Lipoxin A(4) and aspirin-triggered 15-epi-lipoxin A(4) antagonize TNF-alpha-stimulated neutrophil-enterocyte interactions in vitro and attenuate TNF-alpha-induced chemokine release and colonocyte apoptosis in human intestinal mucosa ex vivo

Molecular Targets and Mechanisms of 6,7-Dihydroxy-2,4-dimethoxyphenanthrene from Chinese Yam Modulating NF-κB/COX-2 Signaling Pathway: The Application of Molecular Docking and Gene Silencing

Chinese yam (Dioscorea opposita) tuber has a significant effect of invigorating the intestine and improving the symptoms of long-term diarrhea according to the records of the Chinese Pharmacopoeia. Phenanthrene polyphenols from Chinese yam, with higher inhibition of cyclooxygenase-2 (COX-2) than anti-inflammatory drugs, are an important material basis in alleviating ulcerative colitis via nuclear factor kappa-B (NF-κB)/COX-2 pathway, based on our previous research. The present study further explored the target and molecular mechanisms of phenanthrenes' modulation of the NF-κB/COX-2 signaling pathway by means of molecular docking and gene silencing. Firstly, interleukin-8 (IL-8) and tumor necrosis factor-α (TNF-α) expression of 6-hydroxy-2,4,7-trimethoxyphenanthrene (PC2)/6,7-dihydroxy-2,4-dimethoxyphe-nanthrene (PC4) were compared on TNF-α induced human colon adenocarcinoma (Caco-2) cells. Secondly, molecular docking and dynamics simulation were implemented for PC2/PC4 and COX-2. Finally, COX-2 silencing was performed on TNF-α induced Caco-2 cells to confirm the target of PC4 on NF-κB/COX-2 pathway. Lower expression of IL-8 and TNF-α in PC4 treated Caco-2 cells indicated that PC4 had stronger anti-inflammatory activity than PC2. The binding of PC4 and COX-2 was stronger due to the hydrogen bond between hydroxyl group and Tyr385. No significant differences were found in phosphorylation nuclear factor kappa-B inhibitor alpha (pIkBα), phosphorylation NF-κB (pNF-κB) and phosphorylation extracellular signal-regulated kinase 1/2 (pERK1/2) expression between control and PC4 group after silencing, while these protein expressions significantly decreased in PC4 group without silencing, which confirmed that COX-2 was the important target for PC4 in alleviating ulcerative colitis. These findings indicate that PC4 was supposed to have inhibited NF-κB pathway mediated inflammation via suppression of positive feedback targeting COX-2.

Lipoxin Mimetics and the Resolution of Inflammation

Inflammation and its timely resolution are critical to ensure effective host defense and appropriate tissue repair after injury and or infection. Chronic, unresolved inflammation typifies many prevalent pathologies. The key mediators that initiate and drive the inflammatory response are well defined and targeted by conventional anti-inflammatory therapeutics. More recently, there is a growing appreciation that specific mediators, including arachidonate-derived lipoxins, are generated in self-limiting inflammatory responses to promote the resolution of inflammation and endogenous repair mechanisms without compromising host defense. We discuss the proresolving biological actions of lipoxins and recent efforts to harness their therapeutic potential through the development of novel, potent lipoxin mimetics generated via efficient, modular stereoselective synthetic pathways. We consider the evidence that lipoxin mimetics may have applications in limiting inflammation and reversing fibrosis and the underlying mechanisms.

Bioactive lipids in inflammatory bowel diseases - From pathophysiological alterations to therapeutic opportunities

Inflammatory bowel diseases (IBDs), such as Crohn's disease and ulcerative colitis, are lifelong diseases that remain challenging to treat. IBDs are characterized by alterations in intestinal barrier function and dysregulation of the innate and adaptive immunity. An increasing number of lipids are found to be important regulators of inflammation and immunity as well as gut physiology. Therefore, the study of lipid mediators in IBDs is expected to improve our understanding of disease pathogenesis and lead to novel therapeutic opportunities. Here, through selected examples - such as fatty acids, specialized proresolving mediators, lysophospholipids, endocannabinoids, and oxysterols - we discuss how lipid signaling is involved in IBD physiopathology and how modulating lipid signaling pathways could affect IBDs.

Lipoxin A4 reduces house dust mite and TNFα-induced hyperreactivity in the mouse trachea

Lipoxin A₄ (LXA₄) is considered a specialised pro-resolving mediator that decreases inflammation: however, pro-inflammatory effects have been described in the airways. Here, we investigated whether LXA₄ could influence airway hyperreactivity induced in mouse trachea by house dust mite extract (HDM) or TNFα. Intranasal instillation of HDM caused a serotonin (5-HT) mediated airway hyperreactivity ex vivo (E_max: 78.1 ± 16.2 % versus control 12.8 ± 1.0 %) that was reduced by LXA₄ installation one hour prior to HDM (E_max: 49.9 ± 11.4 %). Also, in isolated tracheal segments cultured for four days, HDM induced a hyperreactivity (E_max: 33.2 ± 3.1 % versus control 9.0 ± 0.7 %) that was decreased by LXA₄ (E_max: 18.7 ± 1.5 %). One part of the HDM-induced hyperreactivity could be inhibited by the TNFα-inhibitor etanercept. TNFα-induced upregulation of 5-HT responses (E_max: 51.3 ± 1.2 % versus control 13.9 ± 0.5 %) was decreased by 10-1000 nM LXA₄. In precontracted tracheal segments, LXA₄ had no relaxing effect. Overall, LXA₄ was able to decrease airway hyperreactivity induced by both HDM and TNFα, thus having a sub-acute anti-inflammatory effect in airway inflammation.

Lipoxin A4 attenuates hyperoxia‑induced lung epithelial cell injury via the upregulation of heme oxygenase‑1 and inhibition of proinflammatory cytokines

The present study examined whether lipoxin A4 (LXA4) increases the expression of HO‑1, and inhibits the production of interleukin 6 (IL‑6) and monocyte chemotactic protein 1 (MCP‑1) in LXA4‑induced protection during hyperoxia‑induced injury in murine lung epithelial cells (MLE‑12) and what signal pathway may participate in the actions of LXA4 inhibiting IL‑6 and MCP‑1. MLE‑12 cells were exposed to air or hyperoxia with or without pretreatment with LXA4, Zinc protoporphyrin IX (ZnPP‑IX), IL‑6, anti‑IL‑6, MCP‑1, anti‑MCP‑1, inhibitors of p38 mitogen‑activated protein kinase (p38 MAPK), protein kinase B (Akt) and extracellular signal‑regulated kinase 1/2 (ERK1/2) signaling pathways. The cell survival rates, cell viability, apoptosis rates, expression of superoxide dismutase (SOD), heme oxygenase‑1 (HO‑1), IL‑6 and MCP‑1, and the activations of p38 MAPK, ERK1/2 and Akt were measured. LXA4 significantly increased the cell survival rates, cell viability, SOD levels and HO‑1 expression, reduced the apoptosis rates, and inhibited the MCP‑1 and IL‑6 levels induced by hyperoxia in cells. ZnPP‑IX, an inhibitor of HO‑1, blocked LXA4‑induced protection on cell viability in cells exposed to hyperoxia. Anti‑IL‑6 and anti‑MCP‑1 improved the cell viability of cells exposed to hyperoxia. Inhibition of p38 MAPK and ERK1/2 blocked the expression of MCP‑1 and IL‑6 induced by hyperoxia. LXA4 inhibited the activation of p38 MAPK and ERK1/2 induced by hyperoxia, and increased the activation of the Akt signaling pathway, which was inhibited by hyperoxia. Therefore, LXA4 attenuated hyperoxia‑induced injury in MLE‑12 cells via the upregulation of HO‑1 expression. The protection of LXA4 in hyperoxia‑induced cell injury may be associated with the downregulation IL‑6 and MCP‑1 levels via the inhibition of the p38 MAPK and ERK1/2 signaling pathways.

Keep calm: the intestinal barrier at the interface of peace and war

Epithelial barriers have to constantly cope with both harmless and harmful stimuli. The epithelial barrier therefore serves as a dynamic and not static wall to safeguard its proper physiological function while ensuring protection. This is achieved through multiple defence mechanisms involving various cell types - epithelial and non-epithelial - that work in an integrated manner to build protective barriers at mucosal sites. Damage may nevertheless occur, due to pathogens, physical insults or dysregulated immune responses, which trigger a physiologic acute or a pathologic chronic inflammatory cascade. Inflammation is often viewed as a pathological condition, particularly due to the increasing prevalence of chronic inflammatory (intestinal) diseases. However, inflammation is also necessary for wound healing. The aetiology of chronic inflammatory diseases is incompletely understood and identification of the underlying mechanisms would reveal additional therapeutic approaches. Resolution is an active host response to end ongoing inflammation but its relevance is under-appreciated. Currently, most therapies aim at dampening inflammation at damaged mucosal sites, yet these approaches do not efficiently shut down the inflammation process nor repair the epithelial barrier. Therefore, future treatment strategies should also promote the resolution phase. Yet, the task of repairing the barrier can be an arduous endeavour considering its multiple integrated layers of defence - which is advantageous for damage prevention but becomes challenging to repair at multiple levels. In this review, using the intestines as a model epithelial organ and barrier paradigm, we describe the consequences of chronic inflammation and highlight the importance of the mucosae to engage resolving processes to restore epithelial barrier integrity and function. We further discuss the contribution of pre-mRNA alternative splicing to barrier integrity and intestinal homeostasis. Following discussions on current open questions and challenges, we propose a model in which resolution of inflammation represents a key mechanism for the restoration of epithelial integrity and function.

Downregulation of TNF-α/TNF-R1 Signals by AT-Lipoxin A4 May Be a Significant Mechanism of Attenuation in SAP-Associated Lung Injury

Our previous studies verified the potent anti-inflammatory effects against severe acute pancreatitis (SAP) of AT-Lipoxin A4 and their analogues. However, the anti-inflammatory effects of AT-Lipoxin A4 on SAP-associated lung injury are not thoroughly known. We used western blot, polymerase chain reaction (PCR), and immunofluorescence to investigate the downregulation of TNF-α signals in cellular and animal models of SAP-associated lung injury following AT-Lipoxin A4 intervention. In vitro, we found that AT-Lipoxin A4 markedly suppressed protein expression in TNF-α signals in human pulmonary microvascular endothelial cell, such as tumor necrosis factor receptor-associated factor 2 (TRAF2), TNF-R1-associated death domain (TRADD), receptor-interacting protein (RIP), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin. Moreover, AT-Lipoxin A4 inhibited downstream signals activated by TNF-α, including NF-κB/p65, JNK/MAPK, and ERK/MAPK. In vivo, AT-Lipoxin A4 significantly decreased pathological scores of the pancreas and lungs and the serum levels of IL-6 and TNF-α. Immunofluorescence, western blotting, and real-time PCR assay showed that AT-Lipoxin A4 significantly attenuated the expression of TNF-R1, TRADD, TRAF2, and RIP in the lungs of SAP rats. In addition, the activation of NF-κB was also downregulated by AT-Lipoxin A4 administration as compared with SAP rats. AT-Lipoxin A4 could inhibit the production of proinflammatory mediators and activation of TNF-α downstream signals such as NF-κB and MAPK. Downregulation of TNF-α signals by AT-Lipoxin A4 may be a significant mechanism in the attenuation of SAP-associated lung injury.

Saving Problematic Mucosae: SPMs in Intestinal Mucosal Inflammation and Repair

The intestinal mucosa serves as a highly selective barrier that allows the absorption of nutrients and water while restricting microbiota access to tissues. This barrier is compromised in inflammatory conditions such as infectious colitis and inflammatory bowel disease (IBD). In response to mucosal injury, there is a temporal recruitment of leukocytes that crosstalk with epithelial cells to orchestrate repair. Specialized pro-resolving mediators (SPMs) play an important role in the resolution of inflammation and epithelial repair. SPMs actively promote resolution of inflammation by contributing to the clearance of neutrophils, stimulating efferocytosis, and promoting epithelial repair. SPMs have potential to serve as targeted therapeutic agents to be used in adjuvant therapy to promote resolution of inflammation and epithelial repair in chronic inflammatory diseases.

Lipoxins Protect Against Inflammation in Diabetes-Associated Atherosclerosis

Increasing evidence points to the fact that defects in the resolution of inflammatory pathways predisposes individuals to the development of chronic inflammatory diseases, including diabetic complications such as accelerated atherosclerosis. The resolution of inflammation is dynamically regulated by the production of endogenous modulators of inflammation, including lipoxin A4 (LXA₄). Here, we explored the therapeutic potential of LXA₄ and a synthetic LX analog (Benzo-LXA₄) to modulate diabetic complications in the streptozotocin-induced diabetic ApoE^-/- mouse and in human carotid plaque tissue ex vivo. The development of diabetes-induced aortic plaques and inflammatory responses of aortic tissue, including the expression of vcam-1, mcp-1, il-6, and il-1β, was significantly attenuated by both LXA₄ and Benzo-LXA₄ in diabetic ApoE^-/- mice. Importantly, in mice with established atherosclerosis, treatment with LXs for a 6-week period, initiated 10 weeks after diabetes onset, led to a significant reduction in aortic arch plaque development (19.22 ± 2.01% [diabetic]; 12.67 ± 1.68% [diabetic + LXA₄]; 13.19 ± 1.97% [diabetic + Benzo-LXA₄]). Secretome profiling of human carotid plaque explants treated with LXs indicated changes to proinflammatory cytokine release, including tumor necrosis factor-α and interleukin-1β. LXs also inhibited platelet-derived growth factor-stimulated vascular smooth muscle cell proliferation and transmigration and endothelial cell inflammation. These data suggest that LXs may have therapeutic potential in the context of diabetes-associated vascular complications.

Pro-resolving lipid mediators: Agents of anti-ageing?

Inflammation is an essential response to injury and its timely and adequate resolution permits tissue repair and avoidance of chronic inflammation. Ageing is associated with increased inflammation, sub-optimal resolution and these act as drivers for a number of ageing-associated pathologies. We describe the role played by specialised proresolving lipid mediators (SPMs) in the resolution of inflammation and how insufficient levels of these mediators, or compromised responsiveness may play a role in the pathogenesis of many ageing-associated pathologies, e.g. Alzheimer's Disease, atherosclerosis, obesity, diabetes and kidney disease. Detailed examination of the resolution phase of inflammation highlights the potential to harness these lipid mediators and or mimetics of their bioactions, in particular, their synthetic analogues to promote effective resolution of inflammation, without compromising the host immune system.

Unraveling the Interaction of Aspirin, Ticagrelor, and Rosuvastatin on the Progression of Atherosclerosis and Inflammation in Diabetic Mice

PURPOSE

We explored the effects of rosuvastatin, aspirin, ticagrelor, and clopidogrel, alone or in combinations on the progression of atherosclerosis and inflammasome activation in diabetic mice. Statins and ticagrelor increase the production of 15-epi-lipoxin A₄ via cyclooxygenase-2. Aspirin alone increases 15-epi-lipoxin A₄, but when combined with statins, cyclooxygenase-2 is completely blocked.

METHODS

ApoE^-/-/db⁺/db⁺ double-knockout mice received rosuvastatin (5 mg/kg/day), aspirin (25 mg/kg/day), ticagrelor (300 mg/kg/day), clopidogrel (75 mg/kg/day), or their combination for 14 weeks. Serum 15-epi-lipoxin A₄ levels and aortic wall cholesterol content, IL-1β, IL-6, and TNF-α levels, and plaque area were assessed.

RESULTS

Aspirin, ticagrelor, and rosuvastatin increased 15-epi-lipoxin A₄ levels. The combination of rosuvastatin + ticagrelor provided an additive effect. Aspirin attenuated the effect of both ticagrelor and rosuvastatin. Aspirin, ticagrelor, and rosuvastatin reduced the area of the atherosclerotic plaque. The combination of ticagrelor + rosuvastatin provided additive effects. There was a negative interaction when aspirin was combined with ticagrelor or rosuvastatin. Aspirin, ticagrelor, and rosuvastatin decreased serum IL-1β and IL-6 levels. There was no interaction between aspirin and ticagrelor or aspirin and rosuvastatin, whereas combining rosuvastatin and ticagrelor provided an additive effect. Aspirin, ticagrelor, and rosuvastatin all decreased TNF-α levels. Aspirin attenuated the effect of both ticagrelor and rosuvastatin, and there was no additive effect of combining ticagrelor + rosuvastatin.

CONCLUSIONS

We found an intricate interaction between aspirin, ticagrelor, and rosuvastatin, as aspirin reduced both ticagrelor and rosuvastatin ability to ameliorate inflammation and atherosclerosis. In contrast, we found additive effects when ticagrelor and rosuvastatin were combined.

Special pro-resolving mediator (SPM) actions in regulating gastro-intestinal inflammation and gut mucosal immune responses

Surfaces covered by epithelial cells, termed mucosal surfaces, serve special functions as selectively permeable barriers that partition the host and the outside world. Given its close association to microbial antigens, the intestinal mucosa has evolved creative mechanisms to maintain homeostasis, to prevent excessive inflammatory responses, and to promote rapid and full inflammatory resolution. In recent years, an active role for the epithelium has been attributed to the local generation of specialized pro-resolving mediators (SPMs) in the maintenance of immunological homeostasis. In this brief review, we highlight evidence that the epithelium actively contributes to coordination and resolution of inflammation, principally through the generation of SPMs. These autacoids are derived from omega-6 and omega-3 polyunsaturated fatty acids. Acting through widely expressed G-protein coupled receptors, SPMs are implicated in the resolution of acute inflammation that manifests specific, epithelial-directed actions focused on mucosal-homeostasis, including regulation of leukocyte trafficking, the generation of antimicrobial peptides, the dampening of endotoxin signaling, and the attenuation of mucosal cytokine responses.

Eicosanoid receptors: Targets for the treatment of disrupted intestinal epithelial homeostasis

The importance of cyclooxygenase and lipoxygenase pathways and the consequent eicosanoid synthesis in the physiology and pathophysiology of the intestinal epithelium is currently being established. Each eicosanoid (prostanoid, leukotriene, hydroxyeicosatetraenoic acid) preferentially recognizes one or more receptors coupled to one or more signal-transduction processes. This overview focuses on the role of eicosanoid receptors in the maintenance of intestinal epithelium physiology through the control of proliferation/differentiation/apoptosis processes. Furthermore, it is reported that the role of these receptors on the regulation of the barrier function of the intestinal epithelium have arisen through the regulation of absorption/secretion processes, tight-junction state and the control of the intestinal immune response. Also, this review considers the implication of AA cascade in the disruption of epithelial homeostasis during inflammatory bowel diseases and colorectal cancer as well as the therapeutic values and potential of the eicosanoid receptors as novel targets for the treatments of the pathologies above mentioned.

Protective effects of n-6 fatty acids-enriched diet on intestinal ischaemia/reperfusion injury involve lipoxin A4 and its receptor

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.

Hyperosmolar stress induces neutrophil extracellular trap formation: implications for dry eye disease

PURPOSE

To determine if hyperosmolar stress can stimulate human neutrophils to form neutrophil extracellular traps (NETs) and to investigate potential strategies to reduce formation of NETs (NETosis) in a hyperosmolar environment.

METHODS

Neutrophils were isolated from peripheral venous blood of healthy subjects and incubated in iso-osmolar (280 mOsM) or hyperosmolar (420 mOsM) media for 4 hours. Neutrophil extracellular traps were quantified using a PicoGreen dye assay to measure extracellular DNA. Two known inhibitors of NETosis, staurosporine and anti-β2 integrin blocking antibody, and two proresolution formyl peptide receptor 2 (FPR2) agonists, annexin/lipocortin-1 mimetic peptide and 15-epi-lipoxin A4, were evaluated as possible strategies to reduce hyperosmolarity-induced NETosis.

RESULTS

The amount of NETs induced by hyperosmolar medium (420 mOsM) increased linearly over time to 3.2 ± 0.3 times that induced by iso-osmolar medium at 4 hours (P < 0.05). NETosis increased exponentially with increasing osmolarity and was independent of the stimulus used to increase osmolarity. Upon neutrophil exposure to hyperosmolar stress, restoration of iso-osmolar conditions decreased NET formation by 52.7% ± 5% (P < 0.05) but did not completely abrogate it. Among the strategies tested to reduce NETosis in a hyperosmolar environment, annexin-1 peptide was the most efficacious.

CONCLUSIONS

Hyperosmolarity induces formation of NETs by neutrophils. This NETosis mechanism may explain the presence of excessive NETs on the ocular surface of patients with dry eye disease. Because they reduce hyperosmolarity-induced NETosis, FPR2 agonists may have therapeutic potential in these patients.

Cannabinoid CB2 receptor activation attenuates cytokine-evoked mucosal damage in a human colonic explant model without changing epithelial permeability

Cannabinoid receptor activation is protective in animal colitis models. We sought to investigate if cannabinoids attenuated colitis-like tissue damage in human colonic specimens, with the hypothesis that cannabinoids would be protective in a cytokine-driven model of human colonic mucosal damage. Healthy human colonic mucosa was incubated with pro-inflammatory cytokines TNF-α and IL-1β to elicit colitis-like tissue damage. The cytokine-driven increase in scored crypt and mucosal damage and lymphocyte density was attenuated with concomitant hydrocortisone pretreatment. The cannabinoid receptor 2 (CB2) receptor-selective agonist JWH-015 significantly reduced colitis scores following cytokine incubation, as evidenced by a reduction in mucosal crypt and luminal epithelial damage and lymphocyte density in the lamina propria. The effect of JWH-015 was reversed in the presence of the CB2 receptor inverse agonist JTE-907. Anandamide was also protective in the cytokine-incubated explant colitis model in a manner reversible with JTE-907, while CB1 receptor agonism with ACEA was without effect. TNF-α and IL-1β together evoked an increase in paracellular epithelial permeability in Caco-2 cell monolayers over 48h of incubation. However, neither CB2 nor CB1 receptor activation altered the cytokine-evoked increase in permeability. These findings support a discrete role for CB2 receptors in the attenuation of detrimental pro-inflammatory cytokine-mediated mucosal damage in the human colon without directly affecting mucosal epithelial barrier function.

Molecular biology for formyl peptide receptors in human diseases

Leukocytes accumulate at sites of inflammation and immunological reaction in response to locally existing chemotactic mediators. The first chemotactic factors structurally defined were N-formyl peptides. Subsequently, numerous ligands were identified to activate formyl peptide receptors (FPRs) that belong to the seven-transmembrane G protein-coupled receptor superfamily. FPRs interact with this menagerie of structurally diverse pro- and anti-inflammatory ligands to possess important regulatory effects in multiple diseases, including inflammation, amyloidosis, Alzheimer's disease, prion disease, acquired immunodeficiency syndrome, obesity, diabetes, and cancer. How these receptors recognize diverse ligands and how they contribute to disease pathogenesis and host defense are basic questions currently under investigation that would open up new avenues for the future management of inflammation-related diseases.

Resolution of inflammation: therapeutic potential of pro-resolving lipids in type 2 diabetes mellitus and associated renal complications

The role of inflammation in the pathogenesis of type 2 diabetes mellitus (T2DM) and its associated complications is increasingly recognized. The resolution of inflammation is actively regulated by endogenously produced lipid mediators such as lipoxins, resolvins, protectins, and maresins. Here we review the potential role of these lipid mediators in diabetes-associated pathologies, specifically focusing on adipose inflammation and diabetic kidney disease, i.e., diabetic nephropathy (DN). DN is one of the major complications of T2DM and we propose that pro-resolving lipid mediators may have therapeutic potential in this context. Adipose inflammation is also an important component of T2DM-associated insulin resistance and altered adipokine secretion. Promoting the resolution of adipose inflammation would therefore likely be a beneficial therapeutic approach in T2DM.

Up-regulation of Annexin-A1 and lipoxin A(4) in individuals with ulcerative colitis may promote mucosal homeostasis

Background

One of the characteristics of an active episode of ulcerative colitis (UC) is the intense mucosal infiltration of leukocytes. The pro-resolution mediators Annexin-A1 (AnxA1) and lipoxin A₄ (LXA₄) exert counter-regulatory effects on leukocyte recruitment, however to date, the dual/cumulative effects of these formyl peptide receptor-2 (FPR2/ALX) agonists in the context of human intestinal diseases are unclear. To define the contribution of these mediators, we measured their expression in biopsies from individuals with UC.

Methods

Colonic mucosal biopsies were collected from two broad patient groups: healthy volunteers without (‘Ctrl’ n = 20) or with a prior history of UC (‘hx of UC’ n = 5); individuals with UC experiencing active disease (‘active’ n = 8), or in medically-induced remission (‘remission’ n = 16). We assessed the mucosal expression of LXA₄, AnxA1, and the FPR2/ALX receptor in each patient group using a combination of fluorescence microscopy, biochemical and molecular analyses.

Results

Mucosal expression of LXA₄ was elevated exclusively in biopsies from individuals in remission (3-fold, P<0.05 vs. Ctrl). Moreover, in this same group we observed an upregulation of AnxA1 protein expression (2.5-fold increase vs. Ctrl, P<.01), concurrent with an increased level of macrophage infiltration, and an elevation in FPR2/ALX mRNA (7-fold increase vs. Ctrl, P<.05). Importantly, AnxA1 expression was not limited to cells infiltrating the lamina propria but was also detected in epithelial cells lining the intestinal crypts.

Conclusions

Our results demonstrate a specific up-regulation of this pro-resolution circuit in individuals in remission from UC, and suggest a significant role for LXA₄ and AnxA1 in promoting mucosal homeostasis.

Lipoxin A4 attenuates adipose inflammation

Aging and adiposity are associated with chronic low-grade inflammation, which underlies the development of obesity-associated complications, including type 2 diabetes mellitus (T2DM). The mechanisms underlying adipose inflammation may include macrophage infiltration and activation, which, in turn, affect insulin sensitivity of adipocytes. There is a growing appreciation that specific lipid mediators (including lipoxins, resolvins, and protectins) can promote the resolution of inflammation. Here, we investigated the effect of lipoxin A4 (LXA4), the predominant endogenously generated lipoxin, on adipose tissue inflammation. Using adipose tissue explants from perigonadal depots of aging female C57BL/6J mice (Animalia, Chordata, Mus musculus) as a model of age-associated adipose inflammation, we report that LXA4 (1 nM) attenuates adipose inflammation, decreasing IL-6 and increasing IL-10 expression (P<0.05). The altered cytokine milieu correlated with increased GLUT-4 and IRS-1 expression, suggesting improved insulin sensitivity. Further investigations revealed the ability of LXA4 to rescue macrophage-induced desensitization to insulin-stimulated signaling and glucose uptake in cultured adipocytes, using vehicle-stimulated cells as controls. This was associated with preservation of Akt activation and reduced secretion of proinflammatory cytokines, including TNF-α. We therefore propose that LXA4 may represent a potentially useful and novel therapeutic strategy to subvert adipose inflammation and insulin resistance, key components of T2DM.

Lipoxin A4 inhibits immune cell binding to salivary epithelium and vascular endothelium

Lipoxins are formed by leukocytes during cell-cell interactions with epithelial or endothelial cells. Native lipoxin A(4) (LXA(4)) binds to the G protein-coupled lipoxin receptors formyl peptide receptor 2 (FPR2)/ALX and CysLT1. Furthermore, LXA(4) inhibits recruitment of neutrophils, by attenuating chemotaxis, adhesion, and transmigration across vascular endothelial cells. LXA(4) thus appears to serve as an endogenous "stop signal" for immune cell-mediated tissue injury (Serhan CN; Annu Rev Immunol 25: 101-137, 2007). The role of LXA(4) has not been addressed in salivary epithelium, and little is known about its effects on vascular endothelium. Here, we determined that interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) receptor activation in vascular endothelium and salivary epithelium upregulated the expression of adhesion molecules that facilitates the binding of immune cells. We hypothesize that the activation of the ALX/FPR2 and/or CysLT1 receptors by LXA(4) decreases this cytokine-mediated upregulation of cell adhesion molecules that enhance lymphocyte binding to both the vascular endothelium and salivary epithelium. In agreement with this hypothesis, we observed that nanomolar concentrations of LXA(4) blocked IL-1β- and TNF-α-mediated upregulation of E-selectin and intercellular cell adhesion molecule-1 (ICAM-1) on human umbilical vein endothelial cells (HUVECs). Binding of Jurkat cells to stimulated HUVECs was abrogated by LXA(4). Furthermore, LXA(4) preincubation with human submandibular gland cell line (HSG) also blocked TNF-α-mediated upregulation of vascular cell adhesion molecule-1 (VCAM-1) in these cells, and it reduced lymphocyte adhesion. These findings suggest that ALX/FPR2 and/or CysLT1 receptor activation in endothelial and epithelial cells blocks cytokine-induced adhesion molecule expression and consequent binding of lymphocytes, a critical event in the pathogenesis of Sjögren's syndrome (SS).

Aspirin and immune system

The time-tested gradual exploration of aspirin's diverse pharmacological properties has made it the most reliable therapeutic agent worldwide. In addition to its well-argued anti-inflammatory effects, many new and exciting data have emerged regarding the role of aspirin in cells of the immune system and certain immunopathological states. For instance, aspirin induces tolerogenic activity in dendritic cells and determines the fate of naive T cells to regulatory phenotypes, which suggests its immunoregulatory potential in relevance to immune tolerance. It also displays some intriguing traits to modulate the innate and adaptive immune responses. In this article, the immunomodulatory relation of aspirin to different immune cells, such as neutrophils, macrophages, dendritic cells (DCs), natural killer (NK) cells, and the T and B lymphocytes has been highlighted. Moreover, the clinical prospects of aspirin in terms of autoimmunity, allograft rejection and immune tolerance have also been outlined.

Deletion of the aryl hydrocarbon receptor enhances the inflammatory response to Leishmania major infection

The aryl hydrocarbon receptor (AhR) is a ligand-activated receptor that mediates the toxicity of environmental pollutants, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Recently, it has been shown that the AhR plays a role in immune and inflammatory regulation. However, most of these studies are based on the activation of AhR by exogenous ligands. Therefore, in the present study, we addressed the role of this transcription factor, in the absent of exogenous ligand, on the immune response to Leishmania major infection. Our results indicate that inactivation of the AhR results in an alteration of the levels of several cytokines. Lymph node cells from infected Ahr-null animals displayed an increase in IFNγ and IL-12 levels, together with a decrease in IL-4 and IL-10 levels compared to wild-type (wt) mice. Ahr-null mice also presented higher serum levels of the pro-inflammatory cytokine TNF-α prior to parasite inoculation and during infection compared to wt mice. Moreover, a 30% decrease in the population of T_reg cells was observed in Ahr-null mice. This decrease was associated with a reduction in Foxp3 mRNA levels. Finally, the alteration in the cytokine profile results in a better resolution of the L. major infection.

Lipoxin A4 impairment of apoptotic signaling in macrophages: implication of the PI3K/Akt and the ERK/Nrf-2 defense pathways

Lipoxin A(4) (LXA(4)) is an endogenous lipid mediator that requires transcellular metabolic traffic for its synthesis. The targets of LXA(4) on neutrophils are well described, contributing to attenuation of inflammation. However, effects of lipoxins on macrophage are less known, particularly the action of LXA(4) on the regulation of apoptosis of these cells. Our data show that pretreatment of human or murine macrophages with LXA(4) at the concentrations prevailing in the course of resolution of inflammation (nanomolar range) significantly inhibits the apoptosis induced by staurosporine, etoposide and S-nitrosoglutathione or by more pathophysiological stimuli, such as LPS/IFNgamma challenge. The release of mitochondrial mediators of apoptosis and the activation of caspases was abrogated in the presence of LXA(4). In addition to this, the synthesis of reactive oxygen species induced by staurosporine was attenuated and antiapoptotic proteins of the Bcl-2 family accumulated in the presence of lipoxin. Analysis of the targets of LXA(4) identified an early activation of the PI3K/Akt and ERK/Nrf-2 pathways, which was required for the observation of the antiapoptotic effects of LXA(4). These data suggest that the LXA(4), released after the recruitment of neutrophils to sites of inflammation, exerts a protective effect on macrophage viability that might contribute to a better resolution of inflammation.

Dichotomy in duration and severity of acute inflammatory responses in humans arising from differentially expressed proresolution pathways

Lipoxins (Lxs) and aspirin-triggered epi-Lxs (15-epi-LxA(4)) act through the ALX/FPRL1 receptor to block leukocyte trafficking, dampen cytokine/chemokine synthesis, and enhance phagocytic clearance of apoptotic leukocytes-key requisites for inflammatory resolution. Although studies using primarily inbred rodents have highlighted resolution as an active event, little is known about the role resolution pathways play in controlling the duration/profile of inflammatory responses in humans. To examine this, we found two types of responders to cantharidin-induced skin blisters in male healthy volunteers: those with immediate leukocyte accumulation and cytokine/chemokine synthesis followed by early resolution and a second group whose inflammation increased gradually over time followed by delayed resolution. In early resolvers, blister 15-epi-LxA(4) and leukocyte ALX were low, but increased as inflammation abated. In contrast, in delayed resolvers, 15-epi-LxA(4) and ALX were high early in the response but waned as inflammation progressed. Elevating 15-epi-LxA(4) in early resolvers using aspirin increased blister leukocyte ALX but reduced cytokines/chemokines as well as polymorphonuclear leukocyte and macrophage numbers. These findings show that two phenotypes exist in humans with respect to inflammation severity/longevity controlled by proresolution mediators, namely 15-epi-LxA(4). These data have implications for understanding the etiology of chronic inflammation and future directions in antiinflammatory therapy.

Reduced levels of hydroxylated, polyunsaturated ultra long-chain fatty acids in the serum of colorectal cancer patients: implications for early screening and detection

BACKGROUND

There are currently no accurate serum markers for detecting early risk of colorectal cancer (CRC). We therefore developed a non-targeted metabolomics technology to analyse the serum of pre-treatment CRC patients in order to discover putative metabolic markers associated with CRC. Using tandem-mass spectrometry (MS/MS) high throughput MS technology we evaluated the utility of selected markers and this technology for discriminating between CRC and healthy subjects.

METHODS

Biomarker discovery was performed using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Comprehensive metabolic profiles of CRC patients and controls from three independent populations from different continents (USA and Japan; total n = 222) were obtained and the best inter-study biomarkers determined. The structural characterization of these and related markers was performed using liquid chromatography (LC) MS/MS and nuclear magnetic resonance technologies. Clinical utility evaluations were performed using a targeted high-throughput triple-quadrupole multiple reaction monitoring (TQ-MRM) method for three biomarkers in two further independent populations from the USA and Japan (total n = 220).

RESULTS

Comprehensive metabolomic analyses revealed significantly reduced levels of 28-36 carbon-containing hydroxylated polyunsaturated ultra long-chain fatty-acids in all three independent cohorts of CRC patient samples relative to controls. Structure elucidation studies on the C28 molecules revealed two families harbouring specifically two or three hydroxyl substitutions and varying degrees of unsaturation. The TQ-MRM method successfully validated the FTICR-MS results in two further independent studies. In total, biomarkers in five independent populations across two continental regions were evaluated (three populations by FTICR-MS and two by TQ-MRM). The resultant receiver-operator characteristic curve AUCs ranged from 0.85 to 0.98 (average = 0.91 +/- 0.04).

CONCLUSIONS

A novel comprehensive metabolomics technology was used to identify a systemic metabolic dysregulation comprising previously unknown hydroxylated polyunsaturated ultra-long chain fatty acid metabolites in CRC patients. These metabolites are easily measurable in serum and a decrease in their concentration appears to be highly sensitive and specific for the presence of CRC, regardless of ethnic or geographic background. The measurement of these metabolites may represent an additional tool for the early detection and screening of CRC.

International Union of Basic and Clinical Pharmacology. LXXIII. Nomenclature for the formyl peptide receptor (FPR) family

Formyl peptide receptors (FPRs) are a small group of seven-transmembrane domain, G protein-coupled receptors that are expressed mainly by mammalian phagocytic leukocytes and are known to be important in host defense and inflammation. The three human FPRs (FPR1, FPR2/ALX, and FPR3) share significant sequence homology and are encoded by clustered genes. Collectively, these receptors bind an extraordinarily numerous and structurally diverse group of agonistic ligands, including N-formyl and nonformyl peptides of different composition, that chemoattract and activate phagocytes. N-formyl peptides, which are encoded in nature only by bacterial and mitochondrial genes and result from obligatory initiation of bacterial and mitochondrial protein synthesis with N-formylmethionine, is the only ligand class common to all three human receptors. Surprisingly, the endogenous anti-inflammatory peptide annexin 1 and its N-terminal fragments also bind human FPR1 and FPR2/ALX, and the anti-inflammatory eicosanoid lipoxin A4 is an agonist at FPR2/ALX. In comparison, fewer agonists have been identified for FPR3, the third member in this receptor family. Structural and functional studies of the FPRs have produced important information for understanding the general pharmacological principles governing all leukocyte chemoattractant receptors. This article aims to provide an overview of the discovery and pharmacological characterization of FPRs, to introduce an International Union of Basic and Clinical Pharmacology (IUPHAR)-recommended nomenclature, and to discuss unmet challenges, including the mechanisms used by these receptors to bind diverse ligands and mediate different biological functions.

Lipoxin a(4) attenuates microvascular fluid leak during inflammation

BACKGROUND

The release of proinflammatory cytokines during inflammation disturbs the endothelial barrier and can initiate significant intravascular volume loss. Proinflammatory cytokines also induce the expression of anti-inflammatory mediators, such as lipoxin, which promote the resolution of inflammation. Our hypothesis is that lipoxin A(4) (LXA(4)) reverses the increased microvascular fluid leak observed during inflammatory conditions.

MATERIALS AND METHODS

Microvascular fluid leak (L(p)) was measured in rat mesenteric venules using a micro-cannulation technique. L(p) was measured under the following conditions: (1) LXA(4) (100 nM) alone (n = 5), (2) LXA(4) (100 nM) administered after endothelial hyperpermeability induced by a continuous perfusion of 10 nM platelet activating factor (PAF) (n = 5), (3) LXA(4) (100 nM) perfused after inflammation induced by a systemic bolus of 10 mg/kg lipopolysaccharide (LPS) (n = 5), and (4) LXA(4) (100 nM) perfused after LPS-induced inflammation during inhibition of c-Jun N-terminal kinase (n = 4).

RESULTS

LXA(4) alone slightly increased L(p) from baseline (L(p)-baseline = 1.05 +/- 0.03, L(p)-LXA(4) = 1.55 +/- 0.04; P < 0.0001). PAF increased L(p) 4-fold (L(p)-baseline = 1.20 +/- 0.10, L(p)-PAF = 4.49 +/- 0.95; P < 0.0001). LXA(4) administration after PAF decreased L(p) 66% versus PAF alone (from 4.49 +/- 0.95 to 1.54 +/- 0.13; P = 0.0004). LPS-induced inflammation increased L(p) over 2-fold (L(p)-baseline = 1.05 +/- 0.03, L(p)-LPS = 2.27 +/- 0.13; P < 0.0001). LXA(4) administration after LPS decreased L(p) 42% versus LPS alone (from 2.27 +/- 0.13 to 1.31 +/- 0.05; P < 0.0001). The effect of c-Jun N-terminal kinase inhibition during LPS-induced inflammation attenuated the decrease in leak cause by LXA(4) by 51% (P = 0.0002).

CONCLUSION

After either LPS or PAF, LXA(4) attenuated the intravascular volume loss caused by these inflammatory mediators. The activity of LXA(4) may be partly mediated by the c-Jun N-terminal kinase signaling pathway. These data support an anti-inflammatory role for LXA(4) and suggests a potential pharmacologic role for LXA(4) during inflammation.

Lipoxins: update and impact of endogenous pro-resolution lipid mediators

Lipoxins (LXs) are endogenously produced eicosanoids that are typically generated by transcellular biosynthesis. These trihydroxytetraene-containing lipid mediators and their stable synthetic analogues possess a wide spectrum of anti-inflammatory and pro-resolution bioactions both in vitro and in vivo. More recently, LXs have emerged as potential anti-fibrotic mediators that may influence pro-fibrotic cytokines and matrix-associated gene expression in response to platelet-derived growth factor (PDGF). Here we review the biosynthesis, metabolism and bioactions of LXs and LX analogues and their therapeutic potential.

Design and synthesis of benzo-lipoxin A4 analogs with enhanced stability and potent anti-inflammatory properties

A new class of chemically and metabolically stable lipoxin analogs featuring a replacement of the tetraene unit of native LXA(4) with a substituted benzo-fused ring system have been designed and studied. These molecules were readily synthesized via a convergent synthetic route involving iterative palladium-mediated cross-coupling, and exhibit enhanced chemical stability, as well as resistance to metabolic inactivation via eicosanoid oxido-reductase. These new LX analogs were evaluated in a model of acute inflammation and were shown to exhibit potent anti-inflammatory properties, significantly decreasing neutrophil infiltration in vivo. The most potent among these was compound 9 (o-[9,12]-benzo-15-epi-LXA(4) methyl ester. Taken together, these findings help identify a new class of stable and easily prepared LX analogs that may serve as novel tools and as promising leads for new anti-inflammatory agents with improved therapeutic profile.

Protective effects of BML-111, a lipoxin A(4) receptor agonist, on carbon tetrachloride-induced liver injury in mice

BACKGROUND

Lipoxins (LX) are trihydroxytetraene-containing eicosanoids that display unique anti-inflammatory and pro-resolving actions during various inflammatory conditions, but the pathophysiological significance of LX in liver disorders remains unknown.

METHODS

In the present study, we used a murine model of carbon tetrachloride (CCl(4))-induced acute liver injury to investigate the effects of LX on the progression of acute liver injury.

RESULTS

The results indicated that the lipoxin A(4) receptor (ALX) was upregulated after giving CCl(4). BML-111, a commercially available ALX agonist, effectively protected the liver from CCl(4)-induced injury as evidenced by decreased serum aminotransferase (ALT, AST) levels and improved histological damage. The dampened liver injury was accompanied byreduced malondialdehyde (MDA) content in liver homogenates and decreased concentration of tumor necrosis factor-alpha (TNF-alpha) in the serum. Most interestingly, BML-111 markedly upregulated hepatic heme oxygenase-1 (HO-1) expression in CCl(4)-treated mice, which might provide antioxidative activities in the liver.

CONCLUSION

These data indicate that ALX agonist BML-111 plays a critical protective role in CCl(4)-induced acute liver injury through limiting the inflammatory response and promoting antioxidative protein expression.

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

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

Lipoxin A4 inhibits connective tissue growth factor-induced production of chemokines in rat mesangial cells

Connective tissue growth factor (CTGF) is involved in mitogenesis, matrix production, and chemotaxis in mesenchymal cells. The effects of CTGF on the production of chemokines remain unclear. The present studies investigate the regulatory role of CTGF in the production of fractalkine, monocyte chemoattractant protein-1 (MCP-1), and RANTES (regulated upon activation, normal T cell expressed and secreted) in cultured mesangial cells of rats, and the modulatory effects of lipoxin A(4) (LXA(4)) on actions of CTGF. CTGF enhanced the mRNA expression and protein release of fractalkine, MCP-1, and RANTES, the expression of phospho (P)-p42/44 mitogen-activated protein kinase (MAPK), P-phosphoinositide 3-kinase (PI3-K), P-Akt, and activity of nuclear factor-kappaB (NF-kappaB) in mesangial cells. P-p42/44 MAPK blockade inhibited the CTGF-induced expression of P-p42/44 MAPK but not NF-kappaB, and partially decreased the levels of the above chemokines in supernatants. P-PI3-K blockade downregulated the CTGF-stimulated expression of P-PI3-K, P-Akt, and NF-kappaB but not P-p42/44 MAPK, and partially decreased the release of the above chemokines. NF-kappaB blockade abrogated the CTGF-activated NF-kappaB and partially decreased the secretion of the above chemokines. LXA(4) dose-dependently inhibited the CTGF-stimulated mRNA expression and protein release of the above chemokines, and the expression of P-p42/44MAPK, P-PI3-K, P-Akt, and NF-kappaB. In conclusion, these results demonstrate that CTGF induces production of fractalkine, MCP-1, and RANTES via the p42/44 MAPK-, PI3-K/Akt-, and NF-kappaB-dependent signal pathway, and LXA(4) downregulates the above effects of CTGF on rat mesangial cells.

Design, synthesis and bioactions of novel stable mimetics of lipoxins and aspirin-triggered lipoxins

The lipoxins (LX) are a class of potent endogenous oxygenated products that are enzymatically generated from arachidonic acid and have novel anti-inflammatory properties and promote resolution. Elucidation of the biochemical pathways involved in the metabolic inactivation of LX and the discovery of the aspirin-triggered lipoxins (ATL) provided the basis for the design and synthesis of stable analogs of LX and ATL. This special issue review describes the efforts that led to the design and synthesis of stable LX/ATL mimetics, which permitted the detailed elucidation of their novel biological roles, leading to the development of new anti-inflammatory agents that mimic their actions. These synthetic molecules provided the means to uncover the physiologic roles of both the LX and the ATL biosynthetic pathways which led to several unexpected discoveries. Among these findings is the involvement of polyisoprenyl phosphates (PIPP) in intracellular signaling mediated by presqualene diphosphate (PSDP), and the recognition of the novel roles of these lipid mediators in regulating cell trafficking during inflammation as well as in promoting resolution of inflammatory processes. These efforts also provided the basis for examining the potential therapeutic role of LX/ATL stable mimetics and led to the development of new analogs with improved pharmacokinetics that opened the way to potentially new approaches to treating human diseases.

Liver: the formation and actions of aspirin-triggered lipoxins

Eicosanoids play a key role in the initiation, progression and resolution of the inflammatory response. Although most current anti-inflammatory strategies are focused on the pharmacological inhibition of pro-inflammatory eicosanoids, such as prostaglandins and leukotrienes, mounting evidence indicates the existence of potent endogenous eicosanoids able to control inflammation and orchestrate its resolution. The first eicosanoids recognized as anti-inflammatory compounds generated by our own organism were the lipoxins (LXs). More recently, a new series of carbon-15 epimers of LXs, with anti-inflammatory properties similar to those of native LXs, was identified during aspirin treatment. Since their formation is specific to this venerable non-steroidal anti-inflammatory drug, the term aspirin-triggered LXs (ATLs) was coined for these compounds. This chapter deals with the biosynthesis of LXs and ATLs in the liver, the largest solid organ/gland in the body, and discusses the most relevant actions of these lipid mediators in the context of liver inflammation and injury.

Cystic fibrosis and lipoxins

Dysregulated neutrophilic inflammation and chronic infection lead to progressive destruction of the airways in cystic fibrosis (CF). Despite considerable recent progress in therapy, the median survival of patients with CF remains around 30 years. The lipoxins are endogenous anti-inflammatory lipid mediators that are important regulators of neutrophilic inflammation. Recent data indicate that there is a pathophysiologically important defect in lipoxin-mediated anti-inflammatory activity in the CF airway, suggesting novel approaches to pathogenesis and therapy in this lethal genetic disease.

Lipoxin A4 inhibits TNF-α-induced production of interleukins and proliferation of rat mesangial cells

BACKGROUND

Studies have shown that lipoxin A(4) (LXA(4)) and its analogues inhibited proliferation of glomerular mesangial cells induced by leukotriene D(4) (LTD(4)) or platelet-derived growth factor (PDGF), reduced the production of proinflammatory cytokines such as interleukin (IL)-1beta and IL-6 in renal tissue of ischemic injury. In the present studies, we examine whether LXA(4) have inhibitory effects on tumor necrosis factor-alpha (TNF-alpha)-induced productions of IL-1beta and IL-6 and proliferation of glomerular mesangial cells of rat, and explore the molecular mechanisms of signal pathway of LXA(4).

METHODS

Cultured glomerular mesangial cells were treated with TNF-alpha (10 ng/mL), with or without preincubation with LXA(4) at the different concentrations. Cell proliferation was assessed by [(3)H]-thymidine incorporation. Proteins of IL-1beta and IL-6 in supernatant were analyzed by enzyme-linked immunosorbent assay (ELISA). Expressions of mRNA of IL-1beta and IL-6 were determined by real-time polymerase chain reaction (PCR) and cyclin E by reverse transcription (RT)-PCR. Proteins of cyclin E, threonine phosphorylated Akt(1) at 308 site (Thr(308)) and p27(kip1) were analyzed by Western blotting studies. Activities of signal transducers and activators of transcription-3 (STAT(3)), nuclear factor-kappaB (NF-kappaB) were determined by electrophroretic mobility shift assay (EMSA). Expression of Src homology (SH) 2-containing protein-tyrosine phosphatase (SHP-2) was assessed by immunoprecipitation and immunoblotting.

RESULTS

TNF-alpha-stimulated proliferation, release of proteins and expressions of mRNA of IL-1beta and IL-6 in mesangial cells were inhibited by LXA(4) in a dose-dependent manner. The marked increments in mRNA expression and protein synthesis of cyclin E induced by TNF-alpha in parallel with proliferation of mesangial cells were down-regulated by LXA(4). LXA(4) antagonized the phosphorylation of SHP-2 and activity of NF-kappaB induced by TNF-alpha. Pretreatment of the cells with NF-kappaB inhibitor pyrrolidine dithio-carbamate (PDTC) blocked the productions of IL-1beta, IL-6, and activation of NF-kappaB induced by TNF-alpha. Stimulation of mesangial cells with TNF-alpha resulted in enhanced DNA-binding activity of STAT(3). This increment was inhibited by LXA(4) in a dose-dependent manner. Threonine phosphorylated Akt(1) protein at 308 site stimulated by TNF-alpha was reduced by LXA(4.) TNF-alpha-induced decrement in expression of p27(kip1) protein was ameliorated by LXA(4) in a dose-dependent manner.

CONCLUSION

TNF-alpha-induced proliferation and increment of cyclin E of rat mesangial cells can be inhibited by LXA(4), and these inhibitory effects might be through the mechanisms of STAT(3) and Akt(1)/p27(kip1) pathway-dependent signal transduction. LXA(4) also antagonized TNF-alpha-stimulated IL-1beta and IL-6 synthesis, and these antagonisms were related to SHP-2 and NF-kappaB pathway-dependent signal transduction.

Vanilloid receptor 1 antagonists attenuate disease severity in dextran sulphate sodium-induced colitis in mice

Neurogenic mechanisms have been implicated in the induction of inflammatory bowel disease (IBD). Vanilloid receptor type 1 (TRPV1) has been visualized on nerve terminals of intrinsic and extrinsic afferent neurones innervating the gastrointestinal tract and local administration of a TRPV1 antagonist, capsazepine, reduces the severity of dextran sulphate sodium (DSS)-induced colitis in rats (Gut 2003; 52: 713-9(1)). Our aim was to test whether systemically or orally administered TRPV1 antagonists attenuate experimental colitis induced by 5% DSS in Balb/c mice. Intraperitoneal capsazepine (2.5 mg kg(-1), bid), significantly reduced the overall macroscopic damage severity compared with vehicle-treated animals (80% inhibition, P < 0.05); however, there was no effect on myeloperoxidase (MPO) levels. An experimental TRPV1 antagonist given orally was tested against DSS-induced colitis, and shown to reverse the macroscopic damage score at doses of 0.5 and 5.0 mg kg(-1). Epithelial damage assessed microscopically was significantly reduced. MPO levels were attenuated by approximately 50%, and diarrhoea scores were reduced by as much as 70%. These results suggest that pharmacological modulation of TRPV1 attenuates indices of experimental colitis in mice, and that development of orally active TRPV1 antagonists might have therapeutic potential for the treatment of IBD.

Lipoxins in asthma: potential therapeutic mediators on bronchial inflammation?

Arachidonic acid metabolism represents an important source of mediators with ambivalent actions. Among these, lipoxins (LXs) are the first agents identified and recognized as anti-inflammatory endogenous lipid mediators, which are involved in the resolution of inflammation and are present in the airways of asthmatic patients. Lipoxins result mainly from the interaction between 5 and 15-lipoxygenases (LO) and their levels are modulated by the degree of bronchial inflammation as well as by the long-term glucocorticoid treatments. In the airways, LX synthesis is higher in mild asthmatics than in severe asthmatics, whereas in vitro chemokine release inhibition by LXs is more effective in cells from severe asthmatics than from mild asthmatics. LipoxinA(4) effects on interleukin (IL)-8 released by blood mononuclear cells and on calcium influx in epithelial cells are mediated by the specific receptor ALX. Lipoxin generation by lung epithelial cells depends mainly on 15-LO activity. Mild asthmatics present higher 15-LOb expression at the epithelium level than severe patients, whereas the LX deficit in severe asthma is associated with an up-regulation of the 15-LOa expressions. Therefore, bronchial epithelial cells become a target for therapeutic intervention and LXs represent a potential therapeutic solution for bronchial inflammation resolution in asthma.

Reduction of the multiple organ injury and dysfunction caused by endotoxemia in 5-lipoxygenase knockout mice and by the 5-lipoxygenase inhibitor zileuton

The role of 5-lipoxygenase (5-LOX) in the pathophysiology of the organ injury/dysfunction caused by endotoxin is not known. Here, we investigate the effects of treatment with 5-LOX inhibitor zileuton in rats and targeted disruption of the 5-LOX gene in mice (5-LOX(-/-)) on multiple organ injury/dysfunction caused by severe endotoxemia. We also investigate the expression of beta2-integrins CD11a/CD18 and CD11b/CD18 on rat leukocytes by flow cytometry. Zileuton [3 mg/kg intravenously (i.v.)] or vehicle (10% dimethyl sulfoxide) was administered to rats 15 min prior to lipopolysaccharide (LPS; Escherichia coli, 6 mg/kg i.v.) or vehicle (saline). 5-LOX(-/-) mice and wild-type littermate controls were treated with LPS (E. coli, 20 mg/kg intraperitoneally) or vehicle (saline). Endotoxemia for 6 h in rats or 16 h in mice resulted in liver injury/dysfunction (increase in the serum levels of aspartate aminotransferase, alanine aminotransferase, gamma-glutamyl transferase, alkaline phosphatase, bilirubin), renal dysfunction (creatinine), and pancreatic injury (lipase, amylase). Absence of functional 5-LOX (zileuton treatment or targeted disruption of the 5-LOX gene) reduced the multiple organ injury/dysfunction caused by endotoxemia. Polymorphonuclear leukocyte infiltration (myeloperoxidase activity) in the lung and ileum as well as pulmonary injury (histology) were markedly reduced in 5-LOX(-/-) mice. Zileuton also reduced the LPS-induced expression of CD11b/CD18 on rat leukocytes. We propose that endogenous 5-LOX metabolites enhance the degree of multiple organ injury/dysfunction caused by severe endotoxemia by promoting the expression of the adhesion molecule CD11b/CD18 and that inhibitors of 5-LOX may be useful in the therapy of the organ injury/dysfunction associated with endotoxic shock.

Reduction of Renal Ischemia-Reperfusion Injury in 5-Lipoxygenase Knockout Mice and by the 5-Lipoxygenase Inhibitor Zileuton

The role of 5-lipoxygenase (5-LOX) in the pathophysiology of renal ischemia/reperfusion (I/R) injury is not known. Here we investigate the effects of 1) the 5-LOX inhibitor zileuton and 2) 5-LOX gene knockout (5-LOX(-/-)) mice on renal dysfunction and injury caused by I/R of the kidney in mice. Wild-type mice treated with zileuton (3 mg/kg i.v.) or 5-LOX(-/-) mice were subjected to bilateral renal artery occlusion (30 min) followed by reperfusion (24 h). Plasma urea, creatinine, and aspartate aminotransferase (AST) were measured as markers of renal dysfunction and reperfusion injury. Kidneys were used for histological evaluation of renal injury. Renal myeloperoxidase activity was measured and used as an indicator of polymorphonuclear leukocyte (PMN) infiltration and renal expression of intercellular adhesion molecule-1 (ICAM-1) was determined using immunohistochemistry. Administration of zileuton before I/R significantly reduced the degree of renal dysfunction (urea, creatinine) and injury (AST, histology). In addition, zileuton reduced the expression of ICAM-1 and the associated PMN infiltration caused by I/R of the mouse kidney. Compared with wild-type mice, the degree of renal dysfunction, injury, and inflammation caused by I/R in 5-LOX(-/-) mice was also significantly reduced, confirming the pathophysiological role of 5-LOX in the development of renal I/R injury. We propose that 1) endogenous 5-LOX metabolites enhance the degree of renal injury, dysfunction, and inflammation caused by I/R of the kidney by promoting the expression of adhesion molecules, and 2) inhibitors of 5-LOX may be useful in the treatment of conditions associated with I/R of the kidney.

Lipoxins: Potential anti-inflammatory, proresolution, and antifibrotic mediators in renal disease

Lipoxins are lipoxygenase-derived lipid mediators with both anti-inflammatory and proresolution properties that have been demonstrated in vivo and in vitro. The bioactivity profile of lipoxins in vitro suggests that they have therapeutic potential in acute renal failure and glomerulonephritis; predictions that have been borne out to date in experimental models of renal disease. We review recent developments on the molecular basis of lipoxin bioactions mediated through receptor crosstalk and the accumulating evidence that lipoxins may have potential as novel anti-inflammatory agents.

Lipoxins: endogenous regulators of inflammation

Over the past decade, compelling in vivo and in vitro studies have highlighted lipoxins (LXs) and aspirin-triggered LXs (ATLs) as endogenously produced anti-inflammatory eicosanoids. LXs and ATLs elicit distinct anti-inflammatory and proresolution bioactions that include inhibition of leukocyte-mediated injury, stimulation of macrophage clearance of apoptotic neutrophils, repression of proinflammatory cytokine production, modulation of cytokine-stimulated metalloproteinase activity, and inhibition of cell proliferation and migration. An overview of recent advances in LX physiology is provided, with particular emphasis on the cellular and molecular processes involved. These data coupled with in vivo models of inflammatory diseases suggest that LX bioactions may be amenable to pharmacological mimicry for therapeutic gain.