4) (LXA(4)) is an arachidonic acid-derived mediator that serves as an agonist for resolution of inflammation.

OBJECTIVES

Airway levels of LXA(4), as well as the expression of lipoxin biosynthetic genes and receptors, in severe asthma.

METHODS

Samples of bronchoalveolar lavage fluid were obtained from subjects with asthma and levels of LXA(4) and related eicosanoids were measured. Expression of lipoxin biosynthetic genes was determined in whole blood, bronchoalveolar lavage cells, and endobronchial biopsies by quantitative polymerase chain reaction, and leukocyte LXA(4) receptors were monitored by flow cytometry.

MEASUREMENTS AND MAIN RESULTS

Individuals with severe asthma had significantly less LXA(4) in bronchoalveolar lavage fluids (11.2 +/- 2.1 pg/ml) than did subjects with nonsevere asthma (150.1 +/- 38.5 pg/ml; P < 0.05). In contrast, levels of cysteinyl leukotrienes were increased in both asthma cohorts compared with healthy individuals. In severe asthma, 15-lipoxygenase-1 mean expression was decreased fivefold in bronchoalveolar lavage cells. In contrast, 15-lipoxgenase-1 was increased threefold in endobronchial biopsies, but expression of both 5-lipoxygenase and 15-lipoxygenase-2 in these samples was decreased. Cyclooxygenase-2 expression was decreased in all anatomic compartments sampled in severe asthma. Moreover, LXA(4) receptor gene and protein expression were significantly decreased in severe asthma peripheral blood granulocytes.

CONCLUSIONS

Mechanisms underlying pathological airway responses in severe asthma include lipoxin underproduction with decreased expression of lipoxin biosynthetic enzymes and receptors. Together, these results indicate that severe asthma is characterized, in part, by defective lipoxin counterregulatory signaling circuits.

Lipid mediators as agonists for the resolution of acute lung inflammation and injury

Resolution of acute lung inflammation and injury is an active process; it is not merely the absence of proinflammatory signals. Restoration of homeostasis is coordinated by specific mediators and cellular events. In response to injury and inflammatory stimuli, infiltrating leukocytes and tissue-resident cells interact to generate lipoxins (LXs), which are bioactive eicosanoids derived from arachidonic acid. In contrast to proinflammatory leukotrienes and prostaglandins, LXs display potent antiinflammatory actions. LXA(4) interacts with a G protein-coupled receptor, termed ALX, that transduces counter-regulatory signals in part via intracellular polyisoprenyl phosphate remodeling. Presqualene diphosphate (PSDP) is a polyisoprenyl phosphate in human neutrophils that is rapidly converted to presqualene monophosphate (PSMP) upon cell activation. PSDP, but not PSMP, directly inhibits phospholipase D, phosphoinositol-3 kinase, and superoxide anion generation. LXs block PSDP turnover in neutrophil membranes to prevent proinflammatory responses. Hence, LX and polyisoprenyl phosphate signaling provide a counter-regulatory circuit to promote resolution of acute lung inflammation. LXA(4) and PSDP mimetics have been prepared with potent protective actions in murine models of asthma and acute lung injury.

Cytochrome P450 4F subfamily: at the crossroads of eicosanoid and drug metabolism

The cytochrome P450 4F (CYP4F) subfamily has over the last few years come to be recognized for its dual role in modulating the concentrations of eicosanoids during inflammation as well as in the metabolism of clinically significant drugs. The first CYP4F was identified because it catalyzed the hydroxylation of leukotriene B(4) (LTB(4)) and since then many additional members of this subfamily have been documented for their distinct catalytic roles and functional significance. Recent evidence emerging in relation to the temporal change of CYP4F expression in response to injury and infection supports an important function for these isozymes in curtailing inflammation. Their tissue-dependent expression, isoform-based catalytic competence and unique response to the external stimuli imply a critical role for them to regulate organ-specific functions. From this standpoint variations in relative CYP4F levels in humans may have direct influence on the metabolic outcome through their ability to generate and/or degrade bioactive eicosanoids or therapeutic agents. This review covers the enzymatic characteristics and regulatory properties of human and rodent CYP4F isoforms and their physiological relevance to major pathways in eicosanoid and drug metabolism.

Cyclooxygenase- and lipoxygenase-derived eicosanoids in bronchoalveolar lavage fluid from patients with scleroderma lung disease: an imbalance between proinflammatory and antiinflammatory lipid mediators

OBJECTIVE

Eicosanoids play a key role in the regulation of inflammation and fibrosis. Recently we showed that levels of 5-lipoxygenase (5-LOX)-derived proinflammatory/profibrotic leukotrienes are elevated in bronchoalveolar lavage (BAL) fluid from patients with scleroderma lung disease (SLD). The present study was undertaken to investigate whether increased levels of leukotrienes are balanced by the antiinflammatory/antifibrotic cyclooxygenase (COX)- and 15-LOX-derived eicosanoids in the lungs of patients with SLD.

METHODS

Levels of 5-LOX-derived leukotriene B(4) (LTB(4)), COX-derived prostaglandin E(2) (PGE(2)), and 15-LOX-derived 15-hydroxyeicosatetraenoic acid (15-HETE) and lipoxin A(4) (LXA(4)) in BAL fluid from systemic sclerosis (SSc) patients with SLD (n = 32) and without SLD (n = 16) and from healthy individuals (n = 12) were measured by enzyme-linked immunosorbent assay.

RESULTS

Levels of LTB(4) (mean +/- SEM 248 +/- 29 pg/ml) and PGE(2) (51 +/- 10 pg/ml) in SSc patients with SLD were significantly higher compared with patients without SLD (LTB(4) 119 +/- 35 pg/ml, PGE(2) 17 +/- 3 pg/ml; P < 0.05 for both) and with healthy controls (85 +/- 12 pg/ml and 19 +/- 2 pg/ml, respectively; P < 0.05 for both). Accordingly, the mean +/- SEM PGE(2):LTB(4) ratio was similar in SSc patients with SLD (0.30 +/- 0.05), SSc patients without SLD (0.29 +/- 0.07), and controls (0.31 +/- 0.07). In contrast, levels of 15-HETE and LXA(4) in patients with SLD did not differ significantly from levels in patients without SLD or in controls. The ratio of LXA(4):LTB(4) in SLD patients (0.16 +/- 0.03) was significantly lower (P < 0.05) than that in patients without SLD (0.40 +/- 0.10) or controls (0.34 +/- 0.08).

CONCLUSION

Increased production of LTB(4) in the lungs of patients with SLD is not balanced by an up-regulation of 15-LOX-derived antiinflammatory/antifibrotic eicosanoids such as 15-HETE or LXA(4). Targeting the 5-LOX/15-LOX balance may be of practical value in the treatment of SLD.

Lipoxins and lipoxin analogs in asthma

The pathobiology of asthma is characterized by production of eicosanoids, a diverse family of bioactive fatty acids that play important roles in regulating airway inflammation and reactivity. Lipoxins (LXs) are products of arachidonic acid metabolism that are distinct from leukotrienes (LTs) and prostaglandins (PGs) in structure and function. Unlike the pro-inflammatory PGs and LTs, LXs display counter-regulatory actions. Cell-type specific biological actions have been uncovered for LXs and LX stable analogs that promote resolution of acute inflammatory responses. At least two classes of receptors, CysLT1 receptors and LXA4 receptors (named ALX), can interact with LXA4 and LXA4 analogs to mediate their biological actions. LXs are generated during asthma and LXA4 signaling blocks asthmatic responses in humans and experimental model systems. Of interest, respiratory diseases of increased severity, such as aspirin-intolerant asthma, cystic fibrosis and steroid-dependent, severe asthma, display defective generation of these protective lipid signals. Together, these findings indicate a pivotal role for LXs in mediating airway homeostasis.

Paradoxical attenuation of leukocyte rolling in response to ischemia- reperfusion and extracorporeal blood circulation in inflamed tissue

In contrast to acute preparations such as the exteriorized mesentery or the cremaster muscle, chronically instrumented chamber models allow one to study the microcirculation under “physiological” conditions, i.e., in the absence of trauma-induced leukocyte rolling along the venular endothelium. To underscore the importance of studying the naive microcirculation, we implanted titanium dorsal skinfold chambers in hamsters and used intravital fluorescence microscopy to study venular leukocyte rolling in response to ischemia-reperfusion injury or extracorporeal blood circulation. The experiments were performed in chambers that fulfilled all well-established criteria for a physiological microcirculation as well as in chambers that showed various extents of leukocyte rolling due to trauma, hemorrhage, or inflammation. In ideal chambers with a physiological microcirculation (<30 rolling leukocytes/mm vessel circumference in 30 s), ischemia-reperfusion injury and extracorporeal blood circulation significantly stimulated leukocyte rolling along the venular endothelium and, subsequently, firm leukocyte adhesion. In contrast, both stimuli failed to elicit leukocyte rolling in borderline chambers (30–100 leukocytes/mm), and in blatantly inflamed chambers with yet higher numbers of rolling leukocytes at baseline (>100 leukocytes/mm), we observed a paradoxical reduction of leukocyte rolling after ischemia-reperfusion injury or extracorporeal blood circulation. A similar effect was observed when we superfused leukotriene B4 (LTB4) onto the chamber tissue. The initial increase in leukocyte rolling in response to an LTB4 challenge was reversed by a second superfusion 90 min later. These observations underscore 1) the benefit of studying leukocyte-endothelial cell interaction in chronically instrumented chamber models and 2) the necessity to strictly adhere to well-established criteria of a physiological microcirculation.

A validated liquid chromatography–mass spectrometry method for the determination of leukotrienes B4 and B5 produced by stimulated human polymorphonuclear leukocytes

A validated high-performance liquid chromatography (HPLC)-mass spectrometry method has been developed for the simultaneous assay of leukotrienes (LTs) B4 and B5, derived from omega-6 arachidonic acid and omega-3 polyunsaturated fatty acids (PUFA), respectively, produced by human polymorphonuclear leukocytes (PMNLs) stimulated with calcium ionophore A23187. The HPLC separation of PMNL ether extracts was performed on a reversed-phase column using a gradient elution program of 15 mM ammonium acetate and MeOH. Detection was performed by electrospray ionization-single quadripole mass spectrometry using single ion reaction monitoring in the negative mode at m/z 333.3 [M-H](-) and m/z 335.2 for prostaglandin B2/LTB5 and LTB4, respectively. The calibration curves for LTB4 and LTB5 were linear over the ranges 165-990 and 0.825-13.2 ng/ml, respectively. The lower limit of quantification for LTB5 was 0.66 ng/ml. The mean absolute recoveries for LTB4 and LTB5 were 81+/-4.8% and 82+/-5.9%, respectively. The method is precise with mean interday CVs for LTB4 and LTB5 within 7.1-10.7, and 3.8-9.4%, respectively, and accurate (range of interday deviations for LTB4 and LTB5 were -7.8 to 1, and -5 to 9% , respectively). The method has been validated and is being applied to the simultaneous quantification of the leukotrienes B4 and B5 in stimulated PMNLs in a clinical protocol studying the influence of a diet enriched in omega-3 PUFA on various surrogate markers of inflammation in young cystic fibrosis patients.

Effect of Cleome arabica leaf extract, rutin and quercetin on soybean lipoxygenase activity and on generation of inflammatory eicosanoids by human neutrophils

The effects of Cleome arabica leaf extract, rutin and quercetin on soybean lipoxygenase (Lox) activity and on calcium ionophore (A23187)-stimulated generation of the leukotriene B4 and prostaglandin E2 by human neutrophils were examined. The extract (25 microg/ml), rutin (25 microM) and quercetin (25 microM) inhibited LTB4 synthesis at all concentrations of A23187 used. The extract at 1-100 microg/ml and rutin at 1-100 microM inhibited LTB4 generation by neutrophils stimulated with 1 microM A23187 by about 50%. PGE2 production in response to different concentrations of A23187 was affected in a biphasic manner by the extract and rutin. Quercetin at 1-100 microM caused concentration-dependent inhibition of LTB4 and PGE2 production. The extract, rutin and quercetin caused concentration-dependent inhibition of soybean Lox activity. These results indicate that rutin, quercetin and an extract of C. arabica containing these compounds inhibit Lox activity, consequently decreasing LTB4 production. Thus, these compounds or extracts containing them may be beneficial for the treatment of inflammatory conditions, particularly those characterised by excessive leukotriene generation.

Lipid peroxidation and 5-lipoxygenase activity in chronic obstructive pulmonary disease

We studied the urinary excretion of the isoprostane 8-iso-prostaglandin F(2alpha) as an index of in vivo oxidant stress, and the production of leukotriene (LT) B(4) (LTB(4)) by neutrophils in subjects with chronic obstructive pulmonary disease (COPD) and normal subjects. Overnight urinary excretion of the isoprostane was significantly higher in patients with COPD than in control subjects, and LTB(4) production by challenge of neutrophils obtained from patients with COPD was also significantly higher than that observed in control neutrophils. Treatment with a standardized polyphenol extract caused a significant decrease in isoprostane excretion, accompanied by a statistically significant increase of Pa(O(2)). Furthermore, changes in FEV(1) significantly correlated with the changes in isoprostane urinary excretion observed from enrollment to the end of treatment. The results of this study suggest that enhanced oxidative stress in subjects with COPD is paralleled by the increased ability of neutrophils to synthesize the chemotactic factor LTB(4), and may ultimately contribute to the infiltration/activation of neutrophils into the airways of subjects with COPD. Antioxidant treatment in subjects with COPD is effective in reducing oxidant stress as shown by the decrease of urinary isoprostane, a reduction that correlates with the severity of the disease, as indicated by changes in Pa(O(2)) and FEV(1).

LTB4 is present in exudative pleural effusions and contributes actively to neutrophil recruitment in the inflamed pleural space

The pleural space is a virtual compartment between the lung and chest wall that becomes filled with fluid and inflammatory cells during a variety of respiratory diseases. Here, we study the potential role of the eicosanoid metabolite leukotriene B4 (LTB4) in disparate diseases leading to acute (pneumonia) or chronic (tuberculosis, cancer) inflammation of the pleural space. LTB4 concentrations were significantly higher in pleural fluid due to pneumonia, tuberculosis and cancer with respect to congestive heart failure and correlated with neutrophil elastase, which is used as an indication of state of activation of neutrophils in the pleural space. Moreover, pleural LTB4 was biologically active, as an anti-LTB4 antibody partially neutralized the chemotactic activity of parapneumonic, tuberculous and cancer effusions. Macrophages, neutrophils, lymphocytes, mesothelial cells and cancer cells all expressed mRNA for 5-lipoxygenase, the enzyme that initiates leukotriene synthesis leading to the production of LTB4, in exudative pleural effusions. Upon stimulation in transudative pleural effusions, pleural macrophages produced, in a time-dependent fashion, a significantly higher concentration of LTB4 than mesothelial cells. These studies demonstrate that different cell types are capable of producing LTB4 in the inflamed pleural space and that this mediator may play a crucial role in the recruitment of neutrophils into the pleural space.

Inflammatory response of human tendon fibroblasts to cyclic mechanical stretching

BACKGROUND

The cellular and molecular mechanisms for the development of tendinopathy are not clear, but inflammatory mediators produced by tendon fibroblasts in response to repetitive mechanical loading may be an important factor.

HYPOTHESES

(1) Cyclic stretching of tendon fibroblasts affects the production of leukotriene B(4) and the expression of 5-lipoxygenase; and (2) the production level of leukotriene B(4) is inversely related to that of prostaglandin E(2).

STUDY DESIGN

Controlled laboratory study.

METHODS

Human patellar tendon fibroblasts were uniaxially stretched in the presence of indomethacin (25 micro M) or MK-886 (10 micro M). After stretching for 4 hours, followed by 4 hours rest, levels of prostaglandin E(2), leukotriene B(4), and expression of 5-lipoxygenase were measured.

RESULTS

Stretched tendon fibroblasts increased the levels of leukotriene B(4) but did not appreciably change the expression of 5-lipoxygenase. Indomethacin decreased the cellular production of prostaglandin E(2) but caused increased leukotriene B(4) levels. MK-886 caused decreased production of leukotriene B(4) but increased production of prostaglandin E(2).

CONCLUSIONS

Cyclic stretching of human tendon fibroblasts increases the production of prostaglandin E(2) and leukotriene B(4). Blocking prostaglandin E(2) production leads to increased leukotriene B(4) levels and vice versa.

CLINICAL RELEVANCE

The use of nonsteroidal anti-inflammatory drugs for the treatment of tendon inflammation might increase the levels of leukotriene B(4) within the tendon, potentially contributing to the development of tendinopathy.

Inflammatory prompts produce isoform-specific changes in the expression of leukotriene B(4) omega-hydroxylases in rat liver and kidney

Cytochrome p450 (CYP) 4Fs metabolize leukotriene B(4) and other inflammatory mediators in the arachidonic acid cascade. Here we show that lipopolysaccharide (LPS) treatment suppresses CYP4F4 and up-regulates CYP4F5 mRNA expression in rat liver whereas renal CYP4Fs are essentially unchanged. BaSO(4) treatment, in contrast, increases both hepatic and renal CYP4F expression levels. Thus, distinct regulatory mechanisms in CYP4F expression might operate under different inflammatory prompts. To examine hepatic totipotency, primary hepatocytes were treated with varying doses of LPS resulting in decrease in all the CYP4F isoforms. Treatment of hepatocytes with 5 ng/ml of interleukin-1beta mimics the in vivo effects of LPS on CYP4F expression.

Mesenteric microvascular inflammatory responses to systemic hypoxia are mediated by PAF and LTB4

Systemic hypoxia produces a rapid microvascular inflammatory response characterized by increased reactive oxygen species (ROS) levels, leukocyte-endothelial adherence and emigration, and increased vascular permeability. The lipid inflammatory mediator leukotriene B(4) (LTB(4)) is involved in the early hypoxia-induced responses (ROS generation and leukocyte adherence). Whether other lipid inflammatory mediators participate in this phenomenon is not known. The objective of these experiments was to study the role of platelet-activating factor (PAF) in the microvascular inflammatory response to hypoxia and its potential interactions with LTB(4) in this response. Intravital microscopy was used to examine mesenteric venules of anesthetized rats. We found that WEB-2086, a PAF receptor antagonist, completely prevented the increase in ROS levels and leukocyte adherence during a brief reduction in inspired Po(2) to anesthetized rats; administration of either WEB-2086 or the LTB(4) antagonist LTB(4)-DMA attenuated leukocyte emigration and the increase in vascular permeability to the same extent during prolonged systemic hypoxia in conscious rats. Furthermore, no additive effect was observed in either response when both antagonists were administered simultaneously. This study demonstrates a role for PAF in the rapid microvascular inflammatory response to hypoxia, as well as contributions of PAF and LTB(4) to the slowly developing responses observed during sustained hypoxia. The incomplete blockade of the hypoxia-induced increases in vascular permeability and leukocyte emigration by combined administration of both antagonists indicates that factors in addition to LTB(4) and PAF participate in these phenomena.

Arachidonic acid activates phospholipase D in human neutrophils; essential role of endogenous leukotriene B4 and inhibition by adenosine A2A receptor engagement

We report in human neutrophils (PMN) that phospholipase D (PLD) was stimulated by micromolar concentrations of arachidonic acid (AA) and nanomolar concentrations of leukotriene B(4) (LTB(4)), and eicosapentaenoic acid was inactive. The stimulatory effect of AA occurred only when adenosine was eliminated from PMN suspensions or when PMN were incubated with adenosine A(2A) receptor antagonists. The mechanism of AA-induced PLD activation was investigated. The results show that AA- and LTB(4)-induced PLD activation were inhibited by the LTB(4) receptor 1 (BLTR1) antagonist CP 105,696, whereas the LTA(4) hydrolase inhibitor SC57461A and the LT biosynthesis inhibitor MK-0591 inhibited AA- but not LTB(4)-mediated PLD activation. The AA-induced ARF1 and RhoA translocation to PMN membranes was inhibited by CP 105,696 and SC57461A. These results provide evidence of a requirement for an autocrine-stimulatory loop involving LTB(4) and BLTR1 in the translocation of small GTPases to membranes and the activation of PMN PLD by AA.

Does increased leukotriene B4 in type 1 diabetes result from elevated cholesteryl ester transfer protein activity?

Elevated cholesteryl ester transfer protein (CETP) activity has been reported in type 1 diabetic subjects and may be one cause of the high incidence of macrovascular complications in these patients. LDL delivers arachidonic acid (AA), in the form of cholesteryl ester (CE), to cells such as monocytes and fibroblasts, as precursor for eicosanoid synthesis. We discovered that AA content in LDL CE was significantly correlated with CETP activity, even after controlling for CETP concentration, in type 1 diabetic children. The production of LTB(4), a potent chemotactic and pro-inflammatory factor which plays a role in atherogenesis, has been shown to be increased in type 1 diabetic patients. We hypothesized that in these subjects, increased AA content in LDL CE, resulting from increased CETP activity and transient hyperinsulinemia, may lead to enhanced synthesis of LTB(4) and subsequently the higher incidence of cardiovascular disease.

Epstein-Barr virus primes human polymorphonuclear leucocytes for the biosynthesis of leukotriene B4

In the present study, we have investigated the effect of the short-term incubation of polymorphonuclear leucocytes (PMN) with infectious Epstein-Barr virus (EBV) on leukotriene B(4) (LTB(4)) biosynthesis. Pre-exposure of PMN to EBV led to an increased production of LTB(4) upon stimulation with either the ionophore A23187, the chemotactic peptide fMLP, or phagocytic particles (zymosan). Experiments performed with viral particles pretreated with a neutralizing antibody raised against the gp350 of the viral envelope revealed that a specific interaction between the PMN surface and the viral glycoprotein gp350 is required for the priming effect of EBV. Preincubation of PMN with EBV resulted in an increased release of arachidonic acid upon stimulation with a second agonist. Moreover, LTB(4) biosynthesis in EBV/A23187-treated PMN was greatly diminished in the presence of an inhibitor of the cytosolic phospholipase A2 (cPLA(2)), suggesting that cPLA(2) plays a critical role in the priming effect of EBV. Accordingly, EBV by itself promoted Ser-505 phosphorylation of cPLA(2) and strongly enhanced fMLP-induced phosphorylation of p38 MAP kinase, an enzyme known to phosphorylate cPLA(2) in human PMN. Furthermore, fMLP-induced translocation of cPLA(2) was strongly enhanced when PMN were previously exposed to EBV. These data indicate that binding of EBV to human PMN results in the activation of intracellular events involved in the release of pro-inflammatory lipid mediators.

p38 MAPK regulates group IIa phospholipase A2 expression in interleukin-1beta -stimulated rat neonatal cardiomyocytes

Group IIa phospholipase A(2) (GIIa PLA(2)) is released by some cells in response to interleukin-1beta. The purpose of this study was to determine whether interleukin-1beta would stimulate the synthesis and release of GIIa PLA(2) from cardiomyocytes, and to define the role of p38 MAPK and cytosolic PLA(2) in the regulation of this process. Whereas GIIa PLA(2) mRNA was not identified in untreated cells, exposure to interleukin-1beta resulted in the sustained expression of GIIa PLA(2) mRNA. Interleukin-1beta also stimulated a progressive increase in cellular and extracellular GIIa PLA(2) protein levels and increased extracellular PLA(2) activity 70-fold. In addition, interleukin-1beta stimulated the p38 MAPK-dependent activation of the downstream MAPK-activated protein kinase, MAPKAP-K2. Treatment with the p38 MAPK inhibitor, SB202190, decreased interleukin-1beta stimulated MAPKAP-K2 activity, GIIa PLA(2) mRNA expression, GIIa PLA(2) protein synthesis, and the release of extracellular PLA(2) activity. Infection with an adenovirus encoding a constitutively active form of MKK6, MKK6(Glu), which selectively phosphorylates p38 MAPK, induced cellular GIIa PLA(2) protein synthesis and the release of GIIa PLA(2) and increased extracellular PLA(2) activity 3-fold. In contrast, infection with an adenovirus encoding a phosphorylation-resistant MKK6, MKK6(A), did not result in GIIa PLA(2) protein synthesis or release by unstimulated cardiomyocytes. In addition, infection with an adenovirus encoding MKK6(A) abrogated GIIa PLA(2) protein synthesis and release by interleukin-1beta-stimulated cells. These results provide direct evidence that p38 MAPK activation was necessary for interleukin-1beta-induced synthesis and release of GIIa PLA(2) by cardiomyocytes.

Leukotriene B(4) promotes reactive oxidant generation and leukocyte adherence during acute hypoxia

Acute systemic hypoxia produces rapid leukocyte adherence in the rat mesenteric microcirculation, although the underlying mechanisms are not fully known. Hypoxia is known to increase reactive oxygen species (ROS) generation, which could result in formation of the lipid inflammatory mediator leukotriene B(4) (LTB(4)). The goal of this study was to examine the role of LTB(4) in hypoxia-induced microvascular alterations. Using intravital microscopy, we determined the effect of the LTB(4) antagonist, LTB(4)-dimethyl amide (LTB(4)-DMA), on ROS generation and leukocyte adherence in mesenteric venules during hypoxia. Exogenous LTB(4) increased ROS generation to 144 +/- 8% compared with control values and also promoted leukocyte adherence. These responses to LTB(4) were blocked by pretreating the mesentery with LTB(4)-DMA. Leukopenia did not significantly attenuate the LTB(4)-induced increase in ROS generation (142 +/- 12.1%). LTB(4)-DMA substantially, though not completely, reduced hypoxia-induced ROS generation from 66 +/- 18% to 11 +/- 4% above control values. Hypoxia-induced leukocyte adherence was significantly attenuated by LTB(4)-DMA. Our results support a role for LTB(4) in the mechanism of hypoxia-induced ROS generation and leukocyte adherence in the rat mesenteric microcirculation.

Lipid mediator class switching during acute inflammation: signals in resolution

Leukotrienes (LTs) and prostaglandins (PGs) amplify acute inflammation, whereas lipoxins (LXs) have unique anti-inflammatory actions. Temporal analyses of these eicosanoids in clinical and experimental exudates showed early coordinate appearance of LT and PG with polymorphonuclear neutrophil (PMN) recruitment. This was followed by LX biosynthesis, which was concurrent with spontaneous resolution. Human peripheral blood PMNs exposed to PGE2 (as in exudates) switched eicosanoid biosynthesis from predominantly LTB4 and 5-lipoxygenase (5-LO)-initiated pathways to LXA4, a 15-LO product that "stopped" PMN infiltration. These results indicate that first-phase eicosanoids promote a shift to anti-inflammatory lipids: functionally distinct lipid-mediator profiles switch during acute exudate formation to "reprogram" the exudate PMNs to promote resolution.

A novel hepatointestinal leukotriene B4 receptor. Cloning and functional characterization

Leukotriene B(4) (LTB(4)) is a product of eicosanoid metabolism and acts as an extremely potent chemotactic mediator for inflammation. LTB(4) exerts positive effects on the immigration and activation of leukocytes. These effects suggest an involvement of LTB(4) in several diseases: inflammatory bowel disease, psoriasis, arthritis, and asthma. LTB(4) elicits actions through interaction with one or more cell surface receptors that lead to chemotaxis and inflammation. One leukotriene B(4) receptor has been recently identified (LTB(4)-R1). In this report we describe cloning of a cDNA encoding a novel 358-amino acid receptor (LTB(4)-R2) that possesses seven membrane-spanning domains and is homologous (42%) and genetically linked to LTB(4)-R1. Expression of LTB(4)-R2 is broad but highest in liver, intestine, spleen, and kidney. In radioligand binding assays, membranes prepared from COS-7 cells transfected with LTB(4)-R2 cDNA displayed high affinity (K(d) = 0.17 nm) for [(3)H]LTB(4). Radioligand competition assays revealed high affinities of the receptor for LTB(4) and LTB(5), and 20-hydroxy-LTB(4), and intermediate affinities for 15(S)-HETE and 12-oxo-ETE. Three LTB(4) receptor antagonists, 14,15-dehydro-LTB(4), LTB(4)-3-aminopropylamide, and U-75302, had high affinity for LTB(4)-R1 but not for LTB(4)-R2. No apparent affinity binding for the receptors was detected for the CysLT1-selective antagonists montelukast and zafirlukast. LTB(4) functionally mobilized intracellular calcium and inhibited forskolin-stimulated cAMP production in 293 cells. The discovery of this new receptor should aid in further understanding the roles of LTB(4) in pathologies in these tissues and may provide a tool in identification of specific antagonists/agonists for potential therapeutic treatments.

Activation of leukotriene synthesis in human neutrophils by exogenous arachidonic acid: inhibition by adenosine A(2a) receptor agonists and crucial role of autocrine activation by leukotriene B(4)

We report here that the apparent inability of isolated human polymorphonuclear leukocytes (PMNs) to efficiently transform arachidonic acid (AA) is the consequence of A(2a) receptor engagement by endogenous adenosine accumulating in incubation media. Indeed, when adenosine is eliminated from PMN suspensions by the addition of adenosine deaminase, or when cells are incubated with adenosine A(2a) receptor antagonists, important quantities (40-80 pmol/10(6) cells) of 5-lipoxygenase products are synthesized by PMN incubated with 1 to 5 microM exogenous AA. The selective A(2a) receptor agonist CGS21680 was a very potent inhibitor of the AA-induced leukotriene (LT) synthesis, showing an IC(50) of approximately 1 nM. The mechanism of AA-induced stimulation of LT synthesis observed in the absence of extracellular adenosine was investigated. In adenosine deaminase-treated PMN, exogenous AA induced Ca(2+) mobilization and the translocation of 5-lipoxygenase to nuclear structures. A time lag of 20 to 60 s (variable between PMN preparations) was observed consistently between the addition of AA and the elevation of intracellular Ca(2+) concentration (and LT synthesis), indicating that AA itself did not trigger the Ca(2+) mobilization in PMN. This AA-induced Ca(2+) mobilization, as well as the corresponding 5-lipoxygenase translocation and stimulation of LT synthesis, was blocked efficiently by the LT synthesis inhibitor MK0591, the LTB(4) receptor antagonists CP105696 and LY223982, and the LTA(4) hydrolase inhibitor SC57461A. These data demonstrate that AA is a highly potent and effective activator of LT synthesis and acts through a mechanism that requires an autocrine stimulatory loop by LTB(4).

Polyisoprenyl phosphate (PIPP) signaling regulates phospholipase D activity: a 'stop' signaling switch for aspirin-triggered lipoxin A4

It is of wide interest to understand how opposing extracellular signals (positive or negative) are translated into intracellular signaling events. Receptor-ligand interactions initiate the generation of bioactive lipids by human neutrophils (PMN), which serve as signals to orchestrate cellular responses important in host defense and inflammation. We recently identified a novel polyisoprenyl phosphate (PIPP) signaling pathway and found that one of its components, presqualene diphosphate (PSDP), is a potent negative intracellular signal in PMN that regulates superoxide anion generation by several stimuli, including phosphatidic acid. We determined intracellular PIPP signaling by autocoids with opposing actions on PMN: leukotriene B4 (LTB4), a potent chemoattractant, and lipoxin A4 (LXA4), a 'stop signal' for recruitment. LTB4 receptor activation initiated a rapid decrease in PSDP levels concurrent with activation of PLD and cellular responses. In sharp contrast, activation of the LXA4 receptor reversed LTB4-initiated PSDP remodeling, leading to an accumulation of PSDP and potent inhibition of both PLD and superoxide anion generation. Thus, an inverse relationship was established for PSDP levels and PLD activity with two PMN ligands that evoke opposing responses. In addition, PSDP directly inhibited both isolated human recombinant (Ki = 6 nM) and plant (Ki = 20 nM) PLD. Together, these findings link PIPP remodeling to intracellular regulation of PMN function and suggest a role for PIPPs as lipid repressors in signal transduction, a novel mechanism that may also explain aspirin's suppressive actions in vivo in cell signaling.

Granulocyte-Macrophage Colony-Stimulating Factor Enhances EBV-Induced Synthesis of Chemotactic Factors in Human Neutrophils

We have recently demonstrated that EBV binds to human neutrophils and stimulates a wide range of activities, including homeotypic aggregation, total RNA synthesis, and expression of the chemokines IL-8 and macrophage inflammatory protein-1α (MIP-1α). Neutrophil function is also known to be modulated by priming with granulocyte-macrophage colony-stimulating factor (GM-CSF). We have therefore investigated the modulation of EBV-induced activation of human neutrophils by GM-CSF. Treatment of neutrophils with GM-CSF before EBV activation enhanced the production of both MIP-1α and IL-8. The IL-8 produced under these conditions was biologically active as determined in the calcium mobilization assay. GM-CSF was also found to increase the ability of EBV to prime neutrophils for increased leukotriene B4 (LTB4) synthesis. Prior treatment of GM-CSF with neutralizing Abs inhibited these effects. GM-CSF also increased the specific binding of FITC-EBV to the neutrophil surface, as evaluated by fluorocytometry. Local production of GM-CSF in tissues invaded by EBV could therefore serve to potentiate a host defense mechanism directed toward the destruction of the infectious virus via increased production of chemotactic factors. Since both IL-8 and MIP-1α are reported to be chemoattractants in vitro for T cells and T and B cells, respectively, the ability of EBV to induce their production by neutrophils may enhance its ability to infect B and T lymphocytes via increased recruitment to sites of infection.

Neutrophil-mediated changes in vascular permeability are inhibited by topical application of aspirin-triggered 15-epi-lipoxin A4 and novel lipoxin B4 stable analogues

Neutrophil (PMN) activation is critical in inflammation and reperfusion injury, suggesting that PMN-directed therapies may be of clinical use. Here, leukotriene B4 (LTB4)-induced PMN influx in ear skin was equivalent between 5-lipoxygenase knockout and wild-type mice. To explore actions of lipoxin (LX) in PMN-mediated tissue injury, we prepared several novel LX stable analogues, including analogues of LXA4 and aspirin-triggered 15-epi-LXA4 as well as LXB4, and examined their impact in PMN infiltration and vascular permeability. Each applied topically to mouse ears inhibited dramatically PMN-mediated increases in vascular permeability (IC50 range of 13-26 nmol) with a rank order of 15(R/S)-methyl-LXA4 > 16-para-fluoro-phenoxy-LXA4 approximately 5(S)-methyl-LXB4 >/= 16-phenoxy-LXA4 > 5(R)-methyl-LXB4. These LX mimetics were as potent as an LTB4 receptor antagonist, yet results from microphysiometry with mouse leukocytes indicated that they do not act as LTB4 receptor level antagonists. In addition, within 24 h of delivery, > 90% were cleared from ear biopsies. Neither IL-8, FMLP, C5a, LTD4, nor platelet-activating factor act topically to promote PMN influx. When applied with LTB4, PGE2 enhanced sharply both infiltration and vascular permeability, which were inhibited by a fluorinated stable analogue of aspirin-triggered LX. These results indicate that mimetics of LXs and aspirin-triggered 15-epi-LXA4 are topically active in this model and are potent inhibitors of both PMN infiltration and PMN-mediated vascular injury.

Characteristics of leukotriene biosynthesis by human granulocytes in presence of plasma

The formation of leukotriene B4 (LTB4) by neutrophils stimulated with the ionophore A23187 or physiological stimuli in heparinized plasma was investigated. In comparison with neutrophils stimulated (A23187) in a protein-free buffered salt solution, neutrophils stimulated in plasma produced only trace amounts of LTB4. The addition of human recombinant LTA4-hydrolase or erythrocytes to plasma prior to A23187 stimulation strongly and selectively stimulated (> 4-fold) the formation of LTB4 supporting that neutrophils activated in plasma with A23187 release in the extracellular milieu most of LTA4 formed by the cells, and indicating that plasma proteins drastically slow down the further metabolism of LTA4 released by neutrophils. The formation of LTB4 was then investigated in GM-CSF-primed neutrophils stimulated with fMLP in plasma; levels of synthesis were very low and the addition of erythrocytes prior to stimulation strongly enhanced LTB4 synthesis, demonstrating that agonist-stimulated neutrophils also release most of LTA4 generated in the extracellular milieu. Investigations on the fate of LTA4 in plasma revealed that LTA4 was slowly degraded through an unknown process, i.e. not through the previously described non-enzymic hydrolysis resulting in the formation of dihydroxy derivatives of LTA4. Using neutrophils labeled with tritiated arachidonate, we also demonstrated that neutrophils stimulated in plasma with fMLP or A23187, almost exclusively use endogenous arachidonate, as opposed to plasma arachidonate, to generate 5-lipoxygenase products. Finally, experiments performed with purified eosinophils indicated that contrary to neutrophils, the eosinophils do not release LTA4, but directly release LTC4.

Suppression of leukotriene B4 biosynthesis by endogenous adenosine in ligand-activated human neutrophils

Adenosine (Ado) has been shown to suppress several functional responses of human polymorphonuclear leukocytes (PMNs). The current study investigated whether endogenous Ado regulates the biosynthesis of leukotriene (LT)B4 in ligand-stimulated PMNs. Measurements of Ado in PMN resuspended in Hanks' buffered salt solution (HBSS) or plasma showed a cell concentration- and time-dependent accumulation of the nucleoside. The removal of endogenous Ado with either Ado deaminase or the blockade of its action by the Ado A2a receptor antagonist, 8-(3-chlorostyryl) caffeine, markedly increased LTB4 biosynthesis upon ligand stimulation in HBSS. Similarly, LTB4 synthesis by ligand-stimulated PMNs in plasma (containing recombinant LTA4 hydrolase to allow the conversion of protein-bound LTA4) was strongly enhanced by addition of Ado deaminase. Addition of red blood cells to suspensions of PMNs in plasma mimicked the effect of adding Ado deaminase and LTA4 hydrolase in enhancing LTB4 biosynthesis upon ligand stimulation. This effect of red blood cells on LTB4 biosynthesis was blocked by dipyridamole, an inhibitor of Ado transport, or captopril, an inhibitor of LTA4 hydrolase. These results demonstrate that endogenous Ado efficiently downregulates ligand-stimulated LTB4 biosynthesis in PMN suspensions, pointing out a potentially important regulatory function of Ado in inflammatory exudates. These results also unveil a dual role for red blood cells in upregulating LTB4 biosynthesis, namely, the removal of endogenous Ado and the conversion of LTA4 released by activated PMNs.

Epstein-Barr Virus Modulates 5-Lipoxygenase Product Synthesis in Human Peripheral Blood Mononuclear Cells

The effect of short-term coincubations of Epstein-Barr virus (EBV) with mononuclear cells on the synthesis of leukotrienes (LT) by monocytes was investigated. Although treatment of mononuclear cells with EBV alone had no significant effect on LT synthesis by monocytes, the preincubation of mononuclear cells with EBV before the further stimulation of the cells with either the ionophore A23187, the chemoattractant formyl-Met-Leu-Phe, or the phagocytic particles zymosan strikingly enhanced the formation of both LTB4 and LTC4 above the levels of synthesis observed with the stimuli alone. Such priming effect of EBV on LT synthesis was maximal after 15 minutes of preincubation of mononuclear cells with EBV and slowly declined at longer preincubation times; the priming effect of EBV was observed both in Hank's Balanced Salt Solution and plasma. The effect of EBV was abolished by prior treatment of viral particles by heat or by antibody raised against the glycoprotein gp350 of the viral envelope, but not by UV irradiation of the viral particles. Exposure of mononuclear cells to EBV was shown to strongly enhance the activation of the 5-lipoxygenase and the release of arachidonic acid induced upon cell stimulation with a second agonist. The release of arachidonic acid by the EBV-treated mononuclear cells was inhibitable by arachidonyl trifluoromethyl ketone, an inhibitor of the 80-kD cytosolic phospholipase A2 . Furthermore, EBV was shown to rapidly increase (maximum effect within 15 minutes) the levels of phosphorylated form of the cytosolic phospholipase A2 (as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analysis), a process related to the activation of this enzyme. These data show that the interaction of EBV with monocytes upregulates the formation of important lipid mediators of inflammation.