Aspirin-triggered 15-epi-lipoxin A4 (LXA4) and LXA4 stable analogues are potent inhibitors of acute inflammation: evidence for anti-inflammatory receptors

Exploring Oxylipins in Host-Microbe Interactions and Their Impact on Infection and Immunity

Plasma lipids are essential components of biological systems, transported through interactions with proteins to maintain cellular functions. These lipids exist in various forms, such as fatty acids, glycerolipids, glycerophospholipids, sphingolipids, sterols, and prenol lipids, derived from dietary intake, adipose tissue, and biosynthesis. While the association between certain fatty acids and cardiovascular diseases has been widely recognized, polyunsaturated fatty acids (PUFAs) exhibit cardioprotective effects, reducing risks of arrhythmias and heart-related mortality. This is due to their role in the production of eicosanoids, which modulate inflammation. Chronic inflammation, particularly in obesity, is significantly influenced by fatty acids, with saturated fatty acids promoting inflammation and PUFAs mitigating it. Oxylipins, bioactive molecules derived from the oxidation of PUFAs, play crucial roles in immune regulation across various organisms, including plants, fungi, and bacteria. These molecules, such as prostaglandins, leukotrienes, and resolvins, regulate immune responses during infection and inflammation. The production of oxylipins extends beyond mammals, with fungi and bacteria synthesizing these molecules to modulate immune responses, promoting both defense and pathogenesis. This review delves into the multifaceted effects of oxylipins, exploring their impact on host and microbial interactions, with a focus on their potential for therapeutic applications in modulating infection and immune response.

A method for MRI-guided bronchoscopy to identify obstructed airway segments

Bronchoscopy is not conventionally guided by prior knowledge of segmental airway obstruction. Hyperpolarized gas magnetic resonance imaging (MRI) ventilation abnormalities and computed tomography (CT) air trapping are related to lung function and asthma severity but have not been used to target segmental inflammation and remodeling. We evaluate the feasibility of using bronchoscopy guided by 3He MRI and CT to reveal differences in inflammatory response, morphology, and cellular activity in poorly- (defect) versus well-ventilated (control) lung regions. Eleven participants (5 female; age, 22.8 ± 3.4 years; 9 asthma) who experienced a cold with increased lower airway symptoms underwent 3He MRI and/or CT at least 6 weeks after recovery. Differences between defect and control regions were compared. In defect as compared to control sites, bronchoalveolar lavage neutrophils (p = 0.06) and granulocytes (p = 0.08) trended towards an increase; inflammatory mediators (i.e., 15-epi-LXA4, LXA4) were also significantly different (p < 0.05) between sites. Correlations were observed between macrophages, neutrophils, and eosinophils with inflammatory mediators (i.e., 15-epi-LXA4, LXA4, LTB4). Correlations were observed for macrophages and neutrophils with 15-epi-LXA4, and eosinophils with LXA4 and leukotriene B4. Basement membrane wall thickness was similar for defect versus control sites (p = 0.9). These results support the feasibility of image-guided methods to identify airway obstruction phenotypes.

Pro-resolving lipid mediators and therapeutic innovations in resolution of inflammation

This review summarizes findings presented at the 19th World Congress of Basic & Clinical Pharmacology 2023 (Glasgow, Scotland, July 3rd to 7th, 2023) from 8 speakers in the field of resolution of inflammation, resolution pharmacology and resolution biology. It is now accepted that the acute inflammatory response is protective to defend the host against infection or tissue injury. Acute inflammation is self-limited and programmed to be limited in space and time: this is achieved through endogenous resolution processes that ensure return to homeostasis. Resolution is brought about by agonist mediators that include specialized pro-resolving lipid mediators (SPMs) and pro-resolving proteins and peptides such as annexin A1 and angiotensin-(1-7), all acting to initiate anti-inflammatory and pro-resolving processes. If the inflammatory reaction remains unchecked through dysfunctional resolution mechanism, it can become chronic and contribute to a plethora of human diseases, including respiratory, cardiovascular, metabolic, allergic diseases, and arthritis. Herein, we discuss how non-resolving inflammation plays a role in the pathogenesis of these diseases. In addition to SPMs, we highlight the discovery, biosynthesis, biofunctions, and latest research updates on innovative therapeutics (including annexin-A1 peptide-mimetic RTP-026, small molecule FPR2 agonist BM-986235/LAR-1219, biased agonist for FPR1/FPR2 Cmpd17b, lipoxin mimetics AT-01-KG and AT-02-CT, melanocortin receptor agonist AP1189, gold nanoparticles, angiotensin-(1-7), and CD300a) that can promote resolution of inflammation directly or through modulation of SPMs production. Drug development strategies based on the biology of the resolution of inflammation can offer novel therapeutic means and/or add-on therapies for the treatment of chronic diseases.

Inflammation and resolution in obesity

Inflammation is an essential physiological defence mechanism, but prolonged or excessive inflammation can cause disease. Indeed, unresolved systemic and adipose tissue inflammation drives obesity-related cardiovascular disease and type 2 diabetes mellitus. Drugs targeting pro-inflammatory cytokine pathways or inflammasome activation have been approved for clinical use for the past two decades. However, potentially serious adverse effects, such as drug-induced weight gain and increased susceptibility to infections, prevented their wider clinical implementation. Furthermore, these drugs do not modulate the resolution phase of inflammation. This phase is an active process orchestrated by specialized pro-resolving mediators, such as lipoxins, and other endogenous resolution mechanisms. Pro-resolving mediators mitigate inflammation and development of obesity-related disease, for instance, alleviating insulin resistance and atherosclerosis in experimental disease models, so mechanisms to modulate their activity are, therefore, of great therapeutic interest. Here, we review current clinical attempts to either target pro-inflammatory mediators (IL-1β, NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome, tumour necrosis factor (TNF) and IL-6) or utilize endogenous resolution pathways to reduce obesity-related inflammation and improve cardiometabolic outcomes. A remaining challenge in the field is to establish more precise biomarkers that can differentiate between acute and chronic inflammation and to assess the functionality of individual leukocyte populations. Such advancements would improve the monitoring of drug effects and support personalized treatment strategies that battle obesity-related inflammation and cardiometabolic disease.

Omega-3 long chain fatty acids and their metabolites in pregnancy outcomes for the modulation of maternal inflammatory- associated causes of preterm delivery, chorioamnionitis and preeclampsia

Preterm birth is a major cause of perinatal complications and neonatal deaths. Furthermore, in the field of obstetrics many clinical entities like uterine contractions or the occurrence of pre- eclampsia remain to be serious complications during pregnancy and represent a major psychological, financial, and economic burden for society. Several published guidelines, studies and recommendations have highlighted the importance of supplementation of omega-3 long chain polyunsaturated fatty acids (PUFAs) during pregnancy. This narrative review aims at giving an overview on the modern perception of inflammatory processes and the role of specialized pro-resolving mediators (SPMs) in their resolution, especially in obstetrics. Additionally, we highlight the possible role of SPMs in the prevention of obstetric complications through oral supplementation using enriched marine oil nutritional's. The intake of PUFAs may result in an overall improvement of pregnancy outcomes by contributing to fetal brain growth and neurological development but more importantly though modulation of inflammation-associated pathologies. Especially the use of SPMs represents a promising approach for the management of obstetric and perinatal complications. SPMs are monohydroxylates derived from enriched marine oil nutritional's that involve certain pro-resolutive metabolites of omega-3 long chains PUFAs and may contribute to an attenuation of inflammatory diseases. This may be obtained through various mechanisms necessary for a proper resolution of inflammation such as the termination of neutrophil tissue infiltration, initiation of phagocytosis, downregulation of pro-inflammatory cytokines or tissue regeneration. In this way, acute and chronic inflammatory diseases associated with serious obstetrical complications can be modulated, which might contribute to an improved pregnancy outcome.

Insight into the role of macrophages in periodontitis restoration and development

Periodontitis is one of the chronic diseases that have the greatest impact on human health, and it is associated with several other chronic diseases. Tissue damage associated with periodontitis is often connected with immune response. Immune cells are a crucial component of the human immune system and are directly involved in periodontitis during the inflammatory phase of the disease. Macrophages, as a key component of the immune system, are responsible for defence, antigen presentation and phagocytosis in healthy tissue. They are also closely linked to the development and resolution of periodontitis, through mechanisms such as macrophage polarization, pattern recognition receptors recognition, efferocytosis, and Specialized Pro-resolving Mediators (SPMs) production. Additionally, apoptosis and autophagy are also known to play a role in the recovery of periodontitis. This review aims to investigate the aforementioned mechanisms in more detail and identify novel therapeutic approaches for periodontitis.

Biased receptor signalling and intracellular trafficking profiles of structurally distinct formylpeptide receptor 2 agonists

BACKGROUND

There is increasing interest in developing FPR2 agonists (compound 43, ACT-389949 and BMS-986235) as potential pro-resolving therapeutics, with ACT-389949 and BMS-986235 having entered phase I clinical development. FPR2 activation leads to diverse downstream outputs. ACT-389949 was observed to cause rapid tachyphylaxis, while BMS-986235 and compound 43 induced cardioprotective effects in preclinical models. We aim to characterise the differences in ligand-receptor engagement and downstream signalling and trafficking bias profile.

EXPERIMENTAL APPROACH

Concentration-response curves to G protein dissociation, β-arrestin recruitment, receptor trafficking and second messenger signalling were generated using FPR2 ligands (BMS-986235, ACT-389949, compound 43 and WKYMVm), in HEK293A cells. Log(τ/KA) was obtained from the operational model for bias analysis using WKYMVm as a reference ligand. Docking of FPR2 ligands into the active FPR2 cryoEM structure (PDBID: 7T6S) was performed using ICM pro software.

KEY RESULTS

Bias analysis revealed that WKYMVm and ACT-389949 shared a very similar bias profile. In comparison, BMS-986235 and compound 43 displayed approximately 5- to 50-fold bias away from β-arrestin recruitment and trafficking pathways, while being 35- to 60-fold biased towards cAMP inhibition and pERK1/2. Molecular docking predicted key amino acid interactions at the FPR2 shared between WKYMVm and ACT-389949, but not with BMS-986235 and compound 43.

CONCLUSION AND IMPLICATIONS

In vitro characterisation demonstrated that WKYMVm and ACT-389949 differ from BMS-986235 and compound 43 in their signalling and protein coupling profile. This observation may be explained by differences in the ligand-receptor interactions. In vitro characterisation provided significant insights into identifying the desired bias profile for FPR2-based pharmacotherapy.

Resolution of inflammation, an active process to restore the immune microenvironment balance: A novel drug target for treating arterial hypertension

The resolution of inflammation, the other side of the inflammatory response, is defined as an active and highly coordinated process that promotes the restoration of immune microenvironment balance and tissue repair. Inflammation resolution involves several key processes, including dampening proinflammatory signaling, specialized proresolving lipid mediator (SPM) production, nonlipid proresolving mediator production, efferocytosis and regulatory T-cell (Treg) induction. In recent years, increasing attention has been given to the effects of inflammation resolution on hypertension. Furthermore, our previous studies reported the antihypertensive effects of SPMs. Therefore, in this review, we aim to summarize and discuss the detailed association between arterial hypertension and inflammation resolution. Additional, the association between gut microbe-mediated immune and hypertension is discussed. This findings suggested that accelerating the resolution of inflammation can have beneficial effects on hypertension and its related organ damage. Exploring novel drug targets by focusing on various pathways involved in accelerating inflammation resolution will contribute to the treatment and control of hypertensive diseases in the future.

Systemic administration of Resolvin D1 reduces cancer-induced bone pain in mice: Lack of sex dependency in pain development and analgesia

AIMS

Bone cancer produces severe pain that is treated with opioids, but serious side effects limit opioid utilization. There is therefore a need to develop effective and safe non-opioid alternatives. The lipid mediator, Resolvin D1 (RvD1), could be a prospective candidate for cancer pain treatment. To assess RvD1 and other potential candidates, appropriate animal models that recapitulate clinical features must be used. Although several preclinical models of cancer pain have been developed, the influence of sex on the development of cancer pain and the effectiveness of RvD1 have not been studied.

RESULTS

Using a mouse model of fibrosarcoma growth in and around the calcaneus bone, we demonstrated that the mechanical hyperalgesia in the tumor-bearing hind paw develops independently of sex, except that it developed a little sooner in female mice. A single intravenous injection of RvD1 (0.001-10 μg/kg) decreased hyperalgesia in both sexes with similar potency (ED50 = 0.0015 μg/kg) and efficacy. Repeated daily administration of 10 μg/kg RvD1 prolonged the analgesic effect and completely abolished hyperalgesia. This was also independent of sex.

CONCLUSION

In this preclinical mouse model of bone cancer pain, the development of pain and the analgesic effectiveness of RvD1 are not influenced by sex.

Advances in the Chemistry and Biology of Specialised Pro-Resolving Mediators (SPMs)

This review article assembles key recent advances in the synthetic chemistry and biology of specialised pro-resolving mediators (SPMs). The major medicinal chemistry developments in the design, synthesis and biological evaluation of synthetic SPM analogues of lipoxins and resolvins have been discussed. These include variations in the top and bottom chains, as well as changes to the triene core, of lipoxins, all changes intended to enhance the metabolic stability whilst retaining or improving biological activity. Similar chemical modifications of resolvins are also discussed. The biological evaluation of these synthetic SPMs is also described in some detail. Original investigations into the biological activity of endogenous SPMs led to the pairing of these ligands with the FPR2/LX receptor, and these results have been challenged in more recent work, leading to conflicting results and views, which are again discussed.

Highlighting the Effect of Pro-inflammatory Mediators in the Pathogenesis of Periodontal Diseases and Alzheimer's Disease

Alzheimer's disease (AD) is a neurological condition that is much more common as people get older. It may start out early or late. Increased levels of pro-inflammatory cytokines and microglial activation, both of which contribute to the central nervous system's inflammatory state, are characteristics of AD. As opposed to this, periodontitis is a widespread oral infection brought on by Gram-negative anaerobic bacteria. By releasing pro-inflammatory cytokines into the systemic circulation, periodontitis can be classified as a "low-grade systemic disease." Periodontitis and AD are linked by inflammation, which is recognized to play a crucial part in both the disease processes. The current review sought to highlight the effects of pro-inflammatory cytokines, which are released during periodontal and Alzheimer's diseases in the pathophysiology of both conditions. It also addresses the puzzling relationship between AD and periodontitis, highlighting the etiology and potential ramifications.

The formyl peptide receptors FPR1 and FPR2 as targets for inflammatory disorders: recent advances in the development of small-molecule agonists

Formyl peptide receptors (FPRs) comprise a class of chemoattractant pattern recognition receptors, for which several physiological functions like host-defences, as well as the regulation of inflammatory responses, have been ascribed. With accumulating evidence that agonism of FPR1/FPR2 can confer pro-resolution of inflammation, increased attention from academia and industry has led to the discovery of new and interesting small-molecule FPR1/FPR2 agonists. Focused attention on the development of appropriate physicochemical and pharmacokinetic profiles is yielding synthesis of new compounds with promising in vivo readouts. This review presents an overview of small-molecule FPR1/FPR2 agonist medicinal chemistry developed over the past 20 years, with a particular emphasis on interrogation in the increasingly sophisticated bioassays which have been developed.

FoxO4 mediates macrophage M2 polarization by promoting LXA4R expression in an ovalbumin-induced allergic asthma model in mice

BACKGROUND

Asthma imposes a heavy burden due to its high prevalence. Forkhead box O4 (FoxO4) proteins participate in the modulation of cell progression. However, the role and mechanism of FoxO4 in asthma remains uncharted.

METHODS

An allergic asthma model was constructed by the induction of ovalbumin and interleukin (IL)-4 in mice and monocyte/macrophage-like Raw264.7 cells, respectively. The role and mechanism of FoxO4 in asthma was determined by pathological staining, immunofluorescence assay, measurement of inflammatory cells in the blood, reverse transcription quantitative polymerase chain reaction (RT-qPCR), Western blot analysis, and flow cytometry.

RESULTS

Ovalbumin treatment triggered an obvious inflammatory cell infiltration with a prominent increase in F4/80⁺ cell numbers. The relative messenger RNA (mRNA) and protein expressions of FoxO4 were increased in both ovalbumin-induced mice and interleukin-4 (IL-4)-induced Raw264.7 cells. Inhibition of FoxO4 via AS1842856 reduced inflammatory cell infiltration, the number of Periodic Acid Schiff+ (PAS+) goblet cells, the numbers of inflammatory cells in the blood, and the airway resistance in ovalbumin-induced mice. Besides, interference of FoxO4 decreased the number of F4/80⁺CD206⁺ cells, and the relative protein expressions of CD163 and Arg1 in vivo and in vitro. Mechanically, suppression of FoxO4 diminished the relative mRNA and protein expressions of LXA4R in both ovalbumin-induced mice and IL-4-induced Raw264.7 cells. Overexpression of LXA4R reversed the outcomes caused by repression of FoxO4, including airway resistance, the number of F4/80+ cells, the proportion of CD206+ cells in ovalbumin-induced mice, and the proportion of F4/80⁺CD206⁺ cells in IL-4-induced Raw264.7 cells.

CONCLUSION

FoxO4/LXA4R axis mediated macrophage M2 polarization in allergic asthma.

Therapeutic activity of lipoxin A4 in TiO2-induced arthritis in mice: NF-κB and Nrf2 in synovial fluid leukocytes and neuronal TRPV1 mechanisms

Background

Lipoxin A4 (LXA4) has anti-inflammatory and pro-resolutive roles in inflammation. We evaluated the effects and mechanisms of action of LXA4 in titanium dioxide (TiO2) arthritis, a model of prosthesis-induced joint inflammation and pain.

Methods

Mice were stimulated with TiO2 (3mg) in the knee joint followed by LXA4 (0.1, 1, or 10ng/animal) or vehicle (ethanol 3.2% in saline) administration. Pain-like behavior, inflammation, and dosages were performed to assess the effects of LXA4 in vivo.

Results

LXA4 reduced mechanical and thermal hyperalgesia, histopathological damage, edema, and recruitment of leukocytes without liver, kidney, or stomach toxicity. LXA4 reduced leukocyte migration and modulated cytokine production. These effects were explained by reduced nuclear factor kappa B (NFκB) activation in recruited macrophages. LXA4 improved antioxidant parameters [reduced glutathione (GSH) and 2,2-azino-bis 3-ethylbenzothiazoline-6-sulfonate (ABTS) levels, nuclear factor erythroid 2-related factor 2 (Nrf2) mRNA and Nrf2 protein expression], reducing reactive oxygen species (ROS) fluorescent detection induced by TiO2 in synovial fluid leukocytes. We observed an increase of lipoxin receptor (ALX/FPR2) in transient receptor potential cation channel subfamily V member 1 (TRPV1)+ DRG nociceptive neurons upon TiO2 inflammation. LXA4 reduced TiO2-induced TRPV1 mRNA expression and protein detection, as well TRPV1 co-staining with p-NFκB, indicating reduction of neuronal activation. LXA4 down-modulated neuronal activation and response to capsaicin (a TRPV1 agonist) and AITC [a transient receptor potential ankyrin 1 (TRPA1) agonist] of DRG neurons.

Conclusion

LXA4 might target recruited leukocytes and primary afferent nociceptive neurons to exert analgesic and anti-inflammatory activities in a model resembling what is observed in patients with prosthesis inflammation.

Resolution Pharmacology: Focus on Pro-Resolving Annexin A1 and Lipid Mediators for Therapeutic Innovation in Inflammation

Chronic diseases that affect our society are made more complex by comorbidities and are poorly managed by the current pharmacology. While all present inflammatory etiopathogeneses, there is an unmet need for better clinical management of these diseases and their multiple symptoms. We discuss here an innovative approach based on the biology of the resolution of inflammation. Studying endogenous pro-resolving peptide and lipid mediators, how they are formed, and which target they interact with, can offer innovative options through augmenting the expression or function of pro-resolving pathways or mimicking their actions with novel targeted molecules. In all cases, resolution offers innovation for the treatment of the primary cause of a given disease and/or for the management of its comorbidities, ultimately improving patient quality of life. By implementing resolution pharmacology, we harness the whole physiology of inflammation, with the potential to bring a marked change in the management of inflammatory conditions.

Lipoxin Mimetics and the Resolution of Inflammation

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

Lipid Metabolic Alterations in KRAS Mutant Tumors: Unmasking New Vulnerabilities for Cancer Therapy

KRAS is one of the most commonly mutated genes, an event that leads to development of highly aggressive and resistant to any type of available therapy tumors. Mutated KRAS drives a complex network of lipid metabolic rearrangements to support the adaptation of cancer cells to harsh environmental conditions and ensure their survival. Because there has been only a little success in the continuous efforts of effectively targeting KRAS-driven tumors, it is of outmost importance to delineate the exact mechanisms of how they get rewired, leading to this distinctive phenotype. Therefore, the aim of this review is to summarize the available data acquired over the last years with regard to the lipid metabolic regulation of KRAS-driven tumors and elucidate their specific characteristics in an attempt to unravel novel therapeutic targets.

The role of oxylipins in NSAID-exacerbated respiratory disease (N-ERD)

Nonsteroidal anti-inflammatory drug (NSAID)-exacerbated respiratory disease (N-ERD) is characterized by nasal polyp formation, adult-onset asthma, and hypersensitivity to all cyclooxygenase-1 (COX-1) inhibitors. Oxygenated lipids are collectively known as oxylipins and are polyunsaturated fatty acids (PUFA) oxidation products. The most extensively researched oxylipins being the eicosanoids formed from arachidonic acid (AA). There are four major classes of eicosanoids including leukotrienes, prostaglandins, thromboxanes, and lipoxins. In N-ERD, the underlying inflammatory process of the upper and lower respiratory systems begins and occurs independently of NSAID consumption and is due to the overproduction of cysteinyl leukotrienes. Leukotriene mediators all induce edema, bronchoconstriction, and airway mucous secretion. Thromboxane A2 is a potent bronchoconstrictor and induces endothelial adhesion molecule expression. Elevated Prostaglandin D2 metabolites lead to vasoconstriction, additionally impaired up-regulation of prostaglandin E2 leads to symptoms seen in N-ERD as it is essential for maintaining homeostasis of inflammatory responses in the airway and has bronchoprotective and anti-inflammatory effects. A characteristic feature of N-ERD is diminished lipoxin levels, this decreased capacity to form endogenous mediators with anti-inflammatory properties could facilitate local inflammatory response and expose bronchial smooth muscle to relatively unopposed actions of broncho-constricting substances. Treatment options, such as leukotriene modifying agents, aspirin desensitization, biologic agents and ESS, appear to influence eicosanoid pathways, however more studies need to be done to further understand the role of oxylipins. Besides AA-derived eicosanoids, other oxylipins may also pay a role but have not been sufficiently studied. Identifying pathogenic N-ERD mechanism is likely to define more effective treatment targets.

Formyl peptide receptor 2 as a potential therapeutic target for inflammatory bowel disease

Inflammatory bowel disease (IBD) is a global health burden whose existing treatment is largely dependent on anti-inflammatory agents. Despite showing some therapeutic actions, their clinical efficacy and adverse events are unacceptable. Resolution as an active and orchestrated phase of inflammation involves improper inflammatory response with three key triggers, specialized pro-resolving mediators (SPMs), neutrophils and phagocyte efferocytosis. The formyl peptide receptor 2 (FPR2/ALX) is a human G protein-coupled receptor capable of binding SPMs and participates in the resolution process. This receptor has been implicated in several inflammatory diseases and its association with mouse model of IBD was established in some resolution-related studies. Here, we give an overview of three reported FPR2/ALX agonists highlighting their respective roles in pro-resolving strategies.

Differential effects of acetylsalicylic acid and mitomycin C on cytokine-induced Tenon's capsule myofibroblast transdifferentiation and activity: Implications for glaucoma surgery

Inflammation-driven scarring is a major contributor to surgical failure after subconjunctival bleb forming glaucoma surgery. The current gold standard anti-scarring adjuvant mitomycin C (MMC) has variable effectiveness and is associated with significant risks. Acetylsalicylic acid (ASA), when delivered locally, repurposes the typically pro-inflammatory cyclooxygenase (COX-2) signaling for the resolution of inflammation and mitigating inflammation-mediated fibrosis. The aim of this study is to compare the effects of ASA and MMC in an in vitro model of subconjunctival scarring. Glaucoma patient-derived Tenon's capsule fibroblasts (HTCFs) were treated with TGFβ1 (2 ng/mL) plus or minus ASA (1600 μg/ml), or MMC (0.05, 0.1, 0.2 mg/mL). In vitro collagen contraction, MTT, LDH, immunofluorescence, and Western blot assays were performed. To elucidate the mechanistic effects of ASA in TGFβ1-induced HTCFs, liquid chromatography tandem mass spectrometry (LC-MS/MS) was used to identify and measure pro-inflammatory and pro-resolving lipid mediator secretion. ASA was at least as effective as MMC in reducing TGFβ1-induced HTCF-mediated collagen contraction, metabolic activity, and pro-fibrotic protein expression, with less cytotoxicity. Within cytokine-activated HTCFs, ASA significantly impaired secretion of pro-inflammatory lipid mediators prostaglandin E2 and 6-keto-prostaglandin F1α and significantly increased secretion of the pro-resolving mediators 5-hydroxyeicosatetraenoic acid (HETE), 15-HETE and 18-hydroxyeicosapentaenoic acid (HEPE). ASA reduces cytokine-induced myofibroblast transdifferentiation in HTCFs, being non-inferior to MMC in vitro. ASA's effects are associated with a unique lipid mediator expression profile, suggesting that the ASA-induced resolution of inflammation may be a promising strategy to mitigate inflammation-mediated scarring and could offer a novel alternative as a surgical adjuvant.

Formylpeptide receptor 2: Nomenclature, structure, signalling and translational perspectives: IUPHAR review 35

We discuss the fascinating pharmacology of formylpeptide receptor 2 (FPR2; often referred to as FPR2/ALX since it binds lipoxin A₄ ). Initially identified as a low-affinity 'relative' of FPR1, FPR2 presents complex and diverse biology. For instance, it is activated by several classes of agonists (from peptides to proteins and lipid mediators) and displays diverse expression patterns on myeloid cells as well as epithelial cells and endothelial cells, to name a few. Over the last decade, the pharmacology of FPR2 has progressed from being considered a weak chemotactic receptor to a master-regulator of the resolution of inflammation, the second phase of the acute inflammatory response. We propose that exploitation of the biology of FPR2 offers innovative ways to rectify chronic inflammatory states and represents a viable avenue to develop novel therapies. Recent elucidation of FPR2 structure will facilitate development of the anti-inflammatory and pro-resolving drugs of next decade.

Specialized Proresolving Lipid Meditators Agonistic to Formyl Peptide Receptor Type 2 Attenuate Ischemia-reperfusion Injury in Rat Lung

BACKGROUND

Lung ischemia-reperfusion injury (IRI) is a form of acute lung injury characterized by nonspecific alveolar damage and lung edema due to robust inflammation. Little is known about the roles of specialized proresolving lipid mediators (SPMs) in lung IRI. Therefore, we aimed to evaluate the dynamic changes in endogenous SPMs during the initiation and resolution of lung IRI and to determine the effects of SPM supplementation on lung IRI.

METHODS

We used a rat left hilar clamp model with 90 min of ischemia, followed by reperfusion. Dynamic changes in endogenous SPMs were evaluated using liquid chromatography-tandem mass spectrometry.

RESULTS

Endogenous SPMs in the left lung showed a decreasing trend after 1 h of reperfusion. Oxygenation improved between 3 and 7 d following reperfusion; however, the level of endogenous SPMs remained low compared with that in the naïve lung. Among SPM receptors, only formyl peptide receptor type 2 (ALX/FPR2) gene expression in the left lung was increased 3 h after reperfusion, and the inflammatory cells were immunohistochemically positive for ALX/FPR2. Administration of aspirin-triggered (AT) resolvin D1 (AT-RvD1) and AT lipoxin A4 (AT-LXA4), which are agonistic to ALX/FPR2, immediately after reperfusion improved lung function, reduced inflammatory cytokine levels, attenuated lung edema, and decreased neutrophil infiltration 3 h after reperfusion. The effects of AT-RvD1 and AT-LXA4 were not observed after pretreatment with the ALX/FPR2 antagonist.

CONCLUSIONS

The level of intrapulmonary endogenous SPMs decreased during lung IRI process and the administration of AT-RvD1 and AT-LXA4 prevented the exacerbation of lung injury via ALX/FPR2.

Acid-Responsive Dual-Targeted Nanoparticles Encapsulated Aspirin Rescue the Immune Activation and Phenotype in Autism Spectrum Disorder

The treatment of autism spectrum disorder (ASD) is one of the most difficult challenges in neurodevelopmental diseases, because of the unclear pathogenesis research and low brain-lesion targeting efficiency. Besides, maternal immune activation has been reported as the most mature and widely used model of ASD and aspirin-triggered lipoxin A4 is a potent anti-inflammatory mediator being involved in the resolution of neuroinflammation in ASD. Therefore, an aspirin encapsulated cascade drug delivery system (Asp@TMNPs) is established, which can successively target the blood-brain barrier (BBB) and microglial cells and response to the acid microenvironment in lysosome. As a result, the mitochondrial oxidative stress, DNA damage, and inflammation of microglial cells are prominently alleviated. After the treatment of Asp@TMNPs, the social interaction, stereotype behavior, and anxious condition of ASD mice are notably improved and the activation of microglial cells is inhibited. Overall, this system successively penetrates the BBB and targets microglial cells, therefore, it significantly enhances the intracephalic drug accumulation and improves anti-neuroinflammatory efficacy of aspirin, providing a promising strategy for ASD treatment.

Formation, Signaling and Occurrence of Specialized Pro-Resolving Lipid Mediators-What is the Evidence so far?

Formation of specialized pro-resolving lipid mediators (SPMs) such as lipoxins or resolvins usually involves arachidonic acid 5-lipoxygenase (5-LO, ALOX5) and different types of arachidonic acid 12- and 15-lipoxygenating paralogues (15-LO1, ALOX15; 15-LO2, ALOX15B; 12-LO, ALOX12). Typically, SPMs are thought to be formed via consecutive steps of oxidation of polyenoic fatty acids such as arachidonic acid, eicosapentaenoic acid or docosahexaenoic acid. One hallmark of SPM formation is that reported levels of these lipid mediators are much lower than typical pro-inflammatory mediators including the monohydroxylated fatty acid derivatives (e.g., 5-HETE), leukotrienes or certain cyclooxygenase-derived prostaglandins. Thus, reliable detection and quantification of these metabolites is challenging. This paper is aimed at critically evaluating i) the proposed biosynthetic pathways of SPM formation, ii) the current knowledge on SPM receptors and their signaling cascades and iii) the analytical methods used to quantify these pro-resolving mediators in the context of their instability and their low concentrations. Based on current literature it can be concluded that i) there is at most, a low biosynthetic capacity for SPMs in human leukocytes. ii) The identity and the signaling of the proposed G-protein-coupled SPM receptors have not been supported by studies in knock-out mice and remain to be validated. iii) In humans, SPM levels were neither related to dietary supplementation with their ω-3 polyunsaturated fatty acid precursors nor were they formed during the resolution phase of an evoked inflammatory response. iv) The reported low SPM levels cannot be reliably quantified by means of the most commonly reported methodology. Overall, these questions regarding formation, signaling and occurrence of SPMs challenge their role as endogenous mediators of the resolution of inflammation.

The utilisation of resolvins in medicine and tissue engineering

Recent advances in the field of regenerative medicine and biomaterial science have highlighted the importance of controlling immune cell phenotypes at the biomaterial interface. These studies have clearly indicated that a rapid resolution of the inflammatory process, mediated by a switch in the macrophage population towards a reparative phenotype, is essential for tissue regeneration to occur. While various biomaterial surfaces have been developed in order to impart immunomodulatory properties to the resulting constructs, an alternative strategy involving the use of reparative biological cues, known as resolvins, is emerging in regenerative medicine. This review reports on the mechanisms via which resolvins participate in the resolution of inflammation and describes their current utilisation in pre-clinical and clinical settings, along with their effectiveness when combined with biomaterial constructs in tissue engineering applications. STATEMENT OF SIGNIFICANCE: The resolution of the inflammatory process is necessary for achieving tissue healing and regeneration. Resolvins are lipid mediators and play a key role in the resolution of the inflammatory response and can be used in as biological cues to promote tissue regeneration. This review describes the various biological inflammatory mechanisms and pathways involving resolvins and how their action results in a pro-healing response. The use of these molecules in the clinical setting is then summarised for various applications along with their limitations. Lastly, the review focuses on the emergence resolvins in tissue engineering products including the use of a more stable form which holds greater prospect for regenerative purposes.

Lipoxin A4 Receptor Stimulation Attenuates Neuroinflammation in a Mouse Model of Intracerebral Hemorrhage

Intracerebral hemorrhage (ICH) is caused by the rupture of blood vessels in the brain. The excessive activation of glial cells and the infiltration of numerous inflammatory cells are observed during bleeding. Thrombin is a key molecule that triggers neuroinflammation in the ICH brain. In this study, we focused on lipoxin A₄ (LXA₄), an arachidonic acid metabolite that has been reported to suppress inflammation and cell migration. LXA₄ and BML-111, an agonist of the LXA₄ receptor/formyl peptide receptor 2 (ALX/FPR2), suppressed microglial activation; LXA₄ strongly inhibited the migration of neutrophil-like cells in vitro. ALX/FPR2 was expressed on neutrophils in the ICH mouse brain and the daily administration of BML-111 attenuated the motor coordination dysfunction and suppressed the production of proinflammatory cytokines in the ICH mouse brain. On the other hand, BML-111 did not show a significant reduction in the number of microglia and neutrophils. These results suggest that systemic administration of ALX/FPR2 agonists may suppress the neuroinflammatory response of microglia and neutrophils without a change in cell numbers. Additionally, their combination with molecules that reduce cell numbers, such as modulators of leukotriene B₄ signaling, may be required in future studies.

Resolvin D1 Attenuates Doxorubicin-Induced Cardiotoxicity by Inhibiting Inflammation, Oxidative and Endoplasmic Reticulum Stress

Resolvin D1 (RvD1) is a lipid mediator that promotes resolution of inflammation. However, the function of RvD1 in doxorubicin- (Dox-) induced cardiotoxicity remains to be clarified. This study aimed to investigate whether RvD1 could attenuate Dox-induced cardiac injury. The mice were divided into three groups: control, Dox (20 mg/kg, once, intraperitoneally), and Dox + RvD1. RvD1 (2.5 μg/kg, intraperitoneally) was injected daily for 5 days. Echocardiography was performed to evaluate the cardiac function, and the heart tissue and serum samples were collected for further analyses. The results showed that RvD1 attenuated the decreased ratio of heart weight/body weight and heart weight/tibia length, the increased level of creatine kinase and activity of lactate dehydrogenase after Dox treatment. RvD1 improved the ejection fraction and fractional shortening of left ventricular and attenuated the severity of apoptosis induced by Dox. As for the underlying pathways, the results showed that RvD1 reduced the expression of IL-1 and IL-6, and attenuated the phosphorylation of P65 in cardiac tissue. RvD1 attenuated the oxidative stress induced by Dox, as demonstrated by the attenuated levels of superoxide dismutase, glutathione, and malondialdehyde, decreased expression of Nox-2 and Nox-4 and increased expression of Nrf-2 and HO-1. In addition, RvD1 also inhibited the endoplasmic reticulum stress induced by Dox. These results indicate the potential therapeutic benefits of RvD1 in Dox-induced cardiotoxicity in mice, and the mechanism may be related to the attenuated inflammation, oxidative stress and endoplasmic reticulum stress.

Specialized pro-resolving mediators as modulators of immune responses

Specialized pro-resolving mediators (SPMs) are endogenous small molecules produced mainly from dietary omega-3 polyunsaturated fatty acids by both structural cells and cells of the active and innate immune systems. Specialized pro-resolving mediators have been shown to both limit acute inflammation and promote resolution and return to homeostasis following infection or injury. There is growing evidence that chronic immune disorders are characterized by deficiencies in resolution and SPMs have significant potential as novel therapeutics to prevent and treat chronic inflammation and immune system disorders. This review focuses on important breakthroughs in understanding how SPMs are produced by, and act on, cells of the adaptive immune system, specifically macrophages, B cells and T cells. We also highlight recent evidence demonstrating the potential of SPMs as novel therapeutic agents in topics including immunization, autoimmune disease and transplantation.

Resolution of inflammation: An organizing principle in biology and medicine

The resolution of inflammation has emerged as a critical endogenous process that protects host tissues from prolonged or excessive inflammation that can become chronic. Failure of the resolution of inflammation is a key pathological mechanism that drives the progression of numerous inflammation-driven diseases. Essential polyunsaturated fatty acid (PUFA)-derived autacoid mediators termed 'specialized pro-resolving mediators' (SPMs) regulate endogenous resolution programs by limiting further neutrophil tissue infiltration and stimulating local immune cell (e.g., macrophage)-mediated clearance of apoptotic polymorphonuclear neutrophils, cellular debris, and microbes, as well as counter-regulating eicosanoid/cytokine production. The SPM superfamily encompasses lipoxins, resolvins, protectins, and maresins. Our understanding of the resolution phase of acute inflammation has grown exponentially in the past three decades with the discovery of novel pro-resolving lipid mediators, their pro-efferocytosis mechanisms, and their receptors. Technological advancement has further facilitated lipid mediator metabolipidomic based profiling of healthy and diseased human tissues, highlighting the extraordinary therapeutic potential of SPMs across a broad array of inflammatory diseases including cancer. As current front-line cancer therapies such as surgery, chemotherapy, and radiation may induce various unwanted side effects such as robust pro-inflammatory and pro-tumorigenic host responses, characterizing SPMs and their receptors as novel therapeutic targets may have important implications as a new direction for host-targeted cancer therapy. Here, we discuss the origins of inflammation resolution, key discoveries and the failure of resolution mechanisms in diseases with an emphasis on cancer, and future directions focused on novel therapeutic applications for this exciting and rapidly expanding field.

Sex Differences in Otolaryngology: Focus on the Emerging Role of Estrogens in Inflammatory and Pro-Resolving Responses

Otolaryngology (also known as ear, nose, and throat (ENT)) diseases can be significantly affected by the level of sex hormones, which indicates that sex differences affect the manifestation, pathophysiology, and outcomes of these diseases. Recently, increasing evidence has suggested that proinflammatory responses in ENT diseases are linked to the level of sex hormones. The sex hormone receptors are present on a wide variety of immune cells; therefore, it is evident that they play crucial roles in regulating the immune system and hence affect the disease progression of ENT diseases. In this review, we focus on how sex hormones, particularly estrogens, regulate ENT diseases, such as chronic rhinosinusitis, vocal fold polyps, thyroid cancer, Sjögren’s syndrome, and head and neck cancers, from the perspectives of inflammatory responses and specialized proresolving mediator-driven resolution. This paper aims to clarify why considering sex differences in the field of basic and medical research on otolaryngology is a key component to successful therapy for both males and females in the future.

Lipoxins and synthetic lipoxin mimetics: Therapeutic potential in renal diseases

Inflammation and its timely resolution are critical to ensuring effective host defence and appropriate tissue repair after injury. Unresolved inflammation typifies many renal pathologies. The key drivers of the inflammatory response are well defined and targeted by conventional anti-inflammatory therapeutics. However, these are associated with undesirable side effects including immune suppression. More recently, there is growing appreciation that specialized lipid mediators [SPMs] including lipoxins promote the resolution of inflammation and endogenous repair mechanisms without compromising host defence. We discuss the pro-resolving bioactions of lipoxins and recent work that aims to harness their therapeutic potential in the context of kidney disease.

A review of non-prostanoid, eicosanoid receptors: expression, characterization, regulation, and mechanism of action

Eicosanoid signaling controls a wide range of biological processes from blood pressure homeostasis to inflammation and resolution thereof to the perception of pain and to cell survival itself. Disruption of normal eicosanoid signaling is implicated in numerous disease states. Eicosanoid signaling is facilitated by G-protein-coupled, eicosanoid-specific receptors and the array of associated G-proteins. This review focuses on the expression, characterization, regulation, and mechanism of action of non-prostanoid, eicosanoid receptors.

Aspirin Actions in Treatment of NSAID-Exacerbated Respiratory Disease

Non-steroidal Anti-inflammatory drugs (NSAID)-exacerbated respiratory disease (N-ERD) is characterized by nasal polyposis, chronic rhinosinusitis, adult-onset asthma and hypersensitive reactions to cyclooxygenase-1 (COX-1) inhibitors. Among the available treatments for this disease, a combination of endoscopic sinus surgery followed by aspirin desensitization and aspirin maintenance therapy has been an effective approach. Studies have shown that long-term aspirin maintenance therapy can reduce the rate of nasal polyp recurrence in patients with N-ERD. However, the exact mechanism by which aspirin can both trigger and suppress airway disease in N-ERD remains poorly understood. In this review, we summarize current knowledge of aspirin effects in N-ERD, cardiovascular disease, and cancer, and consider potential mechanistic pathways accounting for the effects of aspirin in N-ERD.

Specialized Pro-Resolving Mediators and the Lymphatic System

Diminished lymphatic function and abnormal morphology are common in chronic inflammatory diseases. Recent studies are investigating whether it is possible to target chronic inflammation by promoting resolution of inflammation, in order to enhance lymphatic function and attenuate disease. Resolution of inflammation is an active process regulated by bioactive lipids known as specialized pro-resolving mediators (SPMs). SPMs can modulate leukocyte migration and function, alter cytokine/chemokine release, modify autophagy, among other immune-related activities. Here, we summarize the role of the lymphatics in resolution of inflammation and lymphatic impairment in chronic inflammatory diseases. Furthermore, we discuss the current literature describing the connection between SPMs and the lymphatics, and the possibility of targeting the lymphatics with innovative SPM therapy to promote resolution of inflammation and mitigate disease.

Carcinogenesis: Failure of resolution of inflammation?

Inflammation in the tumor microenvironment is a hallmark of cancer and is recognized as a key characteristic of carcinogens. However, the failure of resolution of inflammation in cancer is only recently being understood. Products of arachidonic acid and related fatty acid metabolism called eicosanoids, including prostaglandins, leukotrienes, lipoxins, and epoxyeicosanoids, critically regulate inflammation, as well as its resolution. The resolution of inflammation is now appreciated to be an active biochemical process regulated by endogenous specialized pro-resolving lipid autacoid mediators which combat infections and stimulate tissue repair/regeneration. Environmental and chemical human carcinogens, including aflatoxins, asbestos, nitrosamines, alcohol, and tobacco, induce tumor-promoting inflammation and can disrupt the resolution of inflammation contributing to a devastating global cancer burden. While mechanisms of carcinogenesis have focused on genotoxic activity to induce mutations, nongenotoxic mechanisms such as inflammation and oxidative stress promote genotoxicity, proliferation, and mutations. Moreover, carcinogens initiate oxidative stress to synergize with inflammation and DNA damage to fuel a vicious feedback loop of cell death, tissue damage, and carcinogenesis. In contrast, stimulation of resolution of inflammation may prevent carcinogenesis by clearance of cellular debris via macrophage phagocytosis and inhibition of an eicosanoid/cytokine storm of pro-inflammatory mediators. Controlling the host inflammatory response and its resolution in carcinogen-induced cancers will be critical to reducing carcinogen-induced morbidity and mortality. Here we review the recent evidence that stimulation of resolution of inflammation, including pro-resolution lipid mediators and soluble epoxide hydrolase inhibitors, may be a new chemopreventive approach to prevent carcinogen-induced cancer that should be evaluated in humans.

Role of specialized pro-resolving lipid mediators and their receptors in virus infection: a promising therapeutic strategy for SARS-CoV-2 cytokine storm

Unexpected viral infections outbreaks, significantly affect human health, leading to increased mortality and life disruption. Among them is the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which emerged as a deadly pandemic, calling for intense research efforts on its pathogenicity mechanism and development of therapeutic strategies. In the SARS-CoV-2 cytokine storm, systemic inflammation has been associated with severe illness and mortality. Recent studies have demonstrated special pro-resolving lipids mediators (SPMs) lipoxins, resolvins, maresins, and protectins as potential therapeutic options for abnormal viral-triggered inflammation. Pro-resolving lipids mediators have shown great promise for the treatment of Herpes simplex virus, respiratory syncytial virus, human immunodeficiency virus, and hepatitis C virus. Based on this, studies are being conducted on their therapeutic effects in SARS-CoV-2 infection. In this review, we discussed SPMs and reviewed evidence from recent studies on SPMs as therapeutic options for viral infections, including SARS-CoV2. Based on our analysis of the previous study, we argue that SPMs are a potential treatment for SARS-CoV-2 infection and other viral infections. We expect further research on how SPMs modulate viral-triggered inflammation through G-protein-coupled receptors (GPCRs), and chemical stability and druggability of SPMs.

Therapeutic Effects of Specialized Pro-Resolving Lipids Mediators on Cardiac Fibrosis via NRF2 Activation

Heart disease is the number one mortality disease in the world. In particular, cardiac fibrosis is considered as a major factor causing myocardial infarction and heart failure. In particular, oxidative stress is a major cause of heart fibrosis. In order to control such oxidative stress, the importance of nuclear factor erythropoietin 2 related factor 2 (NRF2) has recently been highlighted. In this review, we will discuss the activation of NRF2 by docosahexanoic acid (DHA), eicosapentaenoic acid (EPA), and the specialized pro-resolving lipid mediators (SPMs) derived from polyunsaturated lipids, including DHA and EPA. Additionally, we will discuss their effects on cardiac fibrosis via NRF2 activation.

The 15-Epilipoxin-A4 Pathway with Prophylactic Aspirin in Preventing Preeclampsia: A Longitudinal Cohort Study

INTRODUCTION

The benefit of aspirin in preventing preeclampsia is increasingly recognized; however, its mechanism of action remains unclear. Nonobstetric studies have described an anti-inflammatory effect of aspirin through the 15-epilipoxin-A4 pathway (aspirin-triggered lipoxin [ATL]). However, the anti-inflammatory mechanism of aspirin in the prevention of preeclampsia remains unknown.

OBJECTIVE/HYPOTHESIS

To examine (1) the difference in longitudinal endogenous lipoxin-A4 (En-Lipoxin-A4) concentration in low-risk (LR) and high-risk (HR) pregnancies, and (2) the effect of aspirin on endogenous ATL concentration and the associated effect on cytokine profile of HR women.

METHODS

Plasma from 220 HR women was collected at 12, 16, 20, 24, 28, 32, and 36 weeks of gestation. Adherence to aspirin was biochemically verified. Plasma En-Lipoxin-A4 and ATL concentrations were analyzed using liquid chromatography mass spectrometry, and cytokines, interleukin (IL)-10, tumor necrosis factor-α, interferon-γ, IL-8, and IL-1β, with the high-sensitivity multibead Luminex® assay.

RESULTS

HR women have up to 70% lower plasma concentration of En-Lipoxin-A4 (P < 0.001) than LR women. HR women with adequate aspirin adherence (HR-AA) (n = 82) had higher plasma concentration of ATL (P < .001), lower concentration of IL-8 from 16 to 36 weeks of gestation (P < .001), and increased IL-10 concentration from 16 to 28 weeks of gestation (P = .03) compared with high-risk women who were not on aspirin (HR-NA). HR-AA who did not develop preeclampsia had higher plasma En-lipoxin-A4 (P < .001), ATL (P = .02), and IL-10 concentrations (P < .001) with lower IL-8 concentration (P = .004) than HR women who developed preeclampsia.

DISCUSSION

Plasma concentration of En-Lipoxin-A4 is lower in HR women than in LR controls. Adequate adherence with aspirin results in an increase in ATL and IL-10 with reduced IL-8 plasma concentration. This study suggests a potential anti-inflammatory role of aspirin through the ATL pathway with prophylactic aspirin in HR pregnant women.

Lipid Mediators in Critically Ill Patients: A Step Towards Precision Medicine

A dysregulated response to systemic inflammation is a common pathophysiological feature of most conditions encountered in the intensive care unit (ICU). Recent evidence indicates that a dysregulated inflammatory response is involved in the pathogenesis of various ICU-related disorders associated with high mortality, including sepsis, acute respiratory distress syndrome, cerebral and myocardial ischemia, and acute kidney injury. Moreover, persistent or non-resolving inflammation may lead to the syndrome of persistent critical illness, characterized by acquired immunosuppression, catabolism and poor long-term functional outcomes. Despite decades of research, management of many disorders in the ICU is mostly supportive, and current therapeutic strategies often do not take into account the heterogeneity of the patient population, underlying chronic conditions, nor the individual state of the immune response. Fatty acid-derived lipid mediators are recognized as key players in the generation and resolution of inflammation, and their signature provides specific information on patients' inflammatory status and immune response. Lipidomics is increasingly recognized as a powerful tool to assess lipid metabolism and the interaction between metabolic changes and the immune system via profiling lipid mediators in clinical studies. Within the concept of precision medicine, understanding and characterizing the individual immune response may allow for better stratification of critically ill patients as well as identification of diagnostic and prognostic biomarkers. In this review, we provide an overview of the role of fatty acid-derived lipid mediators as endogenous regulators of the inflammatory, anti-inflammatory and pro-resolving response and future directions for use of clinical lipidomics to identify lipid mediators as diagnostic and prognostic markers in critical illness.

The Contribution of Formyl Peptide Receptor Dysfunction to the Course of Neuroinflammation: A Potential Role in the Brain Pathology

Chronic inflammatory processes within the central nervous system (CNS) are in part responsible for the development of neurodegenerative and psychiatric diseases. These processes are associated with, among other things, the increased and disturbed activation of microglia and the elevated production of proinflammatory factors. Recent studies indicated that the disruption of the process of resolution of inflammation (RoI) may be the cause of CNS disorders. It is shown that the RoI is regulated by endogenous molecules called specialized pro-resolving mediators (SPMs), which interact with specific membrane receptors. Some SPMs activate formyl peptide receptors (FPRs), which belong to the family of seven-transmembrane G protein-coupled receptors. These receptors take part not only in the proinflammatory response but also in the resolution of the inflammation process. Therefore, the activation of FPRs might have complex consequences.

This review discusses the potential role of FPRs, and in particular the role of FPR2 subtype, in the brain under physiological and pathological conditions and their involvement in processes underlying neurodegenerative and psychiatric disorders as well as ischemia, the pathogenesis of which involves the dysfunction of inflammatory processes.

Polyunsaturated Fatty Acid Diet and Upregulation of Lipoxin A4 Reduce the Inflammatory Response of Preeclampsia

The aim of this study was to investigate the effects and mechanisms of polyunsaturated fatty acids (PUFAs) and lipoxin A4 (LXA4) on preeclampsia (PE). The LXA4 level was significantly reduced in PE rats. The PUFA diet upregulated the expressions of lipoxygenase 12 (LOX12) and lipoxygenase 15 (LOX15) and downregulated those of cyclooxygenase-2, tumor necrosis factor-α (TNF-α), and endoglin. Lipopolysaccharides could inhibit cell growth and cause inflammatory response, while the presence of PUFAs inhibited the inflammatory response and promoted the expressions of LOX12, LOX15, and LXA4. Nordihydroguaiaretic acid (NDGA) regulated LXA4 expression and inflammation levels by affecting LOX. Inhibition of lipoxygenase 5 activity by NDGA upregulated the expressions of LOX12 and LOX15, while LXA4 reversed LXA4, nitric oxide downregulation, and TNF-α upregulation by NDGA. A decrease in LXA4 levels played an important role in the development and progression of PE.

Macrophages and the maintenance of homeostasis

There have been many chapters written about macrophage polarization. These chapters generally focus on the role of macrophages in orchestrating immune responses by highlighting the T-cell-derived cytokines that shape these polarizing responses. This bias toward immunity is understandable, given the importance of macrophages to host defense. However, macrophages are ubiquitous and are involved in many different cellular processes, and describing them as immune cells is undoubtedly an oversimplification. It disregards their important roles in development, tissue remodeling, wound healing, angiogenesis, and metabolism, to name just a few processes. In this chapter, we propose that macrophages function as transducers in the body. According to Wikipedia, “A transducer is a device that converts energy from one form to another.” The word transducer is a term used to describe both the “sensor,” which can interpret a wide range of energy forms, and the “actuator,” which can switch voltages or currents to affect the environment. Macrophages are able to sense a seemingly endless variety of inputs from their environment and transduce these inputs into a variety of different response outcomes. Thus, rather than functioning as immune cells, they should be considered more broadly as cellular transducers that interpret microenvironmental changes and actuate vital tissue responses. In this chapter, we will describe some of the sensory stimuli that macrophages perceive and the responses they make to these stimuli to achieve their prime directive, which is the maintenance of homeostasis.

Dual modulation of formyl peptide receptor 2 by aspirin-triggered lipoxin contributes to its anti-inflammatory activity

The eicosanoid lipoxin A4 and aspirin-triggered 15-epi-lipoxin A4 (ATL) are potent anti-inflammatory agents. How their anti-inflammatory effects are mediated by receptors such as the formyl peptide receptor 2 (FPR2/ALX) remains incompletely understood. In the present study, fluorescent biosensors of FPR2/ALX were prepared and ATL-induced conformational changes were recorded. A biphasic dose curve consisting of a descending phase and an ascending phase was observed, with the descending phase corresponding to diminished FPR2 response such as Ca2+ mobilization induced by the potent synthetic agonist WKYMVm. Preincubation of FPR2-expressing cells with 100 pM of ATL also lowered the threshold for WKYMVm to induce β-arrestin-2 membrane translocation, and inhibited WKYMVm-induced interleukin 8 secretion, suggesting signaling bias favoring anti-inflammatory activities. At 100 pM and above, ATL-induced receptor conformational changes resembling that of the WKYMVm along with a weak but measurable inhibition of forskolin-induced cAMP accumulation. However, no Ca2+ mobilization was induced by ATL until its concentration reached 1 µM. Taken together, these results suggest a dual regulatory mechanism by which ATL exerts anti-inflammatory effects through FPR2/ALX.

Sex-mediated elevation of the specialized pro-resolving lipid mediator levels in a Sjögren's syndrome mouse model

Our previous results showed that the specialized pro-resolving mediator (SPM) Resolvin D1 (RvD1) promotes resolution of inflammation in salivary glands in non-obese diabetic (NOD)/ShiLtJ, a mouse model for Sjögren's syndrome (SS). Additionally, mice lacking the RvD1 receptor ALX/FPR2 show defective innate and adaptive immune responses in salivary glands. Particularly, ALX/FPR2 KO mice exhibit exacerbated inflammation in their salivary glands in response to systemic LPS treatment. Moreover, female ALX/FPR2 KO mice show increased autoantibody production and loss of salivary gland function with age. Together, these studies suggest that an underlying SPM dysregulation could be contributing to SS progression. Therefore, we investigated whether SPM production is altered in NOD/ShiLtJ using metabololipidomics and enzyme-linked immunosorbent assay (ELISA). Our results demonstrate that SPM levels were broadly elevated in plasma collected from NOD/ShiLtJ female mice after disease onset, whereas these drastic changes did not occur in male mice. Moreover, gene expression of enzymes involved in SPM biosynthesis were altered in submandibular glands (SMG) from NOD/ShiLtJ female mice after disease onset, with 5-LOX and 12/15-LOX being downregulated and upregulated, respectively. Despite this dysregulation, the abundances of the SPM products of these enzymes (ie, RvD1 and RvD2) were unaltered in freshly isolated SMG cells suggesting that other cell populations (eg, lymphocytes) may be responsible for the overabundance of SPMs that we observed. The elevation of SPMs noted here appeared to be sex mediated, meaning that it was observed only in one sex (females). Given that SS primarily affects females (roughly 90% of diagnosed cases), these results may provide some insights into the mechanisms underlying the observed sexual dimorphism.

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

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

New Advances in Targeting the Resolution of Inflammation: Implications for Specialized Pro-Resolving Mediator GPCR Drug Discovery

Chronic inflammation is a component of numerous diseases including autoimmune, metabolic, neurodegenerative, and cancer. The discovery and characterization of specialized pro-resolving mediators (SPMs) critical to the resolution of inflammation, and their cognate G protein-coupled receptors (GPCRs) has led to a significant increase in the understanding of this physiological process. Approximately 20 ligands, including lipoxins, resolvins, maresins, and protectins, and 6 receptors (FPR2/ALX, GPR32, GPR18, chemerin₁, BLT₁, and GPR37) have been identified highlighting the complex and multilayered nature of resolution. Therapeutic efforts in targeting these receptors have proved challenging, with very few ligands apparently progressing through to preclinical or clinical development. To date, some knowledge gaps remain in the understanding of how the activation of these receptors, and their downstream signaling, results in efficient resolution via apoptosis, phagocytosis, and efferocytosis of polymorphonuclear leukocytes (mainly neutrophils) and macrophages. SPMs bind and activate multiple receptors (ligand poly-pharmacology), while most receptors are activated by multiple ligands (receptor pleiotropy). In addition, allosteric binding sites have been identified signifying the capacity of more than one ligand to bind simultaneously. These fundamental characteristics of SPM receptors enable alternative targeting strategies to be considered, including biased signaling and allosteric modulation. This review describes those ligands and receptors involved in the resolution of inflammation, and highlights the most recent clinical trial results. Furthermore, we describe alternative mechanisms by which these SPM receptors could be targeted, paving the way for the identification of new therapeutics, perhaps with greater efficacy and fidelity.

Update on oxidative stress and inflammation in pregnant women, unborn children (nasciturus), and newborns - Nutritional and dietary effects

The scientific background of perinatal pathology, regarding both mother and offspring, from the lipidomic perspective, has highlighted the possibility of identifying new, promising clinical markers of oxidative stress and inflammation, closely related to the normal development of unborn and newborn children, together with their application. In this regard, in recent years, significant advances have been achieved, assisted by both newly developed analytical tools and basic knowledge on the biological implications of oxylipins. Hence, in the light of this recent progress, this review aims to provide an update on the relevance of human oxylipins during pregnancy and in the unborn and newborn child, covering two fundamental aspects. Firstly, the evidence from human clinical studies and dietary intervention trials will be used to shed light on the extent to which dietary supplementation can modulate the lipidomic markers of oxidative stress and inflammation in the perinatal state, emphasizing the role of the placenta and metabolic disturbances in the mother and fetus. The second part of this article comprises a review of existing data on specific pathophysiological aspects of human reproduction, in relation to lipidomic markers in pregnant women, unborn children, and newborn children. The information reviewed here evidences the current opportunity to correct reproductive disturbances, in the framework of lipidomics, by fine-tuning dietary interventions.

Omega-3 Polyunsaturated Fatty Acids and Their Bioactive Metabolites in Gastrointestinal Malignancies Related to Unresolved Inflammation. A Review

Chronic inflammation takes part in the pathogenesis of some malignancies of the gastrointestinal tract including colorectal (CRC), gastric, and esophageal cancers. The use of ω3 polyunsaturated fatty acid (ω3-PUFA) supplements for chemoprevention or adjuvant therapy of gastrointestinal cancers is being investigated in recent years. Most evidence has been reported in CRC, although their protective role has also been reported for Helicobacter pylori-induced gastric cancer or Barrett’s esophagus-derived adenocarcinoma. Studies based on ω3-PUFA supplementation in animal models of familial adenomatous polyposis (FAP) and CRC revealed positive effects on cancer prevention, reducing the number and size of tumors, down-regulating arachidonic acid-derived eicosanoids, upregulating anti-oxidant enzymes, and reducing lipid peroxidation, whereas contradictory results have been found in induced colitis and colitis-associated cancer. Beneficial effects have also been found in FAP and ulcerative colitis patients. Of special interest is their positive effect as adjuvants on radio- and chemo-sensitivity, specificity, and prevention of treatment complications. Some controversial results obtained in CRC might be justified by different dietary sources, extraction and preparation procedures of ω3-PUFAs, difficulties on filling out food questionnaires, daily dose and type of PUFAs, adenoma subtype, location of CRC, sex differences, and genetic factors. Studies using animal models of inflammatory bowel disease have confirmed that exogenous administration of active metabolites derived from PUFAs called pro-resolving mediators like lipoxin A4, arachidonic acid-derived, resolvins derived from eicosapentaenoic (EPA), docosahexaenoic (DHA), and docosapentaenoic (DPA) acids as well as maresin 1 and protectins DHA- and DPA-derived improve disease and inflammatory outcomes without causing immunosuppression or other side effects.

The Role of Eicosanoids in Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative disorders known. Estimates from the Alzheimer's Association suggest that there are currently 5.8 million Americans living with the disease and that this will rise to 14 million by 2050. Research over the decades has revealed that AD pathology is complex and involves a number of cellular processes. In addition to the well-studied amyloid-β and tau pathology, oxidative damage to lipids and inflammation are also intimately involved. One aspect all these processes share is eicosanoid signaling. Eicosanoids are derived from polyunsaturated fatty acids by enzymatic or non-enzymatic means and serve as short-lived autocrine or paracrine agents. Some of these eicosanoids serve to exacerbate AD pathology while others serve to remediate AD pathology. A thorough understanding of eicosanoid signaling is paramount for understanding the underlying mechanisms and developing potential treatments for AD. In this review, eicosanoid metabolism is examined in terms of in vivo production, sites of production, receptor signaling, non-AD biological functions, and known participation in AD pathology.

Roles, Actions, and Therapeutic Potential of Specialized Pro-resolving Lipid Mediators for the Treatment of Inflammation in Cystic Fibrosis

Non-resolving inflammation is the main mechanism of morbidity and mortality among patients suffering from cystic fibrosis (CF), the most common life-threatening human genetic disease. Resolution of inflammation is an active process timely controlled by endogenous specialized pro-resolving lipid mediators (SPMs) produced locally in inflammatory loci to restrain this innate response, prevent further damages to the host, and permit return to homeostasis. Lipoxins, resolvins, protectins, and maresins are SPM derived from polyunsaturated fatty acids that limit excessive leukocyte infiltration and pro-inflammatory signals, stimulate innate microbial killing, and enhance resolution. Their unique chemical structures, receptors, and bioactions are being elucidated. Accruing data indicate that SPMs carry protective functions against unrelenting inflammation and infections in preclinical models and human CF systems. Here, we reviewed their roles and actions in controlling resolution of inflammation, evidence for their impairment in CF, and proofs of principle for their exploitation as innovative, non-immunosuppressive drugs to address inflammation and infections in CF.