15-Epi-lipoxin A4 inhibits human neutrophil superoxide anion generation by regulating polyisoprenyl diphosphate phosphatase 1

Possibility of averting cytokine storm in SARS-COV 2 patients using specialized pro-resolving lipid mediators

Fatal "cytokine storms (CS)" observed in critically ill COVID-19 patients are consequences of dysregulated host immune system and over-exuberant inflammatory response. Acute respiratory distress syndrome (ARDS), multi-system organ failure, and eventual death are distinctive symptoms, attributed to higher morbidity and mortality rates among these patients. Consequent efforts to save critical COVID-19 patients via the usage of several novel therapeutic options are put in force. Strategically, drugs being used in such patients are dexamethasone, remdesivir, hydroxychloroquine, etc. along with the approved vaccines. Moreover, it is certain that activation of the resolution process is important for the prevention of chronic diseases. Until recently Inflammation resolution was considered a passive process, rather it's an active biochemical process that can be achieved by the use of specialized pro-resolving mediators (SPMs). These endogenous mediators are an array of atypical lipid metabolites that include Resolvins, lipoxins, maresins, protectins, considered as immunoresolvents, but their role in COVID-19 is ambiguous. Recent evidence from studies such as the randomized clinical trial, in which omega 3 fatty acid was used as supplement to resolve inflammation in COVID-19, suggests that direct supplementation of SPMs or the use of synthetic SPM mimetics (which are still being explored) could enhance the process of resolution by regulating the aberrant inflammatory process and can be useful in pain relief and tissue remodeling. Here we discussed the biosynthesis of SPMs, & their mechanistic pathways contributing to inflammation resolution along with sequence of events leading to CS in COVID-19, with a focus on therapeutic potential of SPMs.

Lipoxin alleviates oxidative stress: a state-of-the-art review

OBJECTIVE

This review aims to summarize the capability of lipoxin in regulating oxidative stress.

BACKGROUND

Oxidative stress is defined as an imbalance between the production of free radicals and the antioxidant system, and it is associated with the existence of a large number of oxidation products, such as reactive oxygen species (ROS) and reaction nitrogen species (RNS), causing damage to human tissues through immunoinflammatory responses. Therefore, reducing oxidative stress is vital to alleviate pathological damage. Lipoxin, an acronym for lipoxygenase interaction product, is a bioactive autacoid metabolite of arachidonic acid made by various cell types. Previous studies have shown that lipoxin is associated with a variety of biological functions, including anti-inflammatory, regulating immune responses, promoting the repair of damaged cells, etc. The deficiency of lipoxin is a critical pathological mechanism in different diseases. Moreover, the ability of lipoxin to attenuate oxidative stress is noteworthy, thereby protecting the human body from diverse diseases.

METHODS

We searched papers from PubMed database using search terms, such as lipoxin, lipoxin A4, oxidative stress, and other relevant terms.

RESULTS

A total of 103 articles published over the past 20 years were identified for inclusion. We summarized the capability of lipoxin in regulating oxidative stress and mechanism.

CONCLUSION

Lipoxin is provided with a protective role in attenuating oxidative stress.

MiR-18a-3p improves cartilage matrix remodeling and inhibits inflammation in osteoarthritis by suppressing PDP1

Osteoarthritis (OA) is a degenerative disease characterized by synovial inflammation. MiR-18a-3p was reported to be downregulated in knee anterior cruciate ligament of OA patients. In the present study, the specific functions and mechanism of miR-18a-3p in OA were explored. An in vitro model of OA was established using 10 ng/ml IL-1β to treat ATDC5 cells, and medial meniscus instability surgery was performed on Wistar rats to establish in vivo rat model of OA. RT-qPCR revealed that miR-18a-3p was downregulated in IL-1β-stimulated ATDC5 cells. MiR-18a-3p overexpression inhibited secretion of inflammatory cytokines and concentration of matrix metalloproteinases, as shown by ELISA and western blotting. The binding relation between miR-18a-3p and pyruvate dehydrogenase phosphatase catalytic subunit 1 (PDP1) was detected by luciferase reporter assays. MiR-18a-3p targeted PDP1 and negatively regulated PDP1 expression. Results of rescue assays revealed that PDP1 upregulation reserved the suppressive effect of miR-18a-3p overexpression on levels of inflammatory cytokines and matrix metalloproteinases in IL-1β-stimulated ATDC5 cells. H&E staining was used to observe pathological changes of synovial tissues in the knee joint of Wistar rats. Safranin O-fast green/hematoxylin was used to stain cartilage samples of knee joints. MiR-18a-3p overexpression suppressed OA progression in vivo. Overall, miR-18a-3p improves cartilage matrix remodeling and suppresses inflammation in OA by targeting PDP1.

Aspirin-triggered resolvin D1 reduces parasitic cardiac load by decreasing inflammation in a murine model of early chronic Chagas disease

Background

Chagas disease, caused by the protozoan Trypanosoma cruzi, is endemic in Latin America and is widely distributed worldwide because of migration. In 30% of cases, after years of infection and in the absence of treatment, the disease progresses from an acute asymptomatic phase to a chronic inflammatory cardiomyopathy, leading to heart failure and death. An inadequate balance in the inflammatory response is involved in the progression of chronic Chagas cardiomyopathy. Current therapeutic strategies cannot prevent or reverse the heart damage caused by the parasite. Aspirin-triggered resolvin D1 (AT-RvD1) is a pro-resolving mediator of inflammation that acts through N-formyl peptide receptor 2 (FPR2). AT-RvD1 participates in the modification of cytokine production, inhibition of leukocyte recruitment and efferocytosis, macrophage switching to a nonphlogistic phenotype, and the promotion of healing, thus restoring organ function. In the present study, AT-RvD1 is proposed as a potential therapeutic agent to regulate the pro-inflammatory state during the early chronic phase of Chagas disease.

Methodology/Principal findings

C57BL/6 wild-type and FPR2 knock-out mice chronically infected with T. cruzi were treated for 20 days with 5 μg/kg/day AT-RvD1, 30 mg/kg/day benznidazole, or the combination of 5 μg/kg/day AT-RvD1 and 5 mg/kg/day benznidazole. At the end of treatment, changes in immune response, cardiac tissue damage, and parasite load were evaluated. The administration of AT-RvD1 in the early chronic phase of T. cruzi infection regulated the inflammatory response both at the systemic level and in the cardiac tissue, and it reduced cellular infiltrates, cardiomyocyte hypertrophy, fibrosis, and the parasite load in the heart tissue.

Conclusions/Significance

AT-RvD1 was shown to be an attractive therapeutic due to its regulatory effect on the inflammatory response at the cardiac level and its ability to reduce the parasite load during early chronic T. cruzi infection, thereby preventing the chronic cardiac damage induced by the parasite.

Chagas disease is prevalent in Latin America and is widely distributed worldwide due to migration. In 30% of patients, if the parasite is left untreated, the disease may progress from an acute symptomless phase to chronic myocardial inflammation, which can cause heart failure and death, years after the infection. Imbalances in the inflammatory response are related to this progression. Current treatments cannot prevent or reverse the cardiac damage inflicted by the parasite. Aspirin-triggered resolvin D1, also named AT-RvD1, can modify cellular and humoral inflammatory responses leading to the resolution of inflammation, thus promoting healing and restoring organ function. In this study, AT-RvD1, in an N-formyl peptide receptor 2 (FPR2)-dependent manner, was shown to regulate local and systemic inflammation and decrease cellular infiltration in the heart tissue of mice chronically infected with the parasite and reduce cardiac hypertrophy and fibrosis in the early stages of the chronic phase of the disease. Importantly, AT-RvD1 was able to decrease parasite load in the infected hearts. Thus, this research indicates that At-RvD1 treatment is a potential therapeutic strategy that offers an improvement on current drug therapies.

Lipid-Derived Mediators are Pivotal to Leukocyte and Lung Cell Responses in Sepsis and ARDS

Acute inflammation in the lung is essential for host defense against pathogens and other injuries but chronic or excessive inflammation can contribute to several common respiratory diseases. In health, the inflammatory response is controlled by several cellular and molecular mechanisms. In addition to anti-inflammatory processes, there are non-phlogistic pro-resolving mechanisms that are engaged to promote the resolution of inflammation and a return to homeostasis. Defects in the production or actions of specialized pro-resolving mediators are associated with diseases characterized by excess or chronic inflammation. In this article, we review cellular and biochemical mechanisms for specialized pro-resolving mediators in health and in sepsis and the acute respiratory distress syndrome as examples of unrestrained inflammatory responses that result in life-threatening pathology. We are honored to contribute to this special edition of the Journal to help celebrate Professor Viswanathan Natarajan's contributions to our understanding of lipid-derived mediators and metabolism in lung cell responses to inflammatory, infectious, or mechanical insults; his foundational discoveries in cell biochemistry and biophysics are continuing to catalyze further advances by the field to uncover the mechanistic underpinnings of important human diseases.

Lipoxin A4 promotes autophagy and inhibits overactivation of macrophage inflammasome activity induced by Pg LPS

Objective

To explore the role of lipoxin A4 (LXA4) on inflammasome and inflammatory activity in macrophages activated by Porphyromonas gingivalis lipopolysaccharide (PgLPS) one of the major causative agents of chronic periodontitis.

Methods

The mouse macrophage cell line RAW264.7 was used to produce an activated inflammation model. Markers of inflammasome and inflammatory activity and autophagy were assessed by ELISA, reverse transcription polymerase chain reaction (RT-PCR), and Western blot assay.

Results

Markers of inflammasome activity, inflammation and autophagy increased with Pg LPS concentration. They also increased with increasing exposure to Pg LPS up to 12h but decreased at 24h. However, markers of autophagy increased. Phosphorylated NF-κBp65 decreased with LXA4, which was similar to results obtained with the autophagy inducer, rapamycin.

Conclusions

LXA4 promoted autophagy and inhibited activation of inflammasomes and inflammation markers in macrophage inflammation induced by PgLPS and this action was linked to the phosphorylation of NF-κB.

LXA4-FPR2 signaling regulates radiation-induced pulmonary fibrosis via crosstalk with TGF-β/Smad signaling

Radiation therapy is an important modality in the treatment of lung cancer, but it can lead to radiation pneumonitis, and eventually radiation fibrosis. To date, only few available drugs can effectively manage radiation-induced pulmonary fibrosis. Lipoxins are endogenous molecules exhibit anti-inflammatory and pro-resolving effects. These molecules play a vital role in reducing excessive tissue injury and chronic inflammation; however, their effects on radiation-induced lung injury (RILI) are unknown. In this study, we investigated the effects of lipoxin A₄ (LXA₄) on RILI using our specialized small-animal model of RILI following focal-ablative lung irradiation (IR). LXA₄ significantly inhibited immune-cell recruitment and reduced IR-induced expression of pro-inflammatory cytokines and fibrotic proteins in the lung lesion sites. In addition, micro-CT revealed that LXA₄ reduced IR-induced increases in lung consolidation volume. The flexiVent^TM assays showed that LXA4 significantly reversed IR-induced lung function damage. Moreover, LXA4 downregulated the activities of NF-κB and the Smad-binding element promoters. The expression of FPR2, an LXA₄ receptor, increased during the development of IR-induced pulmonary fibrosis, whereas silencing of endogenous LXA₄ using an antagonist (WRW4) or FPR2 siRNA resulted in impaired development of pulmonary fibrosis in response to IR. Collectively, these data suggest that LXA₄ could serve as a potent therapeutic agent for alleviating RILI.

Lipoxin A4 attenuates uric acid-activated, NADPH oxidase-dependent oxidative stress by interfering with translocation of p47phox in human umbilical vein endothelial cells

LipoxinA4 (LXA4) is a well-known key mediator of endogenous anti-inflammation and of the resolution of inflammation. Considerable oxidative stress occurs during inflammation due to the generation of reactive oxidative species (ROS). Moreover, high levels of uric acid (UA) contribute to endothelial cell dysfunction, which can promote disease-related morbidity, and NADPH oxidase-derived ROS are crucial regulatory factors in these responses. However, LXA4 also has the potential to reduce oxidative stress. The aim of the present study was to examine whether LXA4 could suppress UA-induced oxidative stress in human umbilical vein endothelial cells (HUVECs) and to investigate its mechanisms of action in vitro. HUVECs were incubated with or without LXA4, followed by the addition of UA. ROS levels were then measured using 2,7-dichlorodihydrofluorescein diacetate and lucigenin-enhanced chemiluminescence was used to evaluate NADPH oxidase activity. p47phox or p22phox small interfering (si)RNA were transfected into HUVECs and protein levels of p47phox were detected using western blot analysis. LXA4 significantly inhibited UA-induced generation of ROS to the same extent as the NADPH oxidase inhibitor, diphenyleneiodonium chloride. Notably, transfection of p47phox siRNA attenuated the generation of ROS and the activation of NADPH oxidase. Cells transfected with p22phox siRNA demonstrated a significant reduction in the expression of p47phox on the membrane. Further experiments demonstrated that LXA4 interfered with the transfer of p47phox from the cytoplasm to the cell membrane. These findings suggested that LXA4 inhibited the release of NADPH oxidase derived ROS in HUVECs stimulated by UA. A potential mechanism of action underlying this effect could be LXA4-mediated suppression of NADPH oxidase activity, leading to inhibition of p47phox translocation from the cytoplasm to the cell membrane.

Novel mediators and mechanisms in the resolution of infectious inflammation: evidence for vagus regulation

Excessive chronic inflammation is linked to many diseases and considered a stress factor in humans (Robbins Pathologic Basis of Disease. Philadelphia: W.B. Saunders Co., 1999, Proc Natl Acad Sci USA, 2008, 105: 17949, Immunity, 44, 2016, 44: 463, N Engl J Med, 2011, 364: 656). Today, the resolution of inflammation is widely recognized as a cellular biochemically active process involving biosynthesis of a novel superfamily of endogenous chemical signals coined specialized pro-resolving mediators (SPMs; Nature, 2014, 510:92). Herein, we review recent evidence, indicating a role for the vagus nerve and vagotomy in the regulation of lipid mediators. Vagotomy reduces pro-resolving mediators, including the lipoxins, resolvins, protectins and maresins, delaying resolution in mouse peritonitis. Vagotomy also delays resolution of Escherichia coli infection in mice. Specifically, right vagus regulates peritoneal Group 3 innate lymphoid cell (ILC-3) number and peritoneal macrophage responses with lipid mediator profile signatures with elevated pro-inflammatory eicosanoids and reduced resolvins, including the novel protective immunoresolvent agonist protectin conjugate in tissue regeneration1 (PCTR1). Acetylcholine upregulates PCTR biosynthesis, and administration of PCTR1 to vagotomized mice restores tissue resolution and host responses to E. coli infections. Results obtained with human vagus ex vivo indicate that vagus can produce both pro-inflammatory eicosanoids, such as prostaglandins and leukotrienes, as well as the SPM. Electrical stimulation of human vagus in vitro reduces both prostaglandins and leukotrienes and enhances resolvins and the other SPM. These results elucidate a host protective mechanism mediated by vagus stimulation of SPM that includes resolvins and PCTR1 to regulate myeloid antimicrobial functions and resolution of infection. Moreover, they define a new pro-resolution of inflammation reflex operative in mice and human tissue that involves a vagus SPM circuit.

Proresolving Lipid Mediators: Endogenous Modulators of Oxidative Stress

Specialized proresolving mediators (SPMs) are a novel class of endogenous lipids, derived by ω-6 and ω-3 essential polyunsaturated fatty acids such as arachidonic acid (AA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) that trigger and orchestrate the resolution of inflammation, which is the series of cellular and molecular events that leads to spontaneous regression of inflammatory processes and restoring of tissue homeostasis. These lipids are emerging as highly effective therapeutic agents that exert their immunoregulatory activity by activating the proresolving pathway, as reported by a consistent bulk of evidences gathered in the last two decades since their discovery. The production of reactive oxygen (ROS) and nitrogen (RNS) species by immune cells plays indeed an important role in the inflammatory mechanisms of host defence, and it is now clear that oxidative stress, viewed as an imbalance between such species and their elimination, can lead to many chronic inflammatory diseases. This review, the first of its kind, is aimed at exploring the manifold effects of SPMs on modulation of reactive species production, along with the mechanisms through which they either inhibit molecular signalling pathways that are activated by oxidative stress or induce the expression of endogenous antioxidant systems. Furthermore, the possible role of SPMs in oxidative stress-mediated chronic disorders is also summarized, suggesting not only that their anti-inflammatory and proresolving properties are strictly associated with their antioxidant role but also that these endogenous lipids might be exploited in the treatment of several pathologies in which uncontrolled production of ROS and RNS or impairment of the antioxidant machinery represents a main pathogenetic mechanism.

Specialized Proresolving Mediators in Innate and Adaptive Immune Responses in Airway Diseases

Airborne pathogens and environmental stimuli evoke immune responses in the lung. It is critical to health that these responses be controlled to prevent tissue damage and the compromise of organ function. Resolution of inflammation is a dynamic process that is coordinated by biochemical and cellular mechanisms. Recently, specialized proresolving mediators (SPMs) have been identified in resolution exudates. These molecules orchestrate anti-inflammatory and proresolving actions that are cell type specific. In this review, we highlight SPM biosynthesis, the influence of SPMs on the innate and adaptive immune responses in the lung, as well as recent insights from SPMs on inflammatory disease pathophysiology. Uncovering these mediators and cellular mechanisms for resolution is providing new windows into physiology and disease pathogenesis.

Resolvins in inflammation: emergence of the pro-resolving superfamily of mediators

Countless times each day, the acute inflammatory response protects us from invading microbes, injuries, and insults from within, as in surgery-induced tissue injury. These challenges go unnoticed because they are self-limited and naturally resolve without progressing to chronic inflammation. Peripheral blood markers of inflammation are present in many common diseases, including inflammatory bowel disease, cardiovascular disease, neurodegenerative disease, and cancer. While acute inflammation is protective, excessive swarming of neutrophils amplifies collateral tissue damage and inflammation. Hence, understanding the mechanisms that control the resolution of acute inflammation provides insight into preventing and treating inflammatory diseases in multiple organs. This Review focuses on the resolution phase of inflammation with identification of specialized pro-resolving mediators (SPMs) that involve three separate biosynthetic and potent mediator families, which are defined using the first quantitative resolution indices to score this vital process. These are the resolvins, protectins, and maresins: bioactive metabolomes that each stimulate self-limited innate responses, enhance innate microbial killing and clearance, and are organ-protective. We briefly address biosynthesis of SPMs and their activation of endogenous resolution programs as terrain for new therapeutic approaches that are not, by definition, immunosuppressive, but rather new immunoresolvent therapies.

Phospholipase D isoforms differentially regulate leukocyte responses to acute lung injury

Phospholipase D (PLD) plays important roles in cellular responses to tissue injury that are critical to acute inflammatory diseases, such as the acute respiratory distress syndrome (ARDS). We investigated the expression of PLD isoforms and related phospholipid phosphatases in patients with ARDS, and their roles in a murine model of self-limited acute lung injury (ALI). Gene expression microarray analysis on whole blood obtained from patients that met clinical criteria for ARDS and clinically matched controls (non-ARDS) demonstrated that PLD1 gene expression was increased in patients with ARDS relative to non-ARDS and correlated with survival. In contrast, PLD2 expression was associated with mortality. In a murine model of self-resolving ALI, lung Pld1 expression increased and Pld2 expression decreased 24 h after intrabronchial acid. Total lung PLD activity was increased 24 h after injury. Pld1^-/- mice demonstrated impaired alveolar barrier function and increased tissue injury relative to WT and Pld2^-/- , whereas Pld2^-/- mice demonstrated increased recruitment of neutrophils and macrophages, and decreased tissue injury. Isoform-specific PLD inhibitors mirrored the results with isoform-specific Pld-KO mice. PLD1 gene expression knockdown in human leukocytes was associated with decreased phagocytosis by neutrophils, whereas reactive oxygen species production and phagocytosis decreased in M2-macrophages. PLD2 gene expression knockdown increased neutrophil and M2-macrophage transmigration, and increased M2-macrophage phagocytosis. These results uncovered selective regulation of PLD isoforms after ALI, and opposing effects of selective isoform knockdown on host responses and tissue injury. These findings support therapeutic strategies targeting specific PLD isoforms for the treatment of ARDS.

Aspirin and blood pressure: Effects when used alone or in combination with antihypertensive drugs

Arterial hypertension is a major risk factor for cardiovascular and renal events. Lowering blood pressure is thus an important strategy for reducing morbidity and mortality. Since low-dose aspirin is a cornerstone in the prevention of adverse cardiovascular outcomes, combined treatment with aspirin and antihypertensive drugs is very common. However, the impact of aspirin therapy on blood pressure control remains a subject of intense debate. Recent data suggest that the cardioprotective action of aspirin extends beyond its well-known antithrombotic effect. Aspirin has been shown to trigger the synthesis of specialized pro-resolving lipid mediators from arachidonic acid and omega-3 fatty acids. These novel anti-inflammatory and pro-resolving mediators actively stimulate the resolution of inflammation and tissue regeneration. Additionally, they may contribute to other protective effects on redox status and vascular reactivity that have also been attributed to aspirin. Of note, aspirin has been shown to improve vasodilation through cyclooxygenase-independent mechanisms. On the other hand, higher aspirin doses have been reported to exert a negative impact on blood pressure due to inhibition of cyclooxygenase-2 activity, which reduces renal blood flow, glomerular filtration rate and sodium and water excretion. This review aims to provide an overview of the effects of aspirin on blood pressure and the underlying mechanisms, focusing on the interaction between aspirin and antihypertensive drugs. Studies in both experimental and human hypertension are presented.

Statins and oxidative stress in chronic heart failure

Statins are the most commonly prescribed drugs for the treatment of dyslipidemia. They are also recommended in primary and secondary prevention of cardiovascular disease. In addition to decreasing cholesterol synthesis, statins interfere with the synthesis of isoprenoid intermediates, which may explain many of their pleiotropic properties, including their antioxidant effects. Oxidative stress is defined as an imbalance between the synthesis of reactive oxygen species and their elimination by antioxidant defense systems, with a prevailing pro-oxidant status that results in macromolecular damage and disruption of cellular redox signaling. Reactive oxygen species interfere with various processes that affect cardiac structure and function, contributing to the contractile dysfunction, myocardial hypertrophy and fibrosis observed in the pathophysiology of heart failure. By regulating several molecular pathways that control nicotinamide adenine dinucleotide phosphate oxidase and endothelial nitric oxide synthase activity, statins help restore redox homeostasis. These drugs also contribute to the control of inflammation and appear to have a protective role in various diseases. The results of observational studies and clinical trials with statins in heart failure have not been consensual. This review aims to analyze the role of oxidative stress in heart failure and the molecular mechanisms underlying statins' antioxidant properties. It also examines current scientific evidence on the use of these drugs as a specific treatment for heart failure.

Attenuation of lipopolysaccharide-induced lung vascular stiffening by lipoxin reduces lung inflammation

Reversible changes in lung microstructure accompany lung inflammation, although alterations in tissue micromechanics and their impact on inflammation remain unknown. This study investigated changes in extracellular matrix (ECM) remodeling and tissue stiffness in a model of LPS-induced inflammation and examined the role of lipoxin analog 15-epi-lipoxin A4 (eLXA4) in the reduction of stiffness-dependent exacerbation of the inflammatory process. Atomic force microscopy measurements of live lung slices were used to directly measure local tissue stiffness changes induced by intratracheal injection of LPS. Effects of LPS on ECM properties and inflammatory response were evaluated in an animal model of LPS-induced lung injury, live lung tissue slices, and pulmonary endothelial cell (EC) culture. In vivo, LPS increased perivascular stiffness in lung slices monitored by atomic force microscopy and stimulated expression of ECM proteins fibronectin, collagen I, and ECM crosslinker enzyme, lysyl oxidase. Increased stiffness and ECM remodeling escalated LPS-induced VCAM1 and ICAM1 expression and IL-8 production by lung ECs. Stiffness-dependent exacerbation of inflammatory signaling was confirmed in pulmonary ECs grown on substrates with high and low stiffness. eLXA4 inhibited LPS-increased stiffness in lung cross sections, attenuated stiffness-dependent enhancement of EC inflammatory activation, and restored lung compliance in vivo. This study shows that increased local vascular stiffness exacerbates lung inflammation. Attenuation of local stiffening of lung vasculature represents a novel mechanism of lipoxin antiinflammatory action.

Physiological impact of abnormal lipoxin A₄ production on cystic fibrosis airway epithelium and therapeutic potential

Lipoxin A4 has been described as a major signal for the resolution of inflammation and is abnormally produced in the lungs of patients with cystic fibrosis (CF). In CF, the loss of chloride transport caused by the mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel gene results in dehydration, mucus plugging, and reduction of the airway surface liquid layer (ASL) height which favour chronic lung infection and neutrophil based inflammation leading to progressive lung destruction and early death of people with CF. This review highlights the unique ability of LXA4 to restore airway surface hydration, to stimulate airway epithelial repair, and to antagonise the proinflammatory program of the CF airway, circumventing some of the most difficult aspects of CF pathophysiology. The report points out novel aspects of the cellular mechanism involved in the physiological response to LXA4, including release of ATP from airway epithelial cell via pannexin channel and subsequent activation of and P2Y11 purinoreceptor. Therefore, inadequate endogenous LXA4 biosynthesis reported in CF exacerbates the ion transport abnormality and defective mucociliary clearance, in addition to impairing the resolution of inflammation, thus amplifying the vicious circle of airway dehydration, chronic infection, and inflammation.

Effects of Lipoxin A4 on antimicrobial actions of neutrophils in sepsis

In sepsis, hyperactivation of neutrophils can lead to tissue injury. Later, neutrophil dysregulation with reduced levels of migration, decreased apoptosis and inadequate phagocytosis may impair the host׳s ability to clear infection. Lipoxin A4 (LXA4) is a pro-resolution lipid mediator which reduces neutrophil migration and inflammatory mediator expression. As neutrophil migration and activation are important in bacterial clearance, the role of LXA4 in regulating neutrophil function for bacterial clearance is unclear. Using the cecal ligation and puncture (CLP) rat model of sepsis, LXA4 given after 1h reduced blood bacterial load at 24h. LXA4 treatment decreased neutrophil migration to the peritoneum but augmented blood neutrophil phagocytic ability and promoted apoptosis without affecting free radical production. In contrast, LXA4 increased peritoneal neutrophil phagocytic ability without affecting apoptosis or free radical production suggesting that in vivo effects of LXA4 were compartment specific. To investigate if LXA4 acted directly on neutrophils, blood and peritoneal leukocytes were taken from CLP rats 1h after surgery and incubated ex vivo with and without LXA4. LXA4 (1nM) increased phagocytosis in blood neutrophils without affecting apoptosis or free radical production. Ex vivo LXA4 had no effect on peritoneal neutrophils which suggests that LXA4 enhanced peritoneal neutrophil phagocytic ability in vivo by an indirect mechanism. The results suggest that LXA4 reduced neutrophil migration, but increased neutrophil bacteria clearing function without excessive free radical production. This phenotype was associated with reduced blood bacteria load.

Retrotaxis of human neutrophils during mechanical confinement inside microfluidic channels

The current paradigm of unidirectional migration of neutrophils from circulation to sites of injury in tissues has been recently challenged by observations in zebrafish showing that neutrophils can return from tissues back into the circulation. However, the relevance of these observations to human neutrophils remains unclear, the forward and reverse migration of neutrophils is difficult to quantify, and the precise conditions modulating the reverse migration cannot be isolated. Here, we designed a microfluidic platform inside which we observed human neutrophil migration in response to chemoattractant sources inside channels, simulating the biochemical and mechanical confinement conditions at sites of injury in tissues. We observed that, after initially following the direction of chemoattractant gradients, more than 90% of human neutrophils can reverse their direction and migrate persistently and for distances longer than one thousand micrometers away from chemoattractant sources (retrotaxis). Retrotaxis is enhanced in the presence of lipoxin A4 (LXA4), a well-established mediator of inflammation resolution, or Tempol, a standard antioxidant. Retrotaxis stops after neutrophils encounter targets which they phagocytise or on surfaces presenting high concentrations of fibronectin. Our microfluidic model suggests a new paradigm for neutrophil accumulation at sites of inflammation, which depends on the balance of three simultaneous processes: chemotaxis along diffusion gradients, retrotaxis following mechanical guides, and stopping triggered by phagocytosis.

The role of Lipoxin A4 in Cystic Fibrosis Lung Disease

In Cystic Fibrosis (CF), mutations of the CFTR gene result in defective Cl(-) secretion and Na(+) hyperabsorption by epithelia which leads to airway lumen dehydration and mucus plugging and favours chronic bacterial colonization, persistent inflammation and progressive lung destruction. Beyond this general description, the pathogenesis of CF lung disease remains obscure due to an incomplete understanding of normal innate airway defense. This mini-review aims to highlight the role of the pro-resolution lipid mediator, Lipoxin A4, which is inadequately produced in CF, on several aspects of innate immunity that are altered in CF airway disease.

Resolution of acute inflammation in the lung

Acute inflammation in the lung is essential to health. So too is its resolution. In response to invading microbes, noxious stimuli, or tissue injury, an acute inflammatory response is mounted to protect the host. To limit inflammation and prevent collateral injury of healthy, uninvolved tissue, the lung orchestrates the formation of specialized proresolving mediators, specifically lipoxins, resolvins, protectins, and maresins. These immunoresolvents are agonists for resolution that interact with specific receptors on leukocytes and structural cells to blunt further inflammation and promote catabasis. This process appears to be defective in several common lung diseases that are characterized by excess or chronic inflammation. Here, we review the molecular and cellular effectors of resolution of acute inflammation in the lung.