A novel role for lipoxin A4 in driving a lymph node-eye axis that controls autoimmunity to the neuroretina

The eicosanoid lipoxin A4 (LXA4) has emerging roles in lymphocyte-driven diseases. We identified reduced LXA4 levels in posterior segment uveitis patients and investigated the role of LXA4 in the pathogenesis of experimental autoimmune uveitis (EAU). Immunization for EAU with a retinal self-antigen caused selective downregulation of LXA4 in lymph nodes draining the site of immunization, while at the same time amplifying LXA4 in the inflamed target tissue. T cell effector function, migration and glycolytic responses were amplified in LXA4-deficient mice, which correlated with more severe pathology, whereas LXA4 treatment attenuated disease. In vivo deletion or supplementation of LXA4 identified modulation of CC-chemokine receptor 7 (CCR7) and sphingosine 1- phosphate receptor-1 (S1PR1) expression and glucose metabolism in CD4+ T cells as potential mechanisms for LXA4 regulation of T cell effector function and trafficking. Our results demonstrate the intrinsic lymph node LXA4 pathway as a significant checkpoint in the development and severity of adaptive immunity.

Fair-Weather Friends: Evidence of Lipoxin Dysregulation in Neurodegeneration

Lipoxins (LXs) are autacoids, specialized proresolving lipid mediators (SPMs) acting locally in a paracrine or autocrine fashion. They belong to a complex superfamily of dietary small polyunsaturated fatty acid (PUFA)-metabolites, which direct potent cellular responses to resolve inflammation and restore tissue homeostasis. Together, these SPM activities have been intensely studied in systemic inflammation and acute injury or infection, but less is known about LX signaling and activities in the central nervous system. LXs are derived from arachidonic acid, an omega-6 PUFA. In addition to well-established roles in systemic inflammation resolution, they have increasingly become implicated in regulating neuroinflammatory and neurodegenerative processes. In particular, chronic inflammation plays a central role in Alzheimer's disease (AD) etiology, and dysregulated LX production and activities have been reported in a variety of AD rodent models and clinical tissue samples, yet with complex and sometimes conflicting results. In addition, reduced LX production following retinal injury has been reported recently by the authors, and an intriguing direct neuronal activity promoting survival and homeostasis in retinal and cortical neurons is demonstrated. Here, the authors review and clarify this growing literature and suggest new research directions to further elaborate the role of lipoxins in neurodegeneration.

Lipoxin A4 Counteracts Synergistic Activation of Human Fibroblast-like Synoviocytes

Excessive production of interleukin-6 (IL-6) and metalloproteinases (MMPs) has been implicated in the pathogenesis of rheumatoid arthritis. Lipoxin A4 (LXA4) and transforming growth factor (32 (TGF-|32) have potential anti-inflammatory activities; these two mediators were tested to determine how they affect IL-1β-dependent release of IL-6 and MMPs in human fibroblast-like synoviocytes. The results revealed dramatic differences between the mediators: TGF-β2 acted synergistically with IL-1β to stimulate IL-6 protein levels, whereas LXA4 inhibited IL-6 expression in a dose- and time-dependent manner. Inhibition, by LXA4 was abrogated when cells were pre-incubated with antibody against the ALXR (Lipoxin A4 Receptor) TGF-β2 by itself had no significant effect on IL-6 or MMP levels. LXA4, at nanomolar concentrations, altered the MMP-1 and MMP-3 expression levels of IL-1β and TGF-β2 stimulated fibroblast-like synoviocytes. Furthermore, IL-1β and TGF-β2 up-regulated ALXR mRNA. These results demonstrate, for the first time, that ALXR mediate the effects of LXA4 on inflammatory responses after stimulation of fibroblast-like synoviocytes with IL-1β plus TGF-β2. These activities might constitute an important mechanism by which LXA4 regulates synovial fibroblast activation.

Simvastatin and Benznidazole-Mediated Prevention of Trypanosoma cruzi-Induced Endothelial Activation: Role of 15-epi-lipoxin A4 in the Action of Simvastatin

Trypanosoma cruzi is the causal agent of Chagas Disease that is endemic in Latin American, afflicting more than ten million people approximately. This disease has two phases, acute and chronic. The acute phase is often asymptomatic, but with time it progresses to the chronic phase, affecting the heart and gastrointestinal tract and can be lethal. Chronic Chagas cardiomyopathy involves an inflammatory vasculopathy. Endothelial activation during Chagas disease entails the expression of cell adhesion molecules such as E-selectin, vascular cell adhesion molecule-1 (VCAM-1) and intercellular cell adhesion molecule-1 (ICAM-1) through a mechanism involving NF-κB activation. Currently, specific trypanocidal therapy remains on benznidazole, although new triazole derivatives are promising. A novel strategy is proposed that aims at some pathophysiological processes to facilitate current antiparasitic therapy, decreasing treatment length or doses and slowing disease progress. Simvastatin has anti-inflammatory actions, including improvement of endothelial function, by inducing a novel pro-resolving lipid, the 5-lypoxygenase derivative 15-epi-lipoxin A4 (15-epi-LXA4), which belongs to aspirin-triggered lipoxins. Herein, we propose modifying endothelial activation with simvastatin or benznidazole and evaluate the pathways involved, including induction of 15-epi-LXA4. The effect of 5 μM simvastatin or 20 μM benznidazole upon endothelial activation was assessed in EA.hy926 or HUVEC cells, by E-selectin, ICAM-1 and VCAM-1 expression. 15-epi-LXA4 production and the relationship of both drugs with the NFκB pathway, as measured by IKK-IKB phosphorylation and nuclear migration of p65 protein was also assayed. Both drugs were administered to cell cultures 16 hours before the infection with T. cruzi parasites. Indeed, 5 μM simvastatin as well as 20 μM benznidazole prevented the increase in E-selectin, ICAM-1 and VCAM-1 expression in T. cruzi-infected endothelial cells by decreasing the NF-κB pathway. In conclusion, Simvastatin and benznidazole prevent endothelial activation induced by T. cruzi infection, and the effect of simvastatin is mediated by the inhibition of the NFκB pathway by inducing 15-epi-LXA4 production.

Lipid mediators in the resolution of inflammation

Mounting of the acute inflammatory response is crucial for host defense and pivotal to the development of chronic inflammation, fibrosis, or abscess formation versus the protective response and the need of the host tissues to return to homeostasis. Within self-limited acute inflammatory exudates, novel families of lipid mediators are identified, named resolvins (Rv), protectins, and maresins, which actively stimulate cardinal signs of resolution, namely, cessation of leukocytic infiltration, counterregulation of proinflammatory mediators, and the uptake of apoptotic neutrophils and cellular debris. The biosynthesis of these resolution-phase mediators in sensu stricto is initiated during lipid-mediator class switching, in which the classic initiators of acute inflammation, prostaglandins and leukotrienes (LTs), switch to produce specialized proresolving mediators (SPMs). In this work, we review recent evidence on the structure and functional roles of these novel lipid mediators of resolution. Together, these show that leukocyte trafficking and temporal spatial signals govern the resolution of self-limited inflammation and stimulate homeostasis.

Immunoinflammatory responses in gastrointestinal tract injury and recovery

Inflammation is a non-specific immune response to infection, irritation or other injury, the key features being redness, warmth, swelling and pain. A number of mediators are released which alter the resistance of mucosa to injury induced by noxious substances. Oxidative stress is a unifying mechanism of injury in many types of disease processes, including gastrointestinal diseases. It has been defined as an imbalance in the activity of pro and antioxidants. Pro-oxidants favour free radical formation while antioxidants inhibit or retard the same. A number of markers of oxidative stress have been identified. This review provides an overview of various mediators of inflammation and oxidative stress, and diverse approaches for prevention and treatment of gastrointestinal inflammation.

Arachidonic acid and lipoxin A4 as possible endogenous anti-diabetic molecules

In both type 1 and type 2 diabetes mellitus, increased production of pro-inflammatory cytokines and reactive oxygen species (ROS) occurs that induce apoptosis of β cells and cause peripheral insulin resistance respectively though the degree of their increased production is higher in type 1 and less in type 2 diabetes mellitus. Despite this, the exact mechanism(s) that lead to increased production of pro-inflammatory cytokines: interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) and ROS is not known. Studies showed that plasma concentrations of arachidonic acid (AA) and lipoxin A4 (LXA4) are low in alloxan-induced type 1 diabetes mellitus in experimental animals and patients with type 2 diabetes mellitus. Prior administration of AA, eicosapentaenoic and docosahexaenoic acids (EPA and DHA, respectively) and transgenic animals that produce increased amounts of EPA and DHA acids were protected from chemical-induced diabetes mellitus that was associated with enhanced formation of LXA4 and resolvins, while protectin D1 ameliorated peripheral insulin resistance. AA, LXA4, resolvins and protectins inhibit IL-6 and TNF-α production and suppress ROS generation. Thus, AA and lipoxins, resolvins and protectins may function as endogenous anti-diabetic molecules implying that their administration could be useful in the prevention and management of both types of diabetes mellitus.

Primary human airway epithelial cell-dependent inhibition of human lung mast cell degranulation

INTRODUCTION

Chronic mast cell activation is a characteristic feature of asthma. BEAS-2B human airway epithelial cells (AEC) profoundly inhibit both constitutive and IgE-dependent human lung mast cell (HLMC) histamine release. The aim of this study was to examine the regulation of HLMC degranulation by primary AEC from healthy and asthmatic subjects, and investigate further the inhibitory mechanism.

METHODS

HLMC were co-cultured with both BEAS-2B and primary AEC grown as monolayers or air-liquid interface (ALI) cultures.

RESULTS

Both constitutive and IgE-dependent HLMC histamine release were attenuated by BEAS-2B, primary AEC monolayers and ALI cultures. This occurred in the absence of HLMC-AEC contact indicating the presence of a soluble factor. Unlike healthy ALI AEC, asthmatic ALI-AEC did not significantly reduce constitutive histamine release. AEC inhibitory activity was transferable in primary AEC monolayer supernatant, but less active than with Transwell co-culture, suggesting that the inhibitory factor was labile. The AEC inhibitory effects were attenuated by both AEC wounding and pertussis toxin, indicating the involvement of a G(0)/G(i) receptor coupled mechanism. Solid phase extraction of lipids (<10 kDa) removed the AEC inhibitory activity. The lipid derivatives resolving D1 and D2 and lipoxin A(4) attenuated HLMC histamine release in a dose-dependent fashion but were not detectable in co-culture supernatants.

CONCLUSIONS

Primary AEC suppress HLMC constitutive and IgE-dependent histamine secretion through the release of a soluble, labile lipid mediator(s) that signals through the G(0)/G(i) receptor coupled mechanism. Manipulation of this interaction may have a significant therapeutic role in asthma.

New pharmaceutical insights related to the pathways of PUFAs

The fatty acyl structure represents the major lipid building block of practically all lipids and therefore is one of the most fundamental categories of these molecules. Fatty acids (FAs) differ particularly in their chain length, number of double bonds and position of the bonds in the chain. The number of double bonds in the unsaturated molecule of FA distinguishes monounsaturated FAs (MUFAs) and polyunsaturated FAs (PUFAs). In the living cell PUFAs represent the dominant substrates for the formation of biologically active compounds--octadecanoids, eicosanoids and docosanoids--classified as oxylipins or as PUFAnoids. The present review focuses only on the groups of PUFAnoids which biological activities comprise a "positive effect" for the cell. This group of omega-3 PUFAnoids consists of lipoxins, resolvins and protectins. All these biologically active lipids are formed mainly in the LOX-pathway. They are part of the cell mechanisms that contribute to the removal of inflammatory cells and restoration of tissue integrity. A new approach to an optimal anti-inflammatory model shows orientation to the dual COX/LOX-inhibition and the stimulation of the protective eicosanoids and docosanoids formation and its considerable therapeutic potential in managing of molecular mechanisms of chronic inflammatory processes.

Mediators and receptors in the resolution of inflammation: drug targeting opportunities

The active resolution of inflammation is recognized as offering new opportunities to generate novel anti-inflammatory agents. The emerging appreciation of the importance of active resolution in regulation of inflammation also creates an imperative to examine developing and existing agents for their potential to influence these pathways. This themed issue of the British Journal of Pharmacology contains papers that discuss the roles of annexin-1, lipoxins and related lipid products of fish oils as well as other mechanisms involved in active resolution and their receptor targets.

Resolving inflammation: dual anti-inflammatory and pro-resolution lipid mediators

Active resolution of acute inflammation is a previously unrecognized interface between innate and adaptive immunity. Once thought to be a passive process, the resolution of inflammation is now shown to involve active biochemical programmes that enable inflamed tissues to return to homeostasis. This Review presents new cellular and molecular mechanisms for the resolution of inflammation, revealing key roles for eicosanoids, such as lipoxins, and recently discovered families of endogenous chemical mediators, termed resolvins and protectins. These mediators have anti-inflammatory and pro-resolution properties, thereby protecting organs from collateral damage, stimulating the clearance of inflammatory debris and promoting mucosal antimicrobial defence.

Role of lipoxin in the modulation of immune response during infection

Pro-inflammatory mediators such as IL-12, IFN-gamma and TNF are essential in controlling parasite growth during Toxoplasma gondii infection. However, it is clear that the exacerbate production of these cytokines results in the host tissue damage. Investigation into the immune response modulation during infectious disease, has revealed that lipoxin (LXA), an anti-inflammatory eicosanoids, plays an important role in regulation of immune response to different pathogens, including T. gondii and Mycobacterium tuberculosis. Here, we review the pro-resolution pathways triggered by LXA that are responsible for control of pro-inflammatory response during chronic disease.

[The role of arachidonic acid metabolites in the regulation of renal function and pathogenesis of hypertension]

Eicosanoids are twenty-carbon compounds derived from arachidonic acid. Lipoxygenases, cyclooxygenases and cytochrome P-450 enzymes contribute to their synthesis. Our review is focused on prostaglandins, leucotrienes, lipoxins, hepoxilins, hydroxyeicosatetraenoic acids, and epoxyeicosatrienoic acids. Most of these compounds have multiple functions and they also participate in blood pressure regulation and excretion of water and solutes in the kidney. They have some roles in the patogenesis of kidney disease, too. Both experimental models (mainly geneticaly modified mice and rats) and human epidemiological and genetical studies are used in the investigation of eicosanoid physiological and patophysiological functions. New information about their enzymatic regulations and receptors have already resulted in the development of new drugs, mainly antiasthmatics, but further investigation should bring about new results in the treatment of hypertension and other cardiovascular and renal diseases.

New endogenous anti-inflammatory and proresolving lipid mediators: implications for rheumatic diseases

Prostaglandins and leukotrienes are lipid mediators that carry out pivotal roles in host defense and acute inflammation. Failure to completely resolve an acute inflammatory response can lead to chronic inflammation, scarring, and eventual loss of tissue function. Until recently, it was thought that tissue resolution of acute inflammation was a passive event. However, it is now known than lipoxins, which--like prostaglandins and leukotrienes--are also derived from arachidonic acid, are active anti-inflammatory and proresolution mediators, acting in part by reducing neutrophil entry to the inflammation site and stimulating the uptake of apoptotic polymorphonuclear leukocytes by macrophages. Novel families of locally acting and locally generated mediators derived from omega-3 polyunsaturated fatty acids have also been identified as biosynthetically active components in the resolution phase of inflammation. The new families of chemical mediators are termed 'resolvins' and 'protectins' because individual members of each family are stereospecific in controlling the duration and magnitude of inflammation in animal models. Possible deficiencies in the biosynthesis of lipoxins, resolvins, and protectins, and/or their signal transduction, might underlie some aspects of pathogenesis in chronic inflammatory diseases.

Eicosanoids in asthma

Eicosanoids belong to a diverse family of bioactive fatty acids that play important roles in regulating airway inflammation and reactivity. They are the key mediators of the pathobiology of asthma. Among the eicosanoids, lipoxins (LXs) were the first agents to be identified and recognized as potential anti-inflammatory endogenous lipid mediators. Lipoxins are biosynthesized in vivo at inflammation sites. They result mainly from the interaction between 5 and 15-lipoxygenases (LOs), which are distinct from leukotrienes (LTs) and prostaglandins (PGs) in structure and function. Leukotrienes are potent proinflammatory mediators and directly and indirectly stimulate fibroblast chemotaxis, proliferation, and collagen synthesis. Prostaglandins have both bronchoconstrictive and bronchoprotective effects and the bronchoconstriction mediated by PGD2 and PGF2alpha is only occurred in asthmatic patients but not in healthy subjects. Lipoxins counter-regulate the proinflammatory actions of LTs and activate resolution of the inflammatory response. At least two classes of receptors, CysLT1 receptors and Asprin-triggered lipoxin A4 (ALX) receptors, can interact with lipoxin A4 (LXA4) and LXA4 analogs to mediate their biologic actions. Allergen challenge initiates airway biosynthesis of LXA4 and increases expression of its receptor. In addition, LXA4 affects the release of interleukin-8 by blood mononuclear cells, and ALX affects calcium influx into epithelial cells. Therefore, the pivotal role of LXs is mediating airway homeostasis, and LXs may be part of a novel, multipronged approach for treating human asthma.

Aspirin-Triggered Lipoxins Override the Apoptosis-Delaying Action of Serum Amyloid A in Human Neutrophils: A Novel Mechanism for Resolution of Inflammation

Elevated plasma levels of the acute-phase reactant serum amyloid A (SAA) have been used as a marker and predictor of inflammatory diseases. SAA regulates leukocyte activation; however, it is not known whether it also modulates neutrophil apoptosis, which is critical to the optimal expression and resolution of inflammation. Culture of human neutrophils with SAA (0.1-20 microg/ml) markedly prolonged neutrophil longevity by delaying constitutive apoptosis. SAA evoked concurrent activation of the ERK and PI3K/Akt signaling pathways, leading to phosphorylation of BAD at Ser(112) and Ser(136), respectively, and to prevention of collapse of mitochondrial transmembrane potential, cytochrome c release, and caspase-3 activation. These actions were abrogated by pharmacological inhibition of the formyl peptide receptor, ERK or PI3K. Furthermore, aspirin-triggered 15-epi-lipoxin A(4) (15-epi-LXA(4)) and its stable analog 15-epi-16-p-fluorophenoxy-LXA(4), which binds to the same receptor as SAA, effectively overrode the antiapoptosis signal from SAA even when neutrophils were treated with 15-epi-LXA(4) at either 1 or 4 h postculture with SAA. 15-Epi-LXA(4) itself did not affect neutrophil survival and apoptosis. Our results indicate that SAA at clinically relevant concentrations promotes neutrophil survival by suppressing the apoptotic machinery, an effect that can be opposed by 15-epi-LXA(4). The opposing actions of SAA and aspirin-triggered 15-epi-LXA(4) may contribute to the local regulation of exacerbation and resolution of inflammation, respectively.

Interdependence of lipoxin A4 and heme-oxygenase in counter-regulating inflammation during corneal wound healing

In the immune-privileged cornea, epithelial wounds heal rapidly with almost no scarring and, unlike in most other tissues, acute inflammation in the absence of infection is beneficial to healing. Molecular mechanisms, which account for this striking property, remain to be clearly defined, but they likely include autacoids that control leukocyte activation. Two prominent enzymes, 12/15-lipoxygenase (LOX), which generates antiinflammatory lipid autacoids, and heme-oxygenase (HO), which generates antioxidants and carbon monoxide, are highly expressed in human and mouse corneas. LXA4, an endogenous 12/15-LOX product, proved to be a potent inhibitor of exacerbated inflammation and significantly increased re-epithelialization in corneal wounds. In vivo deletion of 12/15-LOX correlated with exacerbated inflammation and impaired wound healing in 12/15-LOX(-/-) mice, a phenotype that was rescued by treatment with LXA4. More importantly, 12/15-LOX(-/-) mice demonstrated impaired induction of HO-1 in both acute and exacerbated inflammation. Topical LXA4 restored HO-1 expression in 12/15-LOX(-/-) mice and amplified HO-1 gene expression in human corneal epithelial cells. HO-2(-/-) mice, which fail to induce HO-1, also demonstrated exacerbated inflammation in response to injury, a phenotype that, notably, correlated with a 50% reduction in endogenous LXA4 formation. Collectively, results demonstrate a critical role for LXA4 in inflammatory/reparative responses and provide the first evidence that 12/15-LOX and HO systems function in concert to control inflammation.

Not all eicosanoids are bad

Although considerable attention has been focused on elucidating the factors that drive inflammation, it is becoming clear that this "acceleration" state is offset by an internal "handbrake". A recent study has uncovered an essential component of this handbrake system, revealing that lipoxins trigger suppressors of cytokine signalling to dampen inflammatory responses to infection. This work bolsters the growing interest in understanding how inflammation is controlled from within and draws further attention to novel targets for drug development based on mimicking the actions of endogenous anti-inflammatory and pro-resolution signals.

Leukotriene B4 and lipoxin A4 are regulatory signals for neural stem cell proliferation and differentiation

Leukotrienes (LTs) and lipoxins (LXs) are lipid mediators that play a key role in regulating acute inflammatory responses. Their roles in neural stem cell (NSC) functions are of interest. We showed here that LTB(4) and LXA(4) regulated proliferation and differentiation of murine NSCs that were isolated from embryo brains. Proliferation of NSCs was stimulated by LTB(4) (3 to 100 nM) and blocked by receptor antagonist (IC(50)=2.7 microM). In contrast, LXA(4), and its aspirin-triggered-15-epi-LXA(4) stable analog attenuated growth of NSCs at as little as 1 nM. Both lipoxygenase (LOX) inhibitors and LTB(4) receptor antagonists caused apoptosis and cell death. Gene chip analysis revealed that growth-related gene expressions such as epidermal growth factor (EGF) receptor, cyclin E, p27, and caspase 8 were tightly regulated by LTB(4); LXA(4) gave the opposite gene expressions. In addition to proliferation, LTB(4) induced differentiation of NSCs into neurons as monitored by neurite outgrowth and MAP2 expression. These results indicate for the first time that LTB(4) and LXA(4) directly regulate proliferation and differentiation of NSCs, suggesting these new pathways may be useful in restoring stem cells.

Eicosanoid Transcellular Biosynthesis: From Cell-Cell Interactions to in Vivo Tissue Responses

The biosynthesis of the biologically active metabolites of arachidonic acid involves a number of enzymes that are differentially expressed in cells. Prostaglandins and thromboxanes are derived from the chemically unstable prostaglandin (PG) H(2) intermediate synthesized by PGH synthases (cyclooxygenase-1/2) and leukotrienes from chemically unstable leukotriene A(4) by 5-lipoxygenase. Additional enzymes transform these reactive intermediates to a variety of chemical structures known collectively as the lipid mediators. Although some cells have the complete cassette of enzymes required for the production of biologically active prostaglandins and leukotrienes, the actual biosynthetic events often are a result of cell-cell interaction and a transfer of these chemically reactive intermediates, PGH(2) and leukotriene A(4), between cells. This process has come to be known as transcellular biosynthesis of eicosanoids and requires a donor cell to synthesize and release one component of the biosynthetic cascade and a second, accessory cell to take up that intermediate and process each into the final biologically active product. This review focuses on the evidence for transcellular biosynthetic events for prostaglandins, leukotrienes, and lipoxins occurring during cell-cell interactions. Evidence for arachidonic acid serving as a transcellular biosynthetic intermediate is presented. Experiments for transcellular events taking place in vivo that reveal the true complexity of eicosanoid biosynthesis within tissues are also reviewed.

New perspectives on aspirin and the endogenous control of acute inflammatory resolution

Aspirin is unique among the nonsteroidal anti-inflammatory drugs in that it has both anti-inflammatory as well as cardio-protective properties. The cardio-protective properties arise form its judicious inhibition of platelet-derived thromboxane A₂ over prostacyclin, while its anti-inflammatory effects of aspirin stem from its well-established inhibition of prostaglandin (PG) synthesis within inflamed tissues. Thus aspirin and the other NSAIDs have popularised the notion of inhibiting PG biosynthesis as a common anti-inflammatory strategy based on the erroneous premise that all eicosanoids are generally detrimental to inflammation. However, our fascination with aspirin has shown a more affable side to lipid mediators based on our increasing interest in the endogenous control of acute inflammation and in factors that mediate its resolution. Epi-lipoxins (epi-LXs), for instance, are produced from aspirins acetylation of inducible cyclooxygenase 2 (COX-2) and together with Resolvins represent an increasingly important family of immuno-regulatory and potentially cardio-protective lipid mediators. Aspirin is beginning to teach us what nature knew all along — that not all lipid mediators are bad. It seems that while some eicosanoids are pathogenic in a variety of diseases, others are unarguable protective. In this review we will re-count aspirins colorful history, discuss its traditional mode of action and the controversies associated therewith, as well as highlight some of the new pathways in inflammation and the cardiovascular systems that aspirin has recently revealed.

Lipoxin A(4) regulates bronchial epithelial cell responses to acid injury

Aspiration of gastric acid commonly injures airway epithelium and, if severe, can lead to respiratory failure from acute respiratory distress syndrome. Recently, we identified cyclooxygenase-2 (COX-2)-derived prostaglandin E(2) (PGE(2)) and lipoxin A(4) (LXA(4)) as pivotal mediators in vivo for resolution of acid-initiated acute lung injury. To examine protective mechanisms for these mediators in the airway, we developed an in vitro model of acid injury by transiently exposing well-differentiated normal human bronchial epithelial cells to hydrochloric acid. Transmission electron microscopy revealed selective injury to superficial epithelial cells with disruption of cell attachments and cell shedding. The morphological features of injury were substantially resolved within 6 hours. Acid triggered and early marked increases in COX-2 expression and PGE(2) production, and acid-induced PGE(2) significantly increased epithelial LXA(4) receptor (ALX) expression. LXA(4) is generated in vivo during acute lung injury, and we observed that nanomolar quantities increased basal epithelial cell proliferation and potently blocked acid-triggered interleukin-6 release and neutrophil transmigration across well-differentiated normal human bronchial epithelial cells. Expression of recombinant human ALX in A549 airway epithelial cells uncovered ALX-dependent inhibition of cytokine release by LXA(4). Together, these findings indicate that injured bronchial epithelial cells up-regulate ALX in a COX-2-dependent manner to promote LXA(4)-mediated resolution of airway inflammation.

Lipoxin A4 Redistributes Myosin IIA and Cdc42 in Macrophages: Implications for Phagocytosis of Apoptotic Leukocytes

Lipoxins (LXs) are endogenously produced anti-inflammatory agents that modulate leukocyte trafficking and stimulate nonphlogistic macrophage phagocytosis of apoptotic neutrophils, thereby promoting the resolution of inflammation. Previous data suggest a role for altered protein phosphorylation and cytoskeletal rearrangement in LX-stimulated phagocytosis but the exact mechanisms remain unclear. In this study we examine the effects of LXA4 on the protein phosphorylation pattern of THP-1 cells differentiated into a macrophage-like phenotype. THP-1 cells stimulated with LXA4 (1 nM) exhibit dephosphorylation of a 220-kDa protein. Using mass spectrometry, this protein was identified as MYH9, a nonmuscle myosin H chain II isoform A, which is involved in cytoskeleton rearrangement. THP-1 cells treated with LXA4 adopt a polarized morphology with activated Cdc42 localized toward the leading edge and MYH9 localized at the cell posterior. Polarized distribution of Cdc42 is associated with Akt/PKB-mediated Cdc42 activation. Interestingly, the annexin-derived peptide Ac2-26, a recently described agonist for the LXA4 receptor, also stimulates macrophage phagocytosis, MYH9 dephosphorylation, and MYH9 redistribution. In addition, we demonstrate that LXA4 stimulates the phosphorylation of key polarity organization molecules: Akt, protein kinase Czeta, and glycogen synthase kinase-3beta. Inhibition of LXA4-induced Akt and protein kinase Czeta activity with specific inhibitors prevented LXA4-stimulated phagocytosis of both apoptotic polymorphonuclear neutrophils and lymphocytes, highlighting a potential use for LXA4 in the treatment of autoimmune diseases. Furthermore, phosphorylation and subsequent inactivation of glycogen synthase kinase-3beta resulted in an increase in phagocytosis similar to that of LXA4. These data highlight an integrated mechanism whereby LXA4 regulates phagocytosis through facilitative actin cytoskeleton rearrangement and cell polarization.

Host response modulation in the management of periodontal diseases

OBJECTIVE

To review the biological mechanisms and clinical utility of therapeutic modulation of the host response in the management of periodontal diseases.

MATERIAL AND METHODS

A search of MEDLINE-PubMed was performed up to and including December 2004. The search was limited to in vitro, experimental animal and clinical studies published in English. The selection criteria included all levels of available evidence: systematic reviews, randomised-controlled clinical trials, controlled clinical trials, prospective and retrospective cohort studies and case reports of human and experimental animal studies.

RESULTS

Six targets for non-microbial chemotherapeutic intervention were identified. Clinical trials have demonstrated the ability of non-steroidal anti-inflammatory drugs to slow periodontal disease progression. However, recently reported serious adverse effects preclude the use of cyclooxygenase-2 inhibitors as an adjunct to periodontal therapy. Adjunctive use of subantimicrobial dose doxycycline to non-surgical periodontal therapy is beneficial in the management of chronic periodontitis over 12 months. Controversial data exist on the effects of bisphosphonate administration as an adjunct to periodontal therapy. Evidence on modulation of other host mediators including lipoxins, cytokines and nitric oxide synthase is limited to animal research.

CONCLUSION

After validation in long-term clinical trials, adjunctive host modulation therapy may prove advantageous in the management of periodontal diseases.

Lipoxin analogs and lipoxin formation in vivo

The definition of lipoxin bioactions in vivo and of lipoxin levels in humans, under physiological and pathological conditions, represents a main task toward the clinical use of lipoxins. The introduction of lipoxin stable analogs and of new methodology for immunological measurements of lipoxin A4 in human fluids is significantly contributing to fulfill this task. This chapter reviews the current literature on the use of lipoxin analogs, in vivo, and on measurements of lipoxin A4 in health and disease.

A twist in anti-inflammation: annexin 1 acts via the lipoxin A4 receptor

The inflammatory response is a life-saving protective process mounted by the body to overcome pathogen infection and injury; however, in chronic inflammatory pathologies this response can become deregulated. The existence of specialized anti-inflammatory pathways/mediators that operate in the body to down-regulate inflammation have now emerged. Thus, persistence of inflammation leading to pathology could be due to malfunctioning of one or more of these counter-regulatory pathways. Here we focus on one of them, the anti-inflammatory mediator annexin 1, and provide an update on its inhibitory effects upon the leukocyte trafficking process. In particular, recent evidence that receptors of the formyl-peptide family, which includes also the lipoxin A4 receptor, could be the annexin 1 receptor(s) in the context of anti-inflammation might provide new avenues for exploiting this pathway for drug discovery.

Anti-inflammatory circuitry: lipoxin, aspirin-triggered lipoxins and their receptor ALX

Endogenous chemical mediators or autacoids play key roles in controlling inflammation and its programmed resolution. Among them, it is known that lipoxins (LX) and aspirin-triggered LX (ATL) evoke bioactions in a range of physiologic and pathophysiologic processes and serve as endogenous lipid/chemical mediators that stop neutrophilic infiltration and initiate resolution. LXA4, ATL and their metabolic stable analogs elicit cellular responses and regulate PMN in vivo via interacting with their specific receptor, namely ALX. ALX is the first cloned and identified lipoxygenase-derived eicosanoid receptor with cell type-specific signaling pathways. Also, ALX could regulate PMN by interacting with each class of ligands (lipid vs. peptide) within specific phases of an inflammatory response. Together LX, ATL and ALX may provide new opportunities to design "resolution-targeted" therapies with high degree of precision in controlling inflammation. In this chapter, we give an overview and update of the current actions for LX and ATL, the identification of ALX and their novel anti-inflammatory and pro-resolving signals.

Lipoxins in gastric mucosal health and disease

Lipoxins have well characterized anti-inflammatory properties. In recent years, lipoxin A4 and its epimeric counterpart, which is synthesized via aspirin-acetylated cyclooxygenase-2, have been shown to exert very potent protective effects in the stomach. Indeed, suppression of aspirin-triggered lipoxin synthesis, through co-administration of a selective COX-2 inhibitor, results in a significant exacerbation of gastric injury. The gastroprotective effects of lipoxin A4 appear to be receptor mediated, and may be attributable to the ability of this agent to suppress leukocyte adherence to the vascular endothelium and to elevate gastroduodenal blood flow. These effects may be mediated via lipoxin-induced nitric oxide generation. Lipoxins activate a receptor that can also be activated by annexin-1, another substance involved in resolution of inflammation and gastroprotection.

The role of aspirin-triggered lipoxins in the mechanism of action of aspirin

Few drugs have treated so many diseases, provided us with so much understanding of their pathogenesis, and tested our scientific creativity over the last 100 years as much as aspirin. Originally, the beneficial effects of aspirin were shown to stem from its inhibition of cyclooxygenase (COX 2)-derived prostanoids, fatty acid metabolites that modulate host defense and regulate the cardiovascular system. However, the inhibition of COX 2 enzyme activity and prostaglandin synthesis has never fully explained aspirin's repertoire of anti-inflammatory effects, leaving many questions pertaining to its true mechanism of action unanswered. Here, data from a series of comparatively recent experiments exploring aspirin's unique ability to acetylate the active site of inducible COX 2 and generate a family of lipid mediators called the epi-Lipoxins will be discussed in light of their ability to exert profound modulatory effects on the innate and adaptive immune systems.

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.

Taking insult from injury: lipoxins and lipoxin receptor agonists and phagocytosis of apoptotic cells

Phagocytic clearance of apoptotic cells plays a pivotal role in the resolution of inflammation. Recent evidence has shown that such processes can be regulated by endogenous mediators, suggesting that specific mimetics may have therapeutic potential in chronic inflammation and autoimmune disorders. Here we review the mechanisms underlying recognition and engulfment of apoptotic cells and regulation of these processes by lipoxins and lipoxin receptor agonists.

Lipoxin signaling in neutrophils and their role in periodontal disease

Endogenous molecules involved in counterregulation of inflammatory responses provide an opportunity to explore new therapeutic approaches based on manipulation of new pathways that may reduce the possibility of unwanted toxic side effects. Lipoxins (LX) are trihydroxytetraene-containing eicosanoids that are generated within the vascular lumen during cell-cell interactions or at mucosa through leukocyte-epithelial cell interactions. Transcellular biosynthetic pathways are the major lipoxin biosynthetic routes where LX are formed in vivo during inflammation and serve as "stop signals" that regulate key steps in leukocyte trafficking. In this review, recent findings in lipoxin generation, impact on the resolution of acute inflammation, and organ protection from neutrophil-mediated injury are presented. Periodontitis, specifically localized aggressive periodontitis, which is recognized as an example of neutrophil-mediated tissue injury, is discussed as a disease model where LX and other endogenous pro-resolution pathway mediators could have potential value.

Lipoxins and lipoxin analogs in asthma

The pathobiology of asthma is characterized by production of eicosanoids, a diverse family of bioactive fatty acids that play important roles in regulating airway inflammation and reactivity. Lipoxins (LXs) are products of arachidonic acid metabolism that are distinct from leukotrienes (LTs) and prostaglandins (PGs) in structure and function. Unlike the pro-inflammatory PGs and LTs, LXs display counter-regulatory actions. Cell-type specific biological actions have been uncovered for LXs and LX stable analogs that promote resolution of acute inflammatory responses. At least two classes of receptors, CysLT1 receptors and LXA4 receptors (named ALX), can interact with LXA4 and LXA4 analogs to mediate their biological actions. LXs are generated during asthma and LXA4 signaling blocks asthmatic responses in humans and experimental model systems. Of interest, respiratory diseases of increased severity, such as aspirin-intolerant asthma, cystic fibrosis and steroid-dependent, severe asthma, display defective generation of these protective lipid signals. Together, these findings indicate a pivotal role for LXs in mediating airway homeostasis.

Angiogenesis and lipoxins

Angiogenesis, the growth of new capillaries from pre-existing ones, occurs through dynamic functions of the endothelial cells (EC), including migration, proliferation and maturation, which are essential to achieve an organized formation of the vessel sprout. Aspirin-triggered lipoxins (ATL), the 15R enantiomeric counterparts of native lipoxins, are endogenous lipid mediators generated within the vascular lumen during multicellular responses, which display potent and well-described immunomodulatory actions. Here we present some of the findings regarding the inhibition of EC responses in vitro and in vivo by these novel compounds and the modulation of fundamental steps of the angiogenic process, identifying previously unappreciated vascular actions of locally generated ATL and their longer acting synthetic analogs.

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

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

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.

Lipoxins and aspirin-triggered lipoxins in neutrophil adhesion and signal transduction

Lipoxin A4 (LXA4) and aspirin-triggered 15-epi-LXA4 (ATL) are emerging as endogenous braking signals for neutrophil-mediated tissue injury. LXA4 and ATL and their metabolically stable analogues display potent inhibitory actions in human isolated cells and blood, including attenuation of expression of adhesion molecules on leukocytes and endothelial cells, neutrophil adhesion to endothelial cells and platelets under shear, and IL-8 production, key events of the acute inflammatory response. The underlying molecular mechanisms include interference with MAPK signaling pathways, modulation of the oxidative chemistry of superoxide, NO and ONOO-, inhibition of activation of NF-kappaB and AP-1, and consequently the expression of interleukin-8 and likely other pro-inflammatory genes. Collectively, these results add to the profile of LXA4/ATL rapid actions that contribute to "stop signaling" involved in regulating neutrophil functions during acute inflammation and suggest that aspirin inhibits neutrophil accumulation through triggering the synthesis of 15-epi-LXA4.

Lipoxins in the eye and their role in wound healing

The eye must contain highly evolved programs to limit inflammation and promote wound healing as an errant response can lead to blindness. However, pathways that protect the delicate visual axis and account for its atypical inflammatory responses remain to be clearly defined. Hence, research efforts have been initiated to elucidate the role of the anti-inflammatory LXA4 circuits in the eye. LXA4 is formed in healthy and injured corneas and both its receptor and 12/15-lipoxygenase are predominantly expressed in epithelial cells. An essential role for LXA4 in preserving ocular function is supported by 12/15-LOX deficient mice that exhibit a phenotype of impaired wound healing and LXA4 formation. A novel epithelial bioaction role for LXA4 has been uncovered in the cornea as topical LXA4 promotes wound healing and limits the sequelae of injury. These emerging studies indicate that the LXA4 circuit may hold a fundamental role in maintaining an ocular environment that actively restricts inflammation while promoting wound healing.

Essential fatty acids and acquired immunodeficiency syndrome

Acquired immunodeficiency syndrome (AIDS) is caused by human immunodeficiency virus (HIV) that is characterized by profound immunodeficiency, opportunistic infections and Kaposi's sarcoma. As yet no effective therapy is available for AIDS, though retroviral drugs are able to prolong life and contain HIV proliferation to some extent. I propose that essential fatty acids (EFAs) and their metabolites could be useful in the prevention and management of AIDS. Linoleic acid (LA) and arachidonic acid (AA) inactivate enveloped viruses, linolenic acid-enriched macrophages are markedly tumoricidal, EFAs activate macrophages and neutrophils and induce free radical generation; and cytokines bring about some of their actions by inducing the release of EFAs; gamma-linolenic acid (GLA) and eicosapentaenoic acid (EPA) prevent genetic damage and have tumoricidal actions as well; and are relatively non-toxic when administered orally or parentarally over long periods of time. In view of this, I suggest that further studies with regard to the role of GLA, AA, EPA and/or docosahexaenoic acid (DHA) in the pathobiology of AIDS needs to be performed. It is also proposed that possible use of these fatty acids in the prevention and treatment of AIDS needs serious consideration.

Clues for new therapeutics in osteoporosis and periodontal disease: new roles for lipoxygenases?

Lipoxygenase (LOX) pathways are well appreciated for their ability to regulate key events contributing to the cardinal signs of inflammation. Recent evidence indicates that LOX genes are associated with osteoporosis. Also, overexpression of the 15-LOX Type 1 in transgenic rabbits leads to a reduced inflammatory phenotype and protection from periodontal disease, as well as atherosclerosis. Osteoporosis and inflammation-associated bone degradation, such as periodontitis, affect many individuals worldwide and are known to have pathogenesis that involves local mediators via communication between osteoclasts and osteoblasts during osteogenesis. Evidence has emerged indicating that LOX gene expression is associated with reduced bone strength in murine models of osteoporosis. Overexpression of the 15-LOX gene and its products, such as lipoxins, confers endogenous anti-inflammation. This article discusses the recent findings that may link aberrant LOX pathway expression in these diseases, suggesting new avenues for therapeutic approaches via activation of endogenous pathways for resolution of local inflammation.

Novel ? ? 3-derived local mediators in anti-inflammation and resolution

The integrated inflammatory response of the host is essential in health and disease. Hence, it is important to achieve a more complete understanding of the local cellular and molecular events that govern the formation and actions of local mediators that can serve as endogenous local mediators of resolution. Because these compounds in experimental animal models of inflammation can control the duration and magnitude of inflammation, knowledge of their formation and actions may provide new avenues for appreciating the molecular basis of many inflammatory diseases. The first of these endogenous local counterregulators recognized were the lipoxins, which are trihydroxytetraene-containing mediators generated from arachidonic acid during cell-cell interactions via transcellular biosynthesis. Because this circuit of lipoxin formation appears to be of physiological relevance in resolution, therapeutic modalities targeting this and related systems should allow for the development of novel therapeutic agents (i.e., agonists of the important cellular and physiological responses required for timely resolution). This review offers a general overview of recent advances from studies by the author and colleagues on the biosynthesis and bioactions of the novel anti-inflammatory lipid mediators, resolvins, docosatrienes, and neuroprotectins as well as their endogenous aspirin-triggered epimeric counterparts. These previously unappreciated families of lipid-derived mediators were originally isolated from experimental murine models of acute inflammation captured during the natural spontaneous resolution phase. They possess anti-inflammatory, pro-resolving, and protective properties. Inappropriate resolution mechanism(s) may underlie our current appreciation of the inflammatory phenotype(s) that characterizes many prevalent human diseases where inflammation is now acknowledged to play an important role in the disease process. Moreover, these new pathways give opportunities to appreciate the complex roles of neutrophils in the generation of potent host protective lipid mediators that may be harnessed for the design of novel treatments for a wide range of diseases where inflammation contributes to the pathophysiology of the disorder.

Aspirin-triggered, cyclooxygenase-2-dependent lipoxin synthesis modulates vascular tone

BACKGROUND

Aspirin-triggered production of 15-(R)-epilipoxin A(4) (ATL) has been shown to exert potent antiinflammatory effects and gastric-protective effects, but little is known of its actions on the vasculature. In the present study, we have assessed the contribution of ATL to changes in vascular tone induced by aspirin and have examined the role of nitric oxide (NO) as a mediator of such effects.

METHODS AND RESULTS

Intravenous administration of lipoxin A(4) resulted in a short-lived (3 to 4 minutes) reduction in blood pressure (BP; approximately 13 mm Hg at 2.5 microg/kg). Aspirin administered alone resulted in a significant increase in serum ATL and an increase in BP of approximately 10 mm Hg. When ATL synthesis was inhibited by pretreatment with a selective cyclooxygenase-2 inhibitor (celecoxib) or a 5-lipoxygenase inhibitor (zileuton), the aspirin-induced increase in BP was significantly augmented. These agents alone did not affect BP. A lipoxin receptor antagonist, Boc2, also increased the pressor effects of aspirin. Moreover, immunodepletion of neutrophils, a major source of 5-lipoxygenase, resulted in a significant reduction of ATL formation and augmented aspirin's pressor effects. Studies of rat aortic and mesenteric artery ring segments confirmed the vasorelaxant effects of lipoxin A(4) and showed them to be endothelium dependent.

CONCLUSIONS

Aspirin-triggered lipoxin synthesis can modulate vascular tone, possibly contributing to changes in regional blood flow during inflammatory reactions, and to the modulation of systemic BP.

A novel role for phospholipase A2 isoforms in the checkpoint control of acute inflammation

Acute inflammation can be considered in terms of a series of checkpoints where each phase of cellular influx, persistence, and clearance is controlled by endogenous stop and go signals. It is becoming increasingly apparent that in addition to initiating the inflammatory response, eicosanoids may also mediate resolution. This suggests there are two phases of arachidonic acid release: one at onset for the generation of proinflammatory eicosanoids and one at resolution for the synthesis of proresolving eicosanoids. What is unclear is the identity of the phospholipase (PLA2) isoforms involved in this biphasic release of arachidonic acid. We show here that type VI iPLA2 drives the onset of acute pleurisy through the synthesis of PGE2, LTB4, PAF, and IL-1beta. However, during resolution there is a switch to a sequential induction of first sPLA2 (types IIa and V) that mediates the release of PAF and lipoxin A4, which, in turn, are responsible for the subsequent induction of type IV cPLA2 that mediates the release of arachidonic acid for the synthesis of proresolving prostaglandins. This study is the first of its kind to address the respective roles of PLA2 isoforms in acute resolving inflammation and to identify type VI iPLA2 as a potentially selective target for the treatment of inflammatory diseases.

Reduced inflammation and tissue damage in transgenic rabbits overexpressing 15-lipoxygenase and endogenous anti-inflammatory lipid mediators

PGs and leukotrienes (LTs) mediate cardinal signs of inflammation; hence, their enzymes are targets of current anti-inflammatory therapies. Products of arachidonate 15-lipoxygenases (LO) types I and II display both beneficial roles, such as lipoxins (LXs) that stereoselectively signal counterregulation, as well as potential deleterious actions (i.e., nonspecific phospholipid degradation). In this study, we examined transgenic (TG) rabbits overexpressing 15-LO type I and their response to inflammatory challenge. Skin challenges with either LTB(4) or IL-8 showed that 15-LO TG rabbits give markedly reduced neutrophil (PMN) recruitment and plasma leakage at dermal sites with LTB(4). PMN from TG rabbits also exhibited a dramatic reduction in LTB(4)-stimulated granular mobilization that was not evident with peptide chemoattractants. Leukocytes from 15-LO TG rabbits gave enhanced LX production, underscoring differences in lipid mediator profiles compared with non-TG rabbits. Microbe-associated inflammation and leukocyte-mediated bone destruction were assessed by initiating acute periodontitis. 15-LO TG rabbits exhibited markedly reduced bone loss and local inflammation. Because enhanced LX production was associated with an increased anti-inflammatory status of 15-LO TG rabbits, a stable analog of 5S,6R,15S-trihydroxyeicosa-7E,9E,11Z,13E-tetraenoic acid (LXA(4)) was applied to the gingival crevice subject to periodontitis. Topical application with the 15-epi-16-phenoxy-para-fluoro-LXA(4) stable analog (ATLa) dramatically reduced leukocyte infiltration, ensuing bone loss as well as inflammation. These results indicate that overexpression of 15-LO type I and LXA(4) is associated with dampened PMN-mediated tissue degradation and bone loss, suggesting that enhanced anti-inflammation status is an active process. Moreover, they suggest that LXs can be targets for novel approaches to diseases, e.g., periodontitis and arthritis, where inflammation and bone destruction are features.