Arachidonic acid metabolism among human mononuclear leukocytes. Lipoxygenase-related pathways

Inhibition of bovine mononuclear cell proliferation, interleukin-2 synthesis, protein-tyrosine kinase and leukotriene B4 production by a protein-tyrosine kinase inhibitor, genistein

Genistein, an isoflavanoid compound, a selective inhibitor of protein-tyrosine kinase (PTK), inhibited PHA-stimulated bovine peripheral blood mononuclear cell proliferation (PBMC), interleukin-2 (IL-2) production, phosphorylation of PTK p56lck. Further, genistein also inhibited leukotriene B4 production from A-23187 stimulated cultures. Our data suggest that the PTK plays an important role in the signal transduction of bovine PBMC proliferation.

Lipoxin A4 metabolism by differentiated HL-60 cells and human monocytes: conversion to novel 15-oxo and dihydro products

Lipoxins are tetraene-containing eicosanoids that possess biological activity in several organ systems. To determine their route of further metabolism, [11,12-3H]lipoxin A4 was prepared and incubated with human neutrophils, promyelocytic leukemia (HL-60) cells, and adherent monocytes. Intact neutrophils and undifferentiated HL-60 cells did not significantly metabolize [11,12-3H]LXA4, while HL-60 cells differentiated with PMA to monocyte/macrophage lineage rapidly (< 15 s) transformed this eicosanoid. The major radiolabeled LXA4-derived metabolites were characterized by physical methods and were shown to be 15-oxo-LXA4, 13,14-dihydro-15-oxo-LXA4, and 13,14-dihydro-LXA4. Substrate competition with cell-free supernatants from differentiated HL-60 cells suggests that lipoxins compete for 15-hydroxyprostaglandin dehydrogenase activity or an equivalent enzyme system. In addition, adherent monocytes exposed to [11,12-3H]LXA4 rapidly metabolized (> 60% within 30 s) the label to its oxo and dihydro derivatives. These results indicate that, unlike leukotrienes, LXA4 is subject to dehydrogenation and reduction of its conjugated tetraene to form triene-containing products. Moreover, they suggest that monocytes participate in lipoxin metabolism in their local milieu.

The effects of beta 2-adrenoceptor agonists and a corticosteroid, budesonide, on the secretion of inflammatory mediators from monocytes

1. The in vitro effects of the beta 2-adrenoceptor agonists (1 x 10(-9)-10(-5) M), terbutaline, salmeterol, and formoterol, on the release of inflammatory mediators, i.e. the eicosanoids leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) and the cytokine interleukin-1 beta (IL-1 beta), were assessed in cultures of human blood monocytes. For comparison, the effects of a 5-lipoxygenase inhibitor, BW A4C (1 x 10(-9)-10(-5) M), and a corticosteroid, budesonide (1 x 10(-10)-10(-5) M) were also examined. Sotalol was used to investigate whether the actions of beta 2-agonists were mediated through beta-adrenoceptors. 2. Terbutaline, like budesonide, had no significant effect on LTB4 release, whereas BW A4C (IC50 = 2 x 10(-8) M) was a potent inhibitor. All concentrations of formoterol approximately halved the LTB4 secretion, whereas high concentrations (1 x 10(-7)-10(-5) M) only, of salmeterol, inhibited release. Only salmeterol, at high concentrations (greater than 1 x 10(-6) M), lowered the secretion of PGE2 in monocyte cultures. Formoterol and salmeterol reduced the secretion of IL-1 beta only at the highest dose (1 x 10(-5) M). In contrast, budesonide (greater than or equal to 1 x 10(-9) M) was a potent suppressant of this secretion. 3. Treatment of monocyte cultures with sotalol (1 x 10(-5) M) did not significantly antagonize the inhibitory effects of salmeterol and formoterol. These results suggest that the inhibitory action of these beta 2-agonists on the release of eicosanoids or IL-1 beta, is not mediated via beta 2-adrenoceptors.4. This study does not support a therapeutic importance of the anti-release effects of beta2-agonists since high concentrations were generally required. Furthermore, the anti-secretory action of beta2-agonists was distinct from that of corticosteroids.

Differential turnover of enzymes involved in human monocyte eicosanoid metabolism. Selective inhibition of cyclooxygenase product formation by cycloheximide in the absence of effects on 5-lipoxygenase or phospholipase A2

Human monocytes treated with cycloheximide (CHX) demonstrated a concentration- and time-dependent inhibition of prostaglandin E2 (PGE2) synthesis and release in response to stimulation with phorbol myristate acetate, ionomycin, serum-treated zymosan, or concanavalin A. The effect of CHX required preincubation and was largely reversible within 2 hr. Thromboxane A2 release was affected similarly but no comparable effects were observed on labeled arachidonic acid release or leukotriene B4 generation. The PGE2 response was also inhibited by CHX when monocytes were given exogenous arachidonic acid with or without stimulation. CHX pretreatment also comparably decreased the amount of immunoreactive cyclooxygenase in resting and stimulated monocytes. These data indicate that monocyte cyclooxygenase, in contrast to phospholipase A2 or 5-lipoxygenase and their regulatory proteins, turns over rapidly and may be a target for up- or down-regulation by pharmacologic or (potentially) physiologic agents which affect protein synthesis or degradation.

In human monocytes interleukin-1 stimulates a phospholipase C active on phosphatidylcholine and inactive on phosphatidylinositol

Interleukin-1 (IL-1) can initiate the synthesis of prostaglandins which in turn act as endogenous modulators of IL-1 production. The human monocyte/macrophage synthesizes various eicosanoids through the activation of the cellular phospholipase system. Cell stimulation results in the activation of phospholipase A2 (PLA2) whose major substrate is phosphatidylcholine (PC) and the release of the eicosanoid precursor arachidonic acid (AA) from PC. Another pathway is the stimulation of a phospholipase C (PLC) mainly active on phosphoinositides and the resulting formation of inositol phosphates (IPs) and diacylglycerol (DAG). Phospholipids other than phosphoinositides can also be hydrolysed by PLC to give rise to DAG. Studies have shown that IL-1 does not activate the IP pathway, but it primarily stimulates a PLC linked to phosphatidylethanolamine in cultured rat mesangial cells, and a PLC linked to PC in Jurkart cells. We have stimulated human monocytes with IL-1 and calcium ionophore A23187 and we have observed their effect on the phospholipase system. The results indicate that IL-1 does not activate the formation of IPs in cells labeled with [3H]myo-inositol. In contrast, in cells labeled with [3H]AA, IL-1 causes the formation of DAG associated with the hydrolysis of PC. Moreover, after stimulation with IL-1 there is no accumulation of free AA which would indicate that there has been no activation of PLA2, which occurs instead with A23187 stimulation. These data suggest that, in monocytes, IL-1 does not directly stimulate a PLA2 or a PLC active on phosphatidylinositol; instead it primarily stimulates a PLC active on PC.

Effect of dihomogammalinolenic acid and its 15-lipoxygenase metabolite on eicosanoid metabolism by human mononuclear leukocytes in vitro: selective inhibition of the 5-lipoxygenase pathway

The purpose of the present study was to determine the effect of the n-6 fatty acid, dihomogammalinolenic acid (DGLA, 20: 3, n-6) on arachidonic acid (AA) (C20: 4) metabolism by human peripheral mononuclear leukocytes (HPML). After incubation of HPML with A23187 (5 microM) and DGLA, the cyclooxygenase (CO) and lipoxygenase (LO) products were separated and quantified by reversed-phase high-performance liquid chromatography (RP-HPLC) combined with radioimmunoassay. DGLA led to no change in PGE2 formation, but at similar concentrations there was a dose-dependent decrease in LTB4 formation (IC50 = 45.0 microM). The inhibition of LTB4 formation by DGLA was associated with a dose-dependent increase in its 15-LO metabolite 15-hydroxyeicosatraenoic acid (15-HETrE) and its CO metabolite prostaglandin E1 (PGE1). Incubation of HPLM with 15-HETrE (0-1.5 microM) alone did not result in a change in PGE2 formation, whereas 15-HETrE was a much more potent inhibitor of LTB4 formation (IC50 = 0.5 microM) than DGLA. These results show that the addition of DGLA to HPML results in a selective inhibition of LTB4 formation, presumably via its metabolite (15-HETrE).

Role of thymus-eicosanoids in the immune response

The present review deals with the role(s) of thymus-eicosanoids in the immune response. It reports the production of cyclooxygenase and lipoxygenase metabolites of arachidonic acid by cells of the thymus microenvironment and the role(s) of these eicosanoids in the differentiation and the maturation of immature T-cells. The possibility that these products may be involved in tolerance to self is discussed. Briefly, it is likely that cells from the monocyte-macrophage lineage which constitute a part of the thymus microenvironment could contribute to the education of immature thymocytes by both presenting self-antigens and producing eicosanoids. Tolerance to self might result from PGE2-driven apoptosis and/or LTB4-induced generation of suppressor cells.

Angioplasty triggers intracoronary leukotrienes and lipoxin A4. Impact of aspirin therapy

BACKGROUND

Percutaneous transluminal coronary angioplasty (PTCA) is a widely used and important method of reperfusing coronary arteries. However, it is also associated with serious complications such as acute reocclusion and accelerated restenosis. The factors as well as the mechanisms involved in PTCA-associated complications remain to be fully elucidated. Because peptidoleukotrienes and lipoxins are potent vasoactive compounds, the formation of which is not inhibited by aspirin (ASA) treatment in vitro, it is possible that these eicosanoids are involved in PTCA-associated untoward events. To test this, we determined the intracoronary levels of peptidoleukotrienes and lipoxin A4 (LXA4) as well as thromboxane (TX) and 5S,12S-dihydroxyeicosatetraenoic acid (5S,12S-DiHETE; a product of double dioxygenation) after plaque rupture and evaluated the impact of ASA therapy.

METHODS AND RESULTS

PTCA was performed on 12 patients with coronary artery disease, six undergoing ASA therapy and six without ASA therapy, for at least 2 weeks before PTCA. By means of a technique that permitted sampling of intracoronary blood at the plaque site in situ, samples were taken immediately before and 10 seconds after initiation of plaque rupture. Lipoxygenase (LO)-derived products, including LXA4 and 5S,12S-DiHETE, and a marker of cyclooxygenase activity, i.e., TXB2, were quantitated after extraction and chromatography using deuterium-labeled internal standards and electron capture negative ion chemical ionization mass spectrometry. Peptidoleukotrienes (LTC4 and LTD4) were quantitated after reverse-phase high-performance liquid chromatography coupled with radioimmunoassay. Intracoronary blood taken before PTCA showed no detectable levels of these eicosanoids (the minimum limits of detection were within the picomole range). In contrast, each of these LO products was detected after PTCA. Patients undergoing ASA treatment showed elevated levels of each LO product examined compared with those not receiving ASA. Eicosanoid levels were (mean +/- SEM): LTC4, 7.10 +/- 1.22 ng/ml (ASA) versus 0.48 +/- 0.10 ng/ml; LTD4, 4.92 +/- 0.56 ng/ml (ASA) versus 1.17 +/- 0.48 ng/ml; LXA4, 24.98 +/- 4.11 ng/ml (ASA) versus 15.83 +/- 2.43 ng/ml; 5S,12S-DiHETE, 19.47 +/- 3.98 ng/ml (ASA) versus 11.98 +/- 1.83 ng/ml; TXB2, complete blockage (ASA) versus 31.04 +/- 7.38 ng/ml (p less than 0.05 for LTC4 and LTD4). To distinguish between dilatation of whole blood versus dilatation of whole blood and atheroma for contribution of eicosanoids, we also monitored their formation in Gore-tex grafts. Upon balloon inflation, TXB2 was generated, but LO products were not detected. In contrast, injection of platelet- and leukocyte-directed agonists within the graft led to both peptidoleukotriene and lipoxin formation.

CONCLUSIONS

The results indicate that PTCA triggers the intraluminal release of peptidoleukotrienes and LXA4 and that ASA therapy enhances their appearance in intracoronary blood. In addition, they provide direct evidence for LO products (LTC4, LTD4, and LXA4) in a local milieu in vivo. Moreover, the presence of the double dioxygenation product 5S,12S-DiHETE (a potential marker of 5- and 12-LO interactions) suggests that transcellular metabolic events can contribute to eicosanoid formation in vivo.

Leukotriene B4 in the immune system

Leukotriene (LT) B4 is a biologically active molecule derived from arachidonic acid via the 5-lipoxygenase pathway. It mediates certain inflammatory and immunological reactions. The role of LTB4 in the immune system has been questioned since lymphocytes have been regarded to lack the enzymes involved in LTB4 formation. This review focuses on the recently described biosynthesis of LTB4 in B-lymphocytes and the effects of this compound on lymphocyte functions.

In vitro inhibition of 5-lipoxygenase metabolite, leukotriene B4, in bovine mononuclear cells by bovine viral diarrhea virus

Bovine viral diarrhea (BVD) virus inhibited phytohemagglutinin (PHA)-, PHA plus phorbol-12-myristate-13 acetate (PMA)- or PHA plus calcium ionophore (A23187)-stimulated bovine peripheral blood mononuclear cell (PBMC) proliferation. Further, BVD-virus inhibited A23187-stimulated leukotriene B4 (LTB4) synthesis into the culture supernatants. Presence of exogenous LTB4 failed to reverse the BVD virus-induced immunosuppression. Our results suggest that BVD virus-induced immunosuppression is due to a factor that may be necessary to induce LTB4 synthesis for normal mononuclear cell proliferation.

Beta-oxidation of 12(S)-hydroxy-5,8,10,14-eicosatetraenoic acid by MOLT-4 lymphocytes

MOLT-4 lymphocytes metabolize 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12(S)-HETE via beta-oxidation with retention of the hydroxyl group at the omega 9 carbon atom. The isolation of 6-hydroxy-4,8-tetradecadienoic acid documents that these cells have the capacity to catabolize the conjugated diene system. 12(S)-HETE was also metabolized to 3,12-dihydroxy-8,10,14-eicosatrienoic acid and 1,9-dihydroxy-5,7,11-heptadecatriene as well as to 17- and 19-carbon aldehydes. When MOLT-4 cells were incubated with the beta-oxidation product, 10-hydroxy-6,8,12-octadecatrienoic acid, it was in part further catabolized but in addition it served as an anabolic precursor as defined by the accumulation 3,12-dihydroxy-8,10,14-eicosatrienoic acid as well as 1,11-dihydroxy-7,9,13-nonadecatriene. Neither 10-hydroxy-6,8,12-octadecatrienoic acid nor 13-hydroxy-5,8,11-octadecatrienic acid was as potent in inhibiting phytohemagglutin-induced lymphocyte mitogenesis as were their parent compounds--i.e., 12(S)- and 15(S)-HETE. These findings argue against the hypothesis that beta-oxidation products of 12(S)- and 15(S)-HETE are the potential modulators of lymphocyte function. However, neither the pathway for synthesis, nor the role of odd chain aldehydes and diols as potential lipid mediators was determined in this study.

Human B lymphocytes possess 5-lipoxygenase activity and convert arachidonic acid to leukotriene B4

Incubation of cell sonicates from monoclonal B cells with arachidonic acid led to the formation of leukotriene (LT) B4 and 5-hydroxy-eicosatetraenoic acid (5-HETE). In contrast, stimulation of intact B cells with the calcium ionophore A23187 +/- arachidonic acid did not, under similar conditions, lead to formation of LTB4. The identification of these products was based on reverse phase- and straight phase-HPLC analysis, UV-spectroscopy and gas chromatography-mass spectrometry. Cell sonicates of highly enriched human tonsillar B lymphocytes also converted arachidonic acid to LTB4 and 5-HETE. Activation of these cells with B cell mitogen and cytokines for three days led to an upregulation of 5-lipoxygenase activity. This study provides evidence for the biosynthesis of LTB4 from arachidonic acid in B cell lines and in normal human tonsillar B lymphocytes.

Leukotriene A4 hydrolase in the human B-lymphocytic cell line Raji: indications of catalytically divergent forms of the enzyme

Leukotriene A4 hydrolase was purified 1400-fold, with an approximate yield of 25%, to apparent homogeneity from the human B-lymphocytic cell line Raji. The purification included ammonium sulfate precipitations followed by anion exchange, hydrophobic interaction, and molecular exclusion fast protein liquid chromatography. Kinetic properties at 2 degrees C varied between different enzyme preparations. Two patterns were observed, one with a Km of about 12 microM and Vmax of about 1.1 mumol LTB4/mg protein/min which correlated well with the properties of the human leukocytic LTA4 hydrolase. In other enzyme preparations a higher catalytic activity was observed. These enzyme batches did not obey Michaelis-Menten kinetics but were compatible with a mixture of enzymatic species. Heat treatment (60 degrees C) led to a time-dependent decline in catalytic activity. However, certain enzyme preparations contained a subfraction of enzymatic activity which was more resistant to heat treatment, yielding a biphasic inactivation pattern. It is thus suggested, on the basis of the kinetic properties and the heat-inactivation pattern, that these enzyme preparations contained an addition form of LTA4 hydrolase.

Effects of monocyte-lymphocyte interaction on the synthesis of leukotriene B4

Human monocytes in monolayers were challenged with the calcium ionophore A23187. Methanol trapping of the products in the cell-free supernatants, followed by analysis on HPLC and by ultraviolet spectroscopy, revealed the presence of two compounds, which exhibited a conjugated-triene spectrum and chromatographed with the compounds formed when synthetic leukotriene (LT) A4 was added to warm acidified methanol. Furthermore, addition of purified LTA4 hydrolase to the cell-free supernatant of monocytes, stimulated with the ionophore A23187, resulted in increased levels of LTB4. These results indicate that monocytes release LTA4 extracellularly after activation with the calcium ionophore. Incubation of monocytes together with monoclonal lymphocytic cells, of both B and T cell lineage, yielded increased levels of LTB4 whereas the non-enzymatic isomers of this compound, i.e. delta 6-trans-LTB4 and 12-epi-delta 6-trans-LTB4, declined. In addition, the sum of LTB4 and its non-enzymatically formed isomers increased in mixed cultures of monocytes and monoclonal lymphocytic cells as compared to monocytes alone. The present study indicates that activated monocytes release LTA4, which is converted into LTB4 by monoclonal lymphocytic cells. Furthermore, the increase of the total amounts of leukotrienes on incubation of monocytes with lymphocytic cells, suggests the presence of an additional mechanism leading to activation of the 5-lipoxygenase pathway in monocytes.

Absence of modulation of monokine production via endogenous cyclooxygenase or 5-lipoxygenase metabolites: MK-886 (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2,2- dimethylpropanoic acid), indomethacin, or arachidonate fail to alter immunoreactive interleukin-1 beta, or TNF-alpha production by human monocytes in vitro

Human peripheral blood monocytes exposed to MK-886 (3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2,2- dimethylpropanoic acid) at doses which abolish formation of 5-lipoxygenase metabolites showed unaltered interleukin-1 beta (IL-1 beta) or tumor necrosis factor-alpha (TNF-alpha) levels in response to phorbol ester, concanavalin A, serum-treated zymosan, or lipopolysaccharide. Indomethacin (10 microM), alone or in combination with MK-886, also failed to modulate monokine production in response to any stimulus. Exogenous arachidonate (3-30 microM) which augmented the formation of PGE2 and LTB4 in the absence of stimulation, also had no effect on monokine production. LPS-induced IL-1 and TNF production occurred despite stimulation of PGE2 synthesis. The results make a role for endogenous prostaglandins and leukotrienes in the regulation of monocyte IL-1 beta and TNF-alpha production unlikely. These data also indicate that MK-886, a novel inhibitor of 5-lipoxygenase product formation, is a potentially useful leukotriene inhibitor which does not affect monokine production.

Interleukin-2-induced lung permeability is mediated by leukotriene B4

Interleukin (IL)-2 therapy leads to respiratory dysfunction due to increased vascular permeability. This study examines the role of the chemoattractant, immunomodulator, and permeability-promoting agent leukotriene (LT) B4 in this setting. Sheep with chronic lung lymph fistulae were given IL-2, 10(5) U/kg as an IV bolus (n = 6). Within 2 hours this led to a significant increase in LTB4 levels in both plasma and lung lymph. The mean pulmonary artery pressure (MPAP) rose while the pulmonary artery wedge pressure was unchanged. Arterial oxygen tension (PaO2) fell. Lung lymph flow (QL) was tripled (P less than 0.05) at 3 hours, coinciding with an increase in the lymph/plasma (L/P) protein ratio (P less than 0.05) resulting in an increase in the lymph protein clearance (P less than 0.05), data documenting increased microvascular permeability to protein. Mild leukopenia and thrombocytopenia (P less than 0.05) occurred. Body temperature rose and shaking chills were common. Pretreatment with the lipoxygenase inhibitor diethylcarbamazine (DEC; n = 6) reduced baseline plasma LTB4 levels and prevented the IL-2-induced increases in LTB4 in plasma and lung lymph (P less than 0.05). In contrast to IL-2 treatment alone, DEC blunted the increase in MPAP and prevented the rises in QL (P less than 0.05), L/P protein ratio (P less than 0.05), and lymph protein clearance (P less than 0.05). DEC also prevented the IL-2-induced leukopenia, the fall in platelet count, and the rise in body temperature (P less than 0.05, respectively). Infusion of IL-2 excipient control (n = 5) did not affect plasma or lymph LTB4 levels but there were mild increases in MPAP (P less than 0.05). The QL also rose but this occurred while the L/P protein ratio fell (P less than 0.05). Body temperature rose moderately. The PaO2, leukocyte, and platelet counts were unaffected. These data indicate that IL-2 administration leads to pulmonary dysfunction manifest by pulmonary hypertension and increased vascular permeability, events associated with LTB4 synthesis and prevented by DEC. Leukotriene B4 appears therefore to mediate the IL-2-induced lung injury.

Metabolism of 13-hydroxy-9,11-octadecadienoic acid by MOLT-4 lymphocytes

MOLT-4 lymphocytes metabolize 13-hydroxy-9,11-octadecadienoic acid, via the beta-oxidation pathway with retention of the omega 6 hydroxyl group and the conjugated diene system. The products which accumulate include 11-hydroxy-7,9-hexadecadienoic acid and 9-hydroxy-5,7-tetradecadienoic acid. In addition, it was possible to isolate two beta-hydroxy acids which were shown to be 3,13-dihydroxy-9,11-octadecadienoic acid and 3,11-dihydroxy-7,9-hexadecadienoic acid. The odd chain aldehyde, 12-hydroxy-8,10-heptadecadien-1-al, also was detected. However, neither the pathway nor the immediate precursor for the synthesis of this compound was established.

Noxious stimulus-induced increase in spinal prostaglandin E2 is noradrenergic terminal-dependent

Prostaglandins (PGs) were measured in perfusate from the lumbar intrathecal (IT) space of pentobarbital anaesthetized rats. The level of PGE2, but not of PGF2 alpha or 6-keto PGF1 alpha, was increased by immersion of a hindpaw in water at a noxious temperature (50 degrees C). No increase in PGE2 was produced by non-noxious thermal stimulation (35 degrees C water). The noxious stimulus-evoked increase in PGE2, and increases in PGE2 during norepinephrine infusion (10 micrograms/ml), were significantly decreased in rats pretreated with intrathecal 6-hydroxydopamine. These data suggest that noxious stimuli induce an increase in the production of spinal PGE2 and that this production derives from, or requires the presence of noradrenergic terminals in the spinal cord.

Inhibitory effects of MK-886 on arachidonic acid metabolism in human phagocytes

1. We have investigated the inhibitory activity of compound MK-886 (formerly L-663,536), an indole derivative, on 5-lipoxygenase product synthesis in various human phagocytes stimulated with either the ionophore A23187, in the presence and absence of exogenous arachidonic acid, or platelet-activating factor (PAF). The lipoxygenase products were analysed by reversed-phase h.p.l.c. 2. MK-886 inhibited the formation of 5-hydroxy-eicosatetraenoic acid (5-HETE), leukotriene B4 (LTB4), its omega-oxidation products and 6-trans-isomers with an IC50 value of 10-14 nM in A23187-stimulated neutrophils. In the same system, nordihydroguaiaretic acid (NDGA), AA-861 and L-655,240 showed IC50 values of 250-510, 110-420 nM and 1.7-3.9 microM, respectively. 3. MK-886 inhibited 5-lipoxygenase product synthesis in A23187-stimulated blood eosinophils and monocytes, and in neutrophils primed with granulocyte-macrophage colony-stimulating factor and stimulated with PAF with IC50 values of 1-13 nM. 4. The inhibitory activity of MK-886 was not reversed by addition of 10 microM arachidonic acid to A23187-stimulated neutrophils. 5. Compound MK-886 had no effect on 15-lipoxygenase product synthesis in blood eosinophils and neutrophils up to a concentration of 1 microM. 6. At 100 nM compound MK-886 had no significant effects on calcium ion mobilization, superoxide anion production and actin polymerization in neutrophils. 7. In conclusion, MK-886 is a very potent and specific inhibitor of both LTB4 and LTC4 synthesis in various types of human phagocytes.

Functional consequences of phospholipase A2 activation in human monocytes

Human monocytes release arachidonic acid upon stimulation with a variety of soluble or particulate agents. These include: phorbol esters (i.e., 12-O-tetradecanoate phorbol-13-acetate, TPA), calcium ionophores (ionomycin), serum-treated zymosan (STZ) concanavalin A (Con A), and, to a minor degree, lipopolysaccharides (LPS). Protein Kinase C activation or increased intracellular Ca2+ are common features of the actions of most, if not all, of these stimuli. Prevention of PKC activation by the use of staurosporine or chelation of extracellular calcium by EGTA selectively impaired AA release, indicating that PLA2 may be regulated by either pathway concurrently. The generation of inositol phosphates and diacylglycerol by the action of phospholipase C, notably upon interaction with opsonized particles during phagocytosis, apparently constitutes the physiological correlate of stimulation via these agents. Release of arachidonic acid by the action of PLA2 or other phospholipid hydrolyzing enzymes leads directly to the formation of cyclooxygenase products. In the presence of markedly elevated calcium concentrations, 5-lipoxygenase (LO) is activated as well, leading to the formation and release of leukotrienes. Agents which stimulate AA release also initiate other monocyte functions, including generation of reactive oxygen intermediates and lymphokine release. This observation makes it tempting to implicate PLA2 activation in many aspects of monocyte physiology. However, no correlation with PLA2 activation and either superoxide or lymphokine release was found when multiple stimuli, including TPA, ionomycin, serum-treated zymosan, concanavalin A, or LPS, were compared simultaneously. Instead, our results indicate that PLA2 activation is regulated by the same mechanisms, including PKC activation and increased Ca2+, as are other enzymes which determine expression of monocyte function. Phospholipase A2 (PLA2) hydrolyzes fatty acid from the sn-2 position of a wide variety of phospholipids. Substrates for this (these) enzyme(s) include species which contain a variety of polar head groups (choline, serine, ethanolamine, etc.) and some phospholipids with either linkages in sn-1. In many cell types, including human monocytes, phospholipase A2 commonly acts on substrates containing arachidonic acid (AA). The liberation of free arachidonate is a first step in the metabolism of prostaglandins, hydroxyeicosatetraeinoic acids, (HETE'S), and leukotrienes (Lt's). Monocytes and macrophages have been shown to be rich sources of arachidonate and its metabolites. Some biologic properties of monocytes, notably their role as immunomodulating cells, have been attributed to eicosanoid production and release. Accordingly, much of the interest regarding PLA2 in human monocytes centers on this aspect of their function.(ABSTRACT TRUNCATED AT 400 WORDS)

Control of human T cell proliferation by platelet-activating factor

Platelet-activating factor, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (PAF), is a membrane phospholipid with immunomodulatory functions. We studied the influence of PAF on mitogen-stimulated proliferation of human peripheral blood mononuclear cells (PBMC), purified T cells and T cell subsets. High concentrations of PAF suppressed the proliferation of all cell populations studied (44% mean inhibition with 5 microM PAF and 78% inhibition with 10 microM PAF). In contrast, the deacetylated metabolite of PAF, lyso-PAF, had no effect on proliferation at micromolar concentrations. Lower, and presumably physiologically relevant, concentrations of PAF (10(-14) to 10(-8) M) stimulated a small increase in the proliferation of unfractionated T cells. When T cells were fractionated into CD4+ and CD8+ subsets, a difference in sensitivity to PAF was observed. PAF stimulated a modest, yet statistically significant, increase in the proliferation of CD4+ T cells at concentrations ranging from 10(-14) to 10(-10) M, while either having no effect or inhibiting the proliferation of CD8+ cells across the entire concentration range. Addition of indomethacin to the cultures further enhanced CD4+ proliferation, possible due to the blockade of PAF-induced PGE2 production by monocytes. The PAF receptor antagonist BN 52021 did not block the PAF effects in this system, and the PAF receptor antagonist SRI 63-675 caused a dose dependent inhibition of T cell subset proliferation. These findings suggest that while high concentrations of PAF suppress T cell proliferation, low concentrations selectively stimulate proliferation of the CD4+ subset, an effect which is partially counteracted by PAF-induced monocyte PGE2 production.

Activation of the human neutrophil 5-lipoxygenase by exogenous arachidonic acid: involvement of pertussis toxin-sensitive guanine nucleotide-binding proteins

1. The mechanism by which incubation of human peripheral blood neutrophils with exogenous arachidonic acid leads to 5-lipoxygenase product synthesis was investigated. 2. Incubation of neutrophils with arachidonic acid caused a concentration- and time-dependent synthesis of leukotriene B4, its omega-oxidation products, and 5-hydroxyeicosatetraenoic acid. 3. The threshold concentration of arachidonic acid required for this effect was equal to, or greater than 3.3 microM and the synthesis increased with up to 33 microM arachidonic acid, the highest concentration used. Synthesis induced by arachidonic acid increased with time for up to 15 min and the major products detected were the omega-oxidation products of leukotriene B4. 4. Pre-incubation of neutrophils with pertussis toxin inhibited the synthesis of 5-lipoxygenase products induced by arachidonic acid by 75% or more, but had no effect on either arachidonic acid-induced synthesis of the 15-lipoxygenase product, 15-hydroxyeicosatetraenoic acid, or activation of the 5-lipoxygenase induced by the calcium ionophore A23187. 5. Pre-incubation of neutrophils with granulocyte-macrophage colony-stimulating factor lead to enhanced leukotriene synthesis in response to arachidonic acid. 6. These results imply that exogenous arachidonic acid is not only used as a substrate, but also activates the 5-lipoxygenase. Possible mechanisms of action are discussed.

Dysregulation of arachidonic acid release and metabolism by atopic mononuclear cells

We studied the ability of monocytes to metabolize [3H]arachidonic acid (AA) provided exogenously by activated T cells, and the extent to which dexamethasone suppressed eicosanoid production by normal and atopic cells. [3H]AA metabolites were identified using a reverse-phase high pressure liquid chromatography system (HPLC). Unstimulated and PHA-stimulated T cells from normal and atopic subjects exhibited a similar uptake and time-dependent release of radiolabel, 90% of which was identified as free AA. The addition of autologous normal and atopic monocytes to these cultures enhanced the release of radiolabel, even in the absence of stimulation with mitogen. Atopic T cell/monocyte cultures released significantly (P = 0.046) more radiolabel than normal cells when stimulated with PHA. Furthermore, the monocytes from both normal and atopic subjects metabolized T cell derived [3H]AA into cyclo-oxygenase (CO) and lipoxygenase (LO) products. Under unstimulated conditions, atopic cells produced significantly (P = 0.04) less CO products than normal cells. In contrast, under PHA and calcium ionophore-stimulated conditions, the atopic cells produced significantly (P = 0.048) more prostaglandins than normal donor cells. Furthermore, although the total release of radioactivity was comparable in both groups, significantly less (P = 0.02) free AA remained in ionophore-stimulated culture supernatants from atopic cells. In order to study the regulation of AA release by normal and atopic T cells, dexamethasone (1 microM) was added to T cell cultures. Dexamethasone inhibited the release of [3H]AA from normal T cells to a significantly (P = 0.003) greater extent than it did to atopic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of single oral administrations of non steroidal antiinflammatory drugs to healthy volunteers on arachidonic acid metabolism in peripheral polymorphonuclear and mononuclear leukocytes

The effects of a single oral administration of acetylsalicylic acid (500 mg), indomethacin (50 mg) and piroxicam (40 mg) to healthy volunteers on functional and biochemical parameters of platelets, polymorphonuclear (PMN) and mononuclear (MNL) leukocytes were evaluated. Blood was collected before and two hours after the drug intake and blood cells separated according to conventional techniques. The considered drugs almost completely suppressed the aggregation of platelets, whereas they did not affect either PMN and MNL aggregation. Superoxide anion generation by leukocytes was (PMN), or no effect (MNL) was observed after piroxicam and indomethacin respectively. The formation of arachidonate metabolites via the 5-lipoxygenase pathway by PMN and MNL challenged with 10 microM A23187 was unchanged following aspirin and indomethacin. In this respect a selective increase of 5-HETE and LTC4 synthesis by MNL only was detected after piroxicam administration. The three drugs similarly reduced TXB2 synthesis by platelets and PMN (-80% for aspirin and indomethacin, and -40% for piroxicam). As far as MNL is concerned, aspirin inhibited this metabolite by 80%, while indomethacin reduced it by 40% only. In contrast piroxicam increased TXB2 synthesis by stimulated MNL. It can be concluded that the considered antiinflammatory drugs 1) differently affect the cyclooxygenase enzyme in platelets and leukocytes; 2) at variance with the situation in platelets, the inhibition of thromboxane formation by leukocytes is not related to modifications of cellular function; 3) the formation of arachidonate metabolites via the 5-lipoxygenase pathway is affected by piroxicam only.

Monocyte functional studies in asymptomatic, human immunodeficiency disease virus (HIV)-infected individuals

Various aspects of monocyte-associated function were evaluated in the peripheral blood mononuclear cells of male homosexuals who were infected with the human immunodeficiency disease virus (HIV). The functional assessments included indomethacin-sensitive regulation of blastogenesis and lymphokine-activated killer (LAK)-cell induction, chemiluminescent responses of mononuclear leukocytes to opsonized zymosan, and the expression of HLA-DR antigen on CD-14-positive monocytes. The results obtained demonstrate that each of these functions is abnormal in asymptomatic individuals who have HIV core antigen (p24) in their circulation. These results suggest that monocyte abnormalities which could contribute to immune dysfunction in HIV-infected patients can be detected early during the course of HIV infection and are associated with the expression of serum HIV antigen.

In vitro inhibition of leukotriene B4 formation by exogeneous 5-lipoxygenase inhibitors is associated with enhanced generation of 15-hydroxy-eicosatetraenoic acid (15-HETE) by human neutrophils

Leukotrienes, products of the 5-lipoxygenase pathway of arachidonic acid metabolism, have been suggested to play a pathogenic role in psoriasis, because of their ability to induce skin inflammation and to stimulate epidermal proliferation. The 15-lipoxygenase product 15-hydroxy-eicosatetraenoic acid (15-HETE) has no proinflammatory capacity. In contrast, it can inhibit the activity of the 5-lipoxygenase. The purpose of the present study was to study the effect of 5-lipoxygenase inhibitors on the formation of 15-HETE by human neutrophils in vitro. Purified neutrophils were incubated with A 23187 (5 microM) and arachidonic acid (25 microM) with and without different inhibitors of 5-lipoxygenase activity (RS 43179, benoxaprofen, NDGA, and CP 66248). Methods for identifying eicosanoids included RP-HPLC and radioimmunoassay. Formation of leukotriene B4 was inhibited in a dose-dependent way, which was strongly correlated with a concomitant increase in the formation of 15-HETE (r = 0.97, p less than 0.01). The cyclooxygenase inhibitor indomethacin did not change 15-HETE formation. The stimulation of 15-HETE formation was not associated with cell damage as assessed by LDH release. Furthermore, identical incubations of T lymphocytes, characterized by a low 5-lipoxygenase activity, did not result in increased 15-HETE formation. These results show that inhibition of 5-lipoxygenase activity can lead to increased formation of 15-HETE. Because 15-HETE inhibits formation of 5-LO products, it may amplify the effect of 5-lipoxygenase inhibitors.

Effects of aggregating agents and of blood cells on the aggregation of whole blood by impedance technique

In this study the effects of different aggregating agents on platelet rich plasma (PRP) and whole blood (WB) aggregation, as determined by the optical and the impedance method, are evaluated. While the response of PRP to PAF, epinephrine and sodium arachidonate was comparable using the two methods, significantly greater amounts of collagen and ADP were required to obtain 50% aggregation of PRP. In addition, when the response of WB to the aggregation induced by different agents was compared to that of PRP (impedance method), no difference between WB and PRP was detected, with exception for ADP and sodium arachidonate induced aggregation. In vitro data on the aggregation of PRP induced by collagen and ADP in the presence of different concentrations of red cells and of white cells, suggest that WC and RC may affect PRP aggregation only in selected experimental conditions.

IgG-, IgA-, and IgE-induced release of leukotriene C4 by monocytes isolated from patients with atopic dermatitis

Purified peripheral blood monocytes isolated from patients with atopic dermatitis (AD) and from nonallergic normal donors were compared for their abilities to release leukotriene C4 (LTC4), leukotriene B4 (LTB4) and beta-glucuronidase in response to challenge with aggregated immunoglobulins or anti-immunoglobulins. The relationship between mediator release and the number of monocytes that formed rosettes with immunoglobulin-coated indicator cells was examined. Patients with AD had twice as many IgA- and three times as many IgE-rosetting monocytes as normal donors (48 +/- 12% versus 27 +/- 10% and 40 +/- 15% versus 14 +/- 3%, respectively), and yet the amounts of IgA- and IgE-induced LTC4 released were similar for both groups. This apparent discrepancy did not result from a decreased capacity for arachidonate metabolism via the C5-lipoxygenase pathway, since stimulation of monocytes from patients and normal donors with the calcium ionophore A23187 induced similar amounts of LTC4 and LTB4 release (LTC4, 3.0 +/- 1.7 versus 3.0 +/- 1.0 ng/10(6) cells; LTB4, 5.3 +/- 0.7 versus 5.2 +/- 0.5 ng/10(6) cells, respectively). In addition, aggregated IgG-induced LTC4 release by monocytes of both groups was similar, concomitant with an equivalent number of IgG-rosetting cells. Determination of cytophilically bound IgG and IgE by flow cytometry demonstrated that monocytes from atopic patients had more IgG bound than monocytes from normal donors. Similar amounts of IgE were detected on most monocytes from both groups, despite the higher serum IgE levels of patients. However, approximately 3% to 8% of monocytes from atopic but not normal donors stained brightly for IgE, suggesting that relatively large amounts of cytophilic IgE were bound to a small percentage of the patients' monocytes. Challenge of monocytes with anti-IgE or anti-IgG induced release of similar amounts of LTC4 for both groups, despite the presence of more cytophilic IgG on monocytes from atopic donors. These data indicate that monocytes from patients with AD release LTC4 and LTB4 in response to challenge with aggregated IgE or anti-IgE, as well as aggregated IgG, IgA, and anti-IgG. However, under our in vitro conditions, stimulation of patients' monocytes with aggregated IgA or IgE was not associated with increased mediator release, despite higher percentages of IgA- and IgE-rosetting cells compared to normal donors.

Leukotriene A4, conversion to leukotriene B4 in human T-cell lines

Human T-cell lines (HSB, MOLT-4 and CCRF-CEM) produced leukotriene B4 when incubated with leukotriene A4. The product was characterized by chromatographic properties, UV-spectroscopy and gas chromatography mass spectrometry. About 10 pmol of leukotriene B4 was obtained per 10(6) cells. When incubated with arachidonic acid plus the calcium ionophore A23187 however, no leukotriene B4 was found, indicating that the T-cell lines lack 5-lipoxygenase yet contain LTA4 hydrolase.

Leukotriene B4 and inflammatory disease

Polymorphonuclear leukocytes (PMNL) are prominent at sites of acute inflammation. Their infiltration is stimulated under pathological conditions by a variety of agents which include bacteria, immune complexes and complement derived chemotactic peptides. Recently attention was focussed on the 5-lipoxygenase product leukotriene B4 (LTB4) which has been demonstrated to induce the key features associated with an acute inflammatory reaction. However, evidence supporting a pro-inflammatory role for LTB4, and therefore the anti-inflammatory efficacy of 5-lipoxygenase inhibitors, is largely circumstantial. Moreover, there are concerns that other chemotactic factors, notably C5a, may compensate for the absence of LTB4. Here we challenge this view and, on the basis of recent experimental and clinical data suggest that LTB4 does not simply duplicate the activity of C5a. Instead we propose that their predominant site(s) of action differ in such a way that they may synergise in mediating PMNL recruitment.

Human B and T lymphocytes convert leukotriene A4 into leukotriene B4

Incubation of human tonsillar B lymphocytes and peripheral blood T lymphocytes with leukotriene A4 led to the formation of leukotriene B4. The purity of these cell suspensions was more than 99%, containing less than 0.5% monocytes. Incubation of purified B or T lymphocytes with the calcium ionophore A23187 did not lead to the formation of any detectable amounts of leukotrienes. Several established cell lines of B and T lymphocytic origin were also found to convert leukotriene A4 into leukotriene B4, showing that monoclonal lymphocytic cells possess leukotriene A4 hydrolase activity.

Studies on the effects of disease-modifying antirheumatic drugs on lipoxygenase product synthesis in human neutrophils in vitro

The disease-modifying antirheumatic drugs sodium aurothiomalate, D-penicillamine and chloroquine phosphate were tested on leukotriene (LT) synthesis in human blood polymorphonuclear leukocytes stimulated with either the ionophore A23187, zymosan or f-Met-Leu-Phe. Lipoxygenase products were analyzed by reversed-phase high-performance liquid chromatography. The study demonstrated that the drugs can either inhibit or enhance 5-lipoxygenase product synthesis in human leukocytes, depending on the stimulus used to activate the cells and the drug concentration. The data also suggested that increased substrate availability accounted for the stimulatory effects of the drugs on leukotriene synthesis.

Stimulated T cell and natural killer (NK) cell lines fail to synthesize leukotriene B4

The ability of leukotriene B4 (LTB4) to influence T cell and natural killer (NK) cell functions makes the question of LTB4 generation by these cells important to address. Consequently, LTB4 generation was evaluated in a human (Jurkat), and in a murine (EL-4) T cell line as well as in a rat NK cell line (RNK-16). Incubation of each of the 3 cell lines with [1-14C]arachidonic acid alone or in the presence of phytohemagglutinin (PHA), of calcium ionophore A23187, or of concanavalin A (Con A) plus the phorbol ester 12-0-tetradecanoylphorbol-13-acetate (TPA) failed to generate radiolabelled LTB4 or other eicosanoids as determined by thin layer radiochromatography. Using two different radioimmunoassays for LTB4 also failed to demonstrate the generation of LTB4 under basal or stimulated conditions. These results support earlier studies that demonstrate that T cells are not capable of de novo synthesis of prostaglandins, thromboxanes, or leukotrienes and also provide evidence that NK cells also do not have the capacity to generate LTB4 or other eicosanoids. Our findings are also critically discussed in relation to studies claiming eicosanoid synthesis by T cells.

Effect of endogenously produced leukotrienes and thromboxane on renal vascular resistance in rabbit hydronephrosis

Ureteral obstruction in rabbits is characterized by mononuclear cell invasion of the renal cortex and proliferative fibrosis that is associated with exaggerated prostaglandin synthesis in response to vasoactive and inflammatory cell agonists. In this investigation, we studied the effects of the chemotactic peptide N-formylmethionyl-leucyl-phenylalanine (fMLP) and bradykinin (BK) on eicosanoid synthesis and renal vascular resistance in the ex vivo perfused hydronephrotic kidney (HNK). Administration of fMLP resulted in the dose-dependent synthesis of leukotrienes, thromboxane A2 (TXA2), prostaglandin E2 (PGE2), and prostacyclin (PGI2). Peptidoleukotriene synthesis was monitored by specific radioimmunoassay and by guinea pig ileum bioassay and it was then validated by inhibition of the ileal contractile activity with the peptidoleukotriene receptor antagonist FPL-55712. The leukotrienes produced were identified as LTB4, LTC4, LTD4, and LTE4 by comigration with authentic standards on reverse phase high-performance liquid chromatography (RP-HPLC) and by ultraviolet spectroscopy. BK administration stimulated the synthesis of TXA2, PGE2, and PGI2 but not the synthesis of leukotrienes, in contrast to the results with fMLP, suggesting the involvement of different cell types. Administration of fMLP to the HNK also resulted in a renal vasoconstriction that was partially inhibited by FPL-55712 and that was completely inhibited by the thromboxane synthase inhibitor OKY-1581. Consistent with this result, exogenous administration of LTC4 resulted in the synthesis of TXA2 and in a renal vasoconstriction that was inhibited by either FPL-55712 or OKY-1581.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of human neutrophil LTA hydrolase activity by phorbol myristate acetate

The phorbol ester, phorbol 12-myristate 13-acetate enhanced leukotriene B4 production stimulated by formyl-methionyl-leucyl-phenylalanine and arachidonic acid and reduced the production of the all-trans isomers of LTB4 by human neutrophils. Production of 5-hydroxyeicosatetraenoic acid was unaffected. These observations are consistent with a stimulatory effect of phorbol ester on LTA hydrolase, the enzyme which catalyses the conversion of LTA4 to LTB4. We demonstrate that a protein of the same molecular weight as LTA hydrolase is phosphorylated upon stimulation of neutrophils with PMA. These data suggest that the activity of LTA hydrolase may be regulated by protein kinase C-dependent phosphorylation.

Release of arachidonic acid metabolites by human monocytes or lymphocytes: effect of treatment with interferon on stimulation by phorbol ester or calcium ionophore

The simultaneous production of prostaglandins, leukotrienes, and hydroxyeicosatetraenoic acids was studied in human peripheral blood monocytes obtained by counter-current centrifugal elutriation. Monocytes prelabeled for 4 hr with [3H]arachidonic acid (AA) released label into the surrounding medium in response to treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) or calcium ionophore (A23187). High-performance liquid chromatography of monocyte supernatants demonstrated that labeled compounds included those which eluted with authentic standards for thromboxane B2, 12-L-hydroxy-5,8,10-heptadecatrienoic acid (HHT), 6-keto-prostaglandin F alpha, prostaglandin E2, and 15-hydroxyeicosatetraenoic acid (HETE). 5-HETE and leukotriene B4 (LtB4) were detected only in response to ionophore treatment. Highly purified lymphocytes did not convert AA to autocoids, despite the release of free arachidonate in response to either stimulus. Pretreatment of monocytes with recombinant human interferon (IFN)-gamma or IFN-alpha for 18 hr resulted in enhanced release of labeled arachidonic acid and increased conversion to autocoids after TPA or ionophore stimulation. Absolute amounts of prostaglandin E2 produced in response to TPA or ionophore treatment were increased as well. These results demonstrate the autocoid profile released by stimulated human monocytes and illustrate the effects of IFN treatment on the production of lipoxygenase metabolites of arachidonic acid as well as cyclooxygenase products.

Phospholipid and arachidonic acid metabolism in zymosan-stimulated human monocytes: modulation by cAMP

Receptor-ligand interaction in mononuclear phagocytes is intimately linked to alterations in membrane phospholipids and release of arachidonic acid (AA). In addition, synthesis of bioactive lipids from released AA can result in further modification of cell responses. Upon challenge with opsonized zymosan, [3H]-arachidonic acid ([3H]-AA)-labeled human monocytes released 25 +/- 2% of their incorporated radiolabel within 30 min. Pretreatment of the monocytes with 5 X 10(-4) M isobutylmethylxanthine (IBMX) or 1 X 10(-3) M dibutyryl cyclic AMP (d-cAMP) inhibited total [3H]-AA release in the presence of zymosan by 47% and 42%, respectively. Analysis of incorporated [3H]-AA in cellular phospholipid pools indicated that significant amounts of label were lost from both phosphatidylcholine (PC) and phosphatidylinositol (PI) during zymosan stimulation. Treatment with d-cAMP substantially inhibited the loss of label from PC, but had no affect on PI. HPLC analysis of cell supernatants from zymosan-treated cells indicated that 5-HETE was the predominant metabolite generated from [3H]-AA, and its production was depressed during treatment with d-cAMP. Phospholipase activity in human monocyte homogenates was not effected by d-cAMP or IBMX at the highest concentrations used, whether these were added directly to the homogenate or by pretreatment of whole cells, demonstrating that inhibition required an intact cell. These results suggest that human monocytes exposed to opsonized zymosan release AA via two mechanisms and that modulation by cAMP is indirectly effecting a phospholipase directed towards PC.