Mechanisms in anti-inflammation and resolution: the role of lipoxins and aspirin-triggered lipoxins

Resolution of inflammation in oral diseases

The resolution of inflammation is an essential endogenous process that protects host tissues from an exaggerated chronic inflammatory response. Multiple interactions between host cells and resident oral microbiome regulate the protective functions that lead to inflammation in the oral cavity. Failure of appropriate regulation of inflammation can lead to chronic inflammatory diseases that result from an imbalance between pro-inflammatory and pro-resolution mediators. Thus, failure of the host to resolve inflammation can be considered an essential pathological mechanism for progression from the late stages of acute inflammation to a chronic inflammatory response. Specialized pro-resolving mediators (SPMs), which are essential polyunsaturated fatty acid (PUFA)-derived autacoid mediators, aid in regulating the endogenous inflammation resolving process by stimulating immune cell-mediated clearance of apoptotic polymorphonuclear neutrophils, cellular debris, and microbes, restricting further neutrophil tissue infiltration, and counter-regulating pro-inflammatory cytokine production. The SPM superfamily contains four specialized lipid mediator families: lipoxins, resolvins, protectins, and maresins that can activate resolution pathways. Understanding the crosstalk between resolution signals in the tissue response to injury has therapeutic application potential for preventing, maintaining, and regenerating chronically damaged tissues. Here, we discuss the fundamental concepts of resolution as an active biochemical process, novel concepts demonstrating the role of resolution mediators in tissue regeneration in periodontal and pulpal diseases, and future directions for therapeutic applications with particular emphasis on periodontal therapy.

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.

Aspirin effect on bone remodeling and skeletal regeneration: Review article

Bone tissues are one of the most complex tissues in the body that regenerate and repair themselves spontaneously under the right physiological conditions. Within the limitations of treating bone defects, mimicking tissue engineering through the recruitment of scaffolds, cell sources and growth factors, is strongly recommended. Aspirin is one of the non-steroidal anti-inflammatory drugs (NSAIDs) and has been used in clinical studies for many years due to its anti-coagulant effect. On the other hand, aspirin and other NSAIDs activate cytokines and some mediators in osteoclasts, osteoblasts and their progenitor cells in a defect area, thereby promoting bone regeneration. It also stimulates angiogenesis by increasing migration of endothelial cells and the newly developed vessels are of emergency in bone fracture repair. This review covers the role of aspirin in bone tissue engineering and also, highlights its chemical reactions, mechanisms, dosages, anti-microbial and angiogenesis activities.

Prior Exposure to Nonsteroidal Anti-inflammatory Drugs Reduces the Rate of Organ Failure and In-Hospital Mortality in Acute Pancreatitis

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been linked recently to a lower expression of pro-inflammatory cytokines in humans with acute pancreatitis. Because it is unclear if this effect results in clinical benefits, the aim of this study was to determine if prior NSAID exposure improves immediate clinical outcomes.

METHODS

Retrospective medical record review of adult patients admitted with acute pancreatitis. Cases were extracted from a national Veterans Affairs database using International Classification of Diseases, Ninth Revision codes. Prior NSAIDs use was determined through pharmacy data claims. The rates of acute kidney injury, respiratory failure, cardiovascular failure, and in-hospital mortality were compared between those with prior NSAID use (AP+NSAID) and those without it (AP-NSAID) using univariate and multivariate analysis.

RESULTS

A total of 31,340 patients were identified: 28,364 AP+NSAID and 2976 AP-NSAID. The median age was 60 years, 68% were white, and the median hospital stay was 4 days. Approximately 2% of patients died during the hospitalization. After adjusting for demographics and other covariates, patients in the AP+NSAID arm had lower rates of acute kidney injury, P = .0002), cardiovascular failure (P = .025), any organ failure (P ≤ .0001), and in-hospital mortality (P < .0001).

CONCLUSION

Prior use of NSAIDs is associated with a lower incidence of organ failure and in-hospital mortality in adult patients with acute pancreatitis. The role of NSAIDs as therapeutic agents in this condition should be evaluated in interventional trials.

Therapeutic potential of pro-resolving mediators in diabetic kidney disease

Renal microvascular disease associated with diabetes [Diabetic kidney disease - DKD] is the leading cause of chronic kidney disease. In DKD, glomerular basement membrane thickening, mesangial expansion, endothelial dysfunction, podocyte cell loss and renal tubule injury contribute to progressive glomerulosclerosis and tubulointerstitial fibrosis. Chronic inflammation is recognized as a major pathogenic mechanism for DKD, with resident and circulating immune cells interacting with local kidney cell populations to provoke an inflammatory response. The onset of inflammation is driven by the release of well described proinflammatory mediators, and this is typically followed by a resolution phase. Inflammation resolution is achieved through the bioactions of endogenous specialized pro-resolving lipid mediators (SPMs). As our understanding of SPMs advances 'resolution pharmacology' based approaches using these molecules are being explored in DKD.

Recent advances in the design and development of formyl peptide receptor 2 (FPR2/ALX) agonists as pro-resolving agents with diverse therapeutic potential

Under physiological conditions the initiation, duration and amplitude of inflammatory responses are tightly regulated to ensure the restoration of homeostasis. The resolution of inflammation in these circumstances is dictated by responses to endogenously generated mediators. Mimicry of such mediators underpins the principle of promoting the resolution of inflammation in treating inflammatory pathologies. The formyl peptide receptor 2 (FPR2/ALX) is a G-protein coupled receptor known to play a crucial role in maintaining host defence and orchestrating the inflammatory process. FPR2/ALX can be activated by a wide range of distinct agonists, including lipids, proteins, peptides, and an array of synthetic small molecule agonists. The focus of this review is to provide a comprehensive overview of recent progress made in the development of FPR2/ALX agonists which promote resolution and tissue regeneration.

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.

Specialized pro-resolving mediators in diabetes: novel therapeutic strategies

Diabetes mellitus (DM) is an important metabolic disorder characterized by persistent hyperglycemia resulting from inadequate production and secretion of insulin, impaired insulin action, or a combination of both. Genetic disorders and insulin receptor disorders, environmental factors, lifestyle choices and toxins are key factors that contribute to DM. While it is often referred to as a metabolic disorder, modern lifestyle choices and nutrient excess induce a state of systemic chronic inflammation that results in the increased production and secretion of inflammatory cytokines that contribute to DM. It is chronic hyperglycemia and the low-grade chronic-inflammation that underlies the development of microvascular and macrovascular complications leading to damage in a number of tissues and organs, including eyes, vasculature, heart, nerves, and kidneys. Improvements in the management of risk factors have been beneficial, including focus on intensified glycemic control, but most current approaches only slow disease progression. Even with recent studies employing SGLT2 inhibitors demonstrating protection against cardiovascular and kidney diseases, kidney function continues to decline in people with established diabetic kidney disease (DKD). Despite the many advances and a greatly improved understanding of the pathobiology of diabetes and its complications, there remains a major unmet need for more effective therapeutics to prevent and reverse the chronic complications of diabetes. More recently, there has been growing interest in the use of specialised pro-resolving mediators (SPMs) as an exciting therapeutic strategy to target diabetes and the chronic complications of diabetes.

Specialized Pro-resolving Lipid Mediators: Modulation of Diabetes-Associated Cardio-, Reno-, and Retino-Vascular Complications

Diabetes and its associated chronic complications present a healthcare challenge on a global scale. Despite improvements in the management of chronic complications of the micro-/macro-vasculature, their growing prevalence and incidence highlights the scale of the problem. It is currently estimated that diabetes affects 425 million people globally and it is anticipated that this figure will rise by 2025 to 700 million people. The vascular complications of diabetes including diabetes-associated atherosclerosis and kidney disease present a particular challenge. Diabetes is the leading cause of end stage renal disease, reflecting fibrosis leading to organ failure. Moreover, diabetes associated states of inflammation, neo-vascularization, apoptosis and hypercoagulability contribute to also exacerbate atherosclerosis, from the metabolic syndrome to advanced disease, plaque rupture and coronary thrombosis. Current therapeutic interventions focus on regulating blood glucose, glomerular and peripheral hypertension and can at best slow the progression of diabetes complications. Recently advanced knowledge of the pathogenesis underlying diabetes and associated complications revealed common mechanisms, including the inflammatory response, insulin resistance and hyperglycemia. The major role that inflammation plays in many chronic diseases has led to the development of new strategies aiming to promote the restoration of homeostasis through the "resolution of inflammation." These strategies aim to mimic the spontaneous activities of the 'specialized pro-resolving mediators' (SPMs), including endogenous molecules and their synthetic mimetics. This review aims to discuss the effect of SPMs [with particular attention to lipoxins (LXs) and resolvins (Rvs)] on inflammatory responses in a series of experimental models, as well as evidence from human studies, in the context of cardio- and reno-vascular diabetic complications, with a brief mention to diabetic retinopathy (DR). These data collectively support the hypothesis that endogenously generated SPMs or synthetic mimetics of their activities may represent lead molecules in a new discipline, namely the 'resolution pharmacology,' offering hope for new therapeutic strategies to prevent and treat, specifically, diabetes-associated atherosclerosis, nephropathy and retinopathy.

Lipoxin B4 Enhances Human Memory B Cell Antibody Production via Upregulating Cyclooxygenase-2 Expression

Vaccination has been the most effective way to prevent or reduce infectious diseases; examples include the eradication of smallpox and attenuation of tetanus and measles. However, there is a large segment of the population that responds poorly to vaccines, in part because they are immunocompromised because of disease, age, or pharmacologic therapy and are unable to generate long-term protection. Specialized proresolving mediators are endogenously produced lipids that have potent proresolving and anti-inflammatory activities. Lipoxin B₄ (LXB₄) is a member of the lipoxin family, with its proresolving effects shown in allergic airway inflammation. However, its effects on the adaptive immune system, especially on human B cells, are not known. In this study, we investigated the effects of LXB₄ on human B cells using cells from healthy donors and donors vaccinated against influenza virus in vitro. LXB₄ promoted IgG Ab production in memory B cells and also increased the number of IgG-secreting B cells. LXB₄ enhanced expression of two key transcription factors involved in plasma cell differentiation, BLIMP1 and XBP1. Interestingly, LXB₄ increased expression of cyclooxygenase-2 (COX2), an enzyme that is required for efficient B cell Ab production. The effects of LXB₄ are at least partially COX2-dependent as COX2 inhibitors attenuated LXB₄-stimulated BLIMP1 and Xpb-1 expression as well as IgG production. Thus, our study reveals for the first time, to our knowledge, that LXB₄ boosts memory B cell activation through COX2 and suggests that LXB₄ can serve as a new vaccine adjuvant.

From blood coagulation to innate and adaptive immunity: the role of platelets in the physiology and pathology of autoimmune disorders

Thrombosis and cardiovascular complications are common manifestations of a variety of pathological conditions, including infections and chronic inflammatory diseases. Hence, there is great interest in determining the hitherto unforeseen immune role of the main blood coagulation executor-the platelet. Platelets store and release a plethora of immunoactive molecules, generate microparticles, and interact with cells classically belonging to the immune system. The observed effects of platelet involvement in immune processes, especially in autoimmune diseases, are conflicting-from inciting inflammation to mediating its resolution. An in-depth understanding of the role of platelets in inflammation and immunity could open new therapeutic pathways for patients with autoimmune disorders. This review aims to summarize the current knowledge on the role of platelets in the patomechanisms of autoimmune disorders and suggests directions for future research.

Patatin-like phospholipases in microbial infections with emerging roles in fatty acid metabolism and immune regulation by Apicomplexa

Emerging lipidomic technologies have enabled researchers to dissect the complex roles of phospholipases in lipid metabolism, cellular signaling and immune regulation. Host phospholipase products are involved in stimulating and resolving the inflammatory response to pathogens. While many pathogen-derived phospholipases also manipulate the immune response, they have recently been shown to be involved in lipid remodeling and scavenging during replication. Animal and plant hosts as well as many pathogens contain a family of patatin-like phospholipases, which have been shown to have phospholipase A₂ activity. Proteins containing patatin-like phospholipase domains have been identified in protozoan parasites within the Apicomplexa phylum. These parasites are the causative agents of some of the most widespread human diseases. Malaria, caused by Plasmodium spp., kills nearly half a million people worldwide each year. Toxoplasma and Cryptosporidium infect millions of people each year with lethal consequences in immunocompromised populations. Parasite-derived patatin-like phospholipases are likely effective drug targets and progress in the tools available to the Apicomplexan field will allow for a closer look at the interplay of lipid metabolism and immune regulation during host infection.

Opposing Regulation of Interleukin-8 and NF-kB Responses by Lipoxin A4 and Serum Amyloid a via the Common Lipoxin a Receptor

Lipoxin A4 (LXA4) is a potent eicosanoid that inhibits IL-1β-induced activation of human fibroblast-like synoviocytes (FLS) via the LXA4 receptor (ALXR). Serum amyloid A (SAA) is an acute phase reactant with cytokine-like properties. SAA has been shown to bind the same seven transmembrane G protein-coupled receptor ligated by LXA4. Here we compared the inflammatory responses of lipid (LXA4) and peptide (SAA) ligands in human FLS via the shared ALX and characterized their downstream signaling. LXA4 induced stimulation of tissue inhibitors of metalloproteinase-2, whereas SAA induced interleukin-8 and matrix metalloproteinase-3 production. SAA up-regulated NF-kB and AP-1 DNA binding activity, while LXA4 markedly inhibited these responses after IL-1β stimulation. A human IL-8 promoter luciferase construct was transfected into CHO cells stably expressing ALXR in order to determine the role of NF-kB and/or AP-1 in the regulation of IL-8 gene expression. The NF-kB pathway proved to be the preeminent for the biological responses elicited by both ligands. These findings suggest that two endogenous molecules, targeting a common receptor, could participate in the pathogenesis of inflammatory arthritis by differentially regulating inflammatory responses in tissues expressing the ALXR.

The role of dyslipidemia in diabetic retinopathy

Diabetic retinopathy (DR) affects over 93million people worldwide and is the number one cause of blindness among working age adults. These indicators coupled with the projected rise of patients diagnosed with diabetes, makes DR a serious and prevalent vision threating disease. Data from recent clinical trials demonstrate that in addition to the well accepted role of hyperglycemia, dyslipidemia is an important, but often overlooked factor in the development of DR. The central aim of this review article is to showcase the critical role of dyslipidemia in DR progression as well as highlight novel therapeutic solutions that take advantage of the vital roles lipid metabolism plays in DR progression.

Effect of Alox-15 Polymorphism on GCF Levels of Lipoxin-A4 in Chronic Periodontitis: A Preliminary Study

Lipoxins play an important role in periodontal resolution, hence, investigation of genetic polymorphism of lipoxin gene may provide important information on the role of lipoxins in periodontal disease pathogenesis. The aim of this study was to investigate a polymorphism of C-to-T substitution at position c.-292 in ALOX15 (reticulocyte-type 15 lipoxygenase 1) gene in patients with chronic periodontitis and to associate the polymorphism with gingival crevicular fluid (GCF) lipoxin A4 (LXA4) levels. Forty-five chronic periodontitis and 45 periodontally healthy patients were included in this case-control study. Plaque index, calculus index, sulcus bleeding index, full mouth probing depth (PD) and clinical attachment loss (CAL) were recorded. GCF and blood samples were collected. GCF was analyzed for LXA4 levels by enzyme linked immunosorbant assay. Genotyping of ALOX15 polymorphism was studied using PCR. Mean LXA4 was lower in periodontitis group compared to the periodontally healthy group. There was a negative correlation between CAL and LXA4. The CC genotype was higher in the study group than in the control group. In the study group, mean CAL was significantly lower among individuals with the CT genotype. Mean LXA4 was significantly lower in CC genotype (45.0±7.11 ng/mL) compared to CT genotype (50.81±5.81 ng/mL) among the patients with periodontitis. The results suggest that LXA4 and c.-292T allele are associated with periodontal health. Polymorphisms in the ALOX15 gene may influence periodontal disease pathogenesis. Hence, investigation of such polymorphisms could benefit the evaluation of lipoxins role in periodontal disease.

Resolvin D1 Alleviates the Lung Ischemia Reperfusion Injury via Complement, Immunoglobulin, TLR4, and Inflammatory Factors in Rats

Lung ischemia-reperfusion injury (LIRI) is still an unsolved medical issue, which negatively affects the prognosis of many lung diseases. The aim of this study is to determine the effects of RvD1 on LIRI and the potential mechanisms involved. The results revealed that the levels of complement, immunoglobulin, cytokines, sICAM-1, MPO, MDA, CINC-1, MCP-1, ANXA-1, TLR4, NF-κBp65, apoptosis index, and pulmonary permeability index were increased, whereas the levels of SOD, GSH-PX activity, and oxygenation index were decreased in rats with LIRI. Except for ANXA-1, these responses induced by LIRI were significantly inhibited by RvD1 treatment. In addition, LIRI-induced structure damages of lung tissues were also alleviated by RvD1 as shown by H&E staining and transmission electron microscopy. The results suggest that RvD1 may play an important role in protection of LIRI via inhibition of complement, immunoglobulin, and neutrophil activation; down-regulation of TLR4/NF-κB; and the expression of a variety of inflammatory factors.

Neutrophil Resolvin E1 Receptor Expression and Function in Type 2 Diabetes

Unresolved inflammation is key in linking metabolic dysregulation and the immune system in type 2 diabetes. Successful regulation of acute inflammation requires biosynthesis of specialized proresolving lipid mediators, such as E-series resolvin (RvE) 1, and activation of cognate G protein-coupled receptors. RvE1 binds to leukotriene B4 (BLT-1) on neutrophils and to ERV-1/ChemR23 on monocyte/macrophages. We show novel actions of RvE1 and expression patterns of neutrophil receptors in type 2 diabetes. Neutrophils from healthy subjects express functional BLT-1, low levels of minimally functional ERV-1, and inversed coexpression when compared to neutrophils from type 2 diabetes subjects. Stimulation with TNF-α or LPS increased the expression of ERV-1 by healthy and diabetic neutrophils. RvE1 counteracted LPS and TNF-α induction of ERV-1 overexpression and endogenous diabetic overexpression, activating phagocytosis and resolution signals. Functional ERV-1 was determined by phosphorylation of the signaling protein ribosomal S6. Receptor-antagonism experiments revealed that the increase in phosphorylation of ribosomal S6 was mediated by BLT-1 in healthy subject neutrophils and by ERV-1 in diabetes. Metabololipidomics reveal a proinflammatory profile in diabetic serum. Cell phagocytosis is impaired in type 2 diabetes and requires RvE1 for activation. The dose of RvE1 required to activate resolution signals in type 2 diabetic neutrophils was significantly higher than in healthy controls. RvE1 rescues the dysregulation seen on neutrophil receptor profile and, following a therapeutic dosage, activates phagocytosis and resolution signals in type 2 diabetes. These findings reveal the importance of resolution receptors in health, disease, and dysregulation of inflammation in type 2 diabetes.

Lipoxin A4 selectively programs the profile of M2 tumor-associated macrophages which favour control of tumor progression

In tumor microenvironments, the macrophage population is heterogeneous, but some macrophages can acquire tumor-promoting characteristics. These tumor-associated macrophages (TAM) exhibit an M2-like profile, with deficient production of NO and ROS, characteristics of pro-inflammatory M1 cytotoxic macrophages. Lipoxins (LX) and 15-epi-lipoxins are lipid mediators which can induce certain features of M2 macrophages in mononuclear cells, but their effects on TAM remain to be elucidated. This study tested the hypothesis that ATL-1, a synthetic analogue of 15-epi-lipoxin A₄ , could modulate TAM activity profile. We show that human macrophages (MΦ) differentiated into TAM-like cells after incubation with conditioned medium from MV3, a human melanoma lineage cell. Contrasting with the effects observed in other M2 subsets and M1 profile macrophages, ATL-1 selectively decreased M2 surface markers in TAM, suggesting unique behavior of this particular M2 subset. Importantly, these results were replicated by the natural lipoxins LXA₄ and the aspirin induced 15-epi-LXA₄ (ATL). In parallel, ATL-1 stimulated TAM to produce NO by increasing the iNOS/arginase ratio and activated NADPH oxidase, triggering ROS production. These alterations in TAM profile induced by ATL-1 led to loss of the anti-apoptotic effects of TAM on melanoma cells and increased their cytotoxic properties. Finally, ATL-1 was found to inhibit tumor progression in a murine model in vivo, which was accompanied by alterations in TAM profile and diminished angiogenesis. Together, the results show an unexpected effect of lipoxin, which induces in TAM a change from an M2- to an M1-like profile, thereby triggering tumor cell apoptosis and down-modulating the tumor progression.

BML-111 Protected LPS/D-GalN-Induced Acute Liver Injury in Rats

Lipoxins (LXs) display unique pro-resolving and anti-inflammatory functions in a variety of inflammatory conditions. The present study was undertaken to investigate the effects of BML-111 (5(S),6(R),7-trihydroxyheptanoic acid methyl ester), the agonist of lipoxin A₄ receptor, in a model of Lipopolysaccharides (LPS) and d-Galactosamine (d-GalN) induced acute liver injury, and to explore the mechanisms. Histopathological analyses were carried out to quantify liver injury degree. The activities of myeloperoxidase (MPO) were examined to evaluate the levels of neutrophil infiltration. The activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in serum were detected to evaluate the functions of the liver. The amounts of tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10), and interleukin-1β (IL-1β) were measured using enzyme-linked immunosorbent assay (ELISA), and the expression levels of transforming growth factor-β1(TGF-β1) and cyclooxygenase-2 (COX-2) were examined using Western blotting. The antioxidant capacity, the activities of inducible nitric oxide synthase (iNOS), the contents of malondialdehyde (MDA) and nitric oxide (NO) were analyzed with the kits via biochemical analysis. We established the model of acute liver injury with lipopolysaccharide and d-Galactosamine (LPS/d-GalN): (1) histopathological results and MPO activities, with the activities of AST and ALT in serum, consistently demonstrated LPS and d-GalN challenge could cause severe liver damage, but BML-111 could prevent pathological changes, inhibit neutrophil infiltration, and improve the hepatic function; (2) LPS/d-GalN increased TNF-α, IL-1β, COX-2, and IL-10, while decreasing TGF-β1. However, BML-111 could repress LPS/d-GalN -induced TNF-α, IL-1β and COX-2, meanwhile increasing the expression levels of TGF-β1 and IL-10; (3) LPS/d-GalN inhibited the activities of superoxide dismutase (SOD), catalase (CAT), total antioxidant capacity (T-AOC), and hydroxyl radical-scavenging ability, simultaneously increasing the levels of MDA and NO, so also the activity of iNOS. Otherwise, BML-111 could reverse all the phenomena. In a word, BML-111 played a protective role in acute liver injury induced by LPS and d-GalN in rats, through improving antioxidant capacity and regulating the balance of inflammatory cytokines.

Lipoxins: nature's way to resolve inflammation

An effective host defense mechanism involves inflammation to eliminate pathogens from the site of infection, followed by the resolution of inflammation and the restoration of tissue homeostasis. Lipoxins are endogenous anti-inflammatory, pro-resolving molecules that play a vital role in reducing excessive tissue injury and chronic inflammation. In this review, the mechanisms of action of lipoxins at the site of inflammation and their interaction with other cellular signaling molecules and transcription factors are discussed. Emphasis has also been placed on immune modulatory role(s) of lipoxins. Lipoxins regulate components of both the innate and adaptive immune systems including neutrophils, macrophages, T-, and B-cells. Lipoxins also modulate levels of various transcription factors such as nuclear factor κB, activator protein-1, nerve growth factor-regulated factor 1A binding protein 1, and peroxisome proliferator activated receptor γ and control the expression of many inflammatory genes. Since lipoxins and aspirin-triggered lipoxins have clinical relevance, we discuss their important role in clinical research to treat a wide range of diseases like inflammatory disorders, renal fibrosis, cerebral ischemia, and cancer. A brief overview of lipoxins in viral malignancies and viral pathogenesis especially the unexplored role of lipoxins in Kaposi’s sarcoma-associated herpes virus biology is also presented.

Mechanisms of nonsteroidal anti-inflammatory drugs in cancer prevention

Various clinical and epidemiologic studies show that nonsteroidal anti-inflammatory drugs (NSAIDs), including aspirin and cyclooxygenase inhibitors (COXIBs) help prevent cancer. Since eicosanoid metabolism is the main inhibitory targets of these drugs the resulting molecular and biological impact is generally accepted. As our knowledge base and technology progress we are learning that additional targets may be involved. This review attempts to summarize these new developments in the field.

Lipoxin A4 inhibits lipopolysaccharide-induced production of inflammatory cytokines in keratinocytes by up-regulating SOCS2 and down-regulating TRAF6

Liopxin A4 (LXA4) is considered to be a crucial modulator in the inflammatory responses. In the present study, we aimed to study the effect of LXA4 on the inflammatory cytokines production induced by lipopolysaccharide (LPS) and the possible mechanism in normal human epidermal keratinocytes (NHEKs). NHEKs were isolated and cultured. The expression of toll-like receptor 4 (TLR4), LXA4 receptor (ALXR) and aryl hydrocarbon receptor (AhR) in NHEKs was detected by reverse transcription polymerase chain reaction (RT-PCR). The mRNA and protein levels of tumor necrosis factor-alpha (TNF-α) and interleukin-1β (IL-1β) were determined in NHEKs stimulated by LPS (10 μg/mL) with or without preincubation with LXA4 (100 nmol/L) for 30 min by real-time quantitative PCR (real-time qPCR) and enzyme-linked immunosorbent assay (ELISA), respectively. The expression levels of tumor necrosis factor receptor-associated factor 6 (TRAF6) and suppressors of cytokine signaling 2 (SOCS2) mRNAs and proteins, and nuclear translocation of NF-kB-p65 were measured by real-time qPCR and Western blotting, respectively. The results showed that NHEKs expressed TLR4, ALXR and AhR. LXA4 significantly inhibited the mRNA and protein expression levels of TNF-α, IL-1β and TRAF6 induced by LPS in NHEKs, and LXA4 obviously increased the expression of SOCS2 at mRNA and protein levels. The nuclear NF-kB-p65 protein expression induced by LPS was inhibited after preincubation with LXA4 in NHEKs. It was concluded that LXA4 inhibits the LPS-induced production of TNF-α and IL-1β in NHEKs by up-regulating SOCS2 and down-regulating TRAF6.

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.

Pulmonary antifibrotic mechanisms aspirin-triggered lipoxin A(4) synthetic analog

No successful therapies are available for pulmonary fibrosis, indicating the need for new treatments. Lipoxins and their 15-epimers, aspirin-triggered lipoxins (ATL), present potent antiinflammatory and proresolution effects (Martins et al., J Immunol 2009;182:5374-5381). We show that ATLa, an ATL synthetic analog, therapeutically reversed a well-established pulmonary fibrotic process induced by bleomycin (BLM) in mice. We investigated the mechanisms involved in its effect and found that systemic treatment with ATLa 1 week after BLM instillation considerably reversed the inflammatory response, total collagen and collagen type 1 deposition, vascular endothelial growth factor, and transforming growth factor (TGF)-β expression in the lung and restored surfactant protein C expression levels. ATLa also inhibited BLM-induced apoptosis and cellular accumulation in bronchoalveolar lavage fluid and in the lung parenchyma as evaluated by light microscopy and flow cytometry (Ly6G(+), F4/80(+), CD11c(+), CD4(+), and B220(+) cells) assays. Moreover, ATLa inhibited the lung production of IL-1β, IL-17, TNF-α, and TGF-β induced by BLM-challenged mice. ATLa restored the balance of inducible nitric oxide synthase-positive and arginase-positive cells in the lungs, suggesting a prevalence of M2 versus M1 macrophages. Together, these effects improved pulmonary mechanics because ATLa treatment brought to normal levels lung resistance and elastance, which were clearly altered at 7 days after BLM challenge. Our findings support ATLa as a promising therapeutic agent to treat lung fibrosis.

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.

Long-term aspirin pretreatment in the prevention of cerulein-induced acute pancreatitis in rats

AIM: To investigate the effects of long term pretreatment with low-, medium- and high-dose aspirin (acetylsalicylic acid, ASA) on a model of acute pancreatitis (AP) induced in rats.

METHODS: Forty male Wistar rats were used. Three experimental groups, each consisting of eight animals, received low- (5 mg/kg per day), medium- (150 mg/kg per day) and high-dose (350 mg/kg per day) ASA in supplemented pellet chow for 100 d. Eight animals, serving as the AP-control group, and another eight, serving as reference value (RV) group, were fed with standard pellet chow for the same period. After pretreatment, AP was induced in the experimental animals by intraperitoneal administration of cerulein (2 × 50 μg/kg), while the RV group received saline in the same way. Twelve hours after the second injection, the animals were sacrificed. Pancreatic tissue and plasma samples were collected. One part of the collected pancreatic tissues was used for histopathological evaluation, and the remaining portion was homogenized. Cytokine levels [tumor necrosis factor, interleukin (IL)-1β, IL-6], hemogram parameters, biochemical parameters (amylase and lipase), nuclear factor-κB, aspirin triggered lipoxins and parameters related to the antioxidant system (malondialdehyde, nitric oxide, hemeoxygenase-1, catalase and superoxide dismutase) were measured.

RESULTS: Cerulein administration induced mild pancreatitis, characterized by interstitial edema (total histopathological score of 5.88 ± 0.44 vs 0.25 ± 0.16, P < 0.001). Subsequent pancreatic tissue damage resulted in an increase in amylase (2829.71 ± 772.48 vs 984.57 ± 49.22 U/L, P = 0.001) and lipase (110.14 ± 75.84 U/L vs 4.71 ± 0.78 U/L, P < 0.001) in plasma, and leucocytes (6.89 ± 0.48 vs 4.36 ± 0.23, P = 0.001) in peripheral blood. Cytokines, IL-1β (18.81 ± 2.55 pg/μg vs 6.65 ± 0.24 pg/μg, P = 0.002) and IL-6 (14.62 ± 1.98 pg/μg vs 9.09 ± 1.36 pg/μg, P = 0.04) in pancreatic tissue also increased. Aspirin pretreatment reduced the increase in the aforementioned parameters to a certain degree and partially improved the histopathological alterations caused by cerulein. No evidence of side effects related to chronic ASA administration (e.g., inflammation or bleeding) was observed in the gastrointestinal tract in macroscopic and histopathological examination.

CONCLUSION: Long term ASA pretreatment could prevent and/or ameliorate certain hematological, serological and histological alterations caused by cerulein-induced AP.

Involvement of K+ channel-dependant pathways in lipoxin A4-induced protective effects on hypoxia/reoxygenation injury of cardiomyocytes

Studies have shown that lipoxin A4 (LXA4) and activation of LXA4 receptor provided protection against myocardial ischemia/reperfusion injury in animal models. However, the mechanisms by which LXA4 induced protective role on myocardial ischemia/reperfusion injury remains unclear. In the present studies, we investigated the protective effects of LXA4 on H9c2 cardiomyocytes exposed to hypoxia/reoxygenation (H/R) injury and involvement of heme oxygenase-1 (HO-1)- and K(+) channel-dependant pathways in the LXA4 action. H9c2 cardiomyocytes were pretreated with or without LXA4 or HO-1 specific interfering RNA (siRNA) or various blockers and openers of K(+) channels before exposing to H/R injury. The levels of lactate dehydrogenase (LDH) and creatine kinase (CK) in cellular supernatants and necrosis factor-α (TNF-α) in cellular lysates were measured by using ELISA. Expressions of HO-1 mRNA and protein were analyzed by using RT-PCR and Western blot respectively. Pretreatment of the cells undergoing H/R injury with LXA4 significantly reduced the LDH and CK levels induced by H/R injury, and increased the expressions and activity of HO-1. However, the protective effects of LXA4 were completely blocked by transfection of the cells with HO-1 siRNA, and were partially but significantly blocked by pretreatment of the cells with various blockers of K(+) channels. The LXA4-induced expressions of HO-1 in the cells were also inhibited by HO-1 siRNA and various blockers of K(+) channels. The inhibitory effects of LXA4 on enhanced TNF-α levels induced by H/R injury were abolished by transfection of the cells with HO-1 siRNA. In conclusion, the protective role of LXA4 on cardiomyocytes against H/R injury is related to upregulation of HO-1 via reduced production of TNF-α and activation of ATP-sensitive K(+) channels and calcium-sensitive K(+) channel.

Cyclo-oxygenase-2 knockout genotype in mice is associated with blunted angiotensin II-induced oxidative stress and hypertension

BACKGROUND

Inflammation and oxidative stress have been identified as integral parts in the pathogenesis of hypertension. Cyclo-oxygenase-2 which could elicit inflammation and free radicals generation appears to be a key enzyme in hypertension. Cyclo-oxygenase-2 expression and oxidative stress in cardiovascular tissues are increased in the angiotensin II model.

METHODS

Cyclo-oxygenase-1 and cyclo-oxygenase-2 deficient mice and their cultured aortic smooth muscle cells were used to investigate the role of these enzymes in angiotensin II induced superoxide production and hypertension.

RESULTS

At resting state, the superoxide production in aortic and cardiac tissues was lower in cyclo-oxygenase-2 deficient than in the wild type or in cyclo-oxygenase-1 deficient mice. Chronic angiotensin II infusion increased the superoxide production in these tissues from both cyclo-oxygenase-deficient and wild-type mice whereas the level in cyclo-oxygenase-2 deficient mice was equivalent to the basal level in wild-type mice. The hypertensive effect of angiotensin II was attenuated in cyclo-oxygenase-2 deficient mice. Aspirin treatment reduced the basal superoxide production and blunted the oxidative and hypertensive effect of angiotensin II in wild type and cyclo-oxygenase-1 deficient mice whereas it lost completely its antioxidative property in angiotensin II-treated aortic smooth muscle cells isolated from cyclo-oxygenase-2 deficient mice.

CONCLUSIONS

Cyclo-oxygenase-2 pathway plays a major role in the superoxide generation as well as in the angiotensin II-induced oxidative stress and blood pressure. Cyclo-oxygenase-1 activity didn't show any influence on these parameters. These results suggest that cyclo-oxygenase-2 is involved in the pathogenesis of hypertension.

Urinary concentrations of 15-epimer of lipoxin A(4) are lower in patients with aspirin-intolerant compared with aspirin-tolerant asthma

BACKGROUND

Although an abnormality in arachidonic acid metabolism may be responsible for aspirin-intolerant asthma (AIA), there is little knowledge about the concentrations of urinary lipoxin A(4) (LXA(4)) and the 15-epimer of LXA(4) (15-epi-LXA(4)) in relation to asthma severity in AIA subjects.

OBJECTIVE

The purpose of this study is to estimate urinary LXA(4) and the 15-epimer concentrations to investigate lipoxins in AIA.

METHODS

In this study, we examined AIA, aspirin-tolerant asthma (ATA) and healthy control groups. The AIA and ATA groups were subdivided into the severe asthma and non-severe asthma subgroups. Urinary LXA(4), 15-epi-LXA(4) and leukotriene E(4) (LTE(4) ) were quantified using enzyme immunoassay after separating these compounds using high-performance liquid chromatography.

RESULTS

The urinary LXA(4) concentration was significantly lower than the 15-epi-LXA(4) concentration in the asthmatic subjects. The AIA group showed significantly lower urinary 15-epi-LXA(4) (P < 0.01) and higher urinary LTE(4) concentrations (P < 0.05) than the ATA group. Comparison of 15-epi-LXA(4) concentrations between the severe asthmatic and non-severe asthmatic subjects in the AIA and ATA groups revealed that the decreased 15-epi-LXA(4) concentration may be related to aspirin intolerance, but not asthma severity. Receiver operator characteristic curves demonstrated that the concentration ratio of LTE(4) to 15-epi-LXA(4) was superior to 15-epi-LXA(4) concentration and LTE(4) concentration as a predictive factor for aspirin intolerance.

CONCLUSIONS AND CLINICAL RELEVANCE

We have demonstrated for the first time that urinary 15-epi-LXA(4) concentration is significantly higher than LXA(4) concentration in both the AIA and ATA groups. 15-Epi-LXA(4) concentration was significantly lower in the AIA group with an increased urinary LTE(4) concentration than in the ATA group. An imbalance between proinflammatory cysteinyl-leukotrienes and anti-inflammatory 15-epi-LXA(4) may be involved in AIA pathogenesis.

Omega fatty acids and resolution of inflammation: A new twist in an old tale

Identification of the factors that regulate immune tolerance and control the appearance of exacerbated inflammatory conditions is crucial for the development of new therapies of inflammatory and autoimmune diseases. Resolution of inflammation and the return of tissues to homeostasis protect us against excessive tissue injury and promote the restoration of function and structure. Resolution of inflammation, which was considered a passive event, is actually an active process where new families of endogenous lipid mediators from omega-3 polyunsaturated fatty acids play an important role in removing proinflammatory mediators generated from arachidonic acid. These chemical mediator families, termed Resolvins and Protectins, are potent stereoselective agonists that control the duration and magnitude of inflammation, along with the Lipoxins as signals in resolution. This review examines the mapping of these circuits and recent advances in our understanding of the biosynthesis and actions of these novel proresolving lipid mediators. A search in the electronical databases PubMed and the Cochrane Central Register of Controlled Trials was carried out. The search strategy applied was: “Omega fatty acid” AND “resolution of inflammation,” including articles from January 1,1985 to October 2009. This resulted in the identification of a total of 52 articles, which were analyzed in full text leading to consideration of only nine full texts.

Human lipoxygenase pathway gene variation and association with markers of subclinical atherosclerosis in the diabetes heart study

Aims. Genes of the 5-lipoxygenase pathway are compelling candidates for atherosclerosis. We hypothesize that polymorphisms in ALOX12, ALOX15, ALOX5, and ALOX5AP genes are associated with subclinical atherosclerosis in multiple vascular beds. Methods. Families with two or more siblings with type 2 diabetes and their nondiabetic siblings were studied as part of the Diabetes Heart Study (DHS). European American diabetic (n = 828) and nondiabetic (n = 170) siblings were genotyped for SNPs in the ALOX12, ALOX15, ALOX5, and ALOX5AP genes. Subclinical measures of atherosclerosis (IMT, coronary (CorCP), carotid (CarCP) and aortic (AorCP) calcified plaque) were obtained. Results. Associations were observed between ALOX12 with CorCP, ALOX5 with CorCP, AorCP, and IMT, and ALOX5AP with CorCP and CarCP, independent of known epidemiologic risk factors. Further, lipoxygenase pathway SNPs that were associated with measures of atherosclerosis were associated with markers of inflammation (CRP, ICAM-1) and calcification (MGP). Conclusions. Polymorphisms within ALOX12, ALOX5, and ALOX5AP are genetically associated with subclinical atherosclerosis and with biomarkers of disease in families with type 2 diabetes. These results suggest that variants in lipoxygenase pathway genes may have pleiotropic effects on multiple components that determine risk of cardiovascular disease.

ATLa, an aspirin-triggered lipoxin A4 synthetic analog, prevents the inflammatory and fibrotic effects of bleomycin-induced pulmonary fibrosis

Despite an increase in the knowledge of mechanisms and mediators involved in pulmonary fibrosis, there are no successful therapeutics available. Lipoxins (LX) and their 15-epimers, aspirin-triggered LX (ATL), are endogenously produced eicosanoids with potent anti-inflammatory and proresolution effects. To date, few studies have been performed regarding their effect on pulmonary fibrosis. In the present study, using C57BL/6 mice, we report that bleomycin (BLM)-induced lung fibrosis was prevented by the concomitant treatment with an ATL synthetic analog, ATLa, which reduced inflammation and matrix deposition. ATLa inhibited BLM-induced leukocyte accumulation and alveolar collapse as evaluated by histology and morphometrical analysis. Moreover, Sirius red staining and lung hydroxyproline content showed an increased collagen deposition in mice receiving BLM alone that was decreased upon treatment with the analog. These effects resulted in benefits to pulmonary mechanics, as ATLa brought to normal levels both lung resistance and compliance. Furthermore, the analog improved mouse survival, suggesting an important role for the LX pathway in the control of disease establishment and progression. One possible mechanism by which ATLa restrained fibrosis was suggested by the finding that BLM-induced myofibroblast accumulation/differentiation in the lung parenchyma was also reduced by both simultaneous and posttreatment with the analog (alpha-actin immunohistochemistry). Interestingly, ATLa posttreatment (4 days after BLM) showed similar inhibitory effects on inflammation and matrix deposition, besides the TGF-beta level reduction in the lung, reinforcing an antifibrotic effect. In conclusion, our findings show that LX and ATL can be considered as promising therapeutic approaches to lung fibrotic diseases.

Therapeutic effects of nitric oxide-aspirin hybrid drugs

This review examines the therapeutic potential and mechanisms of action of drugs known as nitric oxide (NO)-aspirins. Drugs of this class have an NO-releasing moiety joined by ester linkage to the aspirin molecule. NO-aspirins have the capability to release NO in addition to retaining the cyclooxygenase-inhibitory action of aspirin. The protective nature of NO led to the development of NO-aspirins in the hope that they might avoid the gastric side effects associated with aspirin. However, it has become apparent that the drug-derived NO instills potential for a wide range of added beneficial effects over the parent compound. In this review, the authors focus on the analgesic, anti-inflammatory, cardiovascular and chemopreventative actions of compounds of this emerging drug class.

Signal transduction involved in protective effects of 15(R/S)-methyl- lipoxin A(4) on mesangioproliferative nephritis in rats

Studies have shown that lipoxin A(4) (LXA(4)) inhibited proliferation of mesangial cells in vitro induced by platelet-derived growth factor, epidermal growth factor, leukotriene D(4) or tumor necrosis factor-alpha. In this study, we investigated the protective effects of 15(R/S)-methyl-LXA(4) on mesangioproliferative nephritis in rats and the signal transduction involved in actions of 15(R/S)-methyl-LXA(4). Mesangioproliferative nephritis was induced by a single intravenous injection of the mouse monoclonal anti-Thy1.1 antibodies. The nephritic rats were treated by intravenous injection of 15(R/S)-methyl-LXA(4) every 8h until the rats were sacrificed. There were increments in glomerular infiltration of leukocytes, expressions of protein and mRNA of interleukin (IL)-1beta and IL-6, activities of nuclear factor-kappaB (NF-kappaB) in nephritic rats from day 1 to 4 after induction of nephritis. The enhanced proteinuria, proliferation score of mesangial cells, glomerular proliferating cell nuclear antigen (PCNA) positive cells, activities of phosphorylated phosphoinositide 3-kinase (PI3-K), Akt(1), alpha-smooth muscle actin (alpha-SMA) and signal transducer and activator of transcription 3(STAT(3)), and reduced expression of p27(kip1) were found on day 4 after induction of nephritis. Treatment of nephritic rats with 15(R/S)-methyl-LXA(4) significantly reduced the protenuria, glomerular infiltration of leukocyte, expressions of protein and mRNA of IL-1beta and IL-6, proliferation score of mesangial cells, glomerular PCNA positive cells, activities of phosphorylated PI3-K, Akt(1), alpha-SMA, NF-kappaB and STAT(3), and ameliorated the decrement in p27(kip1) induced by anti-Thy1.1 antibodies. Protective effects of 15(R/S)-methyl-LXA(4) on nephritis induced by anti-Thy1.1 antibodies were related to PI3-K/Akt(1)/p27(kip1)/cyclin pathway, STAT(3) and NF-kappaB pathway-dependent signal transduction.

Lipoxin A4 inhibits acute edema in mice: Implications for the anti-edematogenic mechanism induced by aspirin

Lipoxin A4 (LXA4) is a lipid mediator that plays an important role in the resolution of inflammation. However, the role of LXA4 and aspirin (ASA)-triggered lipoxins (ATLs) in inflammatory edema formation remains unclear. Here, we investigated the inhibitory role played by LXA4 in the carrageenan-induced and other inflammatory mediator-induced edematogenic response in mice, and also assessed the role of ATLs in the anti-edematogenic action of aspirin. Our results showed that LXA4 (1-20 ng/paw or 5 microg/kg i.p.) was effective in inhibiting carrageenan-induced paw edema from 30 min to 2 h. LXA4 (10 ng/paw) was also able to acutely inhibit PAF-, histamine-, PGE2- or bradykinin-induced paw edema, as well as the PAF-induced myeloperoxidase activity increase in the paws. Likewise, LXA4 (10 ng/cavity) also inhibited the pleural edema triggered by histamine (1h), and this response was not followed by leukocyte accumulation. Of note, the lipoxin receptor (ALX-r) antagonist Boc2 (butoxycarbonyl-Phe-Leu-Phe-Leu-Phe, 200 ng/paw) significantly reverted the anti-edematogenic effect of ASA (300 mg/kg p.o.) against carrageenan, PAF, PGE2 and BK, without affecting the anti-edematogenic action caused by indomethacin (3 mg/kg i.p.) in the carrageenan-induced paw edema. Collectively, our results demonstrate for the first time that LXA4 displays an acute and rapid onset anti-edematogenic activity that does not discriminate among different pro-inflammatory stimuli, an effect that is most likely independent of its action on the leukocyte influx. Finally, the present study demonstrates that ATLs exert a very important role in the acute anti-edematogenic action of ASA.

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

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

Involvement of the Rho-kinase/myosin light chain kinase pathway on human monocyte chemotaxis induced by ATL-1, an aspirin-triggered lipoxin A4 synthetic analog

Lipoxins (LX) are arachidonic acid metabolites able to induce monocyte chemotaxis in vitro and in vivo. Nonetheless, the signaling pathways mediating this process are yet unclear. In this study, we have investigated the mechanisms associated with human monocyte activation in response to 15-epi-16-(para-fluoro)-phenoxy-LXA4 (ATL-1), a stable 15-epi-LXA4 analog. Our results demonstrate that ATL-1-induced monocyte chemotaxis (10-300 nM) is inhibited by pertussis toxin, suggesting an effect via the G-protein-linked LXA4 receptor. Monocytes stimulated with the analog presented an increased ERK-2 phosphorylation, which was reduced by PD98059, a selective inhibitor of the MEK 1/2 pathway. After exposure of the cells to ATL-1, myosin L chain kinase (MLCK) phosphorylation was evident and this effect was inhibited by PD98059 or Y-27632, a specific inhibitor of Rho kinase. In addition, Y-27632 abolished ERK-2 activation, suggesting that the MAPK pathway is downstream of Rho/Rho kinase in MLCK activation induced by ATL-1. The specific MLCK inhibitor ML-7, as well as Y-27632, abrogated monocyte chemotaxis stimulated by the analog, confirming the central role of the Rho kinase/MLCK pathway on ATL-1 action. Together, these results indicate that ATL-1 acts as a potent monocyte chemoattractant via Rho kinase and MLCK. The present study clarifies some of the mechanisms involved on the activation of monocytes by LXs and opens new avenues for investigation of these checkpoint controllers of inflammation.

Cystic fibrosis and lipoxins

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Novel lipid mediator aspirin-triggered lipoxin A4 induces heme oxygenase-1 in endothelial cells

Lipoxins (LX) and aspirin-triggered LX (ATL) are eicosanoids generated during inflammation via transcellular biosynthetic routes that elicit distinct anti-inflammatory and proresolution bioactions, including inhibition of leukocyte-mediated injury, stimulation of macrophage clearance of apoptotic neutrophils, repression of proinflammatory cytokine production, and inhibition of cell proliferation and migration. Recently, it was reported that aspirin induces heme oxygenase-1 (HO-1) expression on endothelial cells (EC) in a COX-independent manner, what confers protection against prooxidant insults. However, the underlying mechanisms remain unclear. In this study, we investigated whether an aspirin-triggered lipoxin A(4) stable analog, 15-epi-16-(para-fluoro)-phenoxy-lipoxin A(4) (ATL-1) was able to induce endothelial HO-1. Western blot analysis showed that ATL-1 increased HO-1 protein expression associated with increased mRNA levels on EC in a time- and concentration-dependent fashion. This phenomenon appears to be mediated by the activation of the G protein-coupled LXA(4) receptor because pertussis toxin and Boc-2, a receptor antagonist, significantly inhibited ATL-1-induced HO-1 expression. We demonstrate that treatment of EC with ATL-1 inhibited VCAM and E-selectin expression induced by TNF-alpha or IL-1beta. This inhibitory effect of the analog is modulated by HO-1 because it was blocked by SnPPIX, a competitive inhibitor that blocks HO-1 activity. Our results establish that ATL-1 induces HO-1 in human EC, revealing an undescribed mechanism for the anti-inflammatory activity of these lipid mediators.