Leukotrienes do not regulate interleukin 1 production by activated macrophages

15-Lipoxygenases regulate the production of chemokines in human lung macrophages

BACKGROUND AND PURPOSE

15-Lipoxygenase (15-LOX) activity is associated with inflammation and immune regulation. The objectives of the present study were to investigate the expression of 15-LOX-1 and 15-LOX-2 and evaluate the enzymes' roles in the polarization of human lung macrophages (LMs) in response to LPS and Th2 cytokines (IL-4/-13).

EXPERIMENTAL APPROACH

LMs were isolated from patients undergoing surgery for carcinoma. The cells were cultured with a 15-LOX inhibitor (PD146176 or ML351), a COX inhibitor (indomethacin), a 5-LOX inhibitor (MK886) or vehicle and then stimulated with LPS (10 ng · mL(-1)), IL-4 (10 ng · mL(-1)) or IL-13 (50 ng · mL(-1)) for 24 h. Levels of ALOX15 (15-LOX-1) and ALOX15B (15-LOX-2) transcripts were determined by real-time quantitative PCR. Immunoassays were used to measure levels of LPS-induced cytokines (TNF-α, CCL2, CCL3, CCL4, CXCL1, CXCL8 and CXCL10) and Th2 cytokine-induced chemokines (CCL13, CCL18 and CCL22) in the culture supernatant.

KEY RESULTS

Stimulation of LMs with LPS was associated with increased expression of ALOX15B, whereas stimulation with IL-4/IL-13 induced the expression of ALOX15. PD146176 and ML351 (10 μM) reduced the release of the chemokines induced by LPS and Th2 cytokines. The effects of these 15-LOX inhibitors were maintained in the presence of indomethacin and MK886. Furthermore, indomethacin revealed the inhibitory effect of PD146176 on TNF-α release.

CONCLUSIONS AND IMPLICATIONS

Inhibition of the 15-LOX pathways is involved in the down-regulation of the in vitro production of chemokines in LMs. Our results suggest that the 15-LOX pathways have a role in the pathogenesis of inflammatory lung disorders and may thus constitute a potential drug target.

Leukotrienes modulate cytokine release from dendritic cells

Leukotriene B(4) (LTB(4)) and cysteinyl leukotrienes (CysLTs) are known as potent mediators of inflammation, whereas their role in the regulation of adaptive immunity remains poorly characterized. Dendritic cells (DCs) are specialized antigen-presenting cells, uniquely capable to initiate primary immune responses. We have found that zymosan, but not lipopolysaccharide (LPS) stimulates murine bone marrow-derived dendritic cells (BM-DCs) to produce large amounts of CysLTs and LTB(4) from endogenous substrates. A selective inhibitor of leukotriene synthesis MK886 as well as an antagonist of the high affinity LTB(4) receptor (BLT(1)) U-75302 slightly inhibited zymosan-, but not LPS-stimulated interleukin (IL)-10 release from BM-DCs. In contrast, U-75302 increased zymosan-stimulated release of IL-12 p40 by approximately 23%. Pre-treatment with transforming growth factor-beta1 enhanced both stimulated leukotriene synthesis and the inhibitory effect of U-75302 and MK886 on IL-10 release from DCs. Consistent with the effects of leukotriene antagonists, exogenous LTB(4) enhanced LPS-stimulated IL-10 release by approximately 39% and inhibited IL-12 p40 release by approximately 22%. Both effects were mediated by the BLT(1) receptor. Ligands of the high affinity CysLTs receptor (CysLT(1)), MK-571 and LTD(4) had little or no effect on cytokine release. Agonists of the nuclear LTB(4) receptor peroxisome proliferator-activated receptor-alpha, 8(S)-hydroxyeicosatetraenoic acid and 5,8,11,14-eicosatetraynoic acid, inhibited release of both IL-12 p40 and IL-10. Our results indicate that both autocrine and paracrine leukotrienes may modulate cytokine release from DCs, in a manner that is consistent with previously reported T helper 2-polarizing effects of leukotrienes.

Respective roles of inflammation and axonal breakdown in the regulation of peripheral nerve hemopexin: an analysis in rats and in C57BL/Wlds mice

We have previously demonstrated that one of the peripheral nerve responses to injury is the overexpression of hemopexin (HPX). Here, we demonstrate that Wallerian degeneration is required for this response, since HPX does not increase in C57BL/Wlds mice, which display a severely impaired Wallerian degeneration. We also show that HPX synthesis is dramatically increased in macrophages during their activation or after IL-6 stimulation. However, IL-6-driven HPX overexpression occurs in vivo and in vitro in the absence of substantial macrophage invasion. We conclude that, after nerve injury, HPX overexpression occurs first in Schwann cells as a result of axotomy and is subsequently regulated by inflammation. Furthermore, our results and those already described suggest that IL-6, synthesized by the various cell types producing HPX, control nerve HPX expression via paracrine and autocrine mechanisms.

Dietary docosahexaenoic acid but not eicosapentaenoic acid suppresses lipopolysaccharide-induced interleukin-1 beta mRNA induction in mouse spleen leukocytes

Mice were fed a diet supplemented either with beef tallow (BT), BT plus ethyl eicosapentaenoate (EPA) or BT plus ethyl docosahexaenoate (DHA) for 9 weeks. EPA and DHA supplementation increased the content of the respective fatty acid in spleen leukocyte lipids, which was associated with the reduction in the arachidonate content. IL-1beta mRNA induction upon lipopolysaccharide (LPS) stimulation in spleen leukocytes in the DHA diet group was significantly lower than in the BT diet group, but the EPA diet was without any significant effect. The amount of prostaglandin E2 (PGE2) released from LPS-stimulated spleen leukocytes was significantly lower in both the EPA and DHA groups than in the BT group. Thus, dietary EPA and DHA inhibited arachidonate metabolism similarly but had different effects on IL-1beta mRNA induction in mouse spleen leukocytes.

The mechanisms of action of disease-modifying antirheumatic drugs: a review with emphasis on macrophage signal transduction and the induction of proinflammatory cytokines

1. Rheumatoid arthritis (RA) is probably the most common source of treatable disability. A major problem in modern rheumatology is that the mechanism(s) of action of the currently used disease-modifying antirheumatic drugs (DMARDs) remain unclear. Many of these drugs entered rheumatology mainly through clinical intuition and have been used for decades. 2. The former T-cell-centered paradigm of rheumatoid inflammation has given way to a model of inflammation highlighting the macrophage and its proinflammatory cytokines. In particular, tumor necrosis factor alpha (TNF-alpha) has gained prominence as a central proinflammatory mediator in RA, and antibodies against TNF-alpha have been successfully used in patients with RA. 3. This review will summarize the recent advances in determining the mechanisms of action of the currently used DMARDs, with particular emphasis on their effects on the induction of TNF-alpha and interleukin 1 (IL-1) in mononuclear phagocytes. Although some DMARDs, such as auranofin, antimalarials and tenidap, act as inhibitors of the induction of these cytokines in monocytes or macrophages or both, other drugs, such as methotrexate, D-penicillamine and aurothiomalate, do not seem to affect either TNF-alpha or IL-1. 4. The drugs' effects on proinflammatory cytokine induction are correlated to those on other macrophage responses.

Effects of nordihydroguaiaretic acid on murine antibody-dependent cellular cytotoxicity

The purpose of this study was to analyze the effects of nordihydroguaiaretic acid, an inhibitor of the lipoxygenase pathway of arachidonic acid, on antibody-dependent cellular cytotoxicity. Antibody-dependent cellular cytotoxicity mediated by murine spleen cells was significantly inhibited by concentrations of nordihydroguaiaretic acid from 10(-5) to 10(-4) M (1C50 = 2 x 10(-5) M). The inhibitory effect of nordihydroguaiaretic acid was also observed on antibody-dependent cellular cytotoxicity mediated by macrophage-depleted spleen cells as well as isolated macrophages. Nordihydroguaiaretic acid was highly effective when added at the beginning of the assay and was always present throughout the assay, but failed to inhibit the binding of effector and target cells. The inhibition produced by nordihydroguaiaretic acid could not be reversed by leukotriene B4, a 5-lipoxygenase product. These results suggest that arachidonic acid metabolites other than leukotriene B4 are released by different populations of spleen cells to positively regulate important events in the postbinding phase of murine antibody-dependent cellular cytotoxicity.

Effects of tenidap on intracellular signal transduction and the induction of proinflammatory cytokines: a review

Tenidap is a novel, once-daily antirheumatic drug which has shown promising results against rheumatoid arthritis in extensive clinical trials. It combines NSAID-like cyclooxygenase inhibition with suppression of the acute phase response. In macrophages, tenidap inhibits the lipopolysaccharide-induced synthesis of interleukins-1 and -6, but it tends to potentiate the lipopolysaccharide-induced synthesis of tumor necrosis factor alpha, due to its cyclooxygenase inhibition. In macrophages, tenidap is a potent inhibitor of zymosan-induced responses, not only the induction of proinflammatory cytokines, but also arachidonate mobilization, protein phosphorylation, and inositol phosphate formation, possibly through interference with the receptor-mediated upregulation of phospholipase C. Tenidap also acts as an intracellular acidifier in many cell types, which may explain at least some of its other effects. Recent studies have indicated that, in addition to modulation of prostanoid and cytokine formation, tenidap has many other effects beneficial in rheumatic disease. It has been shown to inhibit bone resorption, neutrophil adhesion and degranulation, the interleukin-1-induced suppression of glycosaminoglycan synthesis, as well as the production of active metalloproteinases from chondrocytes.

Role of 5'-lipoxygenase metabolites in the activation of peritoneal macrophages for tumoricidal function

Metabolites of arachidonic acid have been shown to be potent biological modulators of macrophage function. While the role of cyclooxygenase metabolites of arachidonic acid have been well studied, metabolites of lipoxygenase have not. In this report, we evaluate the role that select 5'-lipoxygenase (5'-LO) products may play in macrophage activation for select tumoricidal functions. When thioglycollate-elicited macrophages were treated with inhibitors of 5'-LO during activation, cytolytic capacity, nitric oxide production, and tumor necrosis factor-alpha production were significantly inhibited. Moreover, both an inhibitor of the 5'-LO-activating protein and an inhibitor of glutathione-s-transferase (GST) significantly decreased macrophage tumoricidal function. The activating agents used were able to stimulate 5'-LO activity which was measured by quantitating secreted LTC4. Increased production of PGE2 by shunting could have been the cause for decreased macrophage tumoricidal function. However, treatment of macrophages with inhibitors of 5'-LO during lipopolysaccharide stimulation did not increase formation of PGE2. When select 5'-LO metabolites were added to cultures during activation and 5'-LO inhibition, tumoricidal activity could not be restored, even when the metabolites were encapsulated in liposomes. These results suggest that the activity of 5'-LO and GST are important for macrophage activation. However, the specific role of 5'-LO metabolites has not been completely established.

The effect of non-steroidal anti-inflammatory drugs on the accumulation and release of interleukin-1-like activity by peritoneal macrophages from the mouse

1. The non-steroidal anti-inflammatory drugs (NSAIDs) indomethacin, 10 and 100 microM, piroxicam, 100 microM, and sodium meclofenamate, 1 and 100 microM, potentiated the lipopolysaccharide (LPS)-stimulated release of interleukin-1 (IL-1)-like activity from mouse peritoneal macrophages. Aspirin up to 100 microM was without effect. The drugs did not themselves stimulate the release of IL-1-like activity at the concentrations used. 2. LPS, 1 microgram ml-1, stimulated prostaglandin E2 production by mouse peritoneal macrophages and this was totally inhibited by aspirin, 100 microM, indomethacin, 1 microM, piroxicam, 10 microM and sodium meclofenamate, 0.1 microM. 3. The potentiation of LPS-stimulated release of IL-1-like activity produced by indomethacin, 100 microM, piroxicam, 100 microM, or sodium meclofenamate, 10 microM, was inhibited by prostaglandin E2, (PGE2) 10 ng ml-1. 4. Aspirin, 100 microM, indomethacin, 100 nM to 10 microM, piroxicam, 1 to 100 microM, and sodium meclofenamate, 10 nM, all potentiated cell-associated IL-1-like activity in LPS- stimulated macrophages. The drugs had no effect on cell-associated IL-1-like activity by themselves. 5. Exogenous PGE2, 2 to 30 ng ml-1, inhibited the cell-accumulation of IL-1-like activity stimulated by LPS in the presence of indomethacin, 1 microM, or sodium meclofenamate, 0.1 microM. 6. The 5-lipoxygenase inhibitors BWA4C, 0.01 to 10 microM, and L-651,392, 0.01 to 10 microM, had no effect on LPS-stimulated released or cell-associated IL-1-like activity. Over the same concentration-ranges,neither of the 5-lipoxygenase inhibitors affected released or cell-associated IL-1-like activity in LPS stimulated mouse macrophages in the presence of indomethacin, 1 JM.7. The synthetic diacylglycerol, DiC8, 10 to 200 JAM, did not itself increase released or cell-associated IL-I-like activity but in the presence of the diacylglycerol kinase inhibitor, R59022, 10 JM, DiC8increased released and cell-associated IL-i-like activity. The activity of DiC8 on released and cell associated IL-l-like activity was not increased by indomethacin, 100 micro M.8. NSAIDs increase LPS-induced cell-associated IL-i-like activity in mouse macrophages by inhibiting the formation of cyclo-oxygenase products such as PGE2 but at higher concentrations the NSAIDs potentiate LPS-induced release of IL-I-like activity by a mechanism independent of cyclo-oxygenase inhibition. The potentiation of the release of IL-i-like activity appears not to be related to an effect of NSAIDs on either 5-lipoxygenase or diacylglycerol metabolism.

Interactions between cytokines and eicosanoids: a study using human peritoneal macrophages

To examine the interactions between the main pro-inflammatory cytokines and eicosanoids produced by human inflammatory cells, human peritoneal macrophages (hp-M phi) were isolated from ascitic fluid of patients with portal hypertension. Interactions between interleukin-1 beta (IL-1 beta), IL-6, tumor necrosis factor alpha (TNF-alpha), leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) were studied by addition or inhibition of several cytokines and eicosanoids: human recombinant IL-1 beta (hrIL-1 beta) addition, LTB4 addition and 5-lipoxygenase inhibition (6-hydroxy-2-(4-sulfamoylbenzylamino)-4,5,7-trimethylbenzothiaz ole hydrochloride (E6080)), PGE2 addition and cyclooxygenase inhibition (indomethacin). In hp-M phi hrIL-1 beta stimulated the LTB4 production, while the PGE2 production was inhibited. HrIL-1 beta had no significant effect on IL-6 production in hp-M phi. LTB4 did not regulate IL-1 beta and IL-6 production. Increasing PGE2 down regulated the TNF-alpha production, but did not effect the IL-1 beta and IL-6 production.

Production of inflammatory mediators by human macrophages obtained from ascites

Ascites is a readily available source of human macrophages (M phi), which can be used to study M phi functions in vitro. We characterized the mediators of inflammation produced by human peritoneal M phi (hp-M phi) obtained from patients with portal hypertension and ascites. The production of the cytokines interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) was found to be lipopolysaccharide (LPS) concentration dependent (0-10 micrograms/ml) with a maximal production at 10 micrograms/ml and also dependent on the time of exposure to the stimulus (0-36 h). IL-1 beta, IL-6 and TNF-alpha production after LPS administration reached a plateau at 24 h. In vitro stimulation for 24 h with LPS does not influence the eicosanoid production from endogenous arachidonate. 13 min of exposure of the cells to the calcium ionophore A23187 gives a significant increase in eicosanoid production from both exogenous and endogenous arachidonate. The main eicosanoids produced are the 5-lipoxgenase products LTB4 and 5-hydroxyeicosatetraenoic acid (HETE). The increase in production of the other eicosanoids is not significant. The eicosanoid production depends on the stimulus concentration. The optimal A23187 concentration is 1 microM. Oxygen radical production was measured in the M phi by a flowcytometric method. The fluorescence intensity of phorbol 12-myristate 13-acetate stimulated and dihydro-rhodamine 123 loaded hp-M phi increases significantly after 15 min. We conclude that LPS stimulation of hp-M phi from liver disease results in similar production of IL-1 beta, IL-6 and TNF-alpha, but that the profile of the eicosanoid production of these M phi stimulated with LPS and A23187 differs from M phi of other origin and species.

Effects of lipoxygenase and cyclooxygenase inhibitors on murine antibody-dependent cellular cytotoxicity (ADCC)

The purpose of this study was to determine the effects that specific inhibition of arachidonic acid (AA) metabolism has on the antibody-dependent cellular cytotoxicity (ADCC) of murine spleen cells. The action of three inhibitors of the lipoxygenase (LO) pathway--nordihydroguaiaretic acid (NDGA), esculetin (Es), and phenanthroline (Phe)--was compared with that of three inhibitors of the cyclooxygenase (CO) pathway--indomethacin (INDO), acetyl salicylic acid (ASA), and imidazole (IMI). All the LO inhibitors suppressed ADCC function in a dose-dependent manner, but NDGA was the most potent inhibitor of this cytolytic activity. In fact, NDGA inhibited the ADCC function with 97% inhibition at 100 microM, while Phe and Es, at the same concentration, inhibited ADCC by 21% and 19%, respectively. However, CO inhibitors did not markedly affect ADCC function and only some doses of them had a slight, but significant, depressing effect (8-11% inhibition at 0.01-0.1 microM of INDO, 7% inhibition at 400 microM of ASA, and 13% inhibition at 800-1000 microM of IMI). These results suggest the LO pathway of the arachidonic acid metabolism plays an important role in regulating ADCC activity of murine spleen cells and the products of the CO pathway have little effect on ADCC lysis.

Evidence that endogenous interleukin-1 is involved in leukocyte migration in acute experimental inflammation in rats and mice

As a putative mediator of inflammation interleukin-1 has been implicated in the recruitment of leukocytes during the early stages of the inflammatory reaction. In the present report we have investigated the release of endogenous IL-1 in the rat zymosan pleurisy and in the mouse zymosan peritonitis. In both cases the release of the cytokine was maximal 4 hours after zymosan injection and appeared to be time-related to neutrophil migration into the inflammatory site. The effect of in vivo treatment with dexamethasone in rat pleurisy and with polyclonal anti-murine IL-1 beta antibody in mouse peritonitis was also assessed. The steroid reduced both cell migration and the release of IL-1-like activity as well as the formation of exudate and the release of eicosanoids. The anti-IL-1 beta serum inhibited selectively the number of neutrophil that migrated to the inflamed site (approximately 40%) and the IL-1 activity recovered in (approximately 70%) the exudate. In vitro incubation of the inflammatory exudate with polyclonal anti-murine IL-1 alpha or anti-murine IL-1 beta sera allowed the identification of the IL-1 species present. In the rat pleurisy IL-1 biological activity was mainly due to the alpha species, whereas IL-1 beta was the only species apparently present in the mouse peritoneal exudate.

Differential protective activities of site specific lipoxygenase inhibitors in endotoxic shock and production of tumor necrosis factor

Lipoxygenase inhibitors have been shown to exert beneficial effects in experimental models of endotoxin shock. In the present study it was found that lipoxygenase inhibitors prevented LPS, but not tumor necrosis factor alpha (TNF alpha)-evoked leukopenia in mice. These inhibitors protected against endotoxin lethality but not against TNF alpha induced lethality. When the protective potency of the specific 5-lipoxygenase inhibitors (MK 886, CGS 81585) was tested in endotoxin-induced leukopenia and shock, they were found to be ineffective. Site specificity of the inhibitors was assessed by comparison of their effects on the formation of LTC4 and the conversion of linoleic acid to 13-hydroxyoctadecadienoic acid (13-HODD) by macrophages. The 5-lipoxygenase inhibitors interfered with LTC4 formation in macrophages, however, they did not affect endotoxin-induced TNF alpha formation, neither in cell cultures nor in mice. The inhibitory strength of other, less specific lipoxygenase blockers to suppress TNF alpha formation correlated quantitatively with their ability to interfere with 13-HODD synthesis. From these findings it is concluded that lipoxygenase inhibitors interfere with endotoxic effects because they block TNF alpha formation. Since 5-lipoxygenase inhibitors neither prevented the formation of TNF alpha nor endotoxin leukopenia and lethality, it is suggested that a lipoxygenase product distinct from the leukotrienes is involved in TNF alpha synthesis. Based on the fact that a tight correlation exists between inhibition of TNF alpha synthesis and 13-HODD formation, activation of 15-lipoxygenase might be important for TNF alpha formation.