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Lipoxins: Revelations on resolution
Abstract
Lipoxins (LXs) are endogenously produced eicosanoids typically generated during cell-cell interactions. In this article, the compelling evidence from in vitro and in vivo model systems that LXs actively promote the resolution of inflammation is reviewed. Of particular interest are indications that stable synthetic analogues of LXs and aspirin-triggered 15-epi-LXs can mimic many of the desirable anti-inflammatory, "pro-resolution" actions of native LXs. Given the enhanced stability and efficacy of these compounds a role as novel anti-inflammatory therapeutics is proposed.
... Regarding low-grade inflammation, the role of adipokines produced in adipose tissue and released into the blood has been widely studied in recent years [12]. The lipid mediator lipoxin A 4 (LXA 4 ) is an endogenous bioactive product of arachidonic acid that has been reported to regulate a variety of effects in multiple tissues, including anti-inflammation, neutrophil infiltration, and macrophage polarization, and its therapeutic effect on OA has been confirmed by previous studies [13][14][15][16][17]. LXA 4 is formed by activation of the oxylipin pathway in the fat pad below the articular cartilage and the action of 12-lipoxygenase in the capillaries [14,18]. ...
... Regarding low-grade inflammation, the role of adipokines produced in adipose tissue and released into the blood has been widely studied in recent years [12]. The lipid mediator lipoxin A 4 (LXA 4 ) is an endogenous bioactive product of arachidonic acid that has been reported to regulate a variety of effects in multiple tissues, including anti-inflammation, neutrophil infiltration, and macrophage polarization, and its therapeutic effect on OA has been confirmed by previous studies [13][14][15][16][17]. LXA 4 is formed by activation of the oxylipin pathway in the fat pad below the articular cartilage and the action of 12-lipoxygenase in the capillaries [14,18]. These activities of LXA 4 are regulated by the G protein-coupled FPR2/ALX receptor, and recent studies have shown that FPR2 is expressed in human articular chondrocytes [19,20,21]. ...
... OA is usually associated with the early development of mild inflammation, rather than severe inflammation. [14,15,16,17] We, thus, assessed the level of LXA 4 , aside from the commonly known TNF-α and IL-1β markers, to determine the effects of EU extract on early inflammation. Specifically, 250 mg/kg EU extract increased LXA 4 and showed an effective inhibitory effect on the initial inflammatory response. ...
... Lipoxin A 4 (LXA 4 ), a kind of adipokines, is a potent stop signal of inflammation (McMahon et al., 2001;Serhan, 2014). The therapeutic effects of LXA 4 on OA have been confirmed by previous studies (Sodin-Semrl et al., 2000;Chan and Moore, 2010;Conte et al., 2010;Yang et al., 2017). ...
... Cellular and preclinical studies have confirmed the potent anti-inflammatory of LXA 4 (McMahon et al., 2001). In addition, LXA 4 could attenuate adipose inflammation and shift adipose macrophage phenotype toward resolution in vivo (Börgeson et al., 2015;Serhan et al., 2014). ...
... LXA 4 could be formed by the action of 12/15-lipoxygenase (12/15-LO) in the capillaries (McMahon et al., 2001) and the activation of the oxylipin pathway of the infrapatellar fat pad (Gierman et al., 2013). Upregulation of LXA 4 in the knee articular cavity is induced by appropriate treadmill exercise. ...
Lipoxin A4 (LXA4), a kind of adipokines, is a potent stop signal of inflammation. Our preliminary study found that LXA4 of serum and intra-articular lavage fluid (IALF) was rapidly elevated in 2 h and rapidly reduced to normal level at 4 h after moderate-intensity treadmill exercise. The aim was to confirm the therapeutic effects of LXA4 during treadmill exercise on rat model of monosodium iodoacetate (MIA)-induced OA and the detailed mechanism of LXA4 on OA. One hundred and twenty-four male Sprague-Dawley rats were submitted to two different protocols. A single session of treadmill exercise: sixty-four rats were randomly divided into treadmill exercise of different intensities for 60 min only once (n = 4). Formal treadmill exercise: sixty rats were randomly divided into six groups (n = 10): control group (CG), knee OA group (OAG), OA with treadmill exercise of different intensities (OAL, OAM and OAH), and OAM + BOC-2 (an antagonist of LXA4 receptor). The rats were evaluated by ELISA, histology, immunohistochemistry and western blotting. Fibroblast-like synoviocytes (FLSs) were obtained from knee joint of rats. The effects of LXA4 on interleukin (IL)-1β induced FLSs were evaluated by western blotting and immunofluorescence. The results of ELISA, histological evaluation, western blotting and immunohistochemistry indicated that OAM had a better treatment which could be suppressed by BOC-2. Moreover, LXA4 could attenuate the expression of matrix metalloproteinase (MMP)-3 and MMP-13 and suppress the expression of nuclear factor-kappa B (NF-κB) p65 induced by IL-1β in FLSs. The therapeutic effects of LXA4 during treadmill exercise on MIA-induced OA via inhibiting NF-κB signaling pathway.
... However, in the case of OA, overactive immune response or chronic in ammation can lead to tissue damage and brosis [7,8]. Lipoxin A4 (LXA 4 ) is an eicosanoid acid produced in the capillaries and infrapatellar fat pad during cell-cell interactions, and is an end signal of in ammation [9,10]. In our previous studies, we found that LXA 4 was rapidly produced and metabolized during exercise therapy for OA, suggesting an important role in the e cacy of this treatment [11,12]. ...
... The effects of exercise on OA may be divided into systemic effects on the whole body and local effects on the knee joint. Appropriate exercise produces a hypoxic environment in blood vessels which promote platelet aggregation, lipoxygenase activation, and LXA 4 generation [9]. It is proposed that LXA 4 not only prevents chronic in ammation and limits neutrophil in ltration, but also relieves pain, reduces pain sensitivity, and inhibits peripheral nerve ber sensitivity in systemic system of whole body [51,52]. ...
Our previous study found that lipoxin A 4 (LXA 4 ) exerted therapeutic effects on osteoarthritis (OA). In this study, we evaluated the effects of LXA 4 via synovial macrophage M1/M2 subtype polarization on chondrocyte pyroptosis and mechanisms during mechanical stimulation. Synovial macrophages were subjected to various LXA 4 concentrations and cyclic tensile strain (CTS) conditions to determine optimal co-culture conditions. The effects of LXA 4 on chondrocyte pyroptosis, as represented by macrophage M1/M2 subtype polarization, were detected by western blot, immunofluorescence, and flow cytometry analyses. Forty male Sprague-Dawley rats were randomly divided into four groups (n = 10): control group (CG), OA group (OAG), OA with moderate-intensity treadmill exercise (OAE), and OAE + BOC-2 (an LXA 4 antagonist). All rats were evaluated using histology, enzyme-linked immunosorbent assay (ELISA), quantitative PCR, and western blot analyses. We found that LXA 4 was downregulated in articular fluid and that CD 86/Arg 1 was up-regulated in the synovium of patients with increasing Kellgren-Lawrence grade. In vitro , CTS and LXA 4 both promoted M2 subtype polarization of synovial macrophages, inhibiting the nuclear translocation of NF-κB p65 and the NLRP3 formation in chondrocytes. In vivo , the OAE treatment exerted protective effects on articular cartilage and facilitated M2 polarization of synovial macrophages. These effects were suppressed by BOC-2 treatment. We concluded that moderate CTS enhances the therapeutic effects of LXA 4 by inhibiting the nuclear translocation of NF-κB p65 and NLRP3. Furthermore, the therapeutic effects of LXA 4 during treadmill exercise in monoiodoacetate-induced OA were driven by promotion of synovial macrophage M2 subtype polarization.
... These mediators are formed by biosynthetic pathways that convert the arachidonic acid (AA) to lipoxins (LXs), ω-3-derived eicosapentaenoic acid (EPA) to E-series resolvins, and docosahexaenoic acid (DHA) to D-series resolvins, protectins and maresins. Lipoxins are known to inhibit leukocyte activation and infiltration to inflammation sites and to stimulate the uptake and clearance of apoptotic cells by macrophages, while resolvins can directly counterregulate the biosynthesis of pro-inflammatory eicosanoids and suppress the production of pro-inflammatory markers [16,17]. D-series resolvins can act as a potent regulator of both human and murine PMN, may cause reductions in leucocyte infiltration, and can also block Toll-like receptor-mediated activation on macrophages [18]. ...
... Whereas leukotrienes are potent pro-inflammatory mediators that may enhance cytokine and free radical production by leukocytes [61], lipoxins, as presented above, are important mediators of resolution. [17]. Therefore, an imbalance in lipoxin-leukotriene homeostasis may be a key factor in the pathogenesis of aGVHD. ...
Inflammation is an essential reaction of the immune system to infections and sterile tissue injury. However, uncontrolled or unresolved inflammation can cause tissue damage and contribute to the pathogenesis of various inflammatory diseases. Resolution of inflammation is driven by endogenous molecules, known as pro-resolving mediators, that contribute to dampening inflammatory responses, promoting the resolution of inflammation and the recovery of tissue homeostasis. These mediators have been shown to be useful to decrease inflammatory responses and tissue damage in various models of inflammatory diseases. Graft-versus-host disease (GVHD) is a major unwanted reaction following allogeneic hematopoietic stem cell transplantation (allo-HSCT) and is characterized by an exacerbated inflammatory response provoked by antigen disparities between transplant recipient and donor. There is no fully effective treatment or prophylaxis for GVHD. This review explores the effects of several pro-resolving mediators and discusses their potential use as novel therapies in the context of GVHD.
... LXB 4 displayed neuroprotective activity by directly acting on retinal ganglion cells and primary cortical neurons and in vivo increased retinal ganglion cells survival and function in murine models of glaucoma and neurotoxic stress [27]. Formation and actions of LXB 4 in the ocular surface have not been investigated but there is a body of evidence demonstrating that this SPM is protective in several mouse models of inflammatory diseases [130,141]. Future studies are needed that investigate if MSCs release SPM in vivo and if these lipid signals are part of MSC's protective mechanisms at the ocular surface. ...
... Structural analogs have been designed for several SPMs to resist metabolic inactivation and to increase their bioavailability. An impressive body of work has established the efficacy of SPMs and SPM analogs at very low doses in preclinical animal models [10,12,13,15,107,141,152]. However, there are always challenges for meeting industry level drug production and stability standards, which may have delayed moving more SPMs or their structural analogs from bench to bedside. ...
In the last twenty years an impressive body of evidence in diverse inflammatory animal disease models and human tissues, has established polyunsaturated fatty acids (PUFA) derived specialized-pro-resolving mediators (SPM), as essential mediators for controlling acute inflammation, immune responses and wound healing and for resolving acute inflammation in many non-ocular tissues. SPM pathways and receptors are highly expressed in the ocular surface where they regulate wound healing, nerve regeneration, innate immunity and sex-specific regulation of auto-immune responses. Recent evidence indicates that in the eye these resident SPM networks are important for maintaining ocular surface health and immune homeostasis. Here, we will review and discuss evidence for SPMs and other PUFA-derived mediators as important endogenous regulators and biomarkers of ocular surface health and disease and their therapeutic potential.
... The role of adipokines, which are produced by adipose tissue and released into blood participating in low-grade inflammation, has been widely studied in recent years [12]. Lipoxin A 4 (LXA 4 ) is a potent stop signal of inflammation [13] and its therapeutic effect on OA has been confirmed by previous studies [14][15][16]. LXA 4 can be formed by the action of 12-lipoxygenase in the capillaries [17] and the activation of the oxylipin pathway of the infrapatellar fat pad [18]. ...
... Regarding the frequency of exercise, the histopathology findings indicated that OAE3 had a better therapeutic effect than OAE1 and OAE2 on the tibiofemoral joint. LXA 4 is a potent stop signal of inflammation [13] and the therapeutic effect of LXA 4 on OA has been confirmed by previous studies [14][15][16]. Our preliminary experiment found that LXA 4 was rapidly elevated in 2 hours and rapidly reduced to normal level at 4 hours after treadmill exercise. ...
The aim was to investigate the effects of different frequencies treadmill exercise with total exercise time being constancy on articular cartilage, lipoxin A4 (LXA4) and the NF-κB pathway in rat model of monosodium iodoacetate-induced osteoarthritis (OA). Fifty male Sprague-Dawley rats were randomly divided into five groups (n = 10): controls (CG), knee OA model (OAG), OA + treadmill exercise once daily (OAE1), OA + treadmill exercise twice daily, rest interval between exercise>4h (OAE2) and OA + treadmill exercise three times daily, rest interval between exercise>4h (OAE3). Rats were evaluated after completing the treadmill exercise program (speed, 18 m/min; total exercise time 60 min/day; 5 days/week for 8 weeks). Interleukin (IL)-1β, tumor necrosis factor (TNF)-α, and LXA4 in serum and intra-articular lavage fluid were measured by ELISA. Changes in articular cartilage were evaluated by histology, immunohistochemistry, western blotting and quantitative real-time-PCR. LXA4 in the serum and intra-articular lavage fluid increased in all OAE groups, and histological evaluation indicated that the OAE3 group had the best treatment response. The expression of COL2A1 and IκB-β in articular cartilage increased in all OAE groups vs the OAG group, whereas expression of IL-1β, TNF-α, matrix metalloproteinase (MMP)-13, and NF-κB p65 was reduced in all OAE groups compared with the OAG. Under the condition of 60 min treadmill exercise with moderate-intensity, to fulfill in three times would have better chondroprotective effects than to fulfill in two or one time on monosodium iodoacetate-induced OA in rats. And it may be worked through the anti-inflammatory activity of LXA4 and the NF-κB pathway. © 2017 Yang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
... The second pathway is initiated by 15-LO that produces 15S-HETE from AA that is rapidly converted to LX by 5-LO [13]. The anti-inflammatory effects of lipoxins are mediated by an LX receptor termed ALX and include inhibition of PMN neutrophils chemotaxis, modulation of cytokines synthesis, and inhibition of cell proliferation [13,16]. ...
... In contrast, LXA 4 and ATL (aspirin-triggered lipoxin) behave as potent negative regulators of inflammation due their ability to inhibit PMN neutrophil and eosinophil traffic. These effects are achieved by enhancing PMN clearance from inflammatory focus without excessive macrophage activation, modulating cytokine-stimulated metalloproteinase activity and inhibiting cell proliferation [16]. LXA 4 production was also involved in the prevalent synthesis of antiinflammatory cytokines such as IL-10 that play a fundamental role in the resolution of inflammation [54,55]. ...
Cysteinyl leukotrienes (CysLTs) and lipoxins (LXs) are lipid mediators that control inflammation, with the former inducing and
the latter inhibiting this process. Because the role played by these mediators in paracoccidioidomycosis was not investigated, we
aimed to characterize the role of CysLT in the pulmonary infection developed by resistant (A/J) and susceptible (B10.A) mice.
48 h after infection, elevated levels of pulmonary LTC4 and LXA4 were produced by both mouse strains, but higher levels were
found in the lungs of susceptible mice. Blocking the CysLTs receptor by MTL reduced fungal loads in B10.A, but not in A/J mice.
In susceptible mice, MLT treatment led to reduced influx of PMN leukocytes, increased recruitment of monocytes, predominant
synthesis of anti-inflammatory cytokines, and augmented expression of 5- and 15-lipoxygenase mRNA, suggesting a prevalent LXA4
activity. In agreement, MTL-treated macrophages showed reduced fungal burdens associated with decreased ingestion of fungal
cells. Furthermore, the addition of exogenous LX reduced, and the specific blockade of the LX receptor increased the fungal loads
of B10.A macrophages. This study showed for the first time that inhibition of CysLTs signaling results in less severe pulmonary
paracoccidioidomycosis that occurs in parallel with elevated LX activity and reduced infection of macrophages.
... LXA 4 potently blocks ROS action via nuclear factor erythroid 2-related factor 2 (Nrf2)-dependent mechanisms in several animal models (33)(34)(35)(36)(37). LXA 4 also reduces NF-kB activity, accounting for an essential antiinflammatory mechanism (30,(38)(39)(40). LXA 4 acts through G protein coupled receptors (GPCR) for LXA 4 (ALXR), also known as FPRL1 and FPR2 (41)(42)(43). The activation of ALX/FPR2 receptor explains most of the anti-inflammatory, pro-resolving, and protective actions of LXA 4 (29,42,44). ...
Background
Lipoxin A4 (LXA4) has anti-inflammatory and pro-resolutive roles in inflammation. We evaluated the effects and mechanisms of action of LXA4 in titanium dioxide (TiO2) arthritis, a model of prosthesis-induced joint inflammation and pain.
Methods
Mice were stimulated with TiO2 (3mg) in the knee joint followed by LXA4 (0.1, 1, or 10ng/animal) or vehicle (ethanol 3.2% in saline) administration. Pain-like behavior, inflammation, and dosages were performed to assess the effects of LXA4 in vivo.
Results
LXA4 reduced mechanical and thermal hyperalgesia, histopathological damage, edema, and recruitment of leukocytes without liver, kidney, or stomach toxicity. LXA4 reduced leukocyte migration and modulated cytokine production. These effects were explained by reduced nuclear factor kappa B (NFκB) activation in recruited macrophages. LXA4 improved antioxidant parameters [reduced glutathione (GSH) and 2,2-azino-bis 3-ethylbenzothiazoline-6-sulfonate (ABTS) levels, nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA and Nrf2 protein expression], reducing reactive oxygen species (ROS) fluorescent detection induced by TiO2 in synovial fluid leukocytes. We observed an increase of lipoxin receptor (ALX/FPR2) in transient receptor potential cation channel subfamily V member 1 (TRPV1)⁺ DRG nociceptive neurons upon TiO2 inflammation. LXA4 reduced TiO2‐induced TRPV1 mRNA expression and protein detection, as well TRPV1 co-staining with p-NFκB, indicating reduction of neuronal activation. LXA4 down-modulated neuronal activation and response to capsaicin (a TRPV1 agonist) and AITC [a transient receptor potential ankyrin 1 (TRPA1) agonist] of DRG neurons.
Conclusion
LXA4 might target recruited leukocytes and primary afferent nociceptive neurons to exert analgesic and anti-inflammatory activities in a model resembling what is observed in patients with prosthesis inflammation.
... Previous reports suggested that Lipoxin A4, an endogenous eicosanoid of arachidonate metabolism, can actively promote the resolution of inflammation (McMahon et al., 2001) and increase antibiotic efficacy (Thornton et al., 2021). In this study, it was correlated with the largest number of ASVs in the ileum, and the majority of bacteria showed negative correlations with lipoxin A4 (20 ASVs), indicating a potential role of lipoxin A4 in inhibiting the growth of gut bacteria. ...
Gut microbiota plays important roles in host metabolism. Whether and how much the gut microbiota in different gut locations contributes to the variations of host serum metabolites are largely unknown, because it is difficult to obtain microbial samples from different gut locations on a large population scale. Here, we quantified the gut microbial compositions using 16S rRNA gene sequencing for 1070 samples collected from the ileum, cecum and faeces of 544 F6 pigs from a mosaic pig population. Untargeted metabolome measurements determined serum metabolome profiles. We found 1671, 12,985 and 103,250 significant correlations between circulating serum metabolites and bacterial ASVs in the ileum, cecum, and faeces samples. We detected nine serum metabolites showing significant correlations with gut bacteria in more than one gut location. However, most metabolite‐microbiota pairwise associations were gut location‐specific. Targeted metabolome analysis revealed that CDCA, taurine, L‐leucine and N‐acetyl‐L‐alanine can be used as biomarkers to predict porcine fatness. Enriched taxa in fat pigs, for example Prevotella and Lawsonia intracellularis were positively associated with L‐leucine, while enriched taxa in lean pigs, such as Clostridium butyricum, were negatively associated with L‐leucine and CDCA, but positively associated with taurine and N‐acetyl‐L‐alanine. These results suggested that the contributions of gut microbiota in each gut location to the variations of serum metabolites showed spatial heterogeneity.
... Under certain conditions, aspirin-induced acetylation of COX-2 inhibits prostanoid production and promotes the formation of 15-HETE which is then converted by 42 5-LO to either 15-epi-LXA4 or 15-epi-LXB4. These aspirin triggered lipoxins may produce beneficial effects as they can down-regulate the action of certain granulocytes(McMahon et al. 2001). Many of the proinflammatory actions of leukotrienes are inhibited by lipoxins such as leukocyte chemotaxis, adhesion and cytokine production. ...
p>LTs are thought to be derived predominantly from cells of myeloid origin. Airway structural cell types such as human bronchial epithelial (HBE) cells, human airway smooth muscle (HASM) cells and lung fibroblasts generate pro-inflammatory cytokines and lipid mediators such as prostanoids and 15-lipoxygenase products, but their capacity to generate leukotrienes is unclear. In leukocytes LT synthesis is initiated from membrane-derived arachidonic acid by 5-lipoxygenase (5-LO) and its activating protein FLAP, followed by conversion of LTA<sub>4</sub> to LTB<sub>4</sub> by LTA<sub>4</sub> hydrolase or to LTC<sub>4</sub> to LTC<sub>4</sub> synthase. We hypothesised that HBE cells, HASM cells and fibroblasts may express 5-LO pathway enzymes and synthesise LTC<sub>4</sub> to LTB<sub>4</sub>, either spontaneously or in response to stimulation with inflammatory mediators, and that they may also express CysLT<sub>1</sub> and/or BLT.
Using RT-PCR, basal expression of mRNA for 5-LO, FLAP, LTA<sub>4</sub> hydrolase and LTC<sub>4</sub> synthase was detected in primary HBE cells, HASM cells and bronchial fibroblasts, as well as in the 16-HBE cell line.
These results show that HBE cells, HASM cells and fibroblasts constitutively express a complete and active 5-LO pathway for the synthesis of LTB<sub>4</sub> and LTC<sub>4</sub> and that this may be regulated by exposure to inhaled asthma triggers or endogenously released inflammatory cytokines and autacoids. Constutive expression of CysLT<sub>1</sub>R on all three cell-types may be up-regulated in an inflammatory environment leading to increased CysLT<sub>1</sub> mediated effects such as collagen or mucus secretion, bronchoconstriction and proliferation. The role of BLT or HASM cells and fibroblasts is not yet clear, although LTB<sub>4</sub> is chemotactic for fibroblasts. LTs released by HBEC, HASM and fibroblasts may lead both to autocrine effects and to leukocyte infiltration, and in combination with other mediators produced by structural cells, contribute to the vicious circle of inflammation and remodelling within the asthmatic airway.</p
... In contrast to the described effect on PMN, LXA4 and LXB4 stimulate monocyte chemotaxis and adhesion, which may play a role in physiological monocyte movement and/or pathological processes [122]. In addition, lipoxins increase the uptake of apoptotic neutrophils by macrophages [123], which promotes the clearance of apoptotic leukocytes by macrophages at the site of inflammation [123][124][125]. ...
Atherosclerosis is one of the most important problems of modern medicine as it is the leading cause of hospitalizations, disability, and mortality. The key role in the development and progression of atherosclerosis is the imbalance between the activation of inflammation in the vascular wall and the mechanisms of its control. The resolution of inflammation is the most important physiological mechanism that is impaired in atherosclerosis. The resolution of inflammation has complex, not fully known mechanisms, in which lipid mediators derived from polyunsaturated fatty acids (PUFAs) play an important role. Specialized pro-resolving mediators (SPMs) represent a group of substances that carry out inflammation resolution and may play an important role in the pathogenesis of atherosclerosis. SPMs include lipoxins, resolvins, maresins, and protectins, which are formed from PUFAs and regulate many processes related to the active resolution of inflammation. Given the physiological importance of these substances, studies examining the possibility of pharmacological effects on inflammation resolution are of interest.
... In addition, LXA4 stimulates monocyte chemotaxis and adhesion [80] and increases the uptake of apoptotic neutrophils by macrophages [81]. These actions promote clearance of apoptotic leukocytes by macrophages at the site of inflammation [81][82][83]. ...
Lipid metabolism plays an important role in many lung functions. Disorders of lipid metabolism are part of the pathogenesis of chronic obstructive pulmonary disease (COPD). Lipids are involved in numerous cross-linkages with inflammation. Recent studies strongly support the involvement of fatty acids as participants in inflammation. They are involved in the initiation and resolution of inflammation, including acting as a substrate for the formation of lipid mediators of inflammation resolution. Specialized pro-inflammatory mediators (SPMs) belonging to the classes of lipoxins, resolvins, maresins, and protectins, which are formed enzymatically from unsaturated fatty acids, are now described. Disorders of their production and function are part of the pathogenesis of COPD. SPMs are currently the subject of active research in order to find new drugs. Short-chain fatty acids are another important participant in metabolic and immune processes, and their role in the pathogenesis of COPD is of great clinical interest.
... Evidence supports an antiinflammatory role for lipoxins in vasoactive and immunoregulatory function, eg, as counter-regulatory compounds (chalones) of the immune response.Leukotriene C4 (LTC4), leukotriene D4 (LTD4) and leukotriene E4 (LTE4) promote endothelial cell permeability and airway smooth muscle constriction during anaphylactic reactions and asthma.[Fitzpatrick FA,2004; Lands B,2012;McMahon B et al 2001; Smith WL& Murphy RC.2008;Wijendran V &Hayes KC .2004] ...
The general objective of this research is to explore the effect of omega-3 fatty acids supplementation in children with bronchial asthma.
... In addition, endogenous lipid modulators of CB 1 have been documented, and include pregnenolone and lipoxin A 4 [13,14]. Pregnenolone, the inactive precursor of steroid hormones that is structurally related to cholesterol and synthesized from it by mitochondrial cytochrome P450ssc [15], has been shown to act as an endogenous NAM of CB 1 [16]. ...
The recent resolution of the crystal structure of type-1 cannabinoid receptor (CB1), and the discovery of novel modulators for this target open the way to the possibility of elucidating the structural requirements for CB1 binding, and thereby facilitate a rational drug design. Compounds that target the orthosteric site of CB1 in some cases have shown side effects. Allosteric modulators could potentially avoid these side effects by influencing binding and/or efficacy of orthosteric ligands. Here, we summarize and compare previous data on different putative allosteric binding sites observed in CB1 homology models with an in silico docking study of the recently published crystal structure of the same receptor on endogenous and natural hydrophobic ligands that act as positive allosteric modulators (PAMs) and negative allosteric modulators (NAMs) of CB1. In particular, a lipid-exposed pocket targeted by most of the tested molecules is reported and discussed. This article is protected by copyright. All rights reserved
... Trout macrophages and human leukocytes can convert endogenous EPA to 15Scontaining LX or 5-series LX 5 compounds (Hill et al., 1999). It has been suggested that stable synthetic analogues of lipoxins and the ASA-triggered 15-epi-lipoxins can mimic many of the desirable anti-inflammatory, "proresolution" actions of native lipoxins (McMahon et al., 2001). ...
... These function to inhibit leukotrienes and therefore are broadly anti-inflammatory. In addition ALOX15 stimulates the clearance of apoptotic cells and promotes tissue healing (McMahon et al., 2001), which is seen in resistant sheep (Gossner et al., 2012). ALOX15 has not been annotated in the Oar v3.1 genome assembly but analysis using the Bos taurus ALOX15 sequence (NM 174501.2) identifies that the sheep gene is encoded by 14 exons on the plus strand of chromosome 11 (NC 019468.1). ...
The resistance and susceptibility of sheep to the common abomasal nematode parasite, Teladorsagia circumcincta is strongly associated with the differential polarization of the immune response. Resistant animals control larval colonization by the production of a protective antibody response regulated by Th2 T cells. Susceptible sheep respond to infection by developing an inflammatory Th1/Th17 response that fails to control infection. Previous microarray analysis identified genes associated with T cell polarization that were differentially expressed between the resistant and susceptible sheep. RT-qPCR confirmed the microarray data for ALOX15 and IL13. Both ALOX15 exon 9 and IL13 exon 4 were significantly increased in resistant animals and copy number RT-qPCR showed that expression levels of these exons were significantly negatively correlated with quantitative phenotypic traits, including abomasal worm counts and faecal egg counts. Sequencing of the intronic regions 5' to these genes failed to identify any potential genetic links to differential exon usage.
Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.
... Synthetic and metabolic pathways of eicosanoids impact endocannabinoid levels, suggesting functional relationships among endocannabinoids, prostaglandins (10), and lipoxins (11). Lipoxin A 4 (LXA 4 ), the most studied endogenous lipoxin (12), is largely involved in immune system regulation and is linked to resolution of inflammation (13). The metabotropic ALX receptor (also called FPRL-1) is responsible for the immunological effects of LXA 4 and is expressed in peripheral organs, but has negligible occurrence in the central nervous system (CNS) (14). ...
... In in vitro models LXA 4 , LXB 4 , and ATLS inhibit PMN chemotaxis in response to the chemoattractant LTB 4 and inhibit eosinophil responses to platelet activating factor. Stimulation of macrophages with LXA 4 significantly enhances phagocytosis of apoptotic PMN, suggesting that LXA 4 can promote the clearance of apoptotic leukocytes by macrophages at an inflammatory site [30,31]. ...
Lipoxin A4 has been described as a major signal for the resolution of inflammation and is abnormally produced in the lungs of patients with cystic fibrosis (CF). In CF, the loss of chloride transport caused by the mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel gene results in dehydration, mucus plugging, and reduction of the airway surface liquid layer (ASL) height which favour chronic lung infection and neutrophil based inflammation leading to progressive lung destruction and early death of people with CF. This review highlights the unique ability of LXA4 to restore airway surface hydration, to stimulate airway epithelial repair, and to antagonise the proinflammatory program of the CF airway, circumventing some of the most difficult aspects of CF pathophysiology. The report points out novel aspects of the cellular mechanism involved in the physiological response to LXA4, including release of ATP from airway epithelial cell via pannexin channel and subsequent activation of and P2Y11 purinoreceptor. Therefore, inadequate endogenous LXA4 biosynthesis reported in CF exacerbates the ion transport abnormality and defective mucociliary clearance, in addition to impairing the resolution of inflammation, thus amplifying the vicious circle of airway dehydration, chronic infection, and inflammation.
... In in vitro models LXA 4 , LXB 4 , and ATLS inhibit PMN chemotaxis in response to the chemoattractant LTB 4 and inhibit eosinophil responses to platelet activating factor. Stimulation of macrophages with LXA 4 significantly enhances phagocytosis of apoptotic PMN, suggesting that LXA 4 can promote the clearance of apoptotic leukocytes by macrophages at an inflammatory site [30,31]. ...
Lipoxin A4 has been described as a major signal for the resolution of inflammation and is abnormally produced in the lungs of patients with cystic fibrosis (CF). In CF, the loss of chloride transport caused by the mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel gene results in dehydration,mucus plugging, and reduction of the airway surface liquid layer (ASL) height which favour chronic lung infection and neutrophil based inflammation leading to progressive lung destruction and early death of people with CF. This review highlights the unique ability of LXA4 to restore airway surface hydration, to
stimulate airway epithelial repair, and to antagonise the proinflammatory programof theCF airway, circumventing some of themost difficult aspects of CF pathophysiology. The report points out novel aspects of the cellular mechanism involved in the physiological response to LXA4, including release of ATP fromairway epithelial cell via pannexin channel and subsequent activation of and P2Y11 purinoreceptor. Therefore, inadequate endogenous LXA4 biosynthesis reported in CF exacerbates the ion transport abnormality
and defective mucociliary clearance, in addition to impairing the resolution of inflammation, thus amplifying the vicious circle of airway dehydration, chronic infection, and inflammation.
... These metabolites are further transformed into epoxytetraene intermediates by the action of leukocyte 5-LOX yielding LxA4 and LxB4 (Serhan, 1989;Levy et al., 1993;Serhan et al., 2008). In the intestine, resident tissue cells such as intestinal epithelial cells expressed 15-LOX and could further contribute to LxA4 generation by the production of 15S-H(p)ETE (McMahon et al., 2001). Indeed, LxA4 is synthesized in the human gut by colonic mucosa (Mangino et al., 2006). ...
Background and purpose:
Long-term intake of dietary fatty acids is known to predispose to chronic inflammation, but their effects on acute intestinal ischaemia/reperfusion (I/R) injury is unknown. The aim of this study was to determine the consequences of a diet rich in n-3 or n-6 polyunsaturated fatty acids (PUFA) on intestinal I/R-induced damage.
Experimental approach:
Mice were fed three different isocaloric diets: a balanced diet used as a control and two different PUFA-enriched diets, providing either high levels of n-3 or of n-6 PUFA. Intestinal injury was evaluated after intestinal I/R. PUFA metabolites were quantitated in intestinal tissues by LC-MS/MS.
Key results:
In control diet-fed mice, intestinal I/R caused inflammation and increased COX and lipoxygenase-derived metabolites compared with sham-operated animals. Lipoxin A4 (LxA4 ) was significantly and selectively increased after ischaemia. Animals fed a high n-3 diet did not display a different inflammatory profile following intestinal I/R compared with control diet-fed animals. In contrast, intestinal inflammation was decreased in the I/R group fed with high n-6 diet and level of LxA4 was increased post-ischaemia compared with control diet-fed mice. Blockade of the LxA4 receptor (Fpr2), prevented the anti-inflammatory effects associated with the n-6 rich diet.
Conclusions and implications:
This study indicates that high levels of dietary n-6, but not n-3, PUFAs provides significant protection against intestinal I/R-induced damage and demonstrates that the endogenous production of LxA4 can be influenced by diet.
... Leukotrienes are primarily involved in the initiation of a proinflammatory response through the activation of various immune cells, while lipoxins are molecules with potent anti-inflammatory properties [9]. In addition to endogenous generation of lipoxins, aspirin can also trigger the biosynthesis of a group of lipoxins known as aspirin-triggered lipoxin A 4 (ATL), which mimic the anti-inflammatory actions of lipoxins but are more resistant to degradation [10,11]. Increased expression of multiple LOX isoforms, and levels of the pro-inflammatory leukotriene B 4 (LTB 4 ), have been reported in the aged brain; as well as in the AD brain [12][13][14][15]. ...
The initiation of an inflammatory response is critical to the survival of an organism. However, when inflammation fails to reach resolution, a chronic inflammatory state may occur, potentially leading to bystander tissue damage. Accumulating evidence suggests that chronic inflammation contributes to the progression of Alzheimer's disease (AD), and identifying mechanisms to resolve the pro-inflammatory environment stimulated by AD pathology remains an area of active investigation. Previously, we found that treatment with the pro-resolving mediator aspirin-triggered lipoxin A4 (ATL), improved cognition, reduced Aβ levels, and enhanced microglia phagocytic activity in Tg2576 transgenic AD mice. Here, we evaluated the effect of aging on brain lipoxin A4 (LXA4) levels using non-transgenic and 3xTg-AD mice. Additionally, we investigated the effect of ATL treatment on tau pathology in 3xTg-AD mice. We found that LXA4 levels are reduced with age, a pattern significantly more impacted in 3xTg-AD mice. Moreover, ATL delivery enhanced the cognitive performance of 3xTg-AD mice and reduced Aβ levels, as well as decreased the levels of phosphorylated-tau (p-tau). The decrease in p-tau was due in part to an inhibition of the tau kinases GSK-3β and p38 MAPK. In addition, microglial and astrocyte reactivity was inhibited by ATL treatment. Our results suggest that the inability to resolve the immune response during aging might be an important feature that contributes to AD pathology and cognitive deficits. Furthermore, we demonstrate that activation of LXA4 signaling could serve as a potential therapeutic target for AD-related inflammation and cognitive dysfunction.
Prostaglandins (PGs) are important lipid mediators involved in physiological processes, such as inflammation and pregnancy. The pleiotropic effects of the PG isomers and their differential expression from cell types impose the necessity for studying individual isomers locally in tissue to understand the molecular mechanisms. Currently, mass spectrometry (MS)-based analytical workflows for determining the PG isomers typically require homogenization of the sample and a separation method, which results in a loss of spatial information. Here, we describe a method exploiting the cationization of PGs with silver ions for enhanced sensitivity and tandem MS to distinguish the biologically relevant PG isomers PGE2, PGD2, and Δ12-PGD2. The developed method utilizes characteristic product ions in MS3 for training prediction models and is compatible with direct infusion approaches. We discuss insights into the fragmentation pathways of Ag+ cationized PGs during collision-induced dissociation and demonstrate the high accuracy and robustness of the model to predict isomeric compositions of PGs. The developed method is applied to mass spectrometry imaging (MSI) of mouse uterus implantation sites using silver-doped pneumatically assisted nanospray desorption electrospray ionization and indicates localization to the antimesometrial pole and the luminal epithelium of all isomers with different abundances. Overall, we demonstrate, for the first time, isomeric imaging of major PG isomers with a simple method that is compatible with liquid-based extraction MSI methods.
Introduction:
In chronic rhinosinusitis (CRS), a complex pathophysiology results from varied pro-inflammatory stimuli but is consistently characterized by classic cellular, molecular, and microbial alterations. Normally, endogenous specialized pro-resolving mediators (SPM) actively promote resolution of inflammation through numerous pathways including those involved in host antimicrobial defense. However, these pathways appear to be disrupted in CRS.
Areas covered:
This paper describes features of CRS in the context of chronic tissue inflammation, and potential mechanisms by which specialized pro-resolving mediators promote active resolution of tissue inflammation.
Expert opinion:
Temporal phases of resolution must be tightly regulated to successfully resolve inflammation in CRS while preserving tissue functions such as barrier maintenance and special sensory function. Dysregulation of SPM enzymatic pathways has been recently shown in CRS and is associated with disease phenotypes and microbial colonization patterns. Current research in animal models and in vitro human cell culture, as well as human dietary studies, demonstrate relevant changes in cell signaling with lipid mediator bioavailability. Further clinical research may provide insight into the therapeutic value of this approach in CRS.
Bioactive lipids are now widely accepted players in the field of cancer
biology. Targeting components like enzymes, bioactive lipids and receptors
are important for maintaining lipid homeostasis, metabolism, and signaling
so that cell proliferation and metastasis can be reduced. This can be achieved
through various means like modifying functions of enzymes involved in
lipid biosynthesis, altering the structure and composition of bioactive lipids,
disruption of lipid mediated tumor microenvironment, and by promoting
apoptosis. These strategies can encourage the treatment and cure of cancer.
This book is divided into three parts: chemistry, formulation, and
mechanism of bioactive lipids in cancer. In the chemistry portion, Mal et
al. stated that ceramides act as second messengers for apoptosis. There
are several pieces of evidence to support the use of exogenous C2 and C6
ceramides and ceramide modulators like FTY720, PDMP, NOE, Tamoxifen,
etc., with different chemotherapeutic agents to fight cancer in a better way.
Another chapter by Rati Kailash Prasad Tripathi states that lipoxins and
their epimers, viz. epi-lipoxins, are involved in the performance of crucial
functions causing attenuation of the cancer-associated inflammation, which
portrays a synergic rationale that integrates the anti-inflammatory hallmarks
and raises anti-tumor immunity. Das et al. states that resolvins have the
potential for the growth of further anticancer agents. Malik et al. states
that Sphingosine-1 phosphate (SIP) functions as both the first and second
messenger and act both extracellularly and intracellularly. Although the cell
proliferating activity of SIP is good in different disease conditions, it does
not affect cancer very well.
Another part of this book is based upon formulation of bioactive lipids
in cancer. Basu et al. states that lipid synthesis and its signaling are the
commonly recognized players in the genetics of cancer. Jain and Pillai state
that exosomes have lipids as one of their contents and serve as their natural
transporters carrying them to distant cells. So, exosomes can be explored
for their utility as prognostic/diagnostic marker and future pharmacological
targets.
The next part is based on the mechanism of bioactive lipids in cancer.
In this category, Garg et al. state that computational techniques are helpful
in the identification of bioactive lipid drugs and their targets. However, it is essential to use these techniques correctly way to get reliable information.
Singh et al. state that hypoxic cancer cells remain in high demand of lipids,
and the increasing demand cannot be accomplished only through glucose
metabolism. Therefore, HIF-1α acts at the genetic level to enhance lipid
synthesis in cancer cells. The utilization of acetate, lactate, glutamate along
with glucose for fatty acid synthesis makes them a crucial metabolite both
in the diagnosis and treatment of solid hypoxic tumors. Alongside, enzymes
involved in these pathways could be fascinating targets for newer drugs. Sahu
et al. state that targeted therapies are used to treat advanced colorectal cancer
(CRC) induced by mutated genes. The various novel drug deliveries have
been developed and demonstrated significant inhibition of cancerous cells in
CRC. Pal and Raj, state that avocado can prevent or diagnose or treat various
kinds of human cancer cells (HCCs). If more research work continues, then
in the near future, it becomes an excellent therapeutic agent in cancer therapy.
Mitra and Banerjee state that lipopolysaccharide (LPS) is a potent inducer of
carcinogenesis upon overexposure. The same LPS can be anti-carcinogenic
at optimum levels or if modified. Future studies can focus on selective
immune activation by targeting specific intermediate adaptor proteins of
LPS/TLR-4 interaction to initiate possible immuno-therapy against different
cancer types. Pal and Saha state that LA is a glycerophospholipid and worked
via G-protein-coupled receptors with six subtypes LA1
–LA6
. Among them,
LA2
directly affects the cell survival rate of GRI-977143 (agonist of LA2
)
against lung cancer cell lines. Banerjee et al. state that several clinical pieces
of evidence confirm the anticancer potential of ω-PUFAs. Experimental data
indicates the beneficial effect of these acids in CRC and advanced metastatic
disease, from the primary to tertiary prevention.
So, this complete book summarizes the benefits of bioactive lipids for the
treatment and prevention of cancer.
Objective:
The objective of this study was to discuss the mechanism of artesunate (ART) in improving cartilage damage in osteoarthritis (OA) by regulating the expression levels of MTA1, LXA4, and the downstream JAK2/STAT3 signaling pathway.
Methods:
The OA model in vitro was constructed by stimulating chondrocytes for 24 h with 10 ng/mL IL-1β, and cell proliferation and apoptosis, expression levels of Aggrecan, MTA1, LXA4, MMP3, MMP13, and Collagen II, and inflammatory cytokines in the culture supernatants were examined. Histopathological changes, inflammatory response, and chondrocyte apoptosis of the cartilage tissues of OA mice were performed.
Results:
In vitro cell experiments, ART enhanced cell proliferation capacity, accompanied by decreased apoptosis rate, decreased expression of MMP-3 and MMP-13, elevated expression of Collagen II and Aggrecan, as well as reduced levels of IL-6 and TNF-α in the cell supernatant. ART also ameliorated IL-1β-induced chondrocyte damage by upregulating MTA1. The LXA4 promoter region had two potential binding sites for MTA1. There was a positive correlation between MTA1 and LXA4. MTA1 enhanced the expression of LXA4 through transcription and blocked the activation of the JAK2/STAT3 signaling pathway. In vivo animal model experiments further showed that ART treatment alleviated cartilage tissue damage in OA model mice by up-regulating MTA1.
Conclusion:
Our study demonstrates that ART improves the cartilage damage of OA by up-regulating MTA1 expression and promoting the transcriptional activation of LXA4, and further blocking the JAK2/STAT3 signaling pathway.
Cardiovascular diseases are one of the most important problems of modern medicine. They are associated with a large number of health care visits, hospitalizations and mortality. Prevention of atherosclerosis is one of the most effective strategies and should start as early as possible. Correction of lipid metabolism disorders is associated with definite clinical successes, both in primary prevention and in the prevention of complications of many cardiovascular diseases. A growing body of evidence suggests a multifaceted role for polyunsaturated fatty acids. They demonstrate a variety of functions in inflammation, both participating directly in a number of cellular processes and acting as a precursor for subsequent biosynthesis of lipid mediators. Extensive clinical data also support the importance of polyunsaturated fatty acids, but all questions have not been answered to date, indicating the need for further research.
Our previous study found that lipoxin A4 (LXA4) exerts therapeutic effects on osteoarthritis (OA). In this study, we evaluated the effects of LXA4 via synovial macrophage M1/M2 subtype polarization on chondrocyte pyroptosis and corresponding mechanisms during mechanical stimulation. Synovial macrophages were subjected to various LXA4 concentrations and cyclic tensile strain (CTS) conditions to determine optimal co-culture conditions. The effects of LXA4 on chondrocyte pyroptosis, as represented by macrophage M1/M2 subtype polarization, were detected by western blot, immunofluorescence, and flow cytometry analyses. Forty male Sprague-Dawley rats were randomly divided into four groups (n = 10): control (CG), OA (OAG), OA with moderate-intensity treadmill exercise (OAE), and OAE + BOC-2 (an LXA4 antagonist). All rats were evaluated using histology, enzyme-linked immunosorbent assay, quantitative real-time polymerase chain reaction, and western blot analyses. We found that with increasing Kellgren-Lawrence grade, LXA4 expression was downregulated in articular fluid and that CD86 and Arg1 expression was upregulated in the synovium of patients. In vitro, CTS and LXA4 both promoted M2 subtype polarization of synovial macrophages, which inhibited the nuclear translocation of NF-κB p65 and formation of NLRP3 in chondrocytes. In vivo, the OAE treatment exerted protective effects on articular cartilage and facilitated M2 polarization of synovial macrophages. These effects were suppressed by BOC-2 treatment. We concluded that moderate CTS enhances therapeutic effects of LXA4 by inhibiting the nuclear translocation of NF-κB p65 and NLRP3. Furthermore, the therapeutic effects of LXA4 during treadmill exercise in monoiodoacetate-induced OA were driven by promotion of synovial macrophage M2 subtype polarization.
Asthma is a chronic respiratory disease, which is characterized by airway inflammation, remodeling and airway hyperresponsiveness. Airway remodeling is caused by long-term inflammation of the airways. Lipoxin A4 (LXA4) is a natural eicosanoid with powerful anti-inflammatory properties, and has been shown to serve a critical role in orchestrating pulmonary inflammation and airway hyper-responsiveness in asthmatic mice. However, its effect on airway remodeling is unknown. Female BALB/c mice were used to establish a mouse model of asthma which were sensitized and challenged by ovalbumin (OVA). LXA4 was intranasally administrated prior to the challenge. The results of our study indicated that LXA4 suppressed the OVA-induced inflammatory cell infiltration and T helper type 2 (Th2) cytokines secretion in the mouse model of asthma. Characteristics of airway remodeling, such as thickening of the bronchial wall and smooth muscle, overdeposition of collagen, and overexpression of α-smooth muscle actin (α-SMA) and collagen-I were reversed by LXA4. Furthermore, LXA4 suppressed the aberrant activation of the signal transducer and activator of transcription 3 (STAT3) pathway in the lung tissues of asthmatic mice. In conclusion, these findings demonstrated that LXA4 alleviated allergic airway inflammation and remodeling in asthmatic mice, which may be related to the inhibition of STAT3 pathway.
Inflammation is a protective response of the macroorganism to injury caused by trauma, noxious chemicals or microbiological toxins. This response is intended to inactivate or destroy invading organisms, remove irritants and set the stage for tissue repair. The inflammatory response consists of immunological and non-immunological reactions. The latter are triggered by the release from the injured tissues and migrating cells of lipid-derived autacoids, such as eicosanoids or “platelet-activating factor” (PAF); large peptides, such as interleukin-1; small peptides, such as bradykinin; and amines, such as histamine or 5-hydroxytryptamine. These constitute the chemical network of the inflammatory response and result in clinical and pathological manifestations of inflammation (Table 9.1). The concept of the inflammatory response was introduced over 2000 years ago with its description by Cornelius Celsus as “rubor et tumor cum calore et dolore” (redness and swelling with heat and pain). Centuries later, in the nineteenth century, this definition was extended by Rudolph Virchow to include loss of function (“functio laesa”). It was Virchow and his pupils, including J. Cohnheim, who explained the scientific basis for Celsus’ description of inflammation. They found that the redness and heat reflected increased blood flow and that the swelling was related to the exudation of fluid and to the accumulation of cells, while pain follows [1]. The first understanding of the mechanism of inflammation was introduced by Elie Metchnikoff, who concluded in his book Lectures on the Comparative Pathology of Inflammation published in 1893 that “…inflammation is a local reaction, often beneficial, of living tissue against an irritant substance” [2]. This definition still stands today. For the first time, he observed that this reaction is mainly produced by phagocytic activity of the mesodermic cells and that it includes “the chemical action of the blood plasma and tissue fluids …”, thus introducing the concept of mediators of inflammation [2]. Numerous further studies since then have identified the roles of individual mediators in inflammation, and we are beginning to understand the genetic and molecular aspects of the genesis of the inflammatory process. Inflammatory mediators include a plethora of cell-derived molecules (e.g. chemokines, cytokines, antimicrobial peptides and reactive oxygen and nitrogen species) and of activated biochemical cascades originating in the vascular compartment (e.g. reactive oxygen species, nitric oxide, complement, coagulation and fibrinolytic systems).
Transient receptor potential (TRP) cation channels are a functionally diverse family of proteins. While thorough elucidation of the seemingly endless biological functions that can potentially be performed by, or at least effected by, TRP channels is far from a reality, accumulating experimental evidence for some TRP channels demonstrates vital contributions of select TRP channels to a number of critical physiological functions in select organ systems and cell types. In the respiratory tract, TRP channel expression is highly variable, depending upon anatomical location (i.e., nasal, tracheal, bronchiole/bronchiolar, terminal/alveolar) and cell type (i.e., neuronal, epithelial, endothelial, resident immune, etc.), with high abundance of TRP channels in sensory neurons and some epithelial and endothelial cell types. The focus of this article is on TRP channels in the lung and mechanisms by which select TRP channels contribute to reflex responses, pulmonary inflammation, and injury commonly associated with exposure to a variety of exogenous and endogenous pneumotoxic agents. Both neurogenic (classical) and nonneurogenic (novel) mechanisms by which TRP channels influence respiratory physiology and pulmonary homeostasis will be covered since recent evidence strongly suggests that TRP channels expressed by nonneuronal cells may play equally vital roles in mounting and controlling various phases of inflammatory responses and injury associated with certain stimuli. The article reviews basic immunology and how select components of the immune response act in concert in the respiratory tract, the expression and basic pharmacology of TRP channels, mechanisms by which different TRP channels regulate select components of innate immunity, and specific examples of TRP channel-mediated pneumotoxicity elicited by xenobiotics and a variety of endogenous proinflammatory agents.
The type-1 cannabinoid receptor (CB1) is the main effector of the endocannabinoid system (ECS), which is involved in most brain and body functions. In this Perspective, we provide evidence indicating that CB1 receptor functions are key determinants of bodily coordinated exostatic processes. First, we will introduce the concepts of endostasis and exostasis as compensation or accumulation for immediate or future energy needs and discuss how exostasis has been necessary for the survival of species during evolution. Then, we will argue how different specific biological functions of the CB1 receptor in the body converge to provide physiological exostatic processes. Finally, we will introduce the concept of proactive evolution-induced diseases (PEIDs), which helps explain the seeming paradox that an evolutionary-selected physiological function can become the cause of epidemic pathological conditions, such as obesity. We propose here a possible unifying theory of CB1 receptor functions that can be tested by future experimental studies.
Lipid mediators such as leukotrienes and lipoxines broadly regulate innate and acquired immunity, and their dysfunction causes various immune-mediated disorders. We previously reported a salient feature of arachidonate 5-lipoxyganase (Alox5), which is responsible for the production of such lipid mediators, in the regulation of high affinity antibodies in vivo. The aim of this study was to determine the functional significance of Alox5-related lipid mediators during the processes of acquired humoral responses. The results of in vitro experiments using lymphocytes in tonsils and blood specimens showed that lipoxin A4 (LXA4) and leukotriene B4 (LTB4) have the capacity to differentiate naïve CD4⁺ T cells into T follicular helper (Tfh) cells, which activate naïve B cells to form germinal centers. Such a function of LXA4 was further supported by results of in vitro studies using BML-111 and BOC-2, which are an agonist and an antagonist, respectively, of FPR2 of an LXA4-specific cell-surface receptor. The results suggest that such lipid mediators have a potential role in the development of lymphoid follicles through the regulation of Tfh cell differentiation.
Numerous physiological functions of the body are controlled by endogenous (e.g. steroids, retinoids, lipid mediators) or exogenous molecules (e.g. drugs, xenobiotics) that bind to transcription factors (TF). The biosynthesis and catabolism of these signaling molecules depend, apart from CYPs, on enzymes belonging to the short-chain dehydrogenase/reductase (SDR) superfamily. Moreover, the contribution of SDRs to the metabolism of therapeutic drugs and xenobiotics is increasingly recognized. However, only scarce information exists regarding the transcriptional regulation of most SDR proteins. This work aims to illustrate the role of nuclear receptors (NR) and TF related to oxidative stress, inflammation, hypoxia, and xenobiotics in the regulation of selected human and murine SDRs that play crucial roles in steroid, retinoid, eicosanoid, fatty acid, and xenobiotic metabolism. These include, for example, 17β-hydroxysteroid dehydrogenases, retinol dehydrogenases, and carbonyl reductases. Because existing experimental data are limited, an in silico analysis (TRANSFAC® Professional database) of the 5′-upstream sequences for putative response elements was performed. Experimental and in silico data suggest that pharmaceutical, environmental, or dietary NR ligands may alter SDR-mediated retinoid, steroid, and xenobiotic metabolism, likely affecting basic cellular events like energy expenditure, cell proliferation/differentiation, or aging processes. Also, some SDRs are possibly induced by their own substrates. Further experimental work is urgently needed to fully understand the NR-mediated transcriptional regulation of SDRs. This is essential for deducing their possible involvement in drug side effects and will help to identify new substrates and further physiological functions of these SDRs.
Background Lipoxins (LXs), enclogenous anti-inflammatory and pro-resolving eicosanoids generated during various inflammatory conditions, have novel immunomodulatory properties. Because dendritic cells (DCs) play crucial roles in the initiation and maintenance of immune response, we determined whether LXs could modulate the maturation process of DCs and investigated the effects of lipoxin A(4) (LXA(4)) on lipopolysaccharide (LPS)-induced differentiation of RAW264.7 cells into dendritic-like cells. Methods RAW264.7 cells were cultured in vitro with 1 mu g/ml LIPS in the absence or presence of LXA4 for 24 hours, and cellular surface markers (MHC-II, CD80 (B7-1), CD86(B7-2)) were measured by flow cytometry (FCM). Mixed lymphocyte reaction was performed to evaluate the allostimulatory activity. Cytoplastic I kappa B degradation and nuclear factor kappa B (NF-KB) translocation were detected by Western blotting. Luciferase reporter plasmid was transiently transfected into RAW264.7 cells, and luciferase activity was determined to measure the transcriptional activity of NF-kappa B. Results LXA4 reduced the ratio of LPS-treated RAW264.7 cells to DCs with morphological characteristics and inhibited the expression of MHC II. LPS-induced up-regulation of CD86 was moderately suppressed by LXA4 but no obvious change of CD80 was observed. Moreover, LXA4 weakened the allostimulatory activity of LPS-treated RAW264.7 cells. These alterations of LPS+LXA(4)-treated cells were associated with a marked inhibition of I kappa B degradation, NF-kappa B translocation and then the transcriptional activity of NF-kappa B. Conclusions LXA4 negatively regulates LPS-induced differentiation of RAW264.7 cells into dendritic-like cells. This activity reveals an undescribed mechanism of LXA4 to prevent excessive and sustained immune reaction by regulating maturation of DCs.
Poverty, low birth weight, low life expectation at birth, widespread malnutrition, numerous endemic infections, little or no access to safe water, poor oral hygiene, deplorable environmental sanitation and political instability among other problems, characterise the lives of many Africans, particularly in sub-Saharan Africa. In African countries undergoing rapid urbanisation, health problems associated with undernutrition and overnutrition coexist, and these result from lifestyle changes which promote physical inactivity, increased consumption of fats and refined carbohydrates, as well as abuse of tobacco and alcohol. Thus, in several African countries, inflammatory oral diseases (e.g. periodontal diseases, acute necrotising gingivitis, noma) resulting from inappropriate interactions between microorganisms and the malnourished, immunocompromised host, have continued to pose serious health problems. There are suggestions of increasing incidence of squamous cell carcinoma, probably related to increased use of alcohol and tobacco, which elicit nutrient deficiencies and oxidative stress. Additionally, there is an increase in caries prevalence particularly in the poor urban areas. The latter is related not only to increased availability of refined sugars, but also to limited access to the caries preventive effects of fluorides. Good dietary practices through judicious combination of available foods should therefore feature prominently in the promotion of optimal oral health in Africa.
Transient receptor potential (TRP) cation channels are a functionally diverse family of proteins. While thorough elucidation of the seemingly endless biological functions that can potentially be performed by, or at least effected by, TRP channels is far from a reality, accumulating experimental evidence for some TRP channels demonstrates vital contributions of select TRP channels to a number of critical physiological functions in select organ systems and cell types. In the respiratory tract, TRP channel expression is highly variable, depending upon anatomical location (i.e., nasal, tracheal, bronchiole/bronchiolar, terminal/alveolar) and cell type (i.e., neuronal, epithelial, endothelial, resident immune, etc.), with high abundance of TRP channels in sensory neurons and some epithelial and endothelial cell types. The focus of this chapter is on TRP channels in the lung and mechanisms by which select TRP channels contribute to reflex responses, pulmonary inflammation, and injury commonly associated with exposure to a variety of exogenous and endogenous pneumotoxic agents. Both neurogenic (classical) and nonneurogenic (novel) mechanisms by which TRP channels influence respiratory physiology and pulmonary homeostasis will be covered since recent evidence strongly suggests that TRP channels expressed by nonneuronal cells may play equally vital roles in mounting and controlling various phases of inflammatory responses and injury associated with certain stimuli. The chapter reviews basic immunology and how select components of the immune response act in concert in the respiratory tract, the expression and basic pharmacology of TRP channels, mechanisms by which different TRP channels regulate select components of innate immunity, and specific examples of TRP channel-mediated pneumotoxicity elicited by xenobiotics and a variety of endogenous proinflammatory agents.
Lipoxins (LX), a series of anti-inflammatory mediators, are short lived endogenously produced nonclassic eicosanoids, whose appearance in inflammation signals the resolution of inflammation. Cell-cell interactions and transcellular biosynthesis of mediators are well recognized as important means of generating new signals during multicellular processes in vivo. Lipoxins are generated by two main routes. The first described involves initial lipoxygenation by 15-LO that inserts molecular oxygen in predominantly the S configuration at carbon 15, followed by 5-LO based transformation. A second route, which occurs predominantly as a major intravascular origin within blood vessels when, for example, platelet intracellular glutathione is depleted, involves the conversion of 5-LO-derived LTA4 that is released from leukocytes and subsequently converted to lipoxins. Human platelets do not generate LXs, but become a major intravascular source of LXs when they interact with leukocytes. They are potent signals that counteract the pro-inflammatory mediators which evoke the cardinal signs of inflammation, and as specialized signals generated in the resolution phase they are dual acting signals promoting the important non-phlogistic steps in resolution. Inappropriate control of inflammation and its resolution is now recognized to contribute to many chronic inflammatory diseases as well as those not previously recognized to have inflammation as a basis of their pathophysiology.
The tight regulation of cell growth and division within an organ is essential for the development and maintenance of correct structure and function. Perturbations of renal growth occurring either developmentally or following injury to mature renal cells contribute to the abnormalities observed in a wide range of diseases. The changes in growth are increasingly recognized as an influence on the progression of the initial disease process, and the ultimate clinical outcome. Abnormal cell growth is classified according to the presence of an increase in cell number or cell size. Hyperplasia refers to abnormal growth resulting in an increased absolute number of cells, whereas hypertrophy refers to an increase in individual cell size. Both processes may be present in a given cell population and contribute to the increase in overall kidney size.
The cure of a cow suffering from a bacterial mastitis relies on the balance between the eradication of the pathogen and the resolution of the inflammatory response, two processes that are essential to come back to a normal milk composition with low somatic cell count. The persistence of the inflammatory response, which main consequence is a reduction in milk yield, is a feature of chronic mastitis. This frequent disease depends on inappropriate host-pathogen interactions and is not yet well understood. This review resumes the main defence mechanisms of the bovine mammary gland, emphasizing the predominant roles played by the neutrophil, and brings some precisions on lipoxin implications in the resolution of inflammation. Reasons that may explain the persistence of the inflammatory reaction, a phenomenon found in the Staphylococcus aureus chronic mastitis, are also discussed.
Bioactive derivatives of polyunsaturated fatty acids (most importantly, arachidonic acid, EPA, and DHA) regulate essential aspects of lung function. These mediators include prostaglandins, isoprostanes, leukotrienes, lipoxins, and resolvins. They exert synergistic and opposing effects on bronchial constriction and relaxation, pulmonary vascular tone, and/or the initiation and cessation of immune and inflammatory responses in the lung. The identification in lung tissues of specific receptors for these mediators, as well as the lipid-responsive PPAR-α and PPAR-γ transcription factors, suggests that they are important in maintaining lung homeostasis. Several fatty acid-derived mediators (or their synthetic agonists or antagonists) have demonstrated therapeutic value in correcting derangements of lung function in asthma, pulmonary hypertension, inflammatory lung disease, fibrosis, or acute lung injury.
Cytochrome P450-dependent ω-hydroxylation is a prototypic metabolic reaction of CYP4 family members that is important for the elimination and bioactivation of not only therapeutic drugs, but also endogenous compounds, principally fatty acids. Eicosanoids, derived from arachidonic acid, are key substrates in the latter category. Human CYP4 enzymes, mainly CYP4A11, CYP4F2, and CYP4F3B, hydroxylate arachidonic acid at the omega position to form 20-HETE, which has important effects in tumor progression and on angiogenesis and blood pressure regulation in the vasculature and kidney. CYP4F3A in myeloid tissue catalyzes the ω-hydroxylation of leukotriene B4 to 20-hydroxy leukotriene B4, an inactivation process that is critical for the regulation of the inflammatory response. Here, we review the enzymology, tissue distribution, and substrate selectivity of human CYP4 ω-hydroxylases and their roles as catalysts for the formation and termination of the biological effects of key eicosanoid metabolites in inflammation and cancer progression.
Platelets have an emerging and incompletely understood role in a myriad of host immune responses, extending their role well beyond regulating thrombosis. Acute respiratory distress syndrome is a complex disease process characterized by a range of pathophysiologic processes including oxidative stress, lung deformation, inflammation, and intravascular coagulation. The objective of this review is to summarize existing knowledge on platelets and their putative role in the development and resolution of lung injury.
Copyright © 2015, American Journal of Physiology - Lung Cellular and Molecular Physiology.
N-3 fatty acids, especially docosahexaenoic acid (DHA), play an important role in the prevention of cardiovascular diseases. One metabolite of DHA, protectin DX (PDX), an isomer of protectin D1 (PD1) (Chen P et al., 2009),possesses inhibits blood platelet aggregation. Similar compounds called "poxytrins", which have a conjugated triene with a E,Z,E geometry have also been synthesized from other polyunsaturated fatty acids (PUFA) by soybean lipoxygenase. They have anti-aggregating properties by inhibiting platelet cyclooxygenase and thromboxane A2 receptor (Chen P et al., 2011). In this thesis, we describe new dihydroxy compounds synthesized by the soybean 15-lipoxygenase from alpha-linolenic acid (18:3n-3), an essential PUFA that is consumed in the gram range in human adults . It is converted into monohydroxylated and dihydroxylated derivatives. These compounds were separated by reverse phase high performance liquid chromatography (HPLC) and characterized by gas chromatography-mass spectrometry (GC-MS) after appropriate derivatization. A main monohydroxylated fatty acid, 13(S)-octadecatrienoic acid (13(S)-OH-18:3) and four dihydroxylated fatty acids were detected. The last ones have all a characteristic UV spectrum with a maximum absorbance at 270 nm with two shoulder peaks at 260 and 280 nm. The UV spectra from two of them are superimposable to that of PDX, suggesting a E,Z,E geometry for their conjugated triene. The complete characterization of these compounds was performed by high field nuclear magnetic resonance (NMR) and by GC-MS. These are the 9(R),16(S)-dihydroxy-octadeca-10E,12E,14E-trienoic, 9(S),16(S)-dihydroxy-octadeca-10E,12E,14E-trienoic, 9(S),16(S)-dihydroxy-octadeca-10E,12Z,14E-trienoic and 9(R),16(S)-dihydroxy-octadeca-10E,12Z,14E-trienoic acids. They can also be synthesized by the (type 2) 15 human recombinant lipoxygenase. These dihydroxylated compounds (9,16-diHOTEs)were tested on isolated human blood platelets. We observed that only molecules containing a conjugated triene with a E,Z,E geometry are able to inhibit platelet aggregation induced by collagen, and inhibit sheep cyclooxygenase-1 (COX-1). The anti-inflammatory properties of these products were also studied. All 9,16-diHOTEs isomers having a conjugated triene with a E,Z,E geometry, inhibit human recombinant cyclooxygenase-2 (COX-2) and only 9(R),16(S)-dihydroxy-octadeca-10E,12Z,14E-trienoic acid inhibits polymorphonuclear leukocytes (PMN) 5-lipoxygenase which is involved in the leukotriene synthesis from arachidonic acid. In conclusion, the E,Z,E dihydroxlated compounds from 18:3n-3, as well as PDX, inhibiting the COX-1 and 2 activities appear to be anti-aggregatory and anti-inflammatory agents. These results provide pharmacological perspectives to nutritional recommendations promoting the intake of alpha-linolenic acid.
Lipoxins (LX) are eicosanoids with antiinflammatory activity in glomerulonephritis (GN) and inflammatory diseases, hypersensitivity, and ischemia reperfusion injury. It has been demonstrated that LXA4 stimulates non-phlogistic phagocytosis of apoptotic polymorphonuclear neutrophils (PMN) by monocyte-derived macrophages (Mφ) in vitro, suggesting a role for LX as endogenous pro-resolution lipid mediators. It is here reported that LXA4, LXB4, the aspirin-triggered LX (ATL) epimer, 15-epi-LXB4, and a stable synthetic analogue 15(R/S)-methyl-LXA4 stimulate phagocytosis of exogenously administered excess apoptotic PMN by macrophages (Mφ) in vivo in a classic model of acute inflammation, namely thioglycollate-induced peritonitis. Significant enhancement of phagocytosis in vivo was observed with 15-min exposure to LX and with intraperitoneal doses of LXA4, LXB4, 15(R/S)-methyl-LXA4, and 15-epi-LXB4 of 2.5 to 10 μg/kg. Non-phlogistic LX-stimulated phagocytosis by Mφ was sensitive to inhibition of PKC and PI 3-kinase and associated with increased production of transforming growth factor–β1 (TGF-β1). LX-stimulated phagocytosis was not inhibited by phosphatidylserine receptor (PSR) antisera and was abolished by prior exposure of Mφ to β1,3-glucan, suggesting a novel Mφ-PMN recognition mechanism. Interestingly, the recently described peptide agonists of the LXA4 receptor (MYFINITL and LESIFRSLLFRVM) stimulated phagocytosis through a process associated with increased TGF-β1 release. These data provide the first demonstration that LXA4, LXB4, ATL, and LX stable analogues rapidly promote Mφ phagocytosis of PMN in vivo and support a role for LX as rapidly acting, pro-resolution signals in inflammation. Engagement of the LXR by LX generated during cell-cell interactions in inflammation and by endogenous LXR peptide agonists released from distressed cells may be an important stimulus for clearance of apoptotic cells and may be amenable to pharmacologic mimicry for therapeutic gain.E-mail: cgodson@mater.ie
The aim of this study was to evaluate the plasma levels of lipoxin A4 (LXA4), a mediator involved in the resolution of inflammation in Chinese children with autism spectrum disorders (ASD). From January 2013 to June 2014, a total of 150 children (75 confirmed ASD cases and 75 their age-matched and sex-matched control cases) participated in this study after consent was obtained from their parents. Clinical information was collected. Plasma levels of LXA4 were measured at baseline. The severity of ASD was assessed at admission using the Childhood Autism Rating Scale total score. The results indicated that the mean plasma levels of LXA4 were significantly lower in autistic children compared with the normal children (P<0.0001). There was a significant negative relationship between circulating LXA4 levels and severity of autism evaluated by Childhood Autism Rating Scale scores (P=0.006) after adjustment for the possible covariates. On the basis of the receiver operating characteristic curve, the optimal cutoff value of plasma LXA4 levels as an indicator for an auxiliary diagnosis of ASD was projected to be 81.5 pg/ml, which yielded a sensitivity of 90.7% and a specificity of 76.0%, with the area under the curve at 0.911 (95% confidence interval, 0.867-0.955). These results suggested that autistic children had lower plasma LXA4 levels, suggesting an increased susceptibility to recurring inflammation in these samples.
Background and purpose:
Spinal voltage-gated calcium channels (VGCCs) are pivotal regulators of painful and inflammatory alterations, representing attractive therapeutic targets. We examined the effects of epidural administration of the P/Q- and N-type VGCC blockers Tx3-3 and Phα1β, respectively, isolated from the spider Phoneutria nigriventer, on symptomatic, inflammatory and functional changes allied to mouse cyclophosphamide (CPA)-induced haemorrhagic cystitis (HC). The effects of P. nigriventer-derived toxins were compared with those displayed by MVIIC and MVIIA, extracted from the cone snail Conus magus.
Experimental approach:
HC was induced by a single i.p. injection of CPA (300 mg·kg(-1) ). Dose- and time-related effects of spinally administered P/Q and N-type VGCC blockers were assessed on nociceptive behaviour and macroscopic inflammation elicited by CPA. The effects of toxins were also evaluated on cell migration, cytokine production, oxidative stress, functional cystometry alterations and TRPV1, TRPA1 and NK1 receptor mRNA expression.
Key results:
The spinal blockage of P/Q-type VGCC by Tx3-3 and MVIIC or N-type VGCC by Phα1β attenuated nociceptive and inflammatory events associated with HC, including bladder oxidative stress and cytokine production. CPA produced a slight increase in bladder TRPV1 and TRPA1 mRNA expression, which was reversed by all the toxins tested. Noteworthy, Phα1β strongly prevented bladder neutrophil migration, besides HC-related functional alterations, and its effects were potentiated by co-injecting the selective NK1 receptor antagonist CP-96345.
Conclusions and implications:
Our results shed new light on the role of spinal P/Q and N-type VGCC in bladder dysfunctions, pointing out Phα1β as a promising alternative for treating complications associated with CPA-induced HC.
Lipoxins (LXs) are lipoxygenase-derived eicosanoids and putative endogenous braking signals for inflammation in the gastrointestinal tract and other organs. Aspirin triggers the production of 15-epimers during cell-cell interaction in a cytokine-primed milieu, and aspirin-triggered 15-epi-5(S),6(R),15(S)-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid (15-epi-LXA4) may contribute to the bioactivity profile of this prototype nonsteroidal anti-inflammatory drug in vivo. We determined the effect of LXA4, 15-(R/S)-methyl-11,12-dehydro-LXA4 methyl ester (15-(R/S)-methyl-LXA4), and stable analogs of LXA4 on TNF-α-stimulated neutrophil-enterocyte interaction in vitro and TNF-α-stimulated chemokine release, changes in mucosal architecture, and enterocyte apoptosis in cytokine-activated intact human colonic mucosa ex vivo. LXA4, 15-(R/S)-epi-LXA4, and 16-phenoxy-11,12-dehydro-17,18,19,20-tetranor-LXA4 methyl ester (16-phenoxy-LXA4) inhibited TNF-α-stimulated neutrophil adherence to epithelial monolayers at nanomolar concentrations. In parallel experiments involving human colonic mucosa ex vivo, LXA4potently attenuated TNF-α-stimulated release of the C-X-C chemokine IL-8, and the C-C chemokines monocyte-chemoattractant protein-1 (MCP-1) and RANTES. Exposure of strips of normal human colonic mucosa to TNF-α induced disruption of mucosa architecture and enhanced colonocyte apoptosis via a caspase-3-independent mechanism. Prior exposure of the mucosa strips to 15-(R/S)-methyl-LXA4 attenuated TNF-α-stimulated colonocyte apoptosis and protected the mucosa against TNF-α-induced mucosal damage. In aggregate, our data demonstrate that lipoxins and aspirin-triggered 15-epi-LXA4 are potent antagonists of TNF-α-mediated neutrophil-enterocyte interactions in vitro, attenuate TNF-α-triggered chemokine release and colonocyte apoptosis, and are protective against TNF-α-induced morphological disruption in human colonic strips ex vivo. Our observations further expand the anti-inflammatory profile of these lipoxygenase-derived eicosanoids and suggest new therapeutic approaches for the treatment of inflammatory bowel disease.
The lipoxygenase-derived eicosanoids leukotrienes and lipoxins are well defined regulators of hemeodynamics and leukocyte
recruitment in inflammatory conditions. Here, we describe a novel bioaction of lipoxin A4(LXA4), namely inhibition of leukotriene D4 (LTD4)-induced human renal mesangial cell proliferation, and investigate the signal transduction mechanisms involved. LXA4 blocked LTD4-stimulated phosphatidylinositol 3-kinase (PI 3-kinase) activity in parallel to inhibition of LTD4-induced mesangial cell proliferation. Screening of a human mesangial cell cDNA library revealed expression of the recently
described cys-leukotriene1/LTD4 receptor. LTD4-induced mesangial cell proliferation required both extracellular-related signal regulated kinase (erk) and PI 3-kinase activation
and may involve platelet-derived growth factor receptor transactivation. LTD4-stimulated the MAP kinases erk and p38 via a pertussis toxin (PTX)-sensitive pathway dependent on PI 3-kinase and protein
kinase C activation. On screening a cDNA library, mesangial cells were found to express the previously described LXA4 receptor. In contrast to LTD4, LXA4 showed differential activation of erk and p38. LXA4 activation of erk was insensitive to PTX and PI 3-kinase inhibition, whereas LXA4 activation of p38 was sensitive to PTX and could be blocked by the LTD4 receptor antagonist SKF 104353. These data suggest that LXA4stimulation of the MAP kinase superfamily involves two distinct receptors: one shared with LTD4 and coupled to a PTX-sensitive G protein (Gi) and a second coupled via an alternative G protein, such as Gq or G12, to erk activation. These data expand on the spectrum of LXA4bioactions within an inflammatory milieu.
Lipoxins are bioactive eicosanoids that are immunomodulators. In human myeloid cells, lipoxin (LX) A4 actions are mediated by interaction with a G protein-coupled receptor. To explore functions of LXA4 and aspirin-triggered 5(S),6(R),15(R)-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid (15-epi-LXA4) in vivo, we cloned and characterized a mouse LXA4 receptor (LXA4R). When expressed in Chinese hamster ovary cells, the mouse LXA4R showed specific binding to [3H]LXA4 (K(d) approximately 1.5 nM), and with LXA4 activated GTP hydrolysis. Mouse LXA4R mRNA was most abundant in neutrophils. In addition to LXA4 and 15-epi-LXA4, bioactive LX stable analogues competed with both [3H]LXA4 and [3H]leukotriene D4 (LTD4)-specific binding in vitro to neutrophils and endothelial cells, respectively. Topical application of LXA4 analogues and novel aspirin-triggered 15-epi-LXA4 stable analogues to mouse ears markedly inhibited neutrophil infiltration in vivo as assessed by both light microscopy and reduced myeloperoxidase activity in skin biopsies. The 15(R)-16-phenoxy-17,18, 19,20-tetranor-LXA4 methyl ester (15-epi-16-phenoxy-LXA4), an analogue of aspirin triggered 15-epi-LXA4, and 15(S)-16-phenoxy-17,18,19,20-tetranor-LXA4 methyl ester (16-phenoxy-LXA4) were each as potent as equimolar applications of the anti-inflammatory, dexamethasone. Thus, we identified murine LXA4R, which is highly expressed on murine neutrophils, and showed that both LXA4 and 15-epi-LXA4 stable analogues inhibit neutrophil infiltration in the mouse ear model of inflammation. These findings provide direct in vivo evidence for an anti-inflammatory action for both aspirin-triggered LXA4 and LXA4 stable analogues and their site of action in vivo.
Epithelial cells of the alimentary tract play a central role in mucosal immunophysiology. Pathogens and/or agonists that interact with mucosal surfaces often elicit epithelial responses that upregulate inflammation. Therefore, it was of interest to explore potential epithelial targeted antiinflammatory signals. Here we identified and sequenced a human enterocyte lipoxin (LX) A4 [5(S), 6(R),15(S)-trihydroxy-7,9,13-trans-11-cis eicosatetraenoic acid] receptor, and demonstrate that transcription of this receptor was controlled by cytokines, of which lymphocyte-derived interleukin (IL)-13 and interferon gamma were the most potent. When lipoxins and LXA4 stable analogs were evaluated for enterocyte functional as well as immune responses, lipoxins sharply inhibited TNF-alpha-induced IL-8 release but did not alter either barrier function or agonist-stimulated chloride secretion. 15R/S-methyl-LXA4 and 16-phenoxy-LXA4 each attenuated (IC50 approximately 10 nM) IL-8 release. Cyclooxygenase (COX) II is emerging as an important component in wound healing and proliferation in intestinal epithelia and when acetylated by acetylsalicylic acid (aspirin) initiates the biosynthesis of a LXA4 receptor ligand. We therefore determined whether colonic cell lines (HT-29 Cl.19A, Caco-2, or T84) express the COX II isozyme. Results for RT-PCR and Western blot analysis showed that COX I as well as an IL-1beta- and TNF-alpha-inducible COX II are expressed in HT-29 Cl.19A. In addition, aspirin-treated enterocytes generated 15R-HETE, a precursor of 15-epi-LXA4 biosynthesis, whose potent bioactions were mimicked by the stable analog 15R/S-methyl-LXA4. Taken together, these results identify an endogenous pathway for downregulating mucosal inflammatory events and suggest a potential therapeutic benefit for LXA4 stable analogs.
Enteric pathogens induce intestinal epithelium to secrete chemokines that direct movement of polymorphonuclear leukocytes. Mechanisms that might downregulate secretion of these proinflammatory chemokines and thus contain intestinal inflammation have not yet been elucidated. The antiinflammatory activities exhibited by the arachidonate metabolite lipoxin A4 (LXA4) suggests that this eicosanoid, which is biosynthesized in vivo at sites of inflammation, might play such a role. We investigated whether chemokine secretion could be regulated by stable analogs of LXA4. Monolayers of T84 intestinal epithelial cells were infected with Salmonella typhimurium, which elicits secretion of distinct apical (pathogen-elicited epithelial chemoattractant) and basolateral (IL-8) chemokines. Stable analogs of LXA4 inhibited S. typhimurium-induced (but not phorbol ester-induced) secretion of both IL-8 and pathogen-elicited epithelial chemoattractant. LXA4 stable analogs did not alter bacterial adherence to nor internalization by epithelia, indicating that LXA4 stable analogs did not block all signals that Salmonella typhimurium activates in intestinal epithelia, but likely led to attenuation of signals that mediate chemokine secretion. Inhibition of S. typhimurium-induced IL-8 secretion by LXA4 analogs was concentration- (IC50 approximately 1 nM) and time-dependent (maximal inhibition approximately 1 h). As a result of these effects, LXA4 stable analogs inhibited the ability of bacteria-infected epithelia to direct polymorphonuclear leukocyte movement. These data suggest that LXA4 and its stable analogs may be useful in downregulating active inflammation at mucosal surfaces.
We have previously reported (Badolato, R., J.M. Wang, W.J. Murphy, A. R. Lloyd, D.F. Michiel, L.L. Bausserman, D.J. Kelvin, and J.J. Oppenheim. 1994. J. Exp. Med. 180:203; Xu, L., R. Badolato, W.J. Murphy, D.L. Longo, M. Anver, S. Hale, J.J. Oppenheim, and J.M. Wang. 1995. J. Immunol. 155:1184.) that the acute phase protein serum amyloid A (SAA) is a potent chemoattractant for human leukocytes in vitro and mouse phagocytes in vivo. To identify the signaling mechanisms, we evaluated patterns of cross-desensitization between SAA and other leukocyte chemoattractants. We found that the chemotactic bacterial peptide, N-formyl- methionyl-leucyl-phenylalanine (fMLP), was able to specifically attenuate Ca2+ mobilization in human phagocytes induced by SAA, but only at very high concentrations, suggesting that SAA uses a low affinity fMLP receptor. Here we demonstrate that SAA selectively induced Ca2+ mobilization and migration of HEK cells expressing FPRL1, a human seven-transmembrane domain phagocyte receptor with low affinity for fMLP, and high affinity for lipoxin A4. Furthermore, radiolabeled SAA specifically bound to human phagocytes and FPRL1-transfected 293 cells. In contrast, SAA was not a ligand or agonist for FPR, the high affinity fMLP receptor. Thus, SAA is the first chemotactic ligand identified for FPRL1. Our results suggest that FPRL1 mediates phagocyte migration in response to SAA.
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.
Aspirin (ASA) triggers a switch in the biosynthesis of lipid mediators, inhibiting prostanoid production and initiating 15-epi-lipoxin generation through the acetylation of cyclooxygenase II. These aspirin-triggered lipoxins (ATL) may mediate some of ASA's beneficial actions and therefore are of interest in the search for novel antiinflammatories that could manifest fewer unwanted side effects. Here, we report that design modifications to native ATL structure prolong its biostability in vivo. In mouse whole blood, ATL analogs protected at carbon 15 [15(R/S)-methyl-lipoxin A4 (ATLa1)] and the omega end [15-epi-16-(para-fluoro)-phenoxy-LXA4 (ATLa2)] were recoverable to approximately 90 and 100% at 3 hr, respectively, compared with a approximately 40% loss of native lipoxin A4. ATLa2 retains bioactivity and, at levels as low as approximately 24 nmol/mouse, potently inhibited tumor necrosis factor-alpha-induced leukocyte recruitment into the dorsal air pouch. Inhibition was evident by either local intra-air pouch delivery (approximately 77% inhibition) or systemic delivery by intravenous injection (approximately 85% inhibition) and proved more potent than local delivery of ASA. Rank order for inhibiting polymorphonuclear leukocyte infiltration was: ATLa2 (10 micrograms, i.v.) approximately ATLa2 (10 micrograms, local) approximately dexamethasone (10 micrograms, local) >ASA (1.0 mg, local). Applied topically to mouse ear skin, ATLa2 also inhibited polymorphonuclear leukocyte infiltration induced by leukotriene B4 (approximately 78% inhibition) or phorbol ester (approximately 49% inhibition), which initiates endogenous chemokine production. These results indicate that this fluorinated analog of natural aspirin-triggered lipoxin A4 is bioavailable by either local or systemic delivery routes and is a more potent and precise inhibitor of neutrophil accumulation than is ASA.
Polymorphonuclear neutrophil (PMN) activation is pivotal in acute inflammation and injury from reperfusion. To elucidate components controlling PMNs in vivo, we prepared novel transgenic mice with the human leukotriene (LT) B4 receptor (BLTR) for functional characterization. Overexpression of BLTR in leukocytes dramatically increased PMN trafficking to skin microabscesses and lungs after ischemia-reperfusion, whereas mice deficient in 5-lipoxygenase (5-LO) showed diminished PMN accumulation in reperfused lungs. Hence, both BLTR expression and LT biosynthesis are critical for PMN infiltration in reperfusion-initiated second-organ injury. Also, in BLTR transgenic mice, 5-LO expression and product formation were selectively increased in exudates, demonstrating that receptor overexpression amplifies proinflammatory circuits. Endogenous lipoxin (LX) A4 was produced in ischemic lungs and elevated by reperfusion. Because LXA4 and aspirin-triggered 15-epimeric LXA4 (ATL) selectively regulate leukocyte responses, they were tested in BLTR transgenic mice. Despite excessive PMN recruitment in BLTR transgenic mice, intravenous injection of ATL sharply diminished reperfusion-initiated PMN trafficking to remote organs, and topical application of LX was protective in acute dermal inflammation. These results demonstrate a direct role for BLTR with positive feedback, involving BLTR and 5-LO signaling in controlling PMNs. Moreover, LXA4 and ATL counter BLTR-amplified networks, revealing a novel protective role for LX and ATL in stress responses that has applications in perioperative medicine.
The human 15-lipoxygenase (15-LO) gene was transfected into rat kidneys in vivo via intra-renal arterial injection. Three days later, acute (passive) or accelerated forms of antiglomerular basement membrane
antibody-mediated glomerulonephritis were induced in transfected and nontransfected or sham-transfected controls. Studies
of glomerular functions (filtration and protein excretion) and ex vivo glomerular leukotriene B4 biosynthesis at 3 hr, and up to 4 days, after induction of nephritis revealed preservation or normalization of these parameters
in transfected kidneys that expressed human 15-LO mRNA and mature protein, but not in contralateral control kidneys or sham-transfected
animals. The results provide in vivo-derived data supporting a direct anti-inflammatory role for 15-LO during immune-mediated tissue injury.
Lipoxins are a novel class of endogenous eicosanoid mediators that potently inhibit inflammatory events by signaling via specific receptors expressed on phagocytic cells. Animal models have shown that lipoxin A4 (LXA4) down-regulates inflammation in vivo. Here we demonstrate, for the first time, the expression of LXA4 receptors, and their up-regulation by IL-1 beta, in normal human synovial fibroblasts (SF). We examined whether exogenous LXA4 abrogated IL-1 beta stimulation of SF in vitro. IL-1 beta induced the synthesis of IL-6, IL-8, and matrix metalloproteinases (MMP)-1 and -3. At nanomolar concentrations, LXA4 inhibited these IL-1 beta responses with reduction of IL-6 and IL-8 synthesis, by 45 +/- 7% and 75 +/- 11%, respectively, and prevented IL-1 beta-induced MMP-3 synthesis without significantly affecting MMP-1 levels. Furthermore, LXA4 induced a 2-fold increase of tissue inhibitor of metalloproteinase (TIMP)-1 and a approximately 3-fold increase of TIMP-2 protein levels. LXA4 inhibitory responses were dose dependent and were abrogated by pretreatment with LXA4 receptor antiserum. LXA4-induced changes of IL-6 and TIMP were accompanied by parallel changes in mRNA levels. These results indicate that LXA4 in activated SF inhibits the synthesis of inflammatory cytokines and MMP and stimulates TIMP production in vitro. These findings suggest that LXA4 may be involved in a negative feedback loop opposing inflammatory cytokine-induced activation of SF.
Tissue eosinophilia prevention represents one of the primary targets to new anti-allergic therapies. As lipoxin A4 (LXA4) and aspirin-triggered 15-epi-LXA4 (ATL) are emerging as endogenous "stop signals" produced in distinct pathologies including some eosinophil-related pulmonary disorders, we evaluated the impact of in situ LXA4/ATL metabolically stable analogues on allergen-induced eosinophilic pleurisy in sensitized rats. LXA4/ATL analogues dramatically blocked allergic pleural eosinophil influx, while concurrently increasing circulating eosinophilia, inhibiting the earlier edema and neutrophilia associated with allergic reaction. The mechanisms underlying this LXA4/ATL-driven allergic eosinophilia blockade was independent of mast cell degranulation and involved LXA4/ATL inhibition of both IL-5 and eotaxin generation, as well as platelet activating factor action. These findings reveal LXA4/ATL as a novel class of endogenous anti-allergic mediators, capable of preventing local eosinophilia.
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.
While philosophers seek the meaning of life, cell biologists are becoming ever more interested in the meaning of death. Apoptosis marks unwanted cells with 'eat me' signals that direct recognition, engulfment and degradation by phagocytes. Far from being the end of the story, these clearance events allow scavenger cells to confer meaning upon cell death. But if the phagocytic 'spin doctors' receive or transmit the wrong messages, trouble ensues.
The nociceptin receptor (Noci-R) is a G protein-coupled receptor present in neural tissues and its activation by nociceptin is involved in the processing of pain signals. Here, we report that Noci-R is present and functional on peripheral blood polymorphonuclear leukocytes (PMN). Human PMN express mRNA for Noci-R, its nucleotide sequence determined, and specific binding with [(125)I]-labeled nociceptin gave an apparent K(d) approximately 1.5 nM for this PMN opioid receptor. Nociceptin evoked PMN chemotaxis with maximal activity at 100 pM, without intracellular Ca(2+) mobilization. When injected in murine air pouches, nociceptin elicited leukocyte infiltration in a concentration-dependent fashion. Nociceptin-stimulated PMN infiltration was inhibited by treating mice with a synthetic analog of the aspirin-triggered lipid mediator 15-epi-lipoxin A(4). The present results identify nociceptin as a potent chemoattractant and provide a novel link between the neural and immune systems that are blocked by aspirin-triggered lipid mediators and may be relevant in neurogenic inflammation.
Neutrophils express the G protein-coupled N-formyl peptide receptor (FPR) and its homologue FPRL1, whereas monocytes express FPR, FPRL1, and FPRL2, an orphan receptor
sharing 83% amino acid identity with FPRL1. FPRL1 is a promiscuous receptor activated by serum amyloid A and by different
synthetic peptides, including the hexapeptide Trp-Lys-Tyr-Met-Val-d-Met-NH2 (WKYMVm). By measuring calcium flux in HL-60 cells transfected with FPR, FPRL1, or FPRL2, we show that WKYMVm activated all
three receptors, whereas thel-conformer WKYMVM activated exclusively FPRL1 and FPRL2. The functionality of FPRL2 was further assessed by the ability of
HL-60-FPRL2 cells to migrate toward nanomolar concentrations of hexapeptides. The half-maximal effective concentrations of
WKYMVM for calcium mobilization in HL-60-FPRL1 and HL-60-FPRL2 cells were 2 and 80 nm, respectively. Those of WKYMVm were 75 pmand 3 nm. The tritiated peptide WK[3,5-3H2]YMVM bound to FPRL1 (K
D ∼ 160 nm), but not to FPR. The two conformers similarly inhibited binding of 125I-labeled WKYMVm to FPRL2-expressing cells (IC50 ∼ 2.5–3 μm). Metabolic labeling with orthophosphoric acid revealed that FPRL1 was differentially phosphorylated upon addition of the
l- or d-conformer, indicating that it induced different conformational changes. In contrast to FPRL1, FPRL2 was already phosphorylated
in the absence of agonist and not evenly distributed in the plasma membrane of unstimulated cells. However, both receptors
were internalized upon addition of either of the two conformers. Taken together, the results indicate that neutrophils are
activated by WKYMVM through FPRL1 and that FPRL2 is a chemotactic receptor transducing signals in myeloid cells.
Lipid-derived mediators play critical roles in inflammation and other multicellular vascular processes, including atherosclerosis and thrombosis. The lipoxins (LXs) were first isolated in 1984, and have continued to show intriguing and potentially important biological roles. These compounds carry a trihydroxytetraene structure and are both structurally and functionally unique among arachidonic acid-derived bioactive products. The availability of synthetic materials for evaluation of bioactions as well as appropriate methods of detection to determine when and where LX are generated has, in recent studies, catapulted our understanding of the formation and actions of the lipoxins. This mini-review addresses new concepts in the formation and biological roles of these lipid-derived mediators and considers whether the lipoxins and the newly discovered aspirin-triggered lipoxins (ATL) represent novel approaches for therapeutic opportunities. Recent findings indicate that select cytokines and aspirin initiate and regulate LX biosynthetic events. These circuits involve cell-cell interfacing that facilitates transcellular events to form LX that display anti-inflammatory actions in both in vitro and in vivo models. These recent results suggest that LX biosynthetic circuits assemble to evoke anti-inflammatory actions and generate LX that can serve as "stop signals" in appropriate microenvironments.
The Ah receptor is a ligand-activated transcription factor that mediates many of the biological actions of a large class of environmental compounds. Support for a role of the Ah receptor in normal physiology also has been reported, but an endogenous regulating ligand has not been identified. We have examined candidate endogenous lipophilic substances and report here the ability of the arachidonic acid metabolite, lipoxin A4, to bind to and activate the Ah receptor in Hepa-1 cells. Lipoxin A4 produced a concentration-dependent response in a DRE-driven CAT reporter construct, with a greater than 10-fold increase in CAT activity at 0. 3 microM. Lipoxin A4 transformed the Ah receptor to an active DRE-binding form in a concentration-dependent manner as indicated by gel mobility shift analysis. Results of Ah receptor competitive binding experiments indicated that at a concentration of 100 nM, lipoxin A4 produced a half-maximum displacement (EC50) of [3H]TCDD binding. Results of Northern blot analyses indicated a transient increase in mRNA levels of the Ah receptor-responsive gene CYP1A1, which peaked at 4 h, consistent with the kinetics observed for lipoxin A4-induced CYP1A1 enzyme activity. Further, lipoxin A4 was found to be a competitive inhibitor for the CYP1A1 enzyme, with a calculated Ki = 1.1 microM. These results establish lipoxin A4 as a new class of Ah receptor ligand, one that differs dramatically from classical Ah receptor ligands.
Lipoxins (LX) are lipoxygenase-derived eicosanoids generated during inflammation. LX inhibit polymorphonuclear neutrophil (PMN) chemotaxis and adhesion and are putative braking signals for PMN-mediated tissue injury. In this study, we report that LXA4 promotes another important step in the resolution phase of inflammation, namely, phagocytosis of apoptotic PMN by monocyte-derived macrophages (Mphi). LXA4 triggered rapid, concentration-dependent uptake of apoptotic PMN. This bioactivity was shared by stable synthetic LXA4 analogues (picomolar concentrations) but not by other eicosanoids tested. LXA4-triggered phagocytosis did not provoke IL-8 or monocyte chemoattractant protein-1 release. LXA4-induced phagocytosis was attenuated by anti-CD36, alphavbeta3, and CD18 mAbs. LXA4-triggered PMN uptake was inhibited by pertussis toxin and by 8-bromo-cAMP and was mimicked by Rp-cAMP, a protein kinase A inhibitor. LXA4 attenuated PGE2-stimulated protein kinase A activation in Mphi. These results suggest that LXA4 is an endogenous stimulus for PMN clearance during inflammation and provide a novel rationale for using stable synthetic analogues as anti-inflammatory compounds in vivo.
Asthma is characterized by chronic airway inflammation resulting from overproduction of pro-inflammatory mediators, such as leukotrienes (LT). The authors questioned the biosynthetic capacity of asthmatic patients for lipoxins (LX) and 15-epimer lipoxins (15-epi-LX), endogenous regulators of inflammatory responses that inhibit pro-inflammatory events. Levels of LXA4, 15-epi-LXA4 and LTC4 were determined in 14 clinically characterized aspirin-intolerant asthmatics (AIA), 11 aspirin-tolerant asthmatics (ATA) and eight healthy volunteers using a stimulated whole blood protocol. Both LXA4 and 15-epi-LXA4 were generated in whole blood activated by the divalent cation ionophore, A23187. Higher levels of LXA4 were produced in ATA than either AIA or healthy volunteers. Exposure of AIA whole blood to interleukin-3 prior to A23187 did not elevate their reduced capacity to generate LXA4. Generation of a bronchoconstrictor, LTC4, was similar in both AIA and ATA. Consequently, the ratio of LXA4:LTC4 quantitatively favoured the bronchoconstrictor for AIA and differed from both ATA and healthy subjects. In addition, the capacity for 15-epi-LXA4 generation was also diminished in AIA, since whole blood stimulated in the presence of aspirin gave increased levels only in samples from ATA. The present results indicate that asthmatics possess the capacity to generate both lipoxins and 15-epimer-lipoxins, but aspirin-intolerant asthmatics display a lower biosynthetic capacity than aspirin-tolerant asthmatics for these potentially protective lipid mediators. This previously unappreciated, diminished capacity for lipoxin formation by aspirin-intolerant asthmatic patients may contribute to their more severe clinical phenotype, and represents a novel paradigm for the development of chronic inflammatory disorders.
Lipoxins (LX) are eicosanoids generated via transcellular biosynthetic routes during inflammation, hypersensitivity reaction, and after angioplasty. LXs are modulators of leukocyte trafficking and vascular tone. Their influence on the coagulation cascade has not been determined. In this study, we evaluated the influence of LXs on the expression of tissue factor (TF), a key regulator of coagulation. TF activity was measured in lysates of monocytes, human umbilical vein endothelial cells, and ECV304 cells using a one-stage clotting assay. LXA(4) stimulated TF activity in each cell type. The influence of LXA(4) on TF activity by ECV304 cells was studied further to explore the mechanism of induction of TF expression. LXA(4)-induced TF activity was dose dependent, cycloheximide sensitive, and associated with increased TF mRNA levels. Induction of TF activity was specific for LXA(4) and was not observed with LXB(4), the other major lipoxin generated by mammalian cells. Furthermore, ECV304 cell TF expression was not influenced by 15(R/S)-methyl-LXA(4) or 16-phenoxy-LXA(4), synthetic analogs of LXA(4) that activate the myeloid LXA(4) receptor, and was not modulated by SKF-104353, which blocks LXA(4) bioactivities transduced through the putative shared LXA(4)/LTD(4) receptor. LXA(4)-stimulated TF expression was blunted by pertussis toxin and by GF-109203X, an inhibitor of protein kinase C, and was not associated with degradation of IkappaBalpha. Our results establish that LXA(4) induces TF activity via cell signaling pathways with different structural and receptor requirements from those described for inhibition of leukocyte-endothelial cell interactions. They suggest a role for LXA(4) as a modulator of TF-related vascular events during inflammation and thrombosis.
Aspirin-triggered lipoxin A(4) (ATL, 15-epi-LXA(4)) and leukotriene D(4) (LTD(4)) possess opposing vascular actions mediated via receptors distinct from the LXA(4) receptor (ALX) that is involved in leukocyte trafficking. Here, we identified these receptors by nucleotide sequencing and demonstrate that LTD(4) receptor (CysLT(1)) is induced in human vascular endothelia by interleukin-1beta. Recombinant CysLT(1) receptor gave stereospecific binding with both [(3)H]-LTD(4) and a novel labeled mimetic of ATL ([(3)H]-ATLa) that was displaced with LTD(4) and ATLa ( approximately IC(50) 0.2 to 0.9 nmol/L), but not with a bioinactive ATL isomer. The clinically used CysLT(1) receptor antagonist, Singulair, showed a lower rank order for competition with [(3)H]-ATLa (IC(50) approximately 8.3 nmol/L). In contrast, LTD(4) was an ineffective competitive ligand for recombinant ALX receptor with [(3)H]-ATLa, and ATLa did not compete for [(3)H]-LTB(4) binding with recombinant LTB(4) receptor. Endogenous murine CysLT(1) receptors also gave specific [(3)H]-ATLa binding that was displaced with essentially equal affinity by LTD(4) or ATLa. Systemic ATLa proved to be a potent inhibitor (>50%) of CysLT(1)-mediated vascular leakage in murine skin (200 microg/kg) in addition to its ability to block polymorphonuclear leukocyte recruitment to dorsal air pouch (4 microg/kg). These results indicate that ATL and LTD(4) bind and compete with equal affinity at CysLT(1), providing a molecular basis for aspirin-triggered LXs serving as a local damper of both vascular CysLT(1) signals as well as ALX receptor-regulated polymorphonuclear leukocyte traffic.
Corpse clearance defines the meaning of cell death
- Savill
Local and systemic delivery of a stable-aspirin-triggered lipoxin prevents neutrophil recruitment in vivo
- Clish