Activation of lipoxin A(4) receptors by aspirin-triggered lipoxins and select peptides evokes ligand-specific responses in inflammation

Lipoxin (LX) A(4) and aspirin-triggered LX (ATL) are endogenous lipids that regulate leukocyte trafficking via specific LXA(4) receptors (ALXRs) and mediate antiinflammation and resolution. ATL analogues dramatically inhibited human neutrophil (polymorphonuclear leukocyte [PMN]) responses evoked by a potent necrotactic peptide derived from mitochondria as well as a rogue synthetic chemotactic peptide. These bioactive lipid analogues and small peptides each selectively competed for specific (3)H-LXA(4) binding with recombinant human ALXR, and its N-glycosylation proved essential for peptide but not LXA(4) recognition. Chimeric receptors constructed from receptors with opposing functions, namely ALXR and leukotriene B(4) receptors (BLTs), revealed that the seventh transmembrane segment and adjacent regions of ALXR are essential for LXA(4) recognition, and additional regions of ALXR are required for high affinity binding of the peptide ligands. Together, these findings are the first to indicate that a single seven-transmembrane receptor can switch recognition as well as function with certain chemotactic peptides to inhibitory with ATL and LX (lipid ligands). Moreover, they suggest that ALXR activation by LX or ATL can protect the host from potentially deleterious PMN responses associated with innate immunity as well as direct effector responses in tissue injury by recognition of peptide fragments.     

Synthesis and anti-inflammatory effect of lipoxins in human airway epithelial cells.

In this study, we investigated the synthesis of lipoxins (LXs) and their anti-inflammatory effects in different human airway epithelial cell culture models. After cell incubation with exogenous 5(S),6(R)-dihydroxy-7,9-trans-11,14-cis-eicosatetraenoic acid, LXA(4) was detected in supernatants of differentiated human bronchial epithelial cells by contrast to non-differentiated cells. Exogenous LXA(4) significantly inhibited tumor necrosis factor-alpha (TNF-alpha)-induced interleukin-8 (IL-8) release in the different epithelial cell types and the potency of inhibition was dependent of the accessibility of the specific LXA(4) receptor, formyl-peptide receptor like-1 (FPRL-1) expressed by all these cells. Immunohistochemistry analysis on human bronchial biopsies showed a high expression of FPRL-1 in the epithelium. Finally, an FPRL-1 receptor antagonist, boc-2 peptide reversed LXA(4) effect on IL-8 generation. Together, these findings indicate that differentiated human bronchial epithelium synthesizes LX in vivo which could have autocrine actions through its specific receptor FPRL-1 to promote resolution of airway inflammation.     

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

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

Anti-inflammatory activity of a potent, selective leukotriene A4 hydrolase inhibitor in comparison with the 5-lipoxygenase inhibitor zileuton

Leukotriene A(4) hydrolase (LTA(4)H) catalyzes production of the proinflammatory lipid mediator, leukotriene (LT) B(4), which is implicated in a number of inflammatory diseases. We have identified a potent and selective inhibitor of both the epoxide hydrolase and aminopeptidase activities of recombinant human LTA(4)H (IC(50), approximately 10 nM). In a murine model of arachidonic acid-induced ear inflammation, the LTA(4)H inhibitor, JNJ-26993135 (1-[4-(benzothiazol-2-yloxy)-benzyl]-piperidine-4-carboxylic acid), dose-dependently inhibited ex vivo LTB(4) production in blood, in parallel with dose-dependent inhibition of neutrophil influx (ED(50), 1-3 mg/kg) and ear edema. In murine whole blood and in zymosan-induced peritonitis, JNJ-26993135 selectively inhibited LTB(4) production, without affecting cysteinyl leukotriene production, while maintaining or increasing production of the anti-inflammatory mediator, lipoxin (LX) A(4). The 5-lipoxygenase (5-LO) inhibitor zileuton showed inhibition of LTB(4), LTC(4), and LXA(4) production. Although zileuton inhibited LTB(4) production in the peritonitis model more effectively than the LTA(4)H inhibitor, the influx of neutrophils into the peritoneum after 1 and 2 h was significantly higher in zileuton- versus JNJ-26993135-treated animals. This difference may have been mediated by the increased LXA(4) levels in the presence of the LTA(4)H inhibitor. The selective inhibition of LTB(4) production by JNJ-26993135, while increasing levels of the anti-inflammatory mediator, LXA(4), may translate to superior therapeutic efficacy versus 5-LO or 5-LO-activating protein inhibitors in LTB(4)-mediated inflammatory diseases.     

Lipoxin (LX)A4 and aspirin-triggered 15-epi-LXA4 inhibit tumor necrosis factor 1alpha-initiated neutrophil responses and trafficking: regulators of a cytokine-chemokine axis.

The impact of lipoxin A4 (LXA4) and aspirin-triggered lipoxins (ATLs) was investigated in tumor necrosis factor (TNF)-alpha-initiated neutrophil (polymorphonuclear leukocyte) responses in vitro and in vivo using metabolically stable LX analogues. At concentrations as low as 1-10 nM, the LXA4 and ATL analogues each inhibited TNF-alpha-stimulated superoxide anion generation and IL-1beta release by human polymorphonuclear leukocytes. These LXA4-ATL actions were time and concentration dependent and proved selective for TNF-alpha, as these responses were not altered with either GM-CSF- or zymosan-stimulated cells. TNF-alpha-induced IL-1beta gene expression was also regulated by both anti-LXA4 receptor antibodies and LXA4-ATL analogues. In murine air pouches, 15R/S-methyl-LXA4 dramatically inhibited TNF-alpha-stimulated leukocyte trafficking, as well as the appearance of both macrophage inflammatory peptide 2 and IL-1beta, while concomitantly stimulating IL-4 in pouch exudates. Together, these results indicate that both LXA4 and ATL regulate TNF-alpha-directed neutrophil actions in vitro and in vivo and stimulate IL-4 in exudates, playing a pivotal role in immune responses.     

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.     

Parasite-induced lipoxin A4 is an endogenous regulator of IL-12 production and immunopathology in Toxoplasma gondii infection

The production of interleukin (IL)-12 is critical for the development of interferon (IFN)-gamma-dependent resistance to Toxoplasma gondii. Nevertheless, when this response is dysregulated, such as occurs in the absence of IL-10, the uncontrolled inflammation that results can have lethal consequences for the host. Recently, we demonstrated that lipoxin (LX)A(4), an eicosanoid mediator that depends on 5-lipoxygenase (LO) for its biosynthesis, exerts a regulatory role on dendritic cell IL-12 production triggered artificially by a T. gondii extract. We now formally establish the physiological relevance of this pathway in the systemic control of IL-12 production induced by live T. gondii infection and demonstrate its function to be distinct from that of IL-10. Thus, T. gondii-exposed wild-type, but not 5-LO-deficient animals, produced high levels of serum LXA(4) beginning at the onset of chronic infection. Moreover, 5-LO(-/-), in contrast to wild-type mice, succumbed during the same period displaying a marked encephalitis. The increased mortality of the 5-LO(-/-) animals was also associated with significant elevations of IL-12 and IFN-gamma and was completely prevented by the administration of a stable LXA(4) analogue. Together, these findings demonstrate a new pathway involving the induction of host LXs for the in vivo regulation of proinflammatory responses during microbial infection.     

Lipoxin A4 modulates transmigration of human neutrophils across intestinal epithelial monolayers.

Neutrophil (PMN) migration across intestinal epithelial barriers, such as occurs in many disease states, results in modifications in epithelial barrier. Here, we investigated the impact of lipoxin A4 (LXA4), an eicosanoid with counterregulatory inflammatory roles, on PMN migration across cultured monolayers of the human intestinal epithelial cell line T84. Transepithelial migration of PMN was assessed in the apical-to-basolateral direction and in the basolateral-to-apical direction. In the apical-to-basolateral direction, preexposure of PMN to LXA4 (10 nM, 15 min) stimulated an 87 +/- 5% increase in transepithelial migration of PMN as determined by a PMN myeloperoxidase assay. The LXA4-elicited effect on transmigration was present throughout the 2-h assay period and was not secondary to LXA4 effects on epithelial monolayer integrity as judged by measurement of transepithelial resistance. PMN migration in the basolateral-to-apical direction was modulated by LXA4 with a comparable time- and concentration-dependence to that in the apical-to-basolateral direction. However, qualitative differences in how LXA4 modulates transmigration in the two opposing directions were observed. In the basolateral-to-apical direction, preexposure of PMN to LXA4 (10 nM, 15 min) diminished PMN transepithelial migration by 33 +/- 4%. Structure-function studies revealed that LXA4 and 11-trans-LXA4 (50% of LXA4 effect), but not LXB4, inhibited basolateral-to-apical PMN transmigration. The action of LXA4 was not sensitive to inhibitors of cyclooxygenase or specific leukotriene biosynthesis, but was sensitive to staurosporine, a protein kinase C inhibitor. These results suggest that migration of PMN across epithelia in the physiological direction may be qualitatively different following PMN exposure to eicosanoids. We propose that such retention of PMN at this specific anatomic location may serve an important role in mucosal defense.     

Inhibition of 5-lipoxygenase-activating protein (FLAP) reduces pulmonary vascular reactivity and pulmonary hypertension in hypoxic rats.

Chronically elevated shear stress and inflammation are important in hypertensive lung vessel remodeling. We postulate that 5-lipoxygenase (5-LO) is a molecular determinant of these processes. Immunohistology localized the 5-LO to macrophages of normal and chronically hypoxic rat lungs and also to vascular endothelial cells in chronically hypoxic lungs only. In situ hybridization of normal and chronically hypoxic lungs demonstrated that 5-LO mRNA is expressed in macrophages. Rats hypoxic for 4 wk-developed pulmonary hypertension increased translocation of the lung 5-LO from the cytosol to the membrane fraction and increased levels of lung tissue 5-lipoxygenase-activating protein (FLAP). A FLAP ligand, 3-[l-(4-chlorobenzyl)-3-t-butyl-thio-t-isopropylindol-2-yl]-2,2- dimethylpropanoic acid (MK-886), inhibited the acute angiotensin II and hypoxia-induced pulmonary vasoconstriction in vitro and the development of chronic hypoxic pulmonary hypertension in rats in vivo. Mice bred with the deletion of the 5-LO enzyme (5-LO knockout) developed less right heart hypertrophy than age-matched 5-LO competent mice. Our results support the hypothesis that the 5-LO is involved in lung vascular tone regulation and in the development of chronic pulmonary hypertension in hypoxic rodent models.     

Formation of lipoxins and leukotrienes during receptor-mediated interactions of human platelets and recombinant human granulocyte/macrophage colony-stimulating factor-primed neutrophils

The generation of lipoxygenase products of arachidonic acid is considered an important event in inflammation. This study demonstrates the levels of both lipoxins and leukotrienes (LTC4, LTD4, LTB4, and omega-oxidized LTB4) generated from endogenous sources of arachidonate by PMN primed with recombinant human granulocyte/macrophage colony-stimulating factor and in coincubations with platelets (1:1 to 1:100 ratio). Upon exposure to receptor-mediated stimuli (FMLP and thrombin), the levels of lipoxins generated were within the range of both LTB4 and LTC4. Co-incubation of [1-14C]arachidonate-labeled platelets with primed polymorphonuclear leukocytes (PMN) followed by addition of thrombin and FMLP led to the formation of both 5- and 15-LO products that carried 14C label. Thus, in addition to the transcellular conversion of LTA4 to platelet-derived lipoxins and LTC4, PMN can use platelet-derived arachidonate to generate lipoxygenase products. These results are the first to document the relationship between the levels of lipoxins and leukotrienes generated by receptor-mediated activation of cytokineprimed PMN interacting with platelets. Moreover, they indicate that PMN-platelet interactions utilize bidirectional transcellular routes to contribute to lipoxin formation.     

Cyclooxygenase inhibition in lungs or in neutrophils attenuates neutrophil-dependent edema in rat lungs perfused with phorbol myristate acetate

Results from previous studies indicate that injury in isolated rat lungs perfused with buffer containing phorbol myristate acetate (PMA) and rat neutrophils (PMNs) is dependent on the production of reactive oxygen species and thromboxane (Tx) A2. The purpose of this study was to determine whether the lung or the PMN was the source of TxA2 required to produce lung injury in this model. Prostanoid synthesis by rat lungs or PMNs was inhibited selectively by pretreatment of either rats or isolated PMNs with aspirin (100 mg/kg p.o. or 100 microM, respectively). Unbound aspirin was removed from the lungs and PMNs before use in experiments. Lungs from vehicle-pretreated rats that were perfused with PMA and untreated PMNs exhibited increases in weight, lavage fluid albumin content and TxB2 production with respect to lungs perfused with PMA but no PMNs. Increases in these markers were prevented when cyclooxygenase from either the lungs or the PMNs was inhibited. These results indicate that TxA2 is produced by both PMNs and by lung cells in this preparation, and that TxA2 production by both of these sources is required for the manifestation of edema.     

Inosine monophosphate and aspirin-triggered 15-epi-lipoxin A4 act in concert to regulate neutrophil trafficking: additive actions of two new endogenous anti-inflammatory mediators

Regulation of neutrophil (PMN) trafficking by soluble mediators is a critical component in the outcome of host defense, inflammation resolution, and neutrophil-mediated tissue injury. Elucidation of the endogenous mediators that protect tissues from excess leukocyte traffic and aberrant PMN activation that can lead to tissue damage and chronic inflammation is of considerable interest, especially the endogenous mechanisms of anti-inflammation. To this end, we recently uncovered two new classes of mediators: inosine monophosphate (IMP) and aspirin-triggered 15(R)-epimers of native lipoxin A(4). Here, we examined the combined actions of both classes of compounds in regulating key events in neutrophil trafficking. Neutrophil rolling in mouse microvessels was inhibited by both IMP or 5S,6R,15R-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid (15-epi-LXA(4)) in a concentration-dependent fashion. When combined, IMP (300 nM) and 15-epi-LX (10 nM) demonstrated additive inhibition of neutrophil rolling in microvessels. IMP and 15-epi-LX also significantly inhibited tumor necrosis factor-alpha (TNF-alpha)-induced neutrophil accumulation into the mouse air pouch in a dose-dependent manner. Again, the combination of low dose IMP (10 microg) and LX analog (5 microg) gave additive inhibition of neutrophil accumulation in this model. These results demonstrate the inhibition of neutrophil trafficking in two separate models by two different classes of small endogenous molecules. The additive inhibition by IMP and aspirin-triggered LX may represent key pathways that protect and resolve inflammatory responses that could be harnessed for treatment.     

The lectin-like domain of thrombomodulin confers protection from neutrophil-mediated tissue damage by suppressing adhesion molecule expression via nuclear factor kappaB and mitogen-activated protein kinase pathways

Thrombomodulin (TM) is a vascular endothelial cell (EC) receptor that is a cofactor for thrombin-mediated activation of the anticoagulant protein C. The extracellular NH(2)-terminal domain of TM has homology to C-type lectins that are involved in immune regulation. Using transgenic mice that lack this structure (TM(LeD/LeD)), we show that the lectin-like domain of TM interferes with polymorphonuclear leukocyte (PMN) adhesion to ECs by intercellular adhesion molecule 1-dependent and -independent pathways through the suppression of extracellular signal-regulated kinase (ERK)(1/2) activation. TM(LeD/LeD) mice have reduced survival after endotoxin exposure, accumulate more PMNs in their lungs, and develop larger infarcts after myocardial ischemia/reperfusion. The recombinant lectin-like domain of TM suppresses PMN adhesion to ECs, diminishes cytokine-induced increase in nuclear factor kappaB and activation of ERK(1/2), and rescues ECs from serum starvation, findings that may explain why plasma levels of soluble TM are inversely correlated with cardiovascular disease. These data suggest that TM has antiinflammatory properties in addition to its role in coagulation and fibrinolysis.     

Lipoxin A4 and lipoxin B4 inhibit chemotactic responses of human neutrophils stimulated by leukotriene B4 and N-formyl-L-methionyl-L-leucyl-L-phenylalanine

1. Lipoxin A4 (LXA4) and lipoxin B4 (LXB4) have been evaluated for their capacities to modulate neutrophil (PMN) migration and endothelial cell adherence using compounds prepared by total chemical synthesis. 2. Increased PMN migration was seen with concentrations of LXA4 from 10(-9) mol/l to 10(-7) mol/l. LXA4 was 100-fold less potent than leukotriene B4 (LTB4) and it elicited only one-half of the maximal response of LTB4. 3. The (5S,6S,15S)-isomer of LXA4 induced only a weak migratory response and LXB4 was inactive, suggesting that the activity of LXA4 was stereospecific. 4. Modified chequerboard analysis indicated that LXA4 was a chemokinetic agent. 5. Preincubation of PMN with increasing concentrations of LXA4 induced a very similar dose- and time-dependent inhibition of the subsequent response to 10(-7) mol/l LTB4 or 10(-7) mol/l N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP). The inhibition was observed at 10(-10) mol/l LXA4; the concentration which produced 50% inhibition was 10(-8) mol/l and 100% inhibition of PMN locomotion occurred at 10(-6) mol/l LXA4. 6. The (5S,6S,15S)-isomers of LXA4 and LXB4 were 5- and 100-fold less potent than LXA4, respectively, in suppressing LTB4- or FMLP-induced PMN migration. 7. Preincubation of PMN with LXA4 led to a suppression of calcium mobilization, as assessed by Quin2-AM fluorescence, when the cells were subsequently stimulated under optimal conditions by LTB4 or FMLP. 8. These results suggest that the inhibitory activity of lipoxins may be related to the capacity of these molecules to regulate calcium ion mobilization.     

Cooperation between aspirin-triggered lipoxin and nitric oxide (NO) mediates antiadhesive properties of 2-(Acetyloxy)benzoic acid 3-(nitrooxymethyl)phenyl ester (NCX-4016) (NO-aspirin) on neutrophil-endothelial cell adherence

2-(Acetyloxy)benzoic acid 3-(nitrooxymethyl)phenyl ester (NCX-4016) is a nitric oxide (NO)-releasing derivative of aspirin that inhibits cyclooxygenase (COX) activity and releases NO. Acetylation of COX-2 by aspirin activates a transcellular biosynthetic pathway that switches eicosanoid biosynthesis from prostaglandin E(2) to 15-epi-lipoxin (LX)A(4) or aspirin-triggered lipoxin (ATL). Here, we demonstrate that exposure of neutrophil (PMN)/human umbilical vein endothelial cell (HUVEC) cocultures to aspirin and NCX-4016 triggers ATL formation and inhibits cell-to-cell adhesion induced by endotoxin (LPS) and interleukin (IL)-1beta by 70 to 90%. However, although selective and nonselective COX-2 inhibitors (celecoxib, rofecoxib, and naproxen) or N-t-butoxycarbonylmethionine-leucine-phenylalanine (Boc-1), an LXA(4) receptor antagonist, reduced the antiadhesive properties of aspirin by approximately 70%, antiadhesive effects of NCX-4016 were only marginally affected ( approximately 30%) by COX inhibitors and Boc-1, implying that COX-independent mechanisms mediate the antiadhesive properties of NCX-4016. Indeed, NCX-4016 causes a long-lasting (up to 12 h) release of NO and cGMP accumulation in HUVEC. Scavenging NO with 10 mM hemoglobin, in the presence of celecoxib, reduced the antiadhesive properties of NCX-4016 by approximately 80%. Confirming a role for NO, the NO donor diethylenetriamine-NO also inhibited PMN/HUVEC adhesion by approximately 80%. NCX-4016, but not aspirin, decreased DNA binding of nuclear factor-kappaB (NF-kappaB) on gel shift analysis and HUVEC's overexpression of CD54 and CD62E induced by LPS/IL-1beta. Reduction of binding of the two NF-kappaB subunits p50-p50 and p50-p65 was reversed by dithiothreitol, implying S-nitrosylation as mechanism of inhibition. In summary, our results support that ATL and NO are formed at the PMN/HUVEC interface after exposure to NCX-4016 and mediate the antiadhesive properties of this compound.     

Leukotriene b4 and its metabolites prime the neutrophil oxidase and induce proinflammatory activation of human pulmonary microvascular endothelial cells

Leukotrienes are proinflammatory lipid mediators, derived from arachidonic acid via 5-lipoxygenase (5-LO). Leukotriene B4 (LTB4) is an effective polymorphonuclear neutrophil (PMN) chemoattractant, as well as being a major product of PMN priming. Leukotriene B4 is rapidly metabolized into products that are thought to be inactive, and little is known about the effects of LTB4 on the pulmonary endothelium. We hypothesize that LTB4 and its metabolites are effective PMN priming agents and cause proinflammatory activation of pulmonary endothelial cells. Isolated PMNs were primed (5 min, 37°C) with serial concentrations 10 to 10 M of LTB4 and its metabolites: 6-trans-LTB4, 20-OH-LTB4, and 20-COOH-LTB4, and then activated with fMLP. Primary human pulmonary microvascular endothelial cells (HMVECs) were incubated with these lipids (6 h, 37°C, 5% CO2), and intercellular adhesion molecule 1 was measured by flow cytometry. Polymorphonuclear neutrophil adhesion was measured by myeloperoxidase assays, and to ensure that these reactions were specific to the LTB4 receptors, BLT1 and BLT2 were antagonized with CP105,696 (BLT1) or silenced with siRNA (BLT1 and BLT2). Leukotriene B4 and its metabolites primed PMNs over a wide range of concentrations, depending on the specific metabolite. In addition, at high concentrations these lipids also caused increases in the surface expression of intercellular adhesion molecule 1 on HMVECs and induced HMVEC-mediated adhesion of PMNs. Silencing of BLT2 abrogated HMVEC activation, and blockade of BLT1 inhibited the observed PMN priming activity. We conclude that LTB4 and its ω-oxidation and nonenzymatic metabolites prime PMNs over a range of concentrations and activate HMVECs. These data have expanded the repertoire of causative agents in acute lung injury and postinjury multiple organ failure.     

Native and aspirin-triggered lipoxins control innate immunity by inducing proteasomal degradation of TRAF6

Innate immune signaling is critical for the development of protective immunity. Such signaling is, perforce, tightly controlled. Lipoxins (LXs) are eicosanoid mediators that play key counterregulatory roles during infection. The molecular mechanisms underlying LX-mediated control of innate immune signaling are of interest. In this study, we show that LX and aspirin (ASA)-triggered LX (ATL) inhibit innate immune signaling by inducing suppressor of cytokine signaling (SOCS) 2-dependent ubiquitinylation and proteasome-mediated degradation of TNF receptor-associated factor (TRAF) 2 and TRAF6, which are adaptor molecules that couple TNF and interleukin-1 receptor/Toll-like receptor family members to intracellular signaling events. LX-mediated degradation of TRAF6 inhibits proinflammatory cytokine production by dendritic cells. This restraint of innate immune signaling can be ablated by inhibition of proteasome function. In vivo, this leads to dysregulated immune responses, accompanied by increased mortality during infection. Proteasomal degradation of TRAF6 is a central mechanism underlying LX-driven immune counterregulation, and a hitherto unappreciated mechanism of action of ASA. These findings suggest a new molecular target for drug development for diseases marked by dysregulated inflammatory responses.     

Targeted disruption of the leukotriene B(4) receptor in mice reveals its role in inflammation and platelet-activating factor-induced anaphylaxis

Leukotrienes are derived from arachidonic acid and serve as mediators of inflammation and immediate hypersensitivity. Leukotriene B(4) (LTB(4)) and leukotriene C(4) (LTC(4)) act through G protein-coupled receptors LTB(4) receptor (BLTR) and Cys-LTR, respectively. To investigate the physiological role of BLTR, we produced mice with a targeted disruption of the BLTR gene. Mice deficient for BLTR (BLTR(-/-)) developed normally and had no apparent hematopoietic abnormalities. Peritoneal neutrophils from BLTR(-/-) mice displayed normal responses to the inflammatory mediators C5a and platelet-activating factor (PAF) but did not respond to LTB(4) for calcium mobilization or chemotaxis. Additionally, LTB(4) elicited peritoneal neutrophil influx in control but not in BLTR(-/-) mice. Thus, BLTR is the sole receptor for LTB(4)-induced inflammation in mice. Neutrophil influx in a peritonitis model and acute ear inflammation in response to arachidonic acid was significantly reduced in BLTR(-/-) mice. In mice, intravenous administration of PAF induces immediate lethal anaphylaxis. Surprisingly, female BLTR(-/-) mice displayed selective survival (6 of 9; P = 0.002) relative to male (1 of 11) mice of PAF-induced anaphylaxis. These results demonstrate the role of BLTR in leukotriene-mediated acute inflammation and an unexpected sex-related involvement in PAF-induced anaphylaxis.     

Regulatory expression of lipoxin A4 receptor in physiologically estrus cycle and pathologically endometriosis.

Expression of receptors for prostaglandin (PG) and leukotriene (LT) has been reported to detect in endometrium and smooth muscle of uterus, suggesting involvement of these arachidonic metabolites in endometrial pathology and reproductive biology. Lipoxin (LX), which is produced by lipoxygenases from arachidonic acid, has been characterized as an anti-inflammatory lipid mediator. Biological actions of Lipoxin A4 (LXA4) are mediated through the specific receptor. In order to know roles of LXA4 in female genitalia, expression of LXA4 receptor mRNA was quantified by real-time polymerase chain reaction. Significantly higher expression of the receptor was detected in endometrium and myometrium than ovary in normal rats. Expression of the receptor in endometrium was increased at stage of proestrus cycle under physiological condition. Exogenous administration of progesterone into female rats significantly reduced the expression, while administration of estradiol or pregnant mare serum gonadotropin (PMSG) did not. Both, endometrium in experimental endometriosis induced in rats and the tissues from patients with ectopic endometriosis showed a higher expression of LXA4 receptor compared to the normal tissues. In contrast, expressions of BLT1 and BLT2, receptors for leukotriene B4, did not change in the endometriosis. These observations suggest a possible role of LXA4 and the receptor under physiological estrus cycle and pathological condition as endometriosis.     

Human CMV infection induces 5-lipoxygenase expression and leukotriene B4 production in vascular smooth muscle cells

Leukotrienes (LTs) are powerful proinflammatory lipid mediators that may play a central role in cardiovascular diseases, including arteriosclerosis, myocardial infarction, and stroke. Owing to restricted expression of 5-lipoxygenase (5-LO), the enzyme required for their synthesis, LTs are almost exclusively produced by myeloid cells. Here, we report that human cytomegalovirus (HCMV) infection of human vascular smooth muscle cells (SMCs) increases 5-LO mRNA levels by up to 170-fold in a dose- and time-dependent manner. Infected cells expressed 5-LO protein, as shown by immunohistochemistry, enabling them to synthesize bioactive LTB(4). HCMV-infected vascular SMCs expressing 5-LO protein were readily detected in tissue samples from CMV-infected patients with inflammatory bowel disease or AIDS. Thus, pathogen-induced LT production in HCMV-infected tissues may contribute to local inflammation, consistent with the ability of HCMV to control cellular and immunological functions. HCMV-induced LT biosynthesis in SMCs offers a molecular mechanism to explain HCMV-induced pathogenesis in inflammatory diseases.