Synthesis Of Lipoxins Research Articles

Promising Anti-Inflammatory Tools: Biomedical Efficacy of Lipoxins and Their Synthetic Pathways.

Lipoxins (LXs) have attracted widespread attention as a class of anti-inflammatory lipid mediators that are produced endogenously by the organism. LXs are arachidonic acid (ARA) derivatives that include four different structures: lipoxin A4 (LXA4), lipoxin B4 (LXB4), and the aspirin-induced differential isomers 15-epi-LXA4 and 15-epi-LXB4. Because of their unique biological activity of reducing inflammation in the body, LXs have great potential for neuroprotection, anti-inflammatory treatment of COVID-19, and other related diseases. The synthesis of LXs in vivo is achieved through the action of lipoxygenase (LO). As a kind of important enzyme, LO plays a major role in the physiological processes of living organisms in mammals and functions in some bacteria and fungi. This suggests new options for the synthesis of LXs in vitro. Meanwhile, there are other chemical and biochemical methods to synthesize LXs. In this review, the recent progress on physiological activity and synthetic pathways of LXs is summarized, and new insights into the synthesis of LXs in vitro are provided.

Role of aspirin-triggered lipoxin A4, aspirin, and salicylic acid in the modulation of the oxidative and inflammatory responses induced by plasma from women with pre-eclampsia.

Oxidative stress and inflammation are key events leading to pre-eclampsia, involved in several maternal deaths. Low doses of acetylsalicylic acid (ASA) are used in the prevention and treatment of pre-eclampsia. The synthesis of aspirin-triggered lipoxin (ATL) by cyclooxygenase-2 acetylation is an alternative mechanism of ASA, which could explain the effectiveness of ASA treatments. The aim of this study was to evaluate the role of ASA, salicylates, and ATL in the modulation of the oxidative and inflammatory responses induced by plasma from women with pre-eclampsia. Plasma from 14 women with pre-eclampsia and 17 normotensive pregnant women was probed for inducing oxidative and inflammatory responses on endothelial cells and U937 promonocytes. The role of ATL, ASA, and salicylic acid (SA) on these events was evaluated. Plasma from women with pre-eclampsia induced TBARS and nitrotyrosine production on endothelial and U937 cells. Pre-treatment with both ATL and ASA decreased the TBARS production, while ATL decreased the nitrotyrosine. Pre-eclamptic plasma augmented the translocation of NF-kB on U937 cells, which decreased by a high dose of ASA and SA. Finally, the pre-eclamptic plasma increased the adhesion of leukocytes-PMN and monocytes-to endothelium, and we were able to determine a state of resolution of inflammation, since ATL decreased the PMN adhesion, and conversely, it increased the monocytes adhesion to endothelium. Together, these results suggest that ATL could explain the beneficial actions of ASA and support further research on mechanisms, real efficacy, and rational use of ASA in pre-eclampsia.

Structural Dynamics of 15-Lipoxygenase-2 via Hydrogen-Deuterium Exchange.

Eicosanoids are inflammatory signaling lipids that are biosynthesized in response to cellular injury or threat. They were originally thought to be pro-inflammatory molecules, but members of at least one subclass, the lipoxins, are able to resolve inflammation. One step in lipoxin synthesis is the oxygenation of arachidonic acid by 15-lipoxygenase (15-LOX). 15-LOX contains two domains: a Ca2+ binding PLAT domain and a catalytic domain. 15-LOX is a soluble cytosolic protein until binding of Ca2+ to the PLAT domain promotes translocation to the membrane surface. The role of 15-LOX structural dynamics in this translocation has remained unclear. We investigated the dynamics of 15-LOX isoform B (15-LOX-2) upon binding of Ca2+ and ligands, as well as upon membrane association using hydrogen–deuterium exchange mass spectrometry (HDX-MS). We used HDX-MS to probe the solvent accessibility and backbone flexibility of 15-LOX-2, revealing significant differences in deuterium incorporation between the PLAT and catalytic domains, with the PLAT domain demonstrating higher flexibility. Comparison of HDX for 15-LOX-2 in the presence and absence of Ca2+ indicates there are few differences in structural dynamics. Furthermore, our HDX results involving nanodisc-associated 15-LOX-2 suggest that significant structural and dynamic changes in 15-LOX-2 are not required for membrane association. Our results also show that a substrate lipid binding to the active site in the catalytic domain does induce changes in incorporation of deuterium into the PLAT domain. Overall, our results challenge the previous hypothesis that Ca2+ binding induces major structural changes in the PLAT domain and support the hypothesis that is interdomain communication in 15-LOX-2.

Phospholipase A2 regulates eicosanoid class switching during inflammasome activation.

Initiation and resolution of inflammation are considered to be tightly connected processes. Lipoxins (LX) are proresolution lipid mediators that inhibit phlogistic neutrophil recruitment and promote wound-healing macrophage recruitment in humans via potent and specific signaling through the LXA4 receptor (ALX). One model of lipoxin biosynthesis involves sequential metabolism of arachidonic acid by two cell types expressing a combined transcellular metabolon. It is currently unclear how lipoxins are efficiently formed from precursors or if they are directly generated after receptor-mediated inflammatory commitment. Here, we provide evidence for a pathway by which lipoxins are generated in macrophages as a consequence of sequential activation of toll-like receptor 4 (TLR4), a receptor for endotoxin, and P2X7, a purinergic receptor for extracellular ATP. Initial activation of TLR4 results in accumulation of the cyclooxygenase-2-derived lipoxin precursor 15-hydroxyeicosatetraenoic acid (15-HETE) in esterified form within membrane phospholipids, which can be enhanced by aspirin (ASA) treatment. Subsequent activation of P2X7 results in efficient hydrolysis of 15-HETE from membrane phospholipids by group IVA cytosolic phospholipase A2, and its conversion to bioactive lipoxins by 5-lipoxygenase. Our results demonstrate how a single immune cell can store a proresolving lipid precursor and then release it for bioactive maturation and secretion, conceptually similar to the production and inflammasome-dependent maturation of the proinflammatory IL-1 family cytokines. These findings provide evidence for receptor-specific and combinatorial control of pro- and anti-inflammatory eicosanoid biosynthesis, and potential avenues to modulate inflammatory indices without inhibiting downstream eicosanoid pathways.

Differential Gene Expression in Thrombomodulin (TM; CD141)+ and TM− Dendritic Cell Subsets

Previously we have shown in a mouse model of bronchial asthma that thrombomodulin can convert immunogenic conventional dendritic cells into tolerogenic dendritic cells while inducing its own expression on their cell surface. Thrombomodulin+ dendritic cells are tolerogenic while thrombomodulin− dendritic cells are pro-inflammatory and immunogenic. Here we hypothesized that thrombomodulin treatment of dendritic cells would modulate inflammatory gene expression. Murine bone marrow-derived dendritic cells were treated with soluble thrombomodulin and expression of surface markers was determined. Treatment with thrombomodulin reduces the expression of maturation markers and increases the expression of TM on the DC surface. Thrombomodulin treated and control dendritic cells were sorted into thrombomodulin+ and thrombomodulin− dendritic cells before their mRNA was analyzed by microarray. mRNAs encoding pro-inflammatory genes and dendritic cells maturation markers were reduced while expression of cell cycle genes were increased in thrombomodulin-treated and thrombomodulin+ dendritic cells compared to control dendritic cells and thrombomodulin− dendritic cells. Thrombomodulin-treated and thrombomodulin+ dendritic cells had higher expression of 15-lipoxygenase suggesting increased synthesis of lipoxins. Thrombomodulin+ dendritic cells produced more lipoxins than thrombomodulin− dendritic cells, as measured by ELISA, confirming that this pathway was upregulated. There was more phosphorylation of several cell cycle kinases in thrombomodulin+ dendritic cells while phosphorylation of kinases involved with pro-inflammatory cytokine signaling was reduced. Cultures of thrombomodulin+ dendritic cells contained more cells actively dividing than those of thrombomodulin− dendritic cells. Production of IL-10 is increased in thrombomodulin+ dendritic cells. Antagonism of IL-10 with a neutralizing antibody inhibited the effects of thrombomodulin treatment of dendritic cells suggesting a mechanistic role for IL-10. The surface of thrombomodulin+ dendritic cells supported activation of protein C and procarboxypeptidase B2 in a thrombomodulin-dependent manner. Thus thrombomodulin treatment increases the number of thrombomodulin+ dendritic cells, which have significantly altered gene expression compared to thrombomodulin− dendritic cells in key immune function pathways.

Manifold beneficial effects of acetyl salicylic acid and nonsteroidal anti-inflammatory drugs on sepsis

Acetyl salicylic acid (ASA) and nonsteroidal anti-inflammatory drugs (NSAIDs) may have potential as adjunctive agents for sepsis. This review considers the large body of literature that indicates a basis for sepsis therapy with ASA and suggests an agenda for future intervention studies in sepsis prevention and treatment. ASA and NSAIDs have beneficial effects in numerous experimental models of sepsis. Low doses of ASA of 100 mg/day or less trigger synthesis of lipoxins that are anti-inflammatory and aid in resolution of inflammation. Higher doses of ASA and NSAIDs act to reduce NF-κB stimulation and inhibit numerous septic pathways. While a previous randomised controlled trial of ibuprofen failed to show a reduction in mortality in sepsis, it did reduce clinical manifestations of sepsis. More recent observational studies have shown reduction in sepsis or acute lung injury leading to lower mortality in ICU patients treated with ASA. Low-dose ASA appears to be beneficial in the prevention and treatment of sepsis and SIRS. If proven, this intervention would have a major, cost-effective impact on sepsis care.

The 12/15-lipoxygenase pathway counteracts fibroblast activation and experimental fibrosis

BackgroundIdiopathic and inflammation-dependent fibrotic diseases such systemic sclerosis (SSc) impose a major burden on modern societies. Understanding endogenous mechanisms, which counteract fibrosis, may yield new therapeutic approaches. Lipoxins are highly...

Lipoxygenase-Derived Arachidonic Acid Metabolites in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is characterized by a persistence of inflammation in large and small airways. We hypothesized that this could be caused by the inability of an inflammatory process to resolve. In the resolution of inflammation, a switching of arachidonic acid metabolism from the production of proinflammatory leukotriene B(4) (LtB(4)) to the synthesis of anti-inflammatory lipoxins plays an important role. The aim of our study was to determine the content of lipoxin A(4) (LXA(4)) and LtB(4) in induced sputum of patients with exacerbated COPD and to compare it to healthy controls, as well as to analyze the relationship between proinflammatory and anti-inflammatory mediators and an inflammatory cell spectrum in induced sputum. Induced sputum from 17 COPD patients and 7 healthy controls were analyzed for LXA(4) and LtB(4) content and inflammatory cell spectrum. COPD patients had a significantly lower sputum LXA(4) concentration and LtB(4)/LXA(4) ratio compared with healthy controls. A significant negative correlation was found between the LXA(4) concentration and the relative neutrophil count and between the LtB(4)/LXA(4) ratio and the relative macrophage count. COPD patients during the late phase of exacerbation had a suppressed production of LXA(4) and an elevated LtB(4)/LXA(4) ratio in induced sputum demonstrating a proinflammatory imbalance. The correction of a balance between proinflammatory and anti-inflammatory eicosanoids by the administration of stable analogues of lipoxins could improve the treatment of chronic obstructive pulmonary disease in the future.

Genetic Mechanisms in Aspirin-Exacerbated Respiratory Disease

Aspirin-exacerbated respiratory disease (AERD) refers to the development of bronchoconstriction in asthmatics following the exposure to aspirin or other nonsteroidal anti-inflammatory drugs. The key pathogenic mechanisms associated with AERD are the overproduction of cysteinyl leukotrienes (CysLTs) and increased CysLTR1 expression in the airway mucosa and decreased lipoxin and PGE2 synthesis. Genetic studies have suggested a role for variability of genes in disease susceptibility and the response to medication. Potential genetic biomarkers contributing to the AERD phenotype include HLA-DPB1, LTC4S, ALOX5, CYSLT, PGE2, TBXA2R, TBX21, MS4A2, IL10, ACE, IL13, KIF3A, SLC22A2, CEP68, PTGER, and CRTH2 and a four-locus SNP set composed of B2ADR, CCR3, CysLTR1, and FCER1B. Future areas of investigation need to focus on comprehensive approaches to identifying biomarkers for early diagnosis.

Antioxidant Properties and Associated Mechanisms of Salicylates

The pharmacological action of salicylates has been historically related to their ability to inhibit cyclooxygenases, thereby blocking the synthesis of prostaglandins and thromboxane A2. On the other hand, several studies have suggested that salicylates have a multitude of cyclooxygenase-independent actions specially related with their antioxidant properties, which might contribute to the overall salutary effects of these compounds. Although salicylates are well-known antioxidants through their ability to scavenge hydroxyl radical, their antioxidant mechanisms of action have not been fully compiled and characterized. In this context, several mechanisms of action have been suggested, namely i) scavenging of hydroxyl radical and chelation of transition metals; ii) upregulation of nitric oxide; iii) increased synthesis of lipoxins; iv) inhibition of neutrophil oxidative burst; v) inhibition of NF-κB and AP-1 protein kinases; and vii) inhibiton of lectin-like oxidized LDL receptor-1. The newly discovered acetyl salicylic acid-triggered lipoxins probably play a key role in the maintenance of the oxidative stress balance. Furthermore, salicylates have shown to protect low-density lipoprotein from oxidation and elicit an inhibitory effect on the expression of lectin-like receptors on endothelial cells. This review aims to provide an overview of the various proposed antioxidant mechanisms of salicylates.

Lipoxins, The Novel Mediators of Gastroprotection and Gastric Adaptation to Ulcerogenic action of Aspirin

Previous studies revealed that prostaglandins contribute to the mechanism of maintenance of gastrointestinal integrity and mediate various physiological aspects of mucosal defense. The suppression of prostaglandin synthesis in the stomach is a critical event in terms of the development of mucosal injury after administration of various NSAID including aspirin (ASA). A worldwide use of ASA is now accepted due to its remarkable analgesic, antipyretic and anti-thrombotic prophylactics against myocardial infarct and coronary disorders despite the fact that the use of NSAIDs is associated with the risk of gastrointestinal bleedings, haemorrhagic lesions and ulcerations. It has become clear that other mediators besides prostaglandins can similarly act to protect the gastrointestinal mucosa of experimental animals and humans from injury induced by ASA. For instance, nitric oxide (NO) released from vascular epithelium, epithelial cells of gastrointestinal tract and sensory nerves can influence many of the same components of mucosal defense as do prostaglandins. This review was designed to provide an updated overview based on the experimental and clinical evidence on the involvement COX-2 derived products, lipoxins in the mechanism of gastric defense, gastroprotection and gastric adaptation to ASA. Lipoxins were recently considered as another group of lipid mediators that can protect the stomach similarly as NO-donors known to exert protective influence on the stomach from the injury under condition where the mucosal prostaglandin levels are suppressed. The new class of NO-releasing NSAIDs, including NO-aspirin or NO-naproxen, represent a very promising approach to reducing the toxicity of their parent NSAIDs. Aspirin-triggered lipoxin (ATL) synthesis, via COX-2, acts to reduce the severity of damage induced by this NSAID. Lipoxin analogues may prove to be useful for preventing mucosal injury and for modulating mucosal inflammation. Evidence presented in this review documents that ATL also play in important role in gastric adaptation during chronic ASA administration. Suppression of COX-2 activity by selective COX-2 inhibitors such as rofecoxib or celecoxib was shown to abolish the production of ATL and to diminish the gastric tolerability of ASA and gastric adaptation developed in response to repetitive administration of this NSAID. Synthetic analogues of lipoxins as well as newer class of NSAIDs releasing NO may be used in the future as the therapeutic approach to counteract adverse effects in the stomach associated with NSAIDs ingestion.

Editorial [Hot Topic: Emerging Drugs in Gastrointestinal Tract (Executive Guest Editor: Predrag Sikiric)

There is little doubt that the pathogenesis of gastrointestinal disorders, diagnosis as well as the therapy is a pertinent scientific focus and one of the largest and most intriguing areas in medicine. Likewise, it has been generally accepted that most of the therapy and understanding of pathophysiology in the gastrointestinal tract is well and should be validated in clinical practice. Therefore, there is still an open door for one or more new ways. Hopefully, the most recent findings may provide a new insight into future developments. In this, I hope, in scope of Emerging Drugs in Gastrointestinal Tract, these papers may contribute a new view that may likely improve the future understanding of pathogenesis and therapy in gastrointestinal tract. In this issue, Yanaka (Faculty of Pharmaceutical Sciences, Tokyo University of Science, Japan) reviewed cellular mechanisms by which the nrf2-keap1 system contributes to induction of a variety of antioxidant enzymes during exposure to oxidative stress and introduced the beneficial effects of sulforaphane, an isothiocyanate family, rich in broccoli sprouts, on the gastric mucosa through such mechanisms [1]. Brzozowski and collaborators (Jagiellonian University Medical College, Cracow, Poland and Thuringia-Clinic, Saalfeld, Germany) reviewed COX-2 derived products, “lipoxins” in the mechanism of gastric mucosal defense. Aspirin-triggered lipoxin synthesis via COX-2 plays also an important role in gastric adaptation during chronic aspirin administration, in addition to the mechanism of injury, gastroprotection and healing of acute and chronic gastric ulcers in the gut [2]. Chen and Zhao (Norwegian University of Science and Technology, Trondheim, Norway)reviewed gut-bone axis, based on the various factors affecting bone mass, an issue that may be particularly important. They examined critically the influence of ; acid, serotonin, lowdensity lipoprotein receptor-related protein5, etc, affecting bone mass. They concluded that evidence still could not completely prove a close relationship between these factors and bone mass [3]. Historically, the phenomenon of “cytoprotection” caused a big impact to many GI investigators, like “an epoch-making finding”, and although caused major impacts on GI research & development, the current clinic did not gain adequate advantage. In this, Mozsik (University of Pecs, Hungary) extensively reviewed gastrointestinal cytoprotection (at the level of isolated cells, animal experiments, healthy human beings and patients with different gastrointestinal disorders), including the historic lookback, reviewing the huge range of agents supposed to be involved in cytoprotection [4]. Wood (The Ohio State University College of Medicine Columbus, Ohio, USA)focused on chronic functional abdominal and pelvic pain syndromes. Within the scope of Visceral Pain: Spinal Afferents, Enteric Mast Cells, Enteric Nervous System and Stress, Wood reviews and expands the understanding of visceral hypersensitivity and functional abdominal pain of intestinal origin in relation to the enteric nervous system, spinal sensory neurons and enteric mast cells [5]. Until recently, fat was considered a relatively inactive tissue serving only as a depot for the storage of excess lipid around the body. Over the last decade, however, several studies have established fat as a metabolically active endocrine organ able to affect human pathophysiology at multiple levels. Karagainides and collaborators (David Geffen School of Medicine at the University of California Los Angeles, USA) reviewed the potential pathways by which changes in fat physiology may affect the development and progress of intestinal pathological conditions such as inflammatory bowel disease, and especially discussed the central role of neuropeptides in the pathogenesis and course of inflammatory bowel disease, via adipose tissue associated responses as well as the potential crosstalk between obesity-associated fat tissue and neuropeptides [6]. The role of constitutive and inducible antibacterial peptides has been investigated thoroughly over the recent years ; especially in the gastrointestinal tract, where the balance between luminal bacteria and antibacterial peptides is crucial. Wong and collaborators (The Chinese University of Hong Kong, Shatin, Hong Kong, China) focused on and emphasized the role of defensins and cathelicidins, two of the most popular mammalian antibacterial peptides (produced by neutrophils and epithelial cells and are highly expressed during infection), in gastrointestinal inflammation and cancers as well as other physiological processes such as cell proliferation, wound healing and so on. In addition, they also proposed that the dysregulation of their expressions could be used as a biomarker for early diagnosis, especially for H. pylori-related diseases as well as cancers in the gastrointestinal tract [7]

The structure of human 5-lipoxygenase.

The synthesis of both proinflammatory leukotrienes and anti-inflammatory lipoxins requires the enzyme 5-lipoxygenase (5-LOX). 5-LOX activity is short-lived, apparently in part because of an intrinsic instability of the enzyme. We identified a 5-LOX-specific destabilizing sequence that is involved in orienting the carboxyl terminus, which binds the catalytic iron. Here, we report the crystal structure at 2.4 angstrom resolution of human 5-LOX stabilized by replacement of this sequence.

Leukotriene B4 BLT Receptor Signaling Regulates the Level and Stability of Cyclooxygenase-2 (COX-2) mRNA through Restricted Activation of Ras/Raf/ERK/p42 AUF1 Pathway

Recent studies suggest that active resolution of the inflammatory response in animal models of arthritis may involve leukotriene B(4) (LTB(4))-dependent stimulation of "intermediate" prostaglandin production, which in turn favors the synthesis of "downstream" anti-inflammatory and pro-resolving lipoxins, resolvins, and protectins. We explored a putative mechanism involving LTB(4)-dependent control of cyclooxygenase-2 (COX-2) expression, the rate-limiting step in inflammatory prostaglandin biosynthesis. Indeed, LTB(4) potently up-regulated/stabilized interleukin-1beta-induced COX-2 mRNA and protein expression under conditions of COX-2 inhibitor-dependent blockade of PGE(2) release in human synovial fibroblasts (EC(50) = 16.5 + or - 1.7 nm for mRNA; 19 + or - 2.4 nm for protein, n = 4). The latter response was pertussis toxin-sensitive, and semi-quantitative reverse transcription-PCR confirmed the quantitative predominance of the BLT2 receptor. Transfection experiments, using human COX-2 promoter plasmids and chimeric luciferase-COX-2 mRNA 3'-untranslated region (3'-UTR) reporter constructs, revealed that LTB(4) exerted its stabilizing effect at the post-transcriptional level through a 116-bp adenylate/uridylate-rich sequence in the proximal region of the COX-2 3'-UTR. Using luciferase-COX-2 mRNA 3'-UTR reporter constructs and Ras/c-Raf expression and mutant constructs, we showed that the Ras/c-Raf/MEK1/2/ERK1/2 signaling pathway mediated LTB(4)-dependent COX-2 mRNA stabilization. Knockdown experiments with specific short hairpin RNAs confirmed that LTB(4) stabilization of COX-2 mRNA was apparently mediated through the RNA-binding protein, p42 AUF1. The nuclear export of p42 AUF1 was driven by c-Raf/MEK1/2/ERK1/2 signaling and sensitive to leptomycin B treatment, suggesting a CRM1-dependent mechanism. We conclude that LTB(4) may support the resolution phase of the inflammatory response by stabilizing COX-2, ensuring a reservoir of ambient pro-resolution lipid mediators.

Synthesis of Lipoxin A4by 5-Lipoxygenase Mediates PPARγ-Dependent, Neuroprotective Effects of Rosiglitazone in Experimental Stroke

Peroxisome proliferator-activated receptors gamma (PPARgamma) are nuclear receptors with essential roles as transcriptional regulators of glucose and lipid homeostasis. PPARgamma are also potent anti-inflammatory receptors, a property that contributes to the neuroprotective effects of PPARgamma agonists in experimental stroke. The mechanism of these beneficial actions, however, is not fully elucidated. Therefore, we have explored further the actions of the PPARgamma agonist rosiglitazone in experimental stroke induced by permanent middle cerebral artery occlusion (MCAO) in rodents. Rosiglitazone induced brain 5-lipoxygenase (5-LO) expression in ischemic rat brain, concomitantly with neuroprotection. Rosiglitazone also increased cerebral lipoxin A(4) (LXA(4)) levels and inhibited MCAO-induced production of leukotriene B4 (LTB(4)). Furthermore, pharmacological inhibition and/or genetic deletion of 5-LO inhibited rosiglitazone-induced neuroprotection and downregulation of inflammatory gene expression, LXA(4) synthesis and PPARgamma transcriptional activity in rodents. Finally, LXA(4) caused neuroprotection, which was partly inhibited by the PPARgamma antagonist T0070907, and increased PPARgamma transcriptional activity in isolated nuclei, showing for the first time that LXA(4) has PPARgamma agonistic actions. Altogether, our data illustrate that some effects of rosiglitazone are attributable to de novo synthesis of 5-LO, able to induce a switch from the synthesis of proinflammatory LTB(4) to the synthesis of the proresolving LXA(4). Our study suggests novel lines of study such as the interest of lipoxin-like anti-inflammatory drugs or the use of these molecules as prognostic and/or diagnostic markers for pathologies in which inflammation is involved, such as stroke.

Transgenic fat-1 mouse as a model to study the pathophysiology of cardiovascular, neurological and psychiatric disorders.

Polyunsaturated fatty acids (PUFAs) form an important constituent of all the cell membranes in the body. PUFAs such as arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) form precursors to both pro-inflammatory and anti-inflammatory compounds. Low-grade systemic inflammation occurs in clinical conditions such as insulin resistance, hypertension, type 2 diabetes mellitus, atherosclerosis, coronary heart disease, lupus, schizophrenia, Alzheimer's disease, and other dementias, cancer and non-alcoholic fatty liver disease (NAFLD) that are also characterized by an alteration in the metabolism of essential fatty acids in the form of excess production of pro-inflammatory eicosanoids and possibly, decreased synthesis and release of anti-inflammatory lipoxins, resolvins, protectins and maresins. We propose that low-grade systemic inflammation observed in these clinical conditions is due to an imbalance in the metabolism of essential fatty acids that is more in favour of pro-inflammatory molecules. In this context, transgenic fat-1 mouse that is designed to convert n-6 to n-3 fatty acids could form an ideal model to study the altered metabolism of essential fatty acids in the above mentioned conditions. It is envisaged that low-grade systemic inflammatory conditions are much less likely in the fat-1 mouse and/or these diseases will run a relatively mild course. Identifying the anti-inflammatory compounds from n-3 fatty acids that suppress low-grade systemic inflammatory conditions and understanding their mechanism(s) of action may lead to newer therapeutic strategies.

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-α (TNF-α)-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.

Dual Acting Anti-Inflammatory Drugs

Drugs able to inhibit both cyclooxygenases (COX-1 and COX-2) and 5-lipoxygenase (5-LOX) (dual acting anti-inflammatory drugs) have been designed in order to obtain compounds that retain the activity of classical nonsteroidal anti-inflammatory drugs (NSAIDs) while avoiding their main drawbacks. The classical NSAIDs display their anti-inflammatory action mainly through inhibition of COX and one of their main drawbacks is the curtailed production of gastroprotective prostaglandins (PGs) being associated with the concurrent increased production of the gastro-damaging and bronchoconstrictive leukotrienes (LTs). Leukotrienes and cysteinyl-leukotrienes are moreover pro-inflammatory and increase microvascular permeability. One of the leukotrienes (LTB(4)) is the most potent chemotactic agent and it induces chemotaxis of eosinophils, neutrophils and monocytes in the inflamed tissue, increases superoxide generation and proinflammatory cytokines production. It is further advantageous for a drug to have both COX and 5-LOX inhibiting activities because prostaglandins enhance leukotriene-mediated inflammation. Various structural families of dual inhibitors have been designed and several compounds are currently undergoing clinical development. In the post-COX-2 selective inhibitors era, these dual acting inhibitors may turn out to be promising new drugs to treat inflammatory diseases and possibly other diseases. Indeed, both COX-2 and 5-LOX are also involved in the development and progression of several types of cancer; in these conditions, selective inhibition of COX-2 alone may lead to a shunt of arachidonic acid metabolism towards the leukotriene pathway, and therefore the blockade of both COX-2 and 5-LOX may produce a better anticancer response. In addition, the dual inhibition of both COX and 5-LOX is neuroprotective by suppressing toxic actions of reactive microglia and macrophages, that are increased in aging brain and in age-related degenerative conditions, particularly Alzheimer's and Parkinson's diseases. Finally, the blockade of 5-LOX does not impair the synthesis of lipoxins (LXs), which are mainly produced by further lipoxygenation of 15-HPETE, and which have potent anti-inflammatory properties and can be considered as stop-signal mediators. Leukocyte 15-LOX and platelet 12-LOX by intercellular mechanism via leukocyte/platelet cell-cell interaction convert 15-HPETE into lipoxins.

Uterine transcriptomes of bacteria-induced and ovariectomy-induced preterm labor in mice are characterized by differential expression of arachidonate metabolism genes

The purpose of this study was to identify changes in gene expression that are associated with preterm labor induced by either bacteria or ovariectomy. Pregnant mice (14.5 days of gestation) were allocated to: (1) intrauterine injection of heat-inactivated Escherichia coli; (2) media alone; (3) ovariectomy; or (4) sham operation. The uterine transcriptome was studied with photolithographic, very short oligonucleotide-based microarrays, and arachidonate metabolism genes were assayed with quantitative reverse transcriptase-polymerase chain reaction. Significance was determined by analysis of variance. Microarray-based gene expression changes in the arachidonate metabolism pathway are associated globally with bacteria-induced preterm labor (P < or = .0031) and ovariectomy-induced preterm labor (P < or = .00036). Quantitative real-time reverse transcriptase-polymerase chain reaction measurements demonstrated that bacteria-induced preterm labor substantially increased the expression of genes involved in prostaglandin synthesis. In contrast, ovariectomy-induced preterm labor increased the expression of genes involved in lipoxin, leukotriene, and hydroxyeicosatetraenoic acid synthesis. Bacteria-induced and ovariectomy-induced preterm labor each express a different balance of genes that are required for the synthesis of prostaglandins, lipoxins, leukotrienes, and hydroxyeicosatetraenoic acids.

Myocardial 15-Epi-lipoxin A 4 Generation Provides a New Mechanism for the Immunomodulatory Effects of Statins and Thiazolidinediones

“In matters of observation, chance favors only the prepared mind.” This famous maxim of Louis Pasteur, spoken in 1854 during his inaugural lecture as Professor and Dean at the University of Lille, can be applied today to the fortuitous observation that hydroxymethylglutaryl–coenzyme A (HMG-CoA) reductase inhibitors, in addition to their designed lipid-lowering effects, display a fascinating array of antiinflammatory properties. Post hoc analyses of the West of Scotland Coronary Prevention Study (WOSCOPS) population, and more recently the Cholesterol and Recurrent Events (CARE), Myocardial Ischemia Reduction With Aggressive Cholesterol Lowering (MIRACL), Long-term Intervention With Pravastatin in Ischemic Disease (LIPID), and Heart Protection Study (HPS) trials, have all found benefits conferred by statins that are independent of low-density lipoprotein cholesterol–lowering alone.1 Only through careful analyses of early clinical trials of statins administered for lowering cholesterol and cardiovascular events did scientists uncover additional benefit for these agents in cardiac protection beyond their ability to reduce cholesterol synthesis. Inflammation and immune responses are now appreciated to play pivotal roles in the pathobiology of atherosclerosis,2 and recent clinical and basic investigations have uncovered important immunomodulatory roles for statins.3 Of interest, the peroxisome proliferator-activated receptor family of transcription factors is activated by and cooperates with statins in their antiinflammatory actions. In this issue of Circulation , Birnbaum and colleagues4 present evidence for increased myocardial production of 15-epi-lipoxin (LX)A4 by atorvastatin and the peroxisome proliferator-activated receptor-γ ligand pioglitazone. The generation of 15-epi-LXA4 would provide a novel mechanism for immune regulation by statins because this arachidonic acid–derived chalone displays potent antiinflammatory and proresolving properties,5 including many that have also been observed with statins (Table). View this table: Shared Antiinflammatory Actions of Statins and 15-Epi-lipoxin A4 Article p 929 Cell activation initiates the rapid generation of eicosanoids …