Lipoxins in asthma: potential therapeutic mediators on bronchial inflammation?

Arachidonic acid metabolism represents an important source of mediators with ambivalent actions. Among these, lipoxins (LXs) are the first agents identified and recognized as anti-inflammatory endogenous lipid mediators, which are involved in the resolution of inflammation and are present in the airways of asthmatic patients. Lipoxins result mainly from the interaction between 5 and 15-lipoxygenases (LO) and their levels are modulated by the degree of bronchial inflammation as well as by the long-term glucocorticoid treatments. In the airways, LX synthesis is higher in mild asthmatics than in severe asthmatics, whereas in vitro chemokine release inhibition by LXs is more effective in cells from severe asthmatics than from mild asthmatics. LipoxinA(4) effects on interleukin (IL)-8 released by blood mononuclear cells and on calcium influx in epithelial cells are mediated by the specific receptor ALX. Lipoxin generation by lung epithelial cells depends mainly on 15-LO activity. Mild asthmatics present higher 15-LOb expression at the epithelium level than severe patients, whereas the LX deficit in severe asthma is associated with an up-regulation of the 15-LOa expressions. Therefore, bronchial epithelial cells become a target for therapeutic intervention and LXs represent a potential therapeutic solution for bronchial inflammation resolution in asthma.

Eosinophilic inflammation in sputum of poorly controlled asthmatics.

Despite full effective treatment, asthmatic patients often present with poorly controlled asthma. Airway eosinophilia is associated with asthma, but its relationship with asthma control is still undetermined. To investigate the relationship between airway eosinophilia and asthma control, cellular and biochemical markers of airway inflammation were measured in 19 subjects with poorly controlled asthma, 16 subjects with asthma under control and eight normal volunteers. The severity of asthma was mild-to-moderate persistent in 23 patients (14 poorly controlled) and severe prednisone-dependent in 12 subjects (five poorly controlled). Induced sputum was analysed for total and differential cell counts, leukotriene E4 (LTE4), eosinophil cationic protein (ECP), regulated on activation, normal T-cell expressed and secreted (RANTES), and interleukin (IL)-8. Sputum eosinophils, LTE4, ECP and RANTES levels (but not IL-8) were significantly higher in patients with poorly controlled asthma as compared to patients with controlled asthma. By contrast, sputum cells and sputum inflammatory markers were not different among groups of patients with different severity of asthma. These results suggest that sputum eosinophilia is associated with poorly controlled asthma rather than with the severity of asthma.

Endogenous anti-inflammatory mediators from arachidonate in human neutrophils.

Eicosanoids have been historically involved in the pathogenesis of various inflammatory diseases. Lipoxins (LXs) and epi-LXs show physiological effects relevant to inflammation regulation. In this study, we focused on LX precursors based on the hypothesis that their entrance and metabolism into the cell may facilitate their targeting at the inflammation site. Because compound chirality is of considerable importance in the efficacy of therapeutic agents, our aim was to study the anti-inflammatory effects of various epimers of LXA(4) precursors compared to LXA(4). Blood polymorphonuclear cells (PMNs) were incubated with 15(S)- or 15(R)-hydroxyeicosatetraenoic acid (HETE), 14(R)-,15(S)-, or 14(S),15(S)-diHETE, and LXA(4) and then stimulated with the calcium ionophore A23187. We found that 15(R)-HETE rather than 15(S)-HETE was preferentially metabolized and that 15-epi-LXs were produced in larger amounts than LXs. In contrast, when PMNs were incubated with the diastereoisomers of 14,15(S)-diHETE, 14-epi-LXB(4) was produced in lower amounts than LXB(4). Enantiomers of 15-HETE and diastereoisomers of 14,15-diHETE and LXA(4) were able to significantly decrease LTB(4) release by PMNs. These results suggest a potential resolution of the inflammatory process through endogenous anti-inflammatory mediators released by the way of trans-cellular metabolism.

Effects of glucocorticoids on endogenous and transcellular metabolism of eicosanoids in asthma.

BACKGROUND: Human blood polymorphonuclear cells, which biosynthesize eicosanoids from the 5-lipoxygenase (5-LO) pathway, are likely to be involved in asthma, in which glucocorticoids represent the first line of therapy. Their effects on leukotriene release after a short course of treatment, which have been reported in several studies, are controversial. OBJECTIVE: We sought to investigate whether long-term oral glucocorticoids inhibit lipid mediators from the 5-LO pathway. METHODS: Twelve normal control subjects, 29 asthmatic subjects, and 50 glucocorticoid-dependent asthmatic subjects were included in the study. Polymorphonuclear cells were studied for endogenous and transcellular metabolism of eicosanoids. RESULTS: Total leukotriene B(4) production was significantly lower in cells from glucocorticoid-dependent asthmatic subjects (mean +/- SD, 177 +/- 26 ng/10(7) cells) than in control subjects (406 +/- 27), untreated asthmatic subjects (421 +/- 34), and asthmatic subjects treated with inhaled glucocorticoids (290 +/- 56). When incubated with arachidonic acid, these polymorphonuclear cells released very low amounts of 5(S)- and 12(S)-hydroxy-eicosatetraenoic acid (HETE), whereas endogenous 15(S)-HETE was found in substantial amounts. The transformation of exogenous 15(S)-HETE into 5(S),15(S)-diHETE and lipoxins was significantly more important in untreated asthmatic subjects than in control subjects and glucocorticoid-dependent asthmatic subjects. CONCLUSION: This study showed that long-term oral corticotherapy affects the 5-LO activity and leads to a decrease production of all metabolites in contrast to short-term or inhaled glucocorticoids. This study also questions the site of action of glucocorticoids in regulating the availability of arachidonic acid and potential eicosanoid regulation, as previously held in phospholipase A2 studies.

Generation of eicosanoids from 15(S)-hydroxyeicosatetraenoic acid in blood monocytes from steroid-dependent asthmatic patients.

The aim of this study was to investigate eicosanoid metabolism by human peripheral blood monocytes (PBM) from steroid-dependent asthmatic patients as compared to control subjects and untreated asthmatic patients. Eicosanoid biosynthesis by PBM isolated from venous blood using Percoll gradient centrifugation was evaluated following stimulation of 5 x 10(6) cells with calcium ionophore A23187, with or without exogenous 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE), and analyzed by reverse phase high performance liquid chromatography (RP-HPLC). Without 15(S)-HETE, PBM synthesized leukotriene B4 (LTB4) only (40 +/- 12 ng and 59 +/- 11 ng for untreated and steroid-dependent asthmatics, respectively). In the presence of 15(S)-HETE, PBM produced six-fold smaller amounts of leukotriene B4 (P < 0.0001). They also released 5(S),15(S)-dihydroxyeicosatetraenoic acid (5(S),15(S)-diHETE) in similar amounts for all the populations, whereas low amounts of lipoxins (LXs) were produced by PBM from asthmatics only (2.7 +/- 0.7 ng and 4.6 +/- 2.8 ng for untreated and steroid-dependent asthmatics, respectively). Moreover, PBM were also able to release an unknown compound containing conjugated triene chromophore. Cells from steroid-dependent asthmatic patients synthesized this unknown metabolite in higher amounts than controls and untreated asthmatics (133 +/- 18 ng vs 52 +/- 19 ng and 68 +/- 15 ng, respectively, P < 0.02). This work shows for the first time that human PBM are able to metabolize 15(S)-HETE and lead to lipoxins and to an unknown metabolite, with the amounts of the latter being enhanced by long-term corticosteroid treatment.

Leukotriene E4 plasma levels in adult asthmatic patients with variable disease severity.

Cysteinyl leukotrienes (C-LTs) are local inflammatory mediators involved in bronchial asthma. Seventeen asthmatic patients (FEV1 ranging from 41 to 99.8% of predicted values) and 11 healthy subjects were studied. The clinical severity of asthma was assessed by the Aas score. Plasma C-LTs were measured by enzyme immunoassay (EIA) after sample purification by solid-phase extraction (SPE), to investigate whether differences may exist between asthmatic and control subjects and whether leukotriene E4 (LTE4) levels were related to the severity of disease. LT measurements showed that 87.6 +/- 1.2% was recovered as LTE4 and 9.4 +/- 1.3% as LTC4. In asthmatic subjects, LTE4 plasma levels were found to be significantly higher than those in the control group (1.073 +/- 0.133 and 0.53 +/- 0.19 ng/ml of plasma, respectively; P < 0.002). Moreover, there was a significant correlation between LTE4 plasma levels and the Aas clinical score (P < 0.005). These data suggest that plasma LTE4 levels might be used to assess the severity of asthma.

Synthesis and biological activities of higher homologues of retinoic acid.

Homoretinoic and bishomoretinoic acid have been synthesized. Fast reaction under ultrasonic activation (Wolff rearrangement, saponification) produced compounds in high yields. Only the bishomo analogue exhibits a significative activity alone and a synergistic effect with vitamin D3 on the differentiation of U937 leukemic cell line.

5(S),15(S)-dihydroxyeicosatetraenoic acid and lipoxin generation in human polymorphonuclear cells: dual specificity of 5-lipoxygenase towards endogenous and exogenous precursors.

5-Lipoxygenase activation of human blood polymorphonuclear cells (PMN) from asthmatic patients (asthmatics) was studied to investigate whether differences may exist with healthy subjects (controls). The respective cell capacities to produce lipoxins (LXs), leukotrienes, and 5(S), 15(S)-dihydroxyeicosatetraenoic acid [5(S),15(S)-diHETE] were compared under in vitro stimulation by ionophore A23187, with or without exogenous 15(S)-hydroxyeicosatetraenoic acid [15(S)-diHETE]. Eicosanoids were analyzed by elution with an isocratic reverse-phase high performance liquid chromatography system, and their profiles, detected by simultaneous monitoring at 302, 280, and 246 nm, were evaluated on the basis of chromatographic behavior: UV spectral characteristics and coelution with synthetic standards. In the presence of exogenous 15(S)-HETE, human PMN were able to produce LXs and 5(S),15(S)-diHETE, PMN from asthmatics were able to produce 5(S), 5(S),15(S)-diHETE, and LXs from endogenous sources, whereas in the same experimental conditions, no detectable amounts of these compounds were released by PMN from controls. The levels of 5(S),15(S)-diHETE, and LXs biosynthesized from endogenous arachidonic acid were highly correlated. Two different LX patterns were observed involving two possible metabolic pathways: (a) via the intermediate 5,6-epoxytetraene alone for LXs generation from exogenous 15(S)-HETE; and (b) via 5,6- and/or 14,15-epoxytetraenes leading to the formation of an enzyme-bound delocalized carbocation for LXs generation from endogenous arachidonate, respectively. The enhanced 5-lipoxygenase activation of blood PMN from asthmatics and the metabolism of exogenous 15(S)-HETE may reflect a priming induced by various mediators released from environmental cells, and could be considered as a model of transcellular signalization between PMN and endothelial cells.

Conversion of endogenous arachidonic acid to 5,15-diHETE and lipoxins by polymorphonuclear cells from patients with rheumatoid arthritis.

The conversion of endogenous arachidonic acid (AA) by polymorphonuclear cells (PMN) from patients with rheumatoid arthritis (RA) was studied before (D0) and one day (D1) after antiinflammatory drug therapy. The biosynthesis of 5,15-diHETE and lipoxins (LXS), were investigated ex vivo, after PMN stimulation by ionophore A23187 without exogenous addition of 15-HETE. The eicosanoids were resolved by RP-HPLC and simultaneously detected at 246 and 302 nm respectively. Large amounts of 5,15-diHETE (50 to 400 ng/10(7) PMN) and significant levels of LXS (from 2 to 20 ng/10(7) PMN) were produced with individual differences between donors. Metabolite levels varied between patients but this work showed for the first time a linear relationship between the amounts of 5,15-diHETE and LXS. Moreover LXS production after treatment may be related to long-term clinical improvement of patients.

5-15-diHETE and lipoxins generated by neutrophils from endogenous arachidonic acid as asthma biomarkers.

5-Lipoxygenase (5-LO) activation of human blood polymorphonuclear cells (PMN) from healthy subjects (HS) and from asthmatic patients (AP) was investigated comparing their respective capacities to produce lipoxins, 5,15-dihydroxyeicosatetraenoic acid (5,15-diHETE) and leukotrienes, under in vitro stimulation by ionophore A23187. PMN from AP were able to generate higher leukotriene levels from endogenous sources than PMN from HS. Moreover they produced 5,15-diHETE (from 50 to 280ng/10(7) cells) and lipoxins (from 1 to 30ng/10(7) cells), in a linear manner, whereas in the same experimental conditions no detectable amounts of these compounds appeared in PMN from HS. The enhanced 5-LO activation of blood PMN may reflect transcellular signalisation priming indicating that lipoxins and 5,15-diHETE could be much more specific inflammatory state biomarkers than leukotriene B4.

Enhancement of leukotriene A4 biosynthesis in neutrophils from patients with rheumatoid arthritis after a single glucocorticoid dose.

Human blood polymorphonuclear cells (PMN) from seven patients with active rheumatoid arthritis (RA) were compared for their capacities to produce leukotrienes ex vivo before (D0) and 24 hr (D1) after glucocorticoid pulse therapy. The present study shows for the first time that endogenous arachidonic acid metabolism via 5-lipoxygenase pathway is significantly increased after glucocorticoid administration, leading to increased generation of the unstable precursor leukotriene A4 (LTA4) followed by predominant non-enzymatic LTA4 opening and leukotriene B4 (LTB4) omega-hydroxylation pathway. These results are unexpected since usually glucocorticoids are usually thought to decrease inflammatory mediator biosynthesis and, moreover, they work to the detriment of the clinical improvement of the patient. The results are discussed in terms of product inactivation and cellular cooperation with monocytes and endothelial cells.

Effect of nedocromil sodium on sulfidopeptide leukotrienes-stimulated human alveolar macrophages in asthma.

Alveolar macrophages (AM) may take part in the amplification of the inflammatory mechanism involved in asthma. During an asthma attack, mast cells and eosinophils release arachidonic acid derivative mediators of inflammation such as sulfidopeptide leukotrienes. Among them, LTC4 has been shown to be present in bronchoalveolar fluid. In asthmatic patients, we showed that the ability of AM to transform LTC4 into its derivatives LTD4 and LTE4 was related to the intensity of the local inflammation observed during endoscopy. AM from asthmatics incubated in the presence of LTC4 or LTE4, generated LTB4 and 5-HETE, which are potent chemoattractants. Nedocromil sodium (10(-4) M) decreased LTB4 releasability and intracellular 5-HETE concentrations in zymosan-stimulated AM from asthmatic patients, and was shown to decrease the LTC4 or LTE4-promoted formation of LTB4 and 5-HETE.

Fused pelvic kidneys: case report.

A case of fused pelvic kidneys is presented. We believe this to be the first report using ultrasound, computed tomography, and magnetic resonance imaging for presentation of a rare anatomic renal anomaly.

[Effects of methotrexate on leukotriene and derivated lipoxygenase synthesis in polynuclear neutrophils in rheumatoid polyarthritis]. / Effets du méthotrexate sur la synthèse de leucotriénes et de dérivés de la lipoxygénase par les polynucléaires au cours de la polyarthrite rhumatoïde.

Methotrexate (MTX) has been proved to be effective in rheumatoid arthritis (RA). The mechanism of action of MTX in this disease remains unelucidated but may involve inhibition of the enzyme 5-lipoxygenase. Arachidonic acid metabolites were studied in eight patients with active RA immediately prior to and 24 hours after the first intramuscular injection of 10 mg MTX. None of the patients were taking corticosteroids. Nonsteroidal antiinflammatory drugs were withdrawn four days before the study. Reverse phase high-performance liquid chromatography was used to quantitate metabolites produced by 5-lipoxygenase (5-LO) and 12-LO in plasma (full spectrum of blood cells) and purified neutrophils (PN) after stimulation with calcium ionophore A 21387 (50 microM for 30 minutes and 5 microM for 5 minutes, respectively). LTB4 production by PNs was significantly decreased (-32%, p < 0.01) 24 hours after MTX administration. A moderate (-17%), nonsignificant (NS) fall in LTB4 omega-oxidation products (wP) was seen. Production of 5-HETE was also slightly decreased (-15%, NS). Findings in plasma were comparable, with a significant decrease in total LTB4 (-29.8%, p < 0.01) and moderate falls in wP (-18.8%, NS) and in 5-HETE production (-17%, NS). Production of 12-HETE was unchanged. These findings suggest that MTX in a single dose is responsible for a decrease in the synthesis of LTB4 and 5-LO products in neutrophils and other blood cells in RA patients but does not affect 12-LO activity.

Enhanced esterification process of 5-hydroxyeicosatetraenoic acid (5-HETE) in PMN from asthmatic patients.

Polymorphonuclear neutrophils (PMN) generate 5-HETE which can be retained within cells as free metabolites or esterified into cellular lipids. Since this metabolite has been shown to have certain inflammatory properties, we compared the generation and distribution profile of 5-HETE in A 23187-stimulated PMN from asthmatic patients (AP) and normal subjects (NS). 5-HETE was analyzed using RP-HPLC. After 5 min, total 5 HETE generation was similar in the two populations. However, esterified 5-HETE was significantly enhanced in AP (72 +/- 3% versus 47 +/- 2% of the total synthesis, p less than 0.005), whereas intracellular free 5-HETE was decreased (13 +/- 3% versus 37 +/- 4%, p less than 0.005) and similar low release was observed. Kinetic studies showed that PMN from AP esterified 5-HETE more rapidly and to a greater extent than PMN from NS. By contrast, more intracellular free 5-HETE was recovered in PMN from NS. Esterification seems to be the major pathway of 5-HETE metabolism in PMN from AP. Moreover, we showed that most of the 5-HETE added exogenously was esterified into cellular lipids. In these experimental conditions, PAF-induced migration of PMN was increased. The enhanced ability of PMN to migrate could be due to the increase of 5-HETE esterification process.

Effects of a single dose of methotrexate on 5- and 12-lipoxygenase products in patients with rheumatoid arthritis.

The inhibition of 5-lipoxygenase could be involved in the mechanism of action of methotrexate (MTX). We studied 8 patients with active rheumatoid arthritis (RA) immediately before and the day after the first dose of MTX (10 mg intramuscularly). Leukotriene B4 (LTB4) formation by polymorphonuclear leukocytes was significantly decreased (32%, p less than 0.01). This essentially involved released LTB4. A slight decrease was also obtained in omega-oxidation products. Similar results were obtained for plasma LTB4 (30%, p less than 0.02). A non-significant decrease in 5-HETE was noted. Conversely, 12-HETE was not modified. Our results suggest MTX has an effect on the 5-lipoxygenase pathway, particularly at the LTA4 epoxide hydrolase step, since 5-HETE and 6-trans-LTB4 isomers are not involved.

Arachidonate 5-lipoxygenase metabolism in human neutrophils from patients with asthma: in vitro effect of nedocromil sodium.

Among the cells which participate in amplification of the local inflammatory reaction in asthma, neutrophils (PMN) are pro-inflammatory cells that can generate inflammatory mediators and arachidonic acid derivatives in particular. In asthmatic patients (AP) with attacks, the capacity of blood PMN to produce 5-lipoxygenase metabolites was investigated and compared to the response in healthy subjects (HS). PMN from 6 AP and from 6 HS were stimulated by calcium ionophore A23187 and arachidonate 5-lipoxygenase metabolites were analyzed by reverse-phase HPLC. LTB4, 6-trans LTB4, omega OH-LTB4 and 5-HETE were identified. In AP, total LTB4 synthesis was enhanced as compared to synthesis with PMN in HS. But the total 5-HETE synthesis by PMN from AP was decreased. Thus, the inflammatory potential of PMN from AP was enhanced in comparison to HS. The anti-inflammatory effect of nedocromil sodium (NS) was studied in the 5-lipoxygenase metabolism of arachidonic acid. NS (10(-4) mol/l) inhibited total LTB4 synthesized by PMN in AP but not in HS. We conclude that NS affects leukotriene synthesis only in cells with enhanced inflammatory potential.

Formation of lipoxins and leukotrienes by human alveolar macrophages incubated with 15(S)-HETE: a model for cellular cooperation between macrophages and airway epithelial cells.

Human alveolar macrophages (AM) from bronchoalveolar lavage of asthmatic patients (AP) and healthy volunteers (HS) were compared for their respective capacities to produce lipoxins and leukotrienes when stimulated by calcium ionophore A23187 with or without 15(S)-HETE. The metabolites were analyzed using an isocratic RP-HPLC system and their formation profiles evaluated on the basis of chromatographic behaviour, UV spectral characteristics and co-elution with synthetic standards. Without 15-HETE, AM from AP produced more LTB4 and 5-HETE than those from HS. In the presence of 15-HETE, human AM were able to produce 5,15-diHETE and lipoxins. Moreover, the total amount of lipoxins synthesized by AM from AP was 2 fold higher than that synthesized by AM from HS, thus showing an enhanced cell activation via the 5-lipoxygenase (5-LO) pathway. These results presented AM as in vitro 15-HETE metabolizing cells and suggested some hypothesis about human AM 5-LO regulation mechanism. The enhanced 5-LO activity in AM from AP suggested that in vivo they could participate in cell to cell interaction mechanisms involved in inflammatory lung diseases and might also take up and transform 15-HETE predominantly released by airway epithelial cells.