Inhibition of the lipoxin A4 and resolvin D1 receptor impairs host response to acute lung injury caused by pneumococcal pneumonia in mice.

Resolution of the acute respiratory distress syndrome (ARDS) from pneumonia requires repair of the injured lung endothelium and alveolar epithelium, removal of neutrophils from the distal airspaces of the lung, and clearance of the pathogen. Previous studies have demonstrated the importance of specialized proresolving mediators (SPMs) in the regulation of host responses during inflammation. Although ARDS is commonly caused by Streptococcus pneumoniae, the role of lipoxin A4 (LXA4) and resolvin D1 (RvD1) in pneumococcal pneumonia is not well understood. In the present experimental study, we tested the hypothesis that endogenous SPMs play a role in the resolution of lung injury in a clinically relevant model of bacterial pneumonia. Blockade of formyl peptide receptor 2 (ALX/FPR2), the receptor for LXA4 and RvD1, with the peptide WRW4 resulted in more pulmonary edema, greater protein accumulation in the air spaces, and increased bacteria accumulation in the air spaces and the blood. Inhibition of this receptor was also associated with decreased levels of proinflammatory cytokines. Even in the presence of antibiotic treatment, WRW4 inhibited the resolution of lung injury. In summary, these experiments demonstrated two novel findings: LXA4 and RvD1 contribute to the resolution of lung injury due to pneumococcal pneumonia, and the mechanism of their benefit likely includes augmenting bacterial clearance and reducing pulmonary edema via the restoration of lung alveolar-capillary barrier permeability.

Human NK Cell Cytoskeletal Dynamics and Cytotoxicity Are Regulated by LIM Kinase.

NK cells provide immune surveillance and host protection against viruses and tumors through their cytotoxic effector function. Cytoskeletal rearrangement is necessary for NK cell lytic granule trafficking and immune synapse formation to trigger apoptosis of targeted cells. LIM kinase (LIMK) regulates F-actin remodeling by phosphorylating cofilin to inhibit actin severing and depolymerization. In this study, in human NK cells, the glucocorticoid dexamethasone downregulated LIMK expression, F-actin accumulation at the immune synapse, lytic granule trafficking, and cytotoxicity. In contrast, the specialized proresolving mediator lipoxin A4 promoted NK cell LIMK expression, lytic granule polarization to the immune synapse and cytotoxicity. Using a LIMK inhibitor, we show that LIMK activity is necessary for NK cell cytotoxicity, including lipoxin A4's proresolving actions. Together, our findings identify LIMK as an important control mechanism for NK cell cytoskeletal rearrangement that is differentially regulated by glucocorticoids and specialized proresolving mediators to influence NK cell cytotoxicity.

Simvastatin Attenuates Endothelial Activation through 15-Epi-Lipoxin A4 Production in Murine Chronic Chagas Cardiomyopathy.

Current treatments for chronic Chagas cardiomyopathy, a disease with high mortality rates and caused by the protozoan Trypanosoma cruzi, are unsatisfactory. Myocardial inflammation, including endothelial activation, is responsible for the structural and functional damage seen in the chronic phase. The clinical efficacy of benznidazole could be improved by decreasing chronic inflammation. Statins, which have anti-inflammatory properties, may improve the action of benznidazole. Here, the action of simvastatin in a murine model of chronic Chagas cardiomyopathy and the link with the production of the proresolving eicosanoid 15-epi-lipoxin A4, produced by 5-lipoxygenase, are evaluated. Simvastatin decreased the expression of the adhesion molecules E-selectin, intracellular adhesion molecule type 1 (ICAM-1), and vascular cell adhesion molecule type 1 (VCAM-1) in T. cruzi-infected mice. However, when this drug was administered to 5-lipoxygenase-deficient mice, the anti-inflammatory effect was not observed unless exogenous 15-epi-lipoxin A4 was administered. Thus, in chronic Chagas disease, 5-epi-lipoxin A4 induced by simvastatin treatment could improve the pathophysiological condition of patients by increasing the trypanocidal action of benznidazole.

Glucocorticoids sensitize rat placental inflammatory responses via inhibiting lipoxin A4 biosynthesis.

Inflammation dysregulation in placenta is implicated in the pathogenesis of numerous pregnancy complications. Glucocorticoids (GCs), universally considered anti-inflammatory, can also exert proinflammatory actions under some conditions, whereas whether and how GCs promote placental inflammation have not been intensively investigated. In this paper we report the opposing regulation of rat placental inflammation by synthetic GC dexamethasone (Dex). When Dex was subcutaneously injected 1 h after we administered an intraperitoneal lipopolysaccharide (LPS) challenge, neutrophil infiltration and proinflammatory Il1b, Il6, and Tnfa expression in rat placenta were significantly reduced. In contrast, Dex pretreatment for 24 h potentiated rat placental proinflammatory response to LPS and delayed inflammation resolution, which involved MAPKs and NF-kappaB activation. Mechanically, Dex pretreatment promoted 5-lipoxygenase (ALOX5) activation and increased leukotriene B4 production, whereas it inhibited the anti-inflammatory and proresolving lipid mediator lipoxin A4 (LXA4) biosynthesis in rat placenta via downregulating ALOX15 and ALOX15B expression. Moreover, LXA4 supplementation dampened Dex-potentiated placental inflammation and suppressed Dex-mediated ALOX5 activation in vivo and in vitro. Taken together, these findings suggest that GCs exposure could promote placental inflammation initiation and delay resolution via disrupting LXA4 biosynthesis.

Apolipoprotein A1 potentiates lipoxin A4 synthesis and recovery of allergen-induced disrupted tight junctions in the airway epithelium.

BACKGROUND: Asthma is characterized by chronic airway inflammation triggered by various allergens in the environment. Defects in the bronchial epithelial interface with the external environment are the hallmark of asthma. Apolipoprotein A-1 (ApoA1) or ApoA1 mimetics have demonstrated anti-inflammatory activity and preventive effects in mouse models. OBJECTIVE: We investigated airway levels of ApoA1 in asthmatics and the possible role of ApoA1 in protection of the bronchial epithelium and in resolution of inflammation in cellular and animal models of asthma. METHODS: ApoA1 levels were measured in bronchoalveolar lavage fluid (BALF) from asthmatics and healthy controls. With treatment of ApoA1, mouse model of house dust mite (HDM)-driven asthma and cultured primary bronchial epithelial cells obtained from asthmatics were examined. Tight junction (TJ) expression in the bronchial epithelial cells was assessed by using confocal microscopy and immunoblot. RESULTS: Asthmatics showed significantly lower ApoA1 levels in bronchoalveolar lavage fluid than did healthy controls. Local ApoA1 treatment significantly decreased lung IL-25, IL-33, and thymic stromal lymphopoietin levels in HDM-challenged mice and inhibited allergen-induced production of these cytokines in cultured primary bronchial epithelial cells. ApoA1 promoted recovery of disrupted TJ proteins zonula occludens-1 and occludin in cultured primary bronchial epithelium obtained from asthmatics. ApoA1-induced increases in the TJ proteins were dependent on increased production of lipoxin A4 (LX A4). CONCLUSIONS AND CLINICAL RELEVANCE: ApoA1 enhances resolution of allergen-induced airway inflammation through promoting recovery of damaged TJs in the bronchial epithelium. ApoA1 could be a therapeutic strategy in chronic airway inflammatory diseases that are associated with a defective epithelial barrier, including asthma.

Lipids as targets for novel anti-inflammatory therapies.

Lipids serve important functions as membrane constituents and also as energy storing molecules. Besides these functions certain lipid species have now been recognized as signalling molecules that regulate a multitude of cellular responses including cell growth and death, and also inflammatory reactions. Bioactive lipids are generated by hydrolysis from membrane lipids mainly by phospholipases giving rise to fatty acids and lysophospholipids that either directly exert their function or are further converted to active mediators. This review will summarize the present knowledge about bioactive lipids that either promote or attenuate inflammatory reactions. These lipids include polyunsaturated fatty acids (PUFA), eicosanoids including the epoxyeicosatrienoic acids (EET), peroxisome proliferation activating receptor (PPAR) activators, cannabinoids and the sphingolipids ceramide, sphingosine 1-phosphate and sphingosylphosphorylcholine.

The required role of endogenously produced lipoxin A4 and annexin-1 for the production of IL-10 and inflammatory hyporesponsiveness in mice.

The appropriate development of an inflammatory response is central for the ability of a host to deal with any infectious insult. However, excessive, misplaced, or uncontrolled inflammation may lead to acute or chronic diseases. The microbiota plays an important role in the control of inflammatory responsiveness. In this study, we investigated the role of lipoxin A4 and annexin-1 for the IL-10-dependent inflammatory hyporesponsiveness observed in germfree mice. Administration of a 15-epi-lipoxin A4 analog or an annexin-1-derived peptide to conventional mice prevented tissue injury, TNF-alpha production, and lethality after intestinal ischemia/reperfusion. This was associated with enhanced IL-10 production. Lipoxin A4 and annexin-1 failed to prevent reperfusion injury in IL-10-deficient mice. In germfree mice, there was enhanced expression of both lipoxin A4 and annexin-1. Blockade of lipoxin A4 synthesis with a 5-lipoxygenase inhibitor or Abs against annexin-1 partially prevented IL-10 production and this was accompanied by partial reversion of inflammatory hyporesponsiveness in germfree mice. Administration of BOC-1, an antagonist of ALX receptors (at which both lipoxin A4 and annexin-1 act), or simultaneous administration of 5-lipoxygenase inhibitor and anti-annexin-1 Abs, was associated with tissue injury, TNF-alpha production, and lethality similar to that found in conventional mice. Thus, our data demonstrate that inflammatory responsiveness is tightly controlled by the presence of the microbiota and that the innate capacity of germfree mice to produce IL-10 is secondary to their endogenous greater ability to produce lipoxin A4 and annexin-1.

Lipoxins and aspirin-triggered 15-epi-lipoxins are the first lipid mediators of endogenous anti-inflammation and resolution.

Lipoxins (LXs) or the lipoxygenase interaction products are generated from arachidonic acid via sequential actions of lipoxygenases and subsequent reactions to give specific trihydroxytetraene-containing eicosanoids. These unique structures are formed during cell-cell interactions and appear to act at both temporal and spatially distinct sites from other eicosanoids produced during the course of inflammatory responses and to stimulate natural resolution. Lipoxin A4 (LXA4) and lipoxin B4 (LXB4) are positional isomers that each possesses potent cellular and in vivo actions. These LX structures are conserved across species. The results of numerous studies reviewed in this work now confirm that they are the first recognized eicosanoid chemical mediators that display both potent anti-inflammatory and pro-resolving actions in vivo in disease models that include rabbit, rat, and mouse systems. LXs act at specific GPCRs as agonists to regulate cellular responses of interest in inflammation and resolution. Aspirin has a direct impact in the LX circuit by triggering the biosynthesis of endogenous epimers of LX, termed the aspirin-triggered 15-epi-LX, that share the potent anti-inflammatory actions of LX. Stable analogs of LXA4, LXB4, and aspirin-triggered lipoxin were prepared, and several of these display potent actions in vitro and in vivo. The results reviewed herein implicate a role of LX and their analogs in many common human diseases including airway inflammation, asthma, arthritis, cardiovascular disorders, gastrointestinal disease, periodontal disease, kidney diseases and graft-vs.-host disease, as well as others where uncontrolled inflammation plays a key role in disease pathogenesis. Hence, the LX pathways and mechanisms reviewed to date in this work provide a basis for new approaches to treatment of many common human diseases that involve inflammation.

Evidence that 5-lipoxygenase and acetylated cyclooxygenase 2-derived eicosanoids regulate leukocyte-endothelial adherence in response to aspirin.

(1) Unlike other nonsteroidal anti-inflammatory drugs that inhibit formation of cyclooxygenase (COX)-dependent eicosanoids, acetylation of COX-2 by aspirin switches eicosanoid biosynthesis from prostaglandin E(2) (PGE(2)) to 15-epi-lipoxin A(4) (15-epi-LXA(4) or aspirin-triggered lipoxin, ATL). ATL formation by activated leukocytes (PMN) requires the intervention of 5-lipoxygenase (5-LOX), an enzyme that is involved in leukotriene B(4) (LTB(4)) formation. (2) In the present study, we have examined the role of acetylated COX-2 and 5-LOX in modulating antiadhesive effects of aspirin on adhesion of PMN to endotoxin (LPS)-primed human umbilical endothelial cells (HUVEC). (3) Treating PMN/HUVEC cocultures with aspirin resulted in a concentration-dependent inhibition of cell-to-cell adhesion induced by LPS. Treating HUVEC with selective COX-2 inhibitors, celecoxib and rofecoxib, caused an approximately 70% reversion of antiadhesive effect of aspirin. In contrast, inhibition of neutrophil's 5-LOX pathway with 1 micro M ZD2138, a selective 5-LOX inhibitor, 1 micro M BAY-X-1005, a FLAP inhibitor, or 100 micro M licofelone, a dual COX/5-LOX inhibitor, did not affect antiadhesive properties of aspirin. (4) Exposure to celecoxib (100 micro M) or rofecoxib (10 micro M) completely suppressed ATL formation caused by aspirin without affecting LTB(4) levels. ZD2138, licofelone and BAY-X-1005 inhibited ATL formation as well as LTB(4) generation. (5) Treatment with LXA(4) reduced PMN adhesion to HUVEC and counteracted the proadhesive effect of celecoxib. In contrast, exposure to Boc-1, an LXA(4) antagonist, counteracts the antiadhesive activities of aspirin. Exposure to U75302, an LTB(4) receptor antagonist, enhances the antiadesive effect of aspirin. (6) Reversal of antiadhesive activities of aspirin by celecoxib was associated with increased expression of LFA-1 on PMN and E-selectin on HUVEC. Addition of LXA(4), ZD2138 and U75302 inhibited these changes. (7) The present results support the notion that inhibition of ATL formation is mechanistically linked to the reversal of the antiadhesive activity of aspirin caused by selective COX-1 inhibitors and suggests that the LTB(4)/ATL balance modulates pro- and antiadhesive activity of nonsteroidal anti-inflammatory drugs at the leukocyte-endothelial cell interface.