Control of experimental pulmonary tuberculosis depends more on immunostimulatory leukotrienes than on the absence of immunosuppressive prostaglandins

Prostaglandins (PGs) and leukotrienes (LTs) are produced in Mycobacterium tuberculosis (Mtb)-infected lungs and have immune suppressive and protective effects, respectively. Considering that both of these mediators are produced during mycobacterial infection, we investigated the specific and relative biological importance of each in regulating host response in experimental tuberculosis. Administration of celecoxib, which was found to reduce lung levels of PGE(2) and increase LTB(4), enhanced the 60-day survival of Mtb-infected mice in 14%. However administration of MK-886, which reduced levels of LTB(4) but did not enhance PGE(2), reduced 60-day survival from 86% to 43% in Mtb-infected mice, and increased lung bacterial burden. MK-886 plus celecoxib reduced survival to a lesser extent than MK-886 alone. MK-886- and MK-886 plus celecoxib-treated animals exhibited reduced levels of the protective interleukin-12 and gamma-interferon. Our findings indicate that in this model, the protective effect of LTs dominates over the suppressive effect of PGs.

TLR4/MYD88-dependent, LPS-induced synthesis of PGE2 by macrophages or dendritic cells prevents anti-CD3-mediated CD95L upregulation in T cells

Antigen-presenting cells (APCs) control T-cell responses by multiple mechanisms, including the expression of co-stimulatory molecules and the production of cytokines and other mediators that control T-cell proliferation, survival and differentiation. Here, we demonstrate that soluble factor(s) produced by Toll-like receptor (TLR)-activated APCs suppress activation-induced cell death (AICD). This effect was observed in non-stimulated APCs, but it was significantly increased after lipopolysaccharide (LPS) treatment. Using different KO mice, we found that the LPS-induced protective factor is dependent on TLR4/MyD88. We identified the protective factor as prostaglandin E(2) (PGE(2)) and showed that both APC-derived supernatants and PGE(2) prevented CD95L upregulation in T cells in response to TCR/CD3 stimulation, thereby avoiding both AICD and activated T cell killing of target macrophages. The PGE(2) receptors, EP2 and EP4, appear to be involved since pharmacological stimulation of these receptors mimics the protective effect on T cells and their respective antagonists interfere with the protection induced by either APCs derived or synthetic PGE(2). Finally, the engagement of EP2 and EP4 synergistically activates protein kinase A (PKA) and exchange protein directly activated by cAMP pathways to prevent AICD. Taken together, these results indicate that APCs can regulate T-cell levels of CD95L by releasing PGE(2) in response to LPS through a TLR4/MyD88-dependent pathway, with consequences for both T cell and their own survival.

Cysteinyl leukotrienes: multi-functional mediators in allergic rhinitis

Cysteinyl leukotrienes (CysLTs) are a family of inflammatory lipid mediators synthesized from arachidonic acid by a variety of cells, including mast cells, eosinophils, basophils, and macrophages. This article reviews the data for the role of CysLTs as multi-functional mediators in allergic rhinitis (AR). We review the evidence that: (1) CysLTs are released from inflammatory cells that participate in AR, (2) receptors for CysLTs are located in nasal tissue, (3) CysLTs are increased in patients with AR and are released following allergen exposure, (4) administration of CysLTs reproduces the symptoms of AR, (5) CysLTs play roles in the maturation, as well as tissue recruitment, of inflammatory cells, and (6) a complex inter-regulation between CysLTs and a variety of other inflammatory mediators exists.

Influence of body mass index on the response to asthma controller agents

The incidence of asthma has been positively associated with obesity. Asthma comprises diverse "phenotypes" reflecting heterogeneity in a number of characteristics, including response to therapy. The present authors examined whether body mass index (BMI) influenced the response to placebo, as well as to two asthma controller medications. A post hoc analysis was performed, pooling data from four double-blind, placebo-controlled studies randomising 3,073 moderate asthmatic adults to montelukast (n=1,439), beclomethasone (n=894) or placebo (n=740). The primary end point was asthma control days; other end points were forced expiratory volume in one second, beta-agonist use and nocturnal awakening. Analyses were conducted using BMI classification into normal (<25.0 kg.m-2; 52% of patients), overweight (25-29.9 kg.m-2; 32%) and obese (>or=30.0 kg.m-2; 16%) categories, as well as BMI as a continuous variable. The treatment groups were balanced for BMI, demographic characteristics and parameters of asthma control. The placebo response for all end points was generally lower with increasing BMI. Similarly, the response to the inhaled corticosteroid decreased, whereas the response to the leukotriene antagonist remained stable. In conclusion, post hoc data from the present study suggested that body mass index may influence the natural history of asthma control (as reflected by response to placebo) and may differentially influence response to the two active agents, warranting explicit testing in future prospective studies.

5-lipoxygenase and FLAP

The initial steps in the biosynthesis of leukotrienes from arachidonic acid are carried out by the enzyme 5-lipoxygenase (5-LO). In intact cells, the helper protein 5-LO activating protein (FLAP) is necessary for efficient enzyme utilization of endogenous substrate. The last decade has witnessed remarkable progress in our understanding of these two proteins. Here we review the molecular and cellular aspects of the expression, function, and regulation of 5-LO and FLAP.

A calcium-independent phospholipase activity insensitive to bromoenol lactone mediates arachidonic acid release by lindane in rat myometrial cells

Arachidonic acid release is an important regulatory component of uterine contraction and parturition, and previous studies showed that lindane stimulates arachidonic acid release from myometrium. The present study partially characterized the enzyme activity responsible for lindane-induced arachidonic acid release in myometrial cells. Lindane released arachidonic acid from cultured rat myometrial cells in concentration- and time-dependent manners. This release was primarily from phosphatidylcholine and phosphatidylinositol, and was independent of intracellular and extracellular calcium. In cells prelabeled with [3H]arachidonic acid, 85% of radiolabel was recovered as free arachidonate and only 5% was recovered as eicosanoids. Pretreatment with the antioxidants Cu, Zn-superoxide dismutase, alpha-tocopherol or Trolox did not significantly modify lindane-induced arachidonic acid release. Pretreatment of cells with the phosphatidylcholine-specific phospholipase C inhibitor D609, phosphatidylinositol-specific phospholipase C inhibitor ET-18-OCH3, or an interrupter of the phospholipase D pathway (ethanol) did not suppress lindane-induced arachidonic acid release. Although these results are consistent with calcium-independent phospholipase A2 activation by lindane, the calcium-independent phospholipase A2 inhibitor bromoenol lactone failed to inhibit lindane-induced arachidonic acid release in myometrial cells, even though bromoenol lactone effectively blocked arachidonic acid release in neutrophils. These results suggest that myometrial cells express a novel, previously unidentified phospholipase that is arachidonate-specific, calcium-independent, insensitive to bromoenol lactone, insensitive to reactive oxygen species activation, shows substrate preference for phosphatidylcholine and phosphatidylinositol, and is stimulated by lindane. Moreover, the data show that the overwhelming majority of arachidonic acid released remains as arachidonate, but that lindane does not significantly inhibit metabolism of arachidonate to eicosanoids.

Sulphatides trigger polymorphonuclear granulocyte spreading on collagen-coated surfaces and inhibit subsequent activation of 5-lipoxygenase

Sulphatides are sulphate esters of galactocerebrosides that are present on the surfaces of many cell types and act as specific ligands to selectins. The present study was undertaken to investigate the effect of sulphatides on polymorphonuclear granulocyte (PMN) attachment, spreading and 5-lipoxygenase (5-LO) metabolism. Sulphatides, but not non-sulphated galactocerebrosides, dose-dependently enhanced attachment to collagen, as measured by the myeloperoxidase assay. Studies with blocking antibodies indicated that the increased attachment was mediated by CD11b/CD18 (Mac-1) beta 2 integrin. Scanning electron microscopy indicated that sulphatides also greatly enhanced the degree of cell spreading. In PMNs treated in suspension, sulphatides had no effect on the ionophore A23187-stimulated release of arachidonic acid and the synthesis of 5-LO metabolites. In contrast, in PMNs attached to collagen, the enzymic conversion of arachidonic acid by 5-LO was inhibited by sulphatides. Inhibition of 5-LO metabolism by sulphatides was observed even in the presence of exogenous substrate, suggesting that sulphatides directly inhibited 5-LO action. Consistent with this, sulphatides interfered with ionophore-induced translocation of the 5-LO to the nuclear envelope. Substances competing with sulphatide binding to cells, like dextran sulphate, or a strong inhibitor of cell spreading, like the actin-polymerizing agent jasplakinolide, prevented the effects of sulphatides on PMN attachment and spreading and leukotriene synthesis. We conclude that shape changes occurring in response to sulphatides specifically impair PMN leukotriene synthesis by inhibiting translocation of 5-LO.

Evaluation of phagocytosis and arachidonate metabolism by alveolar macrophages and recruited neutrophils from F344xBN rats of different ages

The incidence of infectious respiratory diseases increases with aging. Resident alveolar macrophages (AMs) and recruited leukocytes (PMNL) mediate cellular defense against bacterial infections in the lung, and phagocytosis and lipid mediator synthesis are important components of their antimicrobial capacity. The objective of this study was to determine if either phagocytic capacity or lipid mediator generation declines with normal aging, in either AMs or PMNL recruited to a site of inflammation. The F344xBN rat hybrid has a lower incidence of pathologies associated with aging, particularly up to 20 months; animals aged 6,12 and 18 months were chosen to evaluate changes associated with normal aging. As previously reported for peripheral blood leukocytes, phagocytosis by recruited PMNL declined with aging: recruited PMNL from 18 months rats showed a significantly decreased capacity to phagocytose live Klebsiella pneumoniae bacteria, compared to PMNL from 6 months rats. Surprisingly, however, the phagocytic capacity of AMs increased with aging: the phagocytic index of AMs from 18 months rats was more than three times that of AMs from 6 months rats. The capacity of AMs and recruited PMNL to release arachidonic acid or synthesize leukotrienes or prostaglandins did not change with aging. This study demonstrates that, although phagocytosis by recruited PMNL declines with aging, other aspects of immune function do not decline, and may actually increase, with normal aging. These results suggest that impaired phagocytosis by recruited PMNL may be an important component of the increased susceptibility to infectious respiratory diseases during normal aging.

Peroxynitrite-induced nitrotyrosination of proteins is blocked by direct 5-lipoxygenase inhibitor zileuton

We have previously shown that the ability of overnight pretreatment with lipopolysaccharide (LPS) to suppress alveolar macrophage (AM) leukotrienes (LT) synthesis is explained by induction of nitric oxide (NO), and reactive oxygen intermediates (ROI). More recently we have demonstrated that the generation of peroxynitrite (ONOO-) from the combination of NO and ROI directly nitrotyrosinates the 5-lipoxygenase (5-LO) enzyme and reduces cell-free and intact AM 5-LO metabolism. This effect of ONOO- was associated with nitrotyrosination of the 5-LO enzyme in intact cells and after treatment of recombinant enzyme. We postulated that LPS treatment of cells resulted in activation of 5-LO with the generation of ROI, which in turn led to autoinactivation of the enzyme. In an effort to suppress ROI generated from activation of 5-LO we examined the effect of a direct 5-LO inhibitor on LPS-induced suppression of LT synthesis. Coincubation with the reversible 5-LO inhibitor zileuton during the LPS pretreatment of intact cells dose dependently blocked the inhibition of 5-LO metabolism by LPS. The effect of zileuton on LPS-induced suppression of LT synthesis was similar to that of N-monomethyl-L-arginine. Zileuton had no effect on inducible nitric-oxide synthase induction. Interestingly, zileuton blocked ONOO--induced nitrotyrosination of recombinant 5-LO in a cell-free system as well as of native enzyme in intact cells. Moreover, zileuton blocked the nitrotyrosination of other proteins. We conclude that the suppression of 5-LO activity occurring with LPS treatment can be blocked by zileuton. The mechanism by which zileuton is effective is in part explained by blocking nitrotyrosination of 5-LO.

Co-localization of leukotriene a4 hydrolase with 5-lipoxygenase in nuclei of alveolar macrophages and rat basophilic leukemia cells but not neutrophils

The synthesis of leukotriene B(4) from arachidonic acid requires the sequential action of two enzymes: 5-lipoxygenase and leukotriene A(4) hydrolase. 5-Lipoxygenase is known to be present in the cytoplasm of some leukocytes and able to accumulate in the nucleoplasm of others. In this study, we asked if leukotriene A(4) hydrolase co-localizes with 5-lipoxygenase in different types of leukocytes. Examination of rat basophilic leukemia cells by both immunocytochemistry and immunofluorescence revealed that leukotriene A(4) hydrolase, like 5-lipoxygenase, was most abundant in the nucleus, with only minor occurrences in the cytoplasm. The finding of abundant leukotriene A(4) hydrolase in the soluble nuclear fraction was substantiated by two different cell fractionation techniques. Leukotriene A(4) hydrolase was also found to accumulate together with 5-lipoxygenase in the nucleus of alveolar macrophages. This result was obtained using both in situ and ex vivo techniques. In contrast to these results, peripheral blood neutrophils contained both leukotriene A(4) hydrolase and 5-lipoxygenase exclusively in the cytoplasm. After adherence of neutrophils, 5-lipoxygenase was rapidly imported into the nucleus, whereas leukotriene A(4) hydrolase remained cytosolic. Similarly, 5-lipoxygenase was localized in the nucleus of neutrophils recruited into inflamed appendix tissue, whereas leukotriene A(4) hydrolase remained cytosolic. These results demonstrate for the first time that leukotriene A(4) hydrolase can be accumulated in the nucleus, where it co-localizes with 5-lipoxygenase. As with 5-lipoxygenase, the subcellular distribution of leukotriene A(4) hydrolase is cell-specific and dynamic, but differences in the mechanisms regulating nuclear import must exist. The degree to which these two enzymes are co-localized may influence their metabolic coupling in the conversion of arachidonic acid to leukotriene B(4).

Selective inhibition of COX-2 improves early survival in murine endotoxemia but not in bacterial peritonitis

Prostaglandins of the E series are believed to act as important mediators of several pathophysiological events that occur in sepsis. Studies were performed to evaluate the effect of cyclooxygenase (COX)-2-specific inhibition on the outcome in murine endotoxemia and cecal ligation and puncture (CLP). We observed a significant time-dependent upregulation of PGE(2) production in both blood and lung homogenates of mice administered lipopolysaccharide intraperitoneally, which was nearly completely suppressed by the administration of the COX-2 inhibitor NS-398. Treatment with NS-398 significantly improved early but not late survival in lipopolysaccharide-challenged mice. On the contrary, elevated PGE(2) levels were found in bronchoalveolar lavage fluid but not in plasma of mice subjected to CLP (21 gauge). Pretreatment with NS-398 failed to significantly improve survival in CLP mice. No significant differences were noted in plasma or lung homogenate proinflammatory cytokine levels or lung neutrophil sequestration between the NS-398-treated and control groups. These results demonstrate that selective COX-2 inhibition confers early but not long-term benefits without affecting the expression of proinflammatory cytokines or the development of lung inflammation.

Microsomal prostaglandin E synthase is regulated by proinflammatory cytokines and glucocorticoids in primary rheumatoid synovial cells

The selective induction of PGE(2) synthesis in inflammation suggests that a PGE synthase may be linked to an inducible pathway for PG synthesis. We examined the expression of the recently cloned inducible microsomal PGE synthase (mPGES) in synoviocytes from patients with rheumatoid arthritis, its modulation by cytokines and dexamethasone, and its linkage to the inducible cyclooxygenase-2. Northern blot analysis showed that IL-1beta or TNF-alpha treatment induces mPGES mRNA from very low levels at baseline to maximum levels at 24 h. IL-1beta-induced mPGES mRNA was inhibited by dexamethasone in a dose-dependent fashion. Western blot analysis demonstrated that mPGES protein was induced by IL-1beta, and maximum expression was sustained for up to 72 h. There was a coordinated up-regulation of cyclooxygenase-2 protein, although peak expression was earlier. Differential Western blot analysis of the microsomal and the cytosolic fractions revealed that the induced expression of mPGES protein was limited to the microsomal fraction. The detected mPGES protein was catalytically functional as indicated by a 3-fold increase of PGES activity in synoviocytes following treatment with IL-1beta; this increased synthase activity was limited to the microsomal fraction. In summary, these data demonstrate an induction of mPGES in rheumatoid synoviocytes by proinflammatory cytokines. This novel pathway may be a target for therapeutic intervention for patients with arthritis.

Colonic mucosal prostaglandin E2 and cyclooxygenase expression before and after low aspirin doses in subjects at high risk or at normal risk for colorectal cancer

Development of potential cancer chemopreventive drugs involves the systematic evaluation of these drugs in preliminary Phase I and II studies in human beings to identify the optimal drug dose, drug toxicity, and surrogate end point biomarker modulation.

OBJECTIVES

We tested the hypothesis that aspirin, at a single, once-daily 81-mg dose, will reduce colonic mucosal concentration of prostaglandin estradiol (E2) in individuals at high risk for colorectal cancer development similar to our prior observations in a young normal-risk population.

METHODS

Aspirin was administered at a dose of 81 mg once daily for 28 days in a cohort of 92 matched high-risk and normal-risk colorectal cancer subjects. Prostaglandin E2 and cyclooxygenase expression were assayed from distal sigmoid biopsies from all of the subjects before and after treatment.

RESULTS

The mean prostaglandin E2 for normal-risk subjects before aspirin treatment was 11.3 +/- 1.7 pg/microg (mean +/- SE) tissue protein and after aspirin treatment was 4.9 +/- 0.91 pg/microg tissue protein (P < 0.0001). In high-risk subjects, mean pretreatment prostaglandin E2 was 14.4 +/- 1.7 pg/microg tissue protein and after aspirin treatment was 4.7 +/- 0.70 pg/microg tissue protein (P < 0.0001). Aspirin treatment did not alter cyclooxygenase-1 protein expression.

CONCLUSIONS

Aspirin treatment at a dose of 81 mg reduces colorectal mucosal prostaglandin E2 concentration after 28 daily doses. Risk for colorectal carcinoma did not modify colorectal mucosal baseline or post-aspirin prostaglandin E2, or cyclooxygenase expression. Colorectal mucosal prostaglandin concentration may be used as a "drug-effect surrogate biomarker," that is, a surrogate to assess sufficient delivery and tissue effect of a chemopreventive agent.

Leukotriene B4 augments neutrophil phagocytosis of Klebsiella pneumoniae

Neutrophils play a critical role in the clearance of bacteria from the lung and other organs by their capacity for phagocytosis and killing. Previously, we identified an important role for the leukotrienes in rat alveolar macrophage phagocytosis of Klebsiella pneumoniae. In this report, we explored the possibility that the leukotrienes play an important role in phagocytosis by neutrophils as well. Inhibition of endogenous leukotriene synthesis by 5-lipoxygenase knockout in mice or by pharmacologic means in human peripheral blood neutrophils attenuated phagocytosis of opsonized K. pneumoniae. Reduced phagocytosis was also observed in human neutrophils pretreated with a leukotriene B4 receptor but not a cysteinyl-leukotriene receptor antagonist. While leukotriene B4 reconstituted defective phagocytosis in leukotriene-deficient neutrophils and enhanced phagocytosis in neutrophils capable of leukotriene synthesis, leukotriene C4, leukotriene D4, 5-hydroperoxyeicosatetraenoic acid, and 5-oxo-eicosatetraenoic acid were ineffective. To determine the opsonin dependence of the leukotriene B4 augmentation of phagocytosis, we assessed the ability of leukotriene B4 to modulate neutrophil phagocytosis and the adherence of sheep erythrocytes opsonized with immunoglobulin G or the complement fragment C3bi. While leukotriene B4 augmented both Fc receptor- and complement receptor-mediated phagocytosis, increased adherence to leukotriene B4-treated neutrophils was limited to complement opsonized targets. In conclusion, we have identified a novel role for leukotriene B4 in the augmentation of neutrophil phagocytosis mediated by either the Fc or complement receptor.

Intracellular compartmentalization of leukotriene synthesis: unexpected nuclear secrets

Leukotrienes are important lipid mediators implicated in the regulation of various cellular processes and in disease states as well as homeostasis. Regulation of leukotriene biosynthesis is therefore of considerable interest. Although the levels of expression and catalytic activity of leukotriene-forming proteins have long been recognized as important determinants of leukotriene biosynthesis, it has recently become apparent that their intracellular compartmentalization also affects the integrated output of this biosynthetic pathway. In this minireview, we focus on the unexpected discovery that the nucleus is the key intracellular site for leukotriene biosynthesis and discuss the mechanisms that regulate protein localization and the potential implications of these findings.

Modulation of alveolar macrophage phagocytosis by leukotrienes is Fc receptor-mediated and protein kinase C-dependent

We have previously established an important role for leukotrienes (LTs) in augmenting rat alveolar macrophage (AM) phagocytosis of Klebsiella pneumoniae opsonized with complete immune serum (IS), which contains the two well-known opsonins, immunoglobulin (Ig) G and complement (C). In this report, the specific opsonin requirements for LT modulation of AM phagocytosis and the dependence of this response on protein kinase (PK) C activity were investigated. Phagocytosis of K. pneumoniae opsonized with IS, non-immune serum, or heat-inactivated immune serum and of inert targets (IgG-opsonized fluorescent microspheres or C-opsonized sheep red blood cells) was examined. Inhibition of endogenous LT synthesis or action attenuated, whereas the addition of exogenous LTs augmented, phagocytosis only of targets opsonized with IgG. LTs had no effect on phagocytosis of C-opsonized or unopsonized targets. LTs did not affect adherence of IgG-opsonized targets, implying instead an enhancement of internalization. Macrophage internalization of phagocytic targets has previously been shown to require PKC activity. Pretreatment of AMs with the PKC inhibitors staurosporine or calphostin C, or with phorbol 12-myristate 13-acetate to deplete PKC, completely inhibited the ability of LTB(4) and largely inhibited the ability of LTC(4) to augment phagocytosis of IgG-opsonized microspheres. These results demonstrate that LT enhancement is confined to Fc receptor (FcR)-mediated phagocytosis. Moreover, PKC activation represents an important mechanism by which LTs promote FcR-mediated phagocytosis.

Prolonged exposure to lipopolysaccharide inhibits macrophage 5-lipoxygenase metabolism via induction of nitric oxide synthesis

LPS from bacteria can result in the development of sepsis syndrome and acute lung injury. Although acute exposure to endotoxin primes leukocytes for enhanced synthesis of leukotrienes (LT), little is known about the effect of chronic exposure. Therefore, we determined the effect of prolonged LPS treatment on 5-lipoxygenase (5-LO) metabolism of arachidonic acid in alveolar macrophages (AM) and in peripheral blood monocytes. Pretreatment of AM with LPS caused time- and dose-dependent suppression of LT synthetic capacity. LPS pretreatment failed to inhibit arachidonic acid (AA) release. The fact that LPS inhibited LT synthesis from endogenous AA more than from exogenous AA suggested an effect on 5-LO-activating protein (FLAP). In addition, an inhibitory effect of LPS treatment on AM 5-LO activity was suggested by cell-free 5-LO enzyme assay. No effect on the expression of either 5-LO or FLAP proteins was observed. New protein synthesis was necessary for LPS-induced reduction of 5-LO metabolism in AM, and immunoblotting demonstrated marked induction of NO synthase (NOS). Inhibition by LPS was reproduced by an NO donor and was abrogated by inhibitors of constitutive and inducible NOS. Compared with AM, peripheral blood monocytes exhibited no suppression by LPS of 5-LO metabolism and no induction of inducible NOS. We conclude that prolonged exposure to LPS impairs AM 5-LO metabolism by NO-mediated suppression of both 5-LO and FLAP function. Because LT contribute to antimicrobial defense, this down-regulation of 5-LO metabolism may contribute to the increased susceptibility to pneumonia in patients following sepsis.

GM-CSF regulates bleomycin-induced pulmonary fibrosis via a prostaglandin-dependent mechanism

To characterize the role of GM-CSF in pulmonary fibrosis, we have studied bleomycin-induced fibrosis in wild-type mice vs mice with a targeted deletion of the GM-CSF gene (GM-CSF-/- mice). Without GM-CSF, pulmonary fibrosis was worse both histologically and quantitatively. These changes were not related to enhanced recruitment of inflammatory cells because wild-type and GM-CSF-/- mice recruited equivalent numbers of cells to the lung following bleomycin. Interestingly, recruitment of eosinophils was absent in GM-CSF-/- mice. We investigated whether the enhanced fibrotic response in GM-CSF-/- animals was due to a deficiency in an endogenous down-regulator of fibrogenesis. Analysis of whole lung homogenates from saline- or bleomycin-treated mice revealed that GM-CSF-/- animals had reduced levels of PGE2. Additionally, alveolar macrophages were harvested from wild-type and GM-CSF-/- mice that had been exposed to bleomycin. Although bleomycin treatment impaired the ability of alveolar macrophages from wild-type mice to synthesize PGE2, alveolar macrophages from GM-CSF-/- mice exhibited a significantly greater defect in PGE2 synthesis than did wild-type cells. Exogenous addition of GM-CSF to alveolar macrophages reversed the PGE2 synthesis defect in vitro. Administration of the PG synthesis inhibitor, indomethacin, to wild-type mice during the fibrogenic phase postbleomycin worsened the severity of fibrosis, implying a causal role for PGE2 deficiency in the evolution of the fibrotic lesion. These data demonstrate that GM-CSF deficiency results in enhanced fibrogenesis in bleomycin-induced pulmonary fibrosis and indicate that one mechanism for this effect is impaired production of the potent antifibrotic eicosanoid, PGE2.

Granulocyte-macrophage colony-stimulating factor upregulates reduced 5-lipoxygenase metabolism in peripheral blood monocytes and neutrophils in acquired immunodeficiency syndrome

Leukotrienes (LT) are mediators derived from the 5-lipoxygenase (5-LO) pathway, which play a role in host defense, and are synthesized by both monocytes (peripheral blood monocyte [PBM]) and neutrophils (PMN). Because 5-LO metabolism is reduced in alveolar macrophages and PMN from acquired immunodeficiency syndrome (AIDS) subjects, we investigated the synthesis of LT by PBM and PMN from these subjects. There was a reduction (74.2% +/- 8.8% of control) in LT synthesis in PBM from human immunodeficiency virus (HIV)-infected compared with normal subjects. Expression of 5-LO (51.2% +/- 8.8% of control), and 5-LO activating protein (FLAP) (48.5% +/- 8.0% of control) was reduced in parallel. We hypothesized that this reduction in LT synthetic capacity in PBM and PMN was due to reduced cytokine production by CD4 T cells, such as granulocyte-macrophage colony-stimulating factor (GM-CSF). We treated 10 AIDS subjects with GM-CSF for 5 days. PBM 5-LO metabolism ex vivo was selectively increased after GM-CSF therapy and was associated with increased 5-LO and FLAP expression. PMN leukotriene B(4) (LTB(4)) synthesis was also augmented and associated with increased 5-LO, FLAP, and cytosolic phospholipase A(2) expression. In conclusion, as previously demonstrated for PMN, PBM from AIDS subjects also demonstrate reduced 5-LO metabolism. GM-CSF therapy reversed this defect in both PBM and PMN. In view of the role of LT in antimicrobial function, cytokine administration in AIDS may play a role as adjunct therapy for infections.

Identification of a bipartite nuclear localization sequence necessary for nuclear import of 5-lipoxygenase

5-Lipoxygenase catalyzes the synthesis of leukotrienes from arachidonic acid. This enzyme can reside either in the cytoplasm or the nucleus; its subcellular distribution is influenced by extracellular factors, and its nuclear import correlates with changes in leukotriene synthetic capacity. To identify sequences responsible for the nuclear import of 5-lipoxygenase, we transfected NIH 3T3 cells and RAW 264.7 macrophages with expression vectors encoding various 5-lipoxygenase constructs fused to green fluorescent protein. Overexpression of wild type 5-lipoxygenase with or without fusion to green fluorescent protein resulted in a predominantly intranuclear pattern of fluorescence, similar to the distribution of native 5-lipoxygenase in primary alveolar macrophages. Within the 5-lipoxygenase protein is a sequence (Arg(638)-Lys(655)) that closely resembles a bipartite nuclear localization signal. Studies using deletion mutants indicated that this region was necessary for nuclear import of 5-lipoxygenase. Analysis of mutants containing specific amino acid substitutions within this sequence confirmed that it was this sequence that was necessary for nuclear import of 5-lipoxygenase and that a specific arginine residue was critical for this function. As nuclear import of 5-lipoxygenase may regulate leukotriene production, natural or induced mutations in this bipartite nuclear localization sequence may also be important in affecting leukotriene synthesis.

Regulation of 5-lipoxygenase metabolism in mononuclear phagocytes by CD4 T lymphocytes

Alveolar macrophages (AM) are the primary resident effector cells in the alveolus. Leukotrienes (LT) are secreted by AM in their role as defender of the lung. 5-Lipoxygenase (5-LO) catalyzes the synthesis of LT in association with 5-LO-activating protein, termed "FLAP." AM demonstrate increased 5-LO metabolism compared to peripheral blood monocytes (PBM). Activated lymphocytes release mediators which upregulate 5-LO metabolism in PBM. The lymphocyte population of the lung consists predominantly of CD4+ helper constitutively "activated" T cells. We hypothesized that mediators released by pulmonary CD4+ T cells may upregulate and maintain of 5-LO metabolism in PBM as they enter the alveolar space and differentiate into AM. 5-LO metabolism in AM from CD4-depleted mice demonstrated reduced LT synthesis (LTC4: 66.9 +/- 8%; LTB4 61.4 +/- 6.2% control). The decrease in 5-LO metabolism was associated with reduced FLAP (30.1 +/- 14.5% of control) and 5-LO expression (49 +/- 13.7% of control). This defect in AM 5-LO metabolism in CD4-depleted mice was further associated with reduced LTC4 levels in bronchoalveolar lavage (BAL) fluid. In summary, factors secreted constitutively by lung lymphocytes, in particular CD4 cells, contribute to the increased 5-LO metabolism in AM.

Stimulation of pregnant rat uterine contraction by the polychlorinated biphenyl (PCB) mixture aroclor 1242 may be mediated by arachidonic acid release through activation of phospholipase A2 enzymes

The polychlorinated biphenyl (PCB) mixture Aroclor 1242 (A1242) increases frequency of contractions of pregnant rat uteri, suggesting a possible mechanism for decreased gestational age and increased spontaneous abortion in women and animals exposed to PCBs. In the present study, we hypothesized that A1242-induced stimulation of uterine contraction is mediated by arachidonic acid released by phospholipase A2 (PLA2) enzymes. Isometric uterine contraction was measured in longitudinal uterine strips isolated from gestation day 10 rat. Pretreatment of uterine strips with the PLA2 inhibitor (E)-6-(bromomethylene)tetrahydro-3-(1-naphthalenyl)-2H-pyran-2-one (HELSS) or manoalide, or an inhibitor of the G protein of PLA2, isotetrandrine, completely prevented the increase of contractile frequency induced by 50 microM A1242. However, the phospholipase C inhibitors 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (NCDC) and neomycin were unable to block stimulation of uterine contraction by A1242. In accordance, A1242 (100 microM) did not release inositol phosphates from myo-[3H]inositol-labeled myometrial cells, whereas myometrial cells prelabeled with [3H]arachidonic acid released arachidonic acid in a concentration- and time-dependent manner after exposure to A1242 (10-100 microM). A1242 significantly stimulated arachidonic acid release in the absence of extracellular calcium, although the release was attenuated. Analysis of the eicosanoids released by A1242 indicated that only 0.83% of released [3H]arachidonic acid was metabolized to eicosanoids and 99.07% remained as free arachidonate. Uterine contraction increased in strips exposed to exogenous arachidonic acid (1-100 microM). This study suggests that A1242 stimulates contraction in pregnant rat uterus by a mechanism involving PLA2-mediated arachidonic acid release, and that arachidonic acid, rather than eicosanoids, may mediate A1242 uterotonic action in the uterus.

Arachidonic acid is preferentially metabolized by cyclooxygenase-2 to prostacyclin and prostaglandin E2

The two cyclooxygenase isoforms, cyclooxygenase-1 and cyclooxygenase-2, both metabolize arachidonic acid to prostaglandin H2, which is subsequently processed by downstream enzymes to the various prostanoids. In the present study, we asked if the two isoforms differ in the profile of prostanoids that ultimately arise from their action on arachidonic acid. Resident peritoneal macrophages contained only cyclooxygenase-1 and synthesized (from either endogenous or exogenous arachidonic acid) a balance of four major prostanoids: prostacyclin, thromboxane A2, prostaglandin D2, and 12-hydroxyheptadecatrienoic acid. Prostaglandin E2 was a minor fifth product, although these cells efficiently converted exogenous prostaglandin H2 to prostaglandin E2. By contrast, induction of cyclooxygenase-2 with lipopol- ysaccharide resulted in the preferential production of prostacyclin and prostaglandin E2. This shift in product profile was accentuated if cyclooxygenase-1 was permanently inactivated with aspirin before cyclooxygenase-2 induction. The conversion of exogenous prostaglandin H2 to prostaglandin E2 was only modestly increased by lipopolysaccharide treatment. Thus, cyclooxygenase-2 induction leads to a shift in arachidonic acid metabolism from the production of several prostanoids with diverse effects as mediated by cyclooxygenase-1 to the preferential synthesis of two prostanoids, prostacyclin and prostaglandin E2, which evoke common effects at the cellular level.

Decreased leukotriene C4 synthesis accompanies adherence-dependent nuclear import of 5-lipoxygenase in human blood eosinophils

The enzyme 5-lipoxygenase (5-LO) catalyzes the synthesis of leukotrienes (LTs) from arachidonic acid (AA). Adherence or recruitment of polymorphonuclear neutrophils (PMN) induces nuclear import of 5-LO from the cytosol, which is associated with enhanced LTB4 synthesis upon subsequent cell stimulation. In this study, we asked whether adherence of human eosinophils (EOS) causes a similar redistribution of 5-LO and an increase in LTC4 synthesis. Purified blood EOS examined either in suspension or after adherence to fibronectin for 5 min contained only cytosolic 5-LO. Cell stimulation resulted in activation of 5-LO, as evidenced by its translocation to membranes and LTC4 synthesis. As with PMN, adherence of EOS to fibronectin for 120 min caused nuclear import of 5-LO. Unexpectedly, however, adherence also caused a time-dependent decrease in LTC4 synthesis: EOS adhered for 120 min produced 90% less LTC4 than did cells adhered for 5 min. Adherence did not diminish the release of [3H]AA from prelabeled EOS or reduce the synthesis of the prostanoids thromboxane and PGE2. Also, inhibition of LTC4 production caused by adherence could not be overcome by the addition of exogenous AA. Adherence increased, rather than decreased, LTC4 synthase activity. However, the stimulation of adherent EOS failed to induce translocation of 5-LO from the nucleoplasm to the nuclear envelope. This resistance to activation of the nuclear pool of 5-LO with diminished LT production represents a novel mode of regulation of the enzyme, distinct from the paradigm of up-regulated LT synthesis associated with intranuclear localization of 5-LO observed in PMN and other cell types.

Alveolar lining fluid regulates mononuclear phagocyte 5-lipoxygenase metabolism

The enzyme 5-lipoxygenase (5-LO) catalyses the synthesis of leukotrienes (LT), which are important in phagocytosis and killing of microorganisms. The alveolar macrophage (AM), the primary resident defender of the alveolar space, has a greater capacity for LT synthesis than its precursor, the peripheral blood monocyte (PBM). This study investigated whether the alveolar lining fluid (ALF) upregulates LT synthetic capacity in mononuclear phagocytes. Rat AM, peritoneal macrophages (PM) and ALF were obtained by lavage from pathogen-free animals. Human PBM were isolated from normal subjects. 5-LO metabolism and expression were measured with and without ALF. Rat ALF increased 5-LO metabolism (136.4+/-15.1% of control) in cultured PBM. This was associated with increased 5-LO activating protein (FLAP) (357+/-29.5 %), and 5-LO expression (188+/-31.3%). Culture of AM for 3 days resulted in a greater decrement in LTB4 synthesis (LTB4 15.4+/-6.9% of day 1) than in PM (54.7+/-8.3% of day 1), suggesting a greater dependence of AM 5-LO metabolism on ALF. 5-LO and FLAP expression decreased to a greater degree in AM than PM in culture. Furthermore, AM cultured with ALF maintained their LT synthetic capacity, FLAP and 5-LO expression compared with control cells cultured in medium alone. In conclusion, alveolar lining fluid increased 5-lipoxygenase metabolism in peripheral blood monocytes and maintained it in cultured alveolar macrophages, by a mechanism of increased 5-lipoxygenase and 5-lipoxygenase activating protein expression. This may boost host defence capabilities.

5-Lipoxygenase reaction products modulate alveolar macrophage phagocytosis of Klebsiella pneumoniae

The leukotrienes are potent lipid mediators of inflammation formed by the 5-lipoxygenase-catalyzed oxidation of arachidonic acid. Although the effects of leukotrienes on neutrophil chemotaxis and activation have been established, their role in modulating innate host defense mechanisms is poorly understood. In a previous study (M. Bailie, T. Standiford, L. Laichalk, M. Coffey, R. Strieter, and M. Peters-Golden, J. Immunol. 157:5221-5224, 1996), we used 5-lipoxygenase knockout mice to establish a critical role for endogenous leukotrienes in pulmonary clearance and alveolar macrophage phagocytosis of Klebsiella pneumoniae. In the present study, we investigated the role of specific endogenous leukotrienes in phagocytosis of K. pneumoniae and explored the possibility that exogenous leukotrienes could restore phagocytosis in alveolar macrophages with endogenous leukotriene synthesis inhibition and enhance this process in leukotriene-competent cells. Rat alveolar macrophages produced leukotriene B4 (LTB4), LTC4, and 5-hydoxyeicosatetraenoic acid (5-HETE) during the process of phagocytosis, and the inhibition of endogenous leukotriene synthesis with zileuton and MK-886 dramatically attenuated phagocytosis. We also observed a reduction in phagocytosis when we treated alveolar macrophages with antagonists to the plasma membrane receptors for either LTB4, cysteinyl-leukotrienes, or both. In leukotriene-competent cells, LTC4 augmented phagocytosis to the greatest extent, followed by 5-HETE and LTB4. These 5-lipoxygenase reaction products demonstrated similar relative abilities to reconstitute phagocytosis in zileuton-treated rat alveolar macrophages and in alveolar macrophages from 5-lipoxygenase knockout mice. We conclude that endogenous synthesis of all major 5-lipoxygenase reaction products plays an essential role in phagocytosis. The restorative and pharmacologic effects of LTC4, LTB4, and 5-HETE may provide a basis for their exogenous administration as an adjunctive treatment for patients with gram-negative bacterial pneumonia.

Granulocyte colony-stimulating factor administration to HIV-infected subjects augments reduced leukotriene synthesis and anticryptococcal activity in neutrophils

Neutrophil (PMN) dysfunction occurs in HIV infection. Leukotrienes (LT) are mediators derived from the 5-lipoxygenase (5-LO) pathway that play a role in host defense and are synthesized by PMN. We investigated the synthesis of LT by PMN from HIV-infected subjects. There was a reduction (4.0+/-1.3% of control) in LT synthesis in PMN from HIV-infected compared with normal subjects. This was associated with reduced expression of 5-LO-activating protein (31.2+/-9.6% of normal), but not of 5-LO itself. Since HIV does not directly infect PMN, we considered that these effects were due to reduced release of cytokines, such as granulocyte colony-stimulating factor (G-CSF). We examined the effect of G-CSF treatment (300 microgram daily for 5 d) on eight HIV-infected subjects. PMN were studied in vitro before therapy (day 1) and on days 4 and 7. LTB4 synthesis was increased on day 4 of G-CSF treatment, and returned toward day 1 levels on day 7. 5-LO and 5-LO-activating protein expression were increased in parallel. As a functional correlate to this increase in PMN LT synthesis by G-CSF, we examined the effects on killing of Cryptococcus neoformans. Anticryptococcal activity of PMN from HIV-infected subjects was less than that of PMN from normal subjects. G-CSF treatment improved fungistatic activity of PMN. This increase in antifungal activity was attenuated by in vitro treatment with the LT synthesis inhibitor, MK-886. In conclusion, PMN from HIV-infected subjects demonstrate reduced 5-LO metabolism and antifungal activity in vitro, which was reversed by in vivo G-CSF therapy.

Altered expression and localization of 5-lipoxygenase accompany macrophage differentiation in the lung

The alveolar macrophage (AM) exhibits a greater capacity to synthesize bioactive leukotrienes from arachidonic acid than does its circulating precursor the peripheral blood monocyte. Macrophage differentiation in the lung entails cellular residence within both the pulmonary interstitial and alveolar compartments. In the present study, we sought to determine 1) whether this enhanced metabolic activity was acquired during maturation within the alveolar space and 2) the underlying mechanisms responsible for this upregulation. Rat AMs were separated by Percoll gradient centrifugation into four density-defined subpopulations thought to reflect their degree of maturation. On stimulation with a calcium ionophore, synthesis of leukotriene B4 increased with the degree of maturation, although it was diminished in the oldest subpopulation. This maturation-dependent upregulation was not explained by increases in arachidonic acid release but was associated with increased expression of 5-lipoxygenase (5-LO) protein as determined by immunoblot analysis. Whereas 5-LO is primarily cytosolic in monocytes, it is known to be primarily intranuclear in unfractionated AMs. Here, the localization of 5-LO was investigated by immunofluorescence microscopy and was found to be predominantly nuclear in all AM subpopulations; by contrast, the protein was cytosolic in interstitial macrophages isolated by mechanical and enzymatic lung digestion. These divergent localization patterns in AMs and interstitial macrophages were verified in situ by immunohistochemical staining of sections of normal rat lung. When unfractionated AMs were isolated and maintained in culture for 3 days, a shift in 5-LO distribution from nucleus to cytosol was observed. We conclude that 1) nuclear import of 5-LO occurs within the alveolar space and is reversible on removal from the alveolar milieu and 2) leukotriene synthetic capacity increases further during AM residence within the alveolar space as a result of a progressive increase in the amount of 5-LO protein.

Regulation of 5-lipoxygenase activity in mononuclear phagocytes: characterization of an endogenous cytosolic inhibitor

The proinflammatory leukotrienes (LT) play important roles in host defense and disease states. However, no endogenous mechanisms to downregulate 5-lipoxygenase (5-LO), the enzyme catalyzing LT synthesis, have been described. We observed that the cytosolic fraction of rat alveolar macrophages (AMs) and peritoneal macrophages (PMs), and of peripheral blood monocytes (PBMs) contain substantial amounts of 5-LO protein, but little detectable 5-LO activity. We therefore examined these mononuclear phagocyte (MNP) cytosolic fractions for inhibitory activity against 5-LO. MNP cytosol dose-dependently reduced the 5-LO activity in neutrophil (PMN) cytosol and AM membrane. Furthermore, MNP cytosol dose-dependently prolonged the lag phase of soybean lipoxygenase (LO) without affecting the rate of product formation. This effect was overcome by subsequent addition of 13(S)-hydroperoxy-9-cis-11-trans-octadecadienoic acid (13-HpOD), suggesting that the active factor scavenges hydroperoxides. Inactivation by boiling and roteinase K suggest that is a protein. We speculate that this cytosolic factor(s) may serve as an endogenous means for the down-regulation of 5-LO in macrophages.

Cell biology of the 5-lipoxygenase pathway

The initial enzymatic steps in leukotriene synthesis occur at the nuclear envelope. Cytosolic phospholipase A2 translocates from the cytoplasm to selectively hydrolyze nuclear envelope phospholipids, releasing free arachidonate. 5-Lipoxygenase-activating protein, an arachidonate transfer protein, then binds arachidonate and presents it to 5-lipoxygenase (5-LO), which catalyzes a two-step reaction to produce leukotriene A4. In resting human and rat peripheral blood neutrophils, 5-LO is localized to the cytoplasm; in rat basophilic leukemia cells and human alveolar macrophages, however, it is found predominantly in the nucleus. Immunofluorescence microscopy studies demonstrate that both cytoplasmic and nuclear 5-LO move to the nuclear envelope following cell activation. Many questions remain unanswered regarding the significance of nuclear 5-LO, potential autocrine actions of leukotrienes, and intracellular trafficking of these enzymes and their products.

Capacity for repeatable leukotriene generation after transient stimulation of mast cells and macrophages

Leukotriene (LT) synthesis is initiated by the enzyme 5-lipoxygenase (5-LO). Prolonged cell stimulation causes the translocation of 5-LO to the nuclear envelope and the synthesis of LT, with subsequent inactivation and persistent membrane association of 5-LO. In this study, we examined whether persistent membrane association of 5-LO, as well as the inactivation of 5-LO, could be prevented by shortening the length of cell stimulation or by blocking LT synthesis. As expected, stimulation of rat basophilic leukaemia (RBL) cells, a mast cell model, or alveolar macrophages (AMs) with calcium ionophore for 15 min caused 5-LO translocation, LT generation and the inactivation and persistent membrane association of 5-LO. When RBL cells or AMs instead were stimulated for 0.5-5 min, translocation of 5-LO and synthesis of LT still occurred. However, after washing and resting, the 5-LO enzyme returned to its original intracellular distribution. Furthermore these cells showed a retained capacity for LT synthesis on subsequent re-stimulation. Similar results were obtained when cells were stimulated with either formyl peptide or zymosan, instead of ionophore. In contrast, blockade of LT synthesis during the initial stimulation, with the selective inhibitors zileuton or MK-886, did not inhibit 5-LO translocation, inactivation or persistent membrane association resulting from prolonged cell stimulation. We conclude that, in long-lived immune cells, 5-LO translocation is reversible when cell stimulation is short, but persistent after prolonged stimulation. In addition 5-LO remains active and LT synthetic capacity is retained after transient stimulation, whereas significant inactivation of 5-LO occurs after prolonged stimulation. Finally, results with LT synthesis inhibitors indicate that inactivation and persistent membrane association of 5-LO can result independently of 5-LO activation.

Distinct phospholipases A2 regulate the release of arachidonic acid for eicosanoid production and superoxide anion generation in neutrophils

Arachidonic acid (AA) released from membrane phospholipids by phospholipase A2 (PLA2) is important as a substrate for eicosanoid formation and as a second messenger for superoxide anion (O2-) generation in neutrophils. Different isoforms of PLA2 in neutrophils might mobilize AA for different functions. To test this possibility, we sought to characterize the PLA2s that are activated by the neutrophil stimuli, Aroclor 1242, a mixture of polychlorinated biphenyls, and A23187, a calcium ionophore. Both Aroclor 1242 and A23187 caused release of [3H]AA; however, O2- production was seen only in response to Aroclor 1242. Eicosanoids accounted for >85% of the radioactivity recovered in the supernatant of A23187-stimulated cells but <20% of the radioactivity recovered from cells exposed to Aroclor 1242. Omission or chelation of calcium abolished A23187-induced AA release, but did not alter AA release in Aroclor 1242-stimulated neutrophils. AA release and O2- production in response to Aroclor 1242 were inhibited by bromoenol lactone (BEL), an inhibitor of calcium-independent PLA2. BEL, however, did not alter Calcium-independent activity was inhibited >80% by BEL, whereas calcium-dependent activity was inhibited <5%. Furthermore, calcium-independent, but not calcium-dependent, PLA2 activity was significantly enhanced by Aroclor 1242. These data suggest that Aroclor 1242 and A23187 activate distinct isoforms of PLA2 that are linked to different functions: Aroclor 1242 activates a calcium-independent PLA2 that releases AA for the generation of O2-, and A23187 activates a calcium-dependent PLA2 that mobilizes AA for eicosanoid production.

Suppression of human colorectal mucosal prostaglandins: determining the lowest effective aspirin dose

BACKGROUND

A variety of studies have supported the finding that regular intake of aspirin (acetylsalicylic acid) or nonsteroidal anti-inflammatory agents can affect colorectal cancer carcinogenesis. These agents inhibit the synthesis of prostaglandins. High levels of prostaglandins are observed in colon cancer tissues.

PURPOSE

Experiments were planned to determine the lowest dose of aspirin that can markedly suppress the levels of mucosal prostaglandins E2 and F(2alpha) in colorectal mucosa and to determine whether a relationship exists between these levels and plasma levels of both acetylsalicylic acid and its metabolite, salicylic acid.

METHODS

Healthy men and women aged 18 years or older participated in the study. The participants took a single, daily dose of aspirin (40.5, 81, 162, 324, or 648 mg) or a placebo for 14 days. Colorectal biopsy specimens were taken at baseline, 24 hours after the first dose of aspirin, and 24-30 hours and 72-78 hours after the last, i.e., fourteenth, daily dose of aspirin. The biopsy specimens were assayed for prostaglandins E2 and F(2alpha) by use of a competitive enzyme immunoassay. Plasma concentrations of acetylsalicylic acid and salicylic acid were determined by use of high-performance liquid chromatography. All P values are two-sided.

RESULTS

A total of 65 subjects (10 receiving placebo, groups of 10 each receiving 40.5, 81, 162, or 324 mg of aspirin, and a group of 15 receiving 648 mg of aspirin) completed the protocol. One subject reported unacceptable drug-induced toxic effects and did not complete the protocol; other subjects reported acceptable side effects. The lowest dose to significantly suppress colorectal mucosal prostaglandin E2 concentrations from baseline at 24 hours after the first dose (by 22.6%; P = .002) and at 24-30 hours after the last dose (by 14.2%; P = .021) was 162 mg. At 72-78 hours after the last dose, there was significant suppression for subjects receiving 81 mg (by 23.7%; P = .008). The lowest dose to significantly suppress colorectal mucosal prostaglandin F(2alpha) concentrations from baseline at 24 hours after the first dose (by 18.3%; P = .032) was 324 mg. The lowest dose causing a marked reduction in the level of prostaglandin F(2alpha) at 24-30 hours (by 15.1%; P = .003) and 72-78 hours (by 23.0%; P = .0002) after the last dose was 40.5 mg. No detectable amounts of acetylsalicylic acid or salicylic acid were present in the plasma at any of the biopsy time points.

CONCLUSIONS

The lowest doses of aspirin taken daily for 14 days to significantly suppress concentrations of colorectal mucosal prostaglandins E2 and F(2alpha) were 81 and 40.5 mg, respectively. The suppression occurred without detectable amounts of aspirin or salicylic acid in the plasma at the time points studied. On the basis of these observations, we recommend a single, daily dose of 81 mg of aspirin in future studies of this drug as a chemopreventive agent for colorectal cancer.

Rapid import of cytosolic 5-lipoxygenase into the nucleus of neutrophils after in vivo recruitment and in vitro adherence

5-Lipoxygenase catalyzes the synthesis of leukotrienes from arachidonic acid. The subcellular distribution of 5-lipoxygenase is known to be cell type-dependent and is cytosolic in blood neutrophils. In this study, we asked whether neutrophil recruitment into sites of inflammation can alter the subcellular compartmentation of 5-lipoxygenase. In peripheral blood neutrophils from rats, 5-lipoxygenase was exclusively cytosolic, as expected. However, in glycogen-elicited peritoneal neutrophils, abundant soluble 5-lipoxygenase was in the nucleus. Upon activation with calcium ionophore A23187, intranuclear 5-lipoxygenase translocated to the nuclear envelope. Elicited neutrophils required a greater concentration of A23187 for activation than did blood neutrophils (half-maximal response, 160 versus 52 nM, respectively) but generated greater amounts of leukotriene B4 upon maximal stimulation (26.6 versus 7.68 ng/10(6) cells, respectively). Intranuclear 5-lipoxygenase was also evident in human blood neutrophils after adherence to a variety of surfaces, suggesting that adherence alone is sufficient to drive 5-lipoxygenase redistribution. These results demonstrate a physiologically relevant circumstance in which the subcellular distribution of 5-lipoxygenase can be rapidly altered in resting cells, independent of 5-lipoxygenase activation. Nuclear import of 5-lipoxygenase may be a universal accompaniment of neutrophil recruitment into sites of inflammation, and this may be associated with alterations in enzymatic function.

Increased 5-lipoxygenase metabolism in the lungs of human subjects exposed to ozone

The environmental pollutant ozone, at sufficiently high levels, is known to induce pulmonary inflammation with resultant airway obstruction in normal subjects. Eicosanoids comprise one group of mediators released from alveolar macrophages which are involved in the pathogenesis of inflammatory lung diseases. We compared the effects of 2-h exposures to 0.4 ppm ozone and filtered air on pulmonary function and eicosanoid levels in bronchoalveolar lavage fluid in 11 normal healthy volunteers. Subjects were exposed to a 6-fold increase in minute ventilation using an adjusted work load on a cycle ergometer. All subjects complained of cough and dyspnea, and demonstrated increased airway obstruction, and increased specific airway resistance following ozone exposure as compared to air exposure. Bronchoalveolar lavage cell count demonstrated a 9-fold increase in the number of neutrophils with a lesser reduction in the number of alveolar macrophages following ozone exposure. Notably, bronchoalveolar lavage fluid leukotriene (LT) C4 (8-fold) and to a lesser extent LTB4 (1.5-fold) levels were higher following ozone exposure compared to air control, with no change in prostaglandins. In a subset of four subjects, alveolar macrophage arachidonic acid metabolism was studied in vitro following separate in vivo exposures to both ozone and air. Alveolar macrophages obtained following ozone exposure released more 5-lipoxygenase (1.5-fold) metabolites, with no change in cyclooxygenase metabolites, than did cells obtained following air exposure. These observations document activation of the 5-lipoxygenase pathway in the lung following ozone exposure, and suggest that alveolar macrophages may participate in the generation of LT, whose actions promote airway inflammation and obstruction.

Leukotriene-deficient mice manifest enhanced lethality from Klebsiella pneumonia in association with decreased alveolar macrophage phagocytic and bactericidal activities

Leukotrienes (LTs) are potent mediators of inflammation derived from the 5-lipoxygenase pathway of arachidonic acid metabolism. Although they are known to enhance leukocyte recruitment and function, their role in antimicrobial host defense has not been established. To determine the role of endogenous LTs in the host response to pulmonary infection, wild-type mice and mice rendered LT-deficient by targeted disruption of the 5-lipoxygenase gene (knockout mice) were studied following intratracheal challenge with Klebsiella pneumoniae. Wild-type mice demonstrated a marked increase in lung LT levels and neutrophil numbers following bacterial challenge. As compared with wild-type animals, knockout animals manifested a greater degree of lethality as well as bacteremia following challenge. Interestingly, they displayed no defect in neutrophil recruitment to the lung. However, alveolar macrophages from knockout animals exhibited impairments in bacterial phagocytosis and killing, and these defects were overcome by in vitro addition of exogenous LTB4. We conclude that endogenous LTs play a critical role in the defense against bacterial pneumonia in this murine model.

Leukotriene-deficient mice manifest enhanced lethality from Klebsiella pneumonia in association with decreased alveolar macrophage phagocytic and bactericidal activities

Leukotrienes (LTs) are potent mediators of inflammation derived from the 5-lipoxygenase pathway of arachidonic acid metabolism. Although they are known to enhance leukocyte recruitment and function, their role in antimicrobial host defense has not been established. To determine the role of endogenous LTs in the host response to pulmonary infection, wild-type mice and mice rendered LT-deficient by targeted disruption of the 5-lipoxygenase gene (knockout mice) were studied following intratracheal challenge with Klebsiella pneumoniae. Wild-type mice demonstrated a marked increase in lung LT levels and neutrophil numbers following bacterial challenge. As compared with wild-type animals, knockout animals manifested a greater degree of lethality as well as bacteremia following challenge. Interestingly, they displayed no defect in neutrophil recruitment to the lung. However, alveolar macrophages from knockout animals exhibited impairments in bacterial phagocytosis and killing, and these defects were overcome by in vitro addition of exogenous LTB4. We conclude that endogenous LTs play a critical role in the defense against bacterial pneumonia in this murine model.

Colchicine inhibits arachidonate release and 5-lipoxygenase action in alveolar macrophages

Although colchicine is known to inhibit leukotriene synthesis in neutrophils, its effect on other aspects of arachidonic acid (AA) metabolism as well as its mechanism of action are unknown. To address these questions, we investigated the effects of colchicine on resident rat alveolar macrophages (AM), cells that generate a variety of lipoxygenase and cyclooxygenase products after stimulation. Pretreatment of AM with 10 microM colchicine for 1 h dramatically inhibited the synthesis of all 5-lipoxygenase (5-LO) metabolites from endogenous AA in ionophore A-23187-stimulated cells. In addition, colchicine inhibited the total release of AA as well as prostanoids to a lesser extent. Similar effects were observed with the other microtubule-disruptive agents nocodazole and vinblastine, and 5-LO product formation stimulated by the particulate agonist zymosan was inhibited as well. A selective inhibitory effect of colchicine on the 5-LO pathway was demonstrated by monitoring the synthesis of 5-LO products from exogenously supplied AA. Cell-free enzyme assays showed that this effect was not through a direct inhibition of the 5-LO enzyme. Moreover, colchicine did not affect the translocation of 5-LO to the nuclear envelope. We next evaluated the effect of colchicine on the levels of the two 5-LO cofactors, ATP and Ca2+. Although colchicine did not affect ATP levels, it did abrogate the ionophore-induced increase in intracellular Ca2+ concentration; the inhibitory effect of colchicine on 5-LO metabolism in AM was partially overcome by stimulation with higher doses of A-23187. We conclude that microtubular disruption inhibits agonist-induced increase in intracellular Ca2+ concentration, with multiple consequences for AA metabolism. These include a reduction in the liberation of AA from membrane phospholipids as well as the selective inhibition of processing of AA by 5-LO.

Age-related enhancement of 5-lipoxygenase metabolic capacity in cattle alveolar macrophages

Arachidonic acid (AA) metabolism was assessed in cultured alveolar macrophages (AM) obtained from newborn (9- and 23-day-old) and adult (2- and 6-yr-old) cattle. The AM were prelabeled in [3H]AA-containing medium and, thereafter, stimulated with either A-23187 or zymosan. The released radiolabeled AA metabolites were measured by high-performance liquid chromatography with on-line radiodetection. The results showed that, among different-aged cattle, the synthesis of total 5-lipoxygenase (5-LO) metabolites [leukotrienes (LT) B4, LTC4, LTD4, and 5-hydroxyeicosatetraenoic acid (5-HETE)] increased with age in spite of similar levels of phospholipase-catalyzed AA release. In response to A-23187 and zymosan, 5-LO metabolic capacity of adult cattle AM was approximately 4- and approximately 10-fold that of 9-day-old cattle AM, respectively. As 5-LO metabolic capacity increased, the release of prostaglandins and thromboxane tended to decrease. Immunoblot analysis showed that the steady-state expression of 5-LO and 5-lipoxygenase-activating protein (FLAP) also increased in an age-dependent manner. In newborn calves, AM do not produce great amounts of LTB4; this factor might contribute to insufficient polymorphonuclear leukocyte recruitment into the alveolar space and the high susceptibility to neonatal lung infection.

Translocation of cytosolic phospholipase A2 to the nuclear envelope elicits topographically localized phospholipid hydrolysis

Cytosolic phospholipase A2 (cPLA2) is a good candidate for mediating the agonist-stimulated release of arachidonic acid (AA) from membrane phospholipids. This enzyme undergoes a Ca(2+)-dependent translocation from the cytosol to a membrane site in a variety of cell types, and this site has recently been identified as the nuclear envelope in leucocytes. The functional correlate of this finding has not yet been established. The present study was therefore undertaken to determine whether translocation of cPLA2 to the nuclear envelope was associated with localized phospholipid hydrolysis at this site. Rat alveolar epithelial cells, previously shown to contain cPLA2, were prelabelled with [3H]AA and stimulated with the model agonist, ionophore A23187. Ionophore-induced AA release exhibited characteristics typical of a cPLA2-mediated response, in that it was Ca(2+)-dependent, sn-2 AA-selective, and inhibited by arachidonyl trifluoromethyl ketone. As determined by indirect immunofluorescence microscopic analysis as well as subcellular fractionation with immunoblotting, ionophore treatment resulted in a translocation of cPLA2 protein from the cytoplasm to the nuclear envelope. To determine whether the nuclear membrane was indeed the source of released AA, prelabelled cells were incubated in the presence or absence of A23187, after which the phospholipid radioactivity was quantified in nuclear and non-nuclear membrane fractions. [3H]AA was distributed in both nuclear and non-nuclear membrane phospholipids. Following A23187 stimulation, the loss of [3H]AA from nuclear membrane phospholipids accounted for 88.1 +/- 5.8% of the total loss from phospholipids and for 92.9 +/- 2.3% of the total [3H]AA released into the medium. These results demonstrate for the first time that agonist-stimulated translocation of cPLA2 to the nuclear envelope is associated with phospholipid hydrolysis which is preferentially localized to that site.