Resolvin D1 (RvD1) and maresin 1 (Mar1) contribute to human macrophage control of M. tuberculosis infection while resolving inflammation

Lipid mediators in neutrophil biology: inflammation, resolution and beyond

PURPOSE OF REVIEW

Acute inflammation is the body's first defense in response to pathogens or injury. Failure to efficiently resolve the inflammatory insult can severely affect tissue homeostasis, leading to chronic inflammation. Neutrophils play a pivotal role in eradicating infectious pathogens, orchestrating the initiation and resolution of acute inflammation, and maintaining physiological functions. The resolution of inflammation is a highly orchestrated biochemical process, partially modulated by a novel class of endogenous lipid mediators known as specialized pro-resolving mediators (SPMs). SPMs mediate their potent bioactions via activating specific cell-surface G protein-coupled receptors (GPCR).

RECENT FINDINGS

This review focuses on recent advances in understanding the multifaceted functions of SPMs, detailing their roles in expediting neutrophil apoptosis, promoting clearance by macrophages, regulating their excessive infiltration at inflammation sites, orchestrating bone marrow deployment, also enhances neutrophil phagocytosis and tissue repair mechanisms under both physiological and pathological conditions. We also focus on the novel role of SPMs in regulating bone marrow neutrophil functions, differentiation, and highlight open questions about SPMs' functions in neutrophil heterogeneity.

SUMMARY

SPMs play a pivotal role in mitigating excessive neutrophil infiltration and hyperactivity within pathological milieus, notably in conditions such as sepsis, cardiovascular disease, ischemic events, and cancer. This significant function highlights SPMs as promising therapeutic agents in the management of both acute and chronic inflammatory disorders.

Bactericidal Permeability-Increasing Protein (BPI) Inhibits Mycobacterium tuberculosis Growth

Bactericidal permeability-increasing protein (BPI) is a multifunctional cationic protein produced by neutrophils, eosinophils, fibroblasts, and macrophages with antibacterial anti-inflammatory properties. In the context of Gram-negative infection, BPI kills bacteria, neutralizes the endotoxic activity of lipopolysaccharides (LPSs), and, thus, avoids immune hyperactivation. Interestingly, BPI increases in patients with Gram-positive meningitis, interacts with lipopeptides and lipoteichoic acids of Gram-positive bacteria, and significantly enhances the immune response in peripheral blood mononuclear cells. We evaluated the antimycobacterial and immunoregulatory properties of BPI in human macrophages infected with Mycobacterium tuberculosis. Our results showed that recombinant BPI entered macrophages, significantly reduced the intracellular growth of M. tuberculosis, and inhibited the production of the proinflammatory cytokine tumor necrosis factor-alpha (TNF-α). Furthermore, BPI decreased bacterial growth directly in vitro. These data suggest that BPI has direct and indirect bactericidal effects inhibiting bacterial growth and potentiating the immune response in human macrophages and support that this new protein's broad-spectrum antibacterial activity has the potential for fighting tuberculosis.

Resolution pharmacology and the treatment of infectious diseases

Inflammation is elicited by the host in response to microbes, and is believed to be essential for protection against infection. However, we have previously hypothesized that excessive or misplaced inflammation may be a major contributor to tissue dysfunction and death associated with viral and bacterial infections. The resolutive phase of inflammation is a necessary condition to achieve homeostasis after acute inflammation. It is possible that targeting inflammation resolution may be beneficial for the host during infection. In this review, we summarize the evidence demonstrating the expression, roles and effects of the best described pro-resolving molecules in the context of bacterial and viral infections. Pro-resolving molecules play a pivotal role in modulating a spectrum of pathways associated with tissue inflammation and damage during both viral and bacterial infections. These molecules offer a blend of anti-inflammatory, pro-resolving and sometimes anti-infective benefits, all the while circumventing the undesired and immune-suppressive unwanted effects associated with glucocorticoids. Whether these beneficial effects will translate into benefits to patients clearly deserve further investigation.

Bactericidal Efficacy of the Combination of Maresin-like Proresolving Mediators and Carbenicillin Action on Biofilm-Forming Burn Trauma Infection-Related Bacteria

Biofilm-associated bacterial infections are the major reason for treatment failure in many diseases including burn trauma infections. Uncontrolled inflammation induced by bacteria leads to materiality, tissue damage, and chronic diseases. Specialized proresolving mediators (SPMs), including maresin-like lipid mediators (MarLs), are enzymatically biosynthesized from omega-3 essential long-chain polyunsaturated fatty acids, especially docosahexaenoic acid (DHA), by macrophages and other leukocytes. SPMs exhibit strong inflammation-resolving activities, especially inflammation provoked by bacterial infection. In this study, we explored the potential direct inhibitory activities of three MarLs on Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa and Escherichia coli) bacteria in their biofilms that are leading bacteria in burn trauma-related infections. We also examined the effects of MarLs on the bactericidal activities of a typical broad-spectrum antibiotic, carbenicillin (carb), on these bacteria in their preformed biofilms. The results revealed that MarLs combined with carbenicillin can inhibit the survival of Gram-positive and Gram-negative bacteria in their biofilms although MarLs alone did not exhibit bactericidal activity. Thus, our findings suggest that the combination of MarLs and carbenicillin can lower the antibiotic requirements to kill the bacteria in preformed biofilms.

Exploring COX-2 inhibitors in tuberculosis: A whole-blood model approach for immune response and adjunt therapy evaluation

Pulmonary tuberculosis (TB) inflammation is an underestimated disease complication which anti-inflammatory drugs may alleviate. This study explored the potential use of the COX-2 inhibitors acetylsalicylic acid (ASA) and celecoxib in 12 TB patients and 12 healthy controls using a whole-blood ex vivo model where TNFα, PGE2, and LTB4 plasma levels were quantitated by ELISA; we also measured COX-2, 5-LOX, 12-LOX, and 15-LOX gene expression. We observed a significant TNFα production in response to stimulation with LPS or M. tuberculosis (Mtb). Celecoxib, but not ASA, reduced TNFα and PGE2 production, while increasing LTB4 in patients after infection with Mtb. Gene expression of COX-2 and 5-LOX was higher in controls, while 12-LOX was significantly higher in patients. 15-LOX expression was similar in both groups. We concluded that COX-2 inhibitors downregulate inflammation after Mtb infection, and our methodology offers a straightforward time-efficient approach for evaluating different drugs in this context. Further research is warranted to elucidate the underlying mechanisms and assess the potential clinical benefit.

Maresin: Macrophage Mediator for Resolving Inflammation and Bridging Tissue Regeneration-A System-Based Preclinical Systematic Review

Maresins are lipid mediators derived from omega-3 fatty acids with anti-inflammatory and pro-resolving properties, capable of promoting tissue regeneration and potentially serving as a therapeutic agent for chronic inflammatory diseases. The aim of this review was to systematically investigate preclinical and clinical studies on maresin to inform translational research. Two independent reviewers performed comprehensive searches with the term "Maresin (NOT) Review" on PubMed. A total of 137 studies were included and categorized into 11 human organ systems. Data pertinent to clinical translation were specifically extracted, including delivery methods, optimal dose response, and specific functional efficacy. Maresins generally exhibit efficacy in treating inflammatory diseases, attenuating inflammation, protecting organs, and promoting tissue regeneration, mostly in rodent preclinical models. The nervous system has the highest number of original studies (n = 25), followed by the cardiovascular system, digestive system, and respiratory system, each having the second highest number of studies (n = 18) in the field. Most studies considered systemic delivery with an optimal dose response for mouse animal models ranging from 4 to 25 μg/kg or 2 to 200 ng via intraperitoneal or intravenous injection respectively, whereas human in vitro studies ranged between 1 and 10 nM. Although there has been no human interventional clinical trial yet, the levels of MaR1 in human tissue fluid can potentially serve as biomarkers, including salivary samples for predicting the occurrence of cardiovascular diseases and periodontal diseases; plasma and synovial fluid levels of MaR1 can be associated with treatment response and defining pathotypes of rheumatoid arthritis. Maresins exhibit great potency in resolving disease inflammation and bridging tissue regeneration in preclinical models, and future translational development is warranted.

Inflammation resolution and specialized pro-resolving lipid mediators in chronic rhinosinusitis

INTRODUCTION

In chronic rhinosinusitis (CRS), a complex pathophysiology results from varied pro-inflammatory stimuli but is consistently characterized by classic cellular, molecular, and microbial alterations. Normally, endogenous specialized pro-resolving mediators (SPM) actively promote resolution of inflammation through numerous pathways, including those involved in host antimicrobial defense. However, these pathways appear to be disrupted in CRS.

AREAS COVERED

This paper describes features of CRS in the context of chronic tissue inflammation, and potential mechanisms by which specialized pro-resolving mediators promote active resolution of tissue inflammation.

EXPERT OPINION

Temporal phases of resolution must be tightly regulated to successfully resolve inflammation in CRS while preserving tissue functions such as barrier maintenance and special sensory function. Dysregulation of SPM enzymatic pathways has been recently shown in CRS and is associated with disease phenotypes and microbial colonization patterns. Current research in animal models and in vitro human cell culture, as well as human dietary studies, demonstrate relevant changes in cell signaling with lipid mediator bioavailability. Further clinical research may provide insight into the therapeutic value of this approach in CRS.

Is there a role for specialized pro-resolving mediators in pulmonary fibrosis?

Pulmonary fibrotic diseases are characterized by proliferation of lung fibroblasts and myofibroblasts and excessive deposition of extracellular matrix proteins. Depending on the specific form of lung fibrosis, there can be progressive scarring of the lung, leading in some cases to respiratory failure and/or death. Recent and ongoing research has demonstrated that resolution of inflammation is an active process regulated by families of small bioactive lipid mediators termed "specialized pro-resolving mediators." While there are many reports of beneficial effects of SPMs in animal and cell culture models of acute and chronic inflammatory and immune diseases, there have been fewer reports investigating SPMs and fibrosis, especially pulmonary fibrosis. Here, we will review evidence that resolution pathways are impaired in interstitial lung disease, and that SPMs and other similar bioactive lipid mediators can inhibit fibroblast proliferation, myofibroblast differentiation, and accumulation of excess extracellular matrix in cell culture and animal models of pulmonary fibrosis, and we will consider future therapeutic implications of SPMs in fibrosis.

Maresin1: A multifunctional regulator in inflammatory bone diseases

Inflammation plays a crucial role in the physical response to danger signals, the elimination of toxic stimuli, and the restoration of homeostasis. However, dysregulated inflammatory responses lead to tissue damage, and chronic inflammation can disrupt osteogenic-osteoclastic homeostasis, ultimately leading to bone loss. Maresin1 (MaR1), a member of the specialized pro-resolving mediators (SPMs) family, has been found to possess significant anti-inflammatory, anti-allergic, pro-hemolytic, pro-healing, and pain-relieving properties. MaR1 is synthesized by macrophages (Mφs) and omega-3 fatty acids, and it may have the potential to promote bone homeostasis and treat inflammatory bone diseases. MaR1 has been found to stimulate osteoblast proliferation through leucine-rich repeat G protein-coupled receptor 6 (LGR6). It also activates Mφ phagocytosis and M2-type polarization, which helps to control the immune system. MaR1 can regulate T cells to exert anti-inflammatory effects and inhibit neutrophil infiltration and recruitment. In addition, MaR1 is involved in antioxidant signaling, including nuclear factor erythroid 2-related factor 2 (NRF2). It has also been found to promote the autophagic behavior of periodontal ligament stem cells, stimulate Mφs against pathogenic bacteria, and regulate tissue regeneration and repair. In summary, this review provides new information and a comprehensive overview of the critical roles of MaR1 in inflammatory bone diseases, indicating its potential as a therapeutic approach for managing skeletal metabolism and inflammatory bone diseases.

Prospective study on Maresin-1 and cytokine levels in medication-naïve adolescents with first-episode major depressive disorder

Background

Inflammation and immune activation may play a role in the pathological mechanism of Major Depressive Disorder (MDD). Evidence from cross-sectional and longitudinal studies of adolescents and adults has shown that MDD is associated with increased plasma pro-inflammatory cytokines (e.g., IL-1β, IL-6). It has been reported that Specialized Pro-resolving Mediators (SPMs) mediate inflammation resolution, and Maresin-1 can activate the process of inflammation and promote inflammation resolution by promoting macrophage phagocytosis. However, no clinical studies have been conducted to evaluate the relationship between the levels of Maresin-1 and cytokine and the severity of MDD symptomatology in adolescents.

Methods

40 untreated adolescent patients with primary and moderate to severe MDD and 30 healthy participants as the healthy control (HC) group aged between 13 and 18 years old were enrolled. They received clinical and Hamilton Depression Rating Scale (HDRS-17) evaluation and then, blood samples were collected. Patients in the MDD group were re-evaluated for HDRS-17, and blood samples were taken after a six to eight-week fluoxetine treatment.

Results

The adolescent patients with MDD had lower serum levels of Maresin-1 and higher serum levels of interleukin 6 (IL-6) compared with the HC group. Fluoxetine treatment alleviated depressive symptoms in MDD adolescent patients, which was reflected by higher serum levels of Maresin-1 and IL-4 and lower HDRS-17 scores, serum levels of IL-6, and IL-1β. Moreover, the serum level of Maresin-1 was negatively correlated with the depression severity scores on the HDRS-17.

Conclusion

Adolescent patients with primary MDD had lower levels of Maresin-1 and higher levels of IL-6 compared with the HC group, implying that the peripheral level of pro-inflammatory cytokines may be elevated in MDD, resulting in the insufficiency of inflammation resolution. The Maresin-1 and IL-4 levels increased after anti-depressant treatment, whereas IL-6 and IL-1β levels decreased significantly. Moreover, Maresin-1 level negatively correlated with depression severity, suggesting that reduced levels of Maresin-1 promoted the progression of MDD.

Expression and function of resolvin RvD1n-3 DPA receptors in oral epithelial cells

Chronic inflammatory responses can inflict permanent damage to host tissues. Specialized pro‐resolving mediators downregulate inflammation but also can have other functions. The aim of this study was to examine whether oral epithelial cells express the receptors FPR2/ALX and DRV1/GPR32, which bind RvD1_{n‐3 DPA}, a recently described pro‐resolving mediator derived from omega‐3 docosapentaenoic acid (DPA), and whether RvD1_{n‐3 DPA} exposure induced significant responses in these cells. Gingival biopsies were stained using antibodies to FPR2/ALX and DRV1/GPR32. Expression of FPR2/ALX and DRV1/GPR32 was examined in primary oral epithelial cells by qRT‐PCR, flow cytometry, and immunofluorescence. The effect of RvD1_{n‐3 DPA} on intracellular calcium mobilization and transcription of beta‐defensins 1 and 2, and cathelicidin was evaluated by qRT‐PCR. FPR2/ALX and DRV1/GPR32 were expressed by gingival keratinocytes in situ. In cultured oral epithelial cells, FPR2/ALX was detected on the cell surface, whereas FPR2/ALX and DRV1/GPR32 were detected intracellularly. Exposure to RvD1_{n‐3 DPA} induced intracellular calcium mobilization, FPR2/ALX internalization, DRV1/GPR32 translocation to the nucleus, and significantly increased expression of genes coding for beta‐defensin 1, beta‐defensin 2, and cathelicidin. This shows that the signal constituted by RvD1_{n‐3 DPA} is recognized by oral keratinocytes and that this can strengthen the antimicrobial and regulatory potential of the oral epithelium.

Sex-Dependent Differential Expression of Lipidic Mediators Associated with Inflammation Resolution in Patients with Pulmonary Tuberculosis

There is a sex bias in tuberculosis’s severity, prevalence, and pathogenesis, and the rates are higher in men. Immunological and physiological factors are fundamental contributors to the development of the disease, and sex-related factors could play an essential role in making women more resistant to severe forms of the disease. In this study, we evaluated sex-dependent differences in inflammatory markers. Serum samples were collected from 34 patients diagnosed with pulmonary TB (19 male and 15 female) and 27 healthy controls (18 male and 9 female). Cytokines IL2, IL4, IL6, IL8, IL10, IFNγ, TNFα, and GM-CSF, and eicosanoids PGE2, LTB4, RvD1, and Mar1 were measured using commercially available immunoassays. The MDA, a product of lipidic peroxidation, was measured by detecting thiobarbituric-acid-reactive substances (TBARS). Differential inflammation patterns between men and women were observed. Men had higher levels of IL6, IL8, and TNFα than women. PGE2 and LTB4 levels were higher in patients than healthy controls, but there were no differences for RvD1 and Mar1. Women had higher RvD1/PGE2 and RvD1/LTB4 ratios among patients. RvD1 plays a vital role in resolving the inflammatory process of TB in women. Men are the major contributors to the typical pro-inflammatory profile observed in the serum of tuberculosis patients.

Maresin-1 and Inflammatory Disease

Inflammation is an essential action to protect the host human body from external, harmful antigens and microorganisms. However, an excessive inflammation reaction sometimes exceeds tissue damage and can disrupt organ functions. Therefore, anti-inflammatory action and resolution mechanisms need to be clarified. Dietary foods are an essential daily lifestyle that influences various human physiological processes and pathological conditions. Especially, omega-3 fatty acids in the diet ameliorate chronic inflammatory skin diseases. Recent studies have identified that omega-3 fatty acid derivatives, such as the resolvin series, showed strong anti-inflammatory actions in various inflammatory diseases. Maresin-1 is a derivative of one of the representative omega-3 fatty acids, i.e., docosahexaenoic acid (DHA), and has shown beneficial action in inflammatory disease models. In this review, we summarize the detailed actions of maresin-1 in immune cells and inflammatory diseases.

Specialized pro-resolving mediators as modulators of immune responses

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

Specialized pro-resolving mediators: biosynthesis and biological role in bacterial infections

Acute inflammation caused by bacterial infections is an essential biological defence mechanism of the host in order to neutralize and clear the invaders and to return to homeostasis. Despite its protective function, inflammation may become persistent and uncontrolled, resulting in chronic diseases and tissue destruction as consequence of the unresolved inflammatory process. Therefore, spatiotemporal induction of endogenous inflammation resolution programs that govern bacterial clearance as well as tissue repair and regeneration, are of major importance in order to enable tissues to restore functions. Lipid mediators that are de-novo biosynthesized from polyunsaturated fatty acids (PUFAs) mainly by lipoxygenases and cyclooxygenases, critically regulate the initiation, the maintenance but also the resolution of infectious inflammation and tissue regeneration. The discovery of specialized pro-resolving mediators (SPMs) generated from omega-3 PUFAs stimulated intensive research in inflammation resolution, especially in infectious inflammation elicited by bacteria. SPMs are immunoresolvents that actively terminate inflammation by limiting neutrophil influx, stimulating phagocytosis, bacterial killing and clearance as well as efferocytosis of apoptotic neutrophils and cellular debris by macrophages. Moreover, SPMs prevent collateral tissue damage, promote tissue repair and regeneration and lower antibiotic requirement. Here, we review the biosynthesis of SPMs in bacterial infections and cover specific mechanisms of SPMs that govern the resolution of bacteria-initiated inflammation.

Maresin-1 suppresses IL-1β-induced MMP-13 secretion by activating the PI3K/AKT pathway and inhibiting the NF-κB pathway in synovioblasts of an osteoarthritis rat model with treadmill exercise

Aim: Maresin-1 is a metabolite of docosahexaenoic acid (DHA) that has potential anti-inflammatory effects. To explore whether maresin-1 changes and has a therapeutic effect in osteoarthritis (OA) model rats undergoing treadmill exercise, we examined endogenous maresin-1 in a single-session treadmill experiment and OA model rats were treated with maresin-1, moreover, we examined the effects of maresin-1 on IL-1β induced rat fibroblast-like synoviocytes (FLSs) and possible mechanisms.Methods: In single-session treadmill experiment, 48 rats were randomly divided into 3 groups and performed three different intensities of exercise (15.2 m/min, 0°; 19.3 m/min, 5°; 26.8 m/min, 10°) for 60 min. Intra-articular lavage fluid (IALF) samples were harvested after 0, 2, and 4 h from each group (n = 4) and maresin-1 levels were evaluated by ELISA. Another 30 rats were treated with monosodium iodoacetate (MIA) to induce osteoarthritis and exogenous maresin-1 (MaR-1) and were divided into three groups (n = 10, OA: MIA, OAM: MIA+MaR1, and CG: control group). The level of injury was evaluated by OARSI and Mankin scores, and the levels of type II collagen and MMP13 were evaluated by immunohistochemistry. FLSs were obtained from the knee joint of SD rats, and the expression of MMP13 and activation of the PI3k/Akt and NF-κB p65 pathways in IL-1β-induced FLSs were evaluated by western blotting.Results: Maresin-1 levels were increased in IALF at 4 h after exercise, and type II collagen increased in cartilage and MMP13 decreased in the synovium after treatment with maresin-1 in MIA-induced osteoarthritis. The results of vitro experiment showed decreased MMP13, activation of the PI3k/Akt pathway, and suppression of the NF-κB p65 pathway upon treatment with maresin-1 in IL-1β-induced FLSs.Conclusions: The changes in maresin-1 in IALF, as seen in our single-section treadmill exercise, provides an explanation for the therapeutic effect of appropriate-strength treadmill exercise on osteoarthritis, and our experiments confirmed the therapeutic effect of maresin-1 both in vivo and in vitro.

Pro-Resolving Ligands Orchestrate Phagocytosis

The resolution of inflammation is a tissue protective program that is governed by several factors including specialized pro-resolving mediators (SPMs), proteins, gasses and nucleotides. Pro-resolving mediators activate counterregulatory programs to quell inflammation and promote tissue repair in a manner that does not compromise host defense. Phagocytes like neutrophils and macrophages play key roles in the resolution of inflammation because of their ability to remove debris, microbes and dead cells through processes including phagocytosis and efferocytosis. Emerging evidence suggests that failed resolution of inflammation and defective phagocytosis or efferocytosis underpins several prevalent human diseases. Therefore, understanding factors and mechanisms associated with enhancing these processes is a critical need. SPMs enhance phagocytosis and efferocytosis and this review will highlight mechanisms associated with their actions.

The Oral Delivery of Water-Soluble Phenol TS-13 Ameliorates Granuloma Formation in an In Vivo Model of Tuberculous Granulomatous Inflammation

The redox-sensitive signaling system Keap1/Nrf2/ARE is a premier protective mechanism against oxidative stress that plays a key role in the pathogenesis and development of various diseases, including tuberculous granulomatous inflammation. We have previously reported that novel water-soluble phenolic antioxidant TS-13 (sodium 3-(4'-methoxyphenyl)propyl thiosulfonate) induces Keap1/Nrf2/ARE and attenuates inflammation. The aim of this study is the examination of the effect of TS-13 on tuberculous granulomatous inflammation. BALB/c mice were administered TS-13 (100 mg kg^-1 day^-1) through their drinking water starting immediately after Bacillus Calmette-Guérin (BCG) intravenous injection. Histological changes, production of reactive oxygen species (ROS) (activity of free-radical oxidation processes), and mRNA expression of Nrf2-driven, NF-κB-, AP-1-, and autophagy-dependent signal pathway genes in the liver and peritoneal exudate were evaluated 30 days later. After the 30th day of infection, the activity of the Keap1/Nrf2/ARE system was decreased and its effector genes entailed increasing ROS production in the liver. Therapeutic intervention with TS-13 is aimed at activating the Keap1/Nrf2/ARE system that leads to an increase in Nrf2 and Nrf2-mediated gene expression and a decrease in NF-κB expression. Changes in these pathways resulted in a decline of ROS production and a decrease in the number and the size of granulomas. In total, the results indicate that the Keap1/Nrf2/ARE system can be an effective pharmacological target in host-adjunctive treatment of tuberculosis.

Protectin DX restores Treg/Th17 cell balance in rheumatoid arthritis by inhibiting NLRP3 inflammasome via miR-20a

Regulatory T-cell (Treg)/T-helper 17 (Th17) cell balance plays an important role in the progression of rheumatoid arthritis (RA). Our study explored the protective effect of protectin DX (PDX), which restored Treg/Th17 cell balance in RA, and the role of the nucleotide-binding domain (NOD)-like receptor protein 3 (NLRP3) inflammasome pathway in this process. Using mass spectrometry, we discovered that level of PDX decreased in active-RA patients and increased in inactive-RA patients compared with HCs, and serum PDX was a potential biomarker in RA activity detection (area under the curve [AUC] = 0.86). In addition, a collagen-induced arthritis (CIA) mice model was constructed and PDX obviously delayed RA progression in the CIA model, upregulating Tregs and anti-inflammatory cytokines while downregulating Th17 cells and pro-inflammatory cytokines. Moreover, NLRP3 knockout and rescue experiments demonstrated that NLRP3 participated in PDX-mediated Treg/Th17 cell balance restoration, joint injury amelioration and inflammatory-response attenuation using Nlrp3-/- mice. Furthermore, microarray and verified experiments confirmed that PDX reduced NLRP3 expression via miRNA-20a (miR-20a). In summary, we confirmed for the first time that PDX could effectively ameliorate CIA progression by restoring Treg/Th17 cell balance, which was mediated by inhibition of the NLRP3 inflammasome pathway via miR-20a.

The Manipulation of the Lipid Mediator Metabolism as Adjunct Host-Directed Therapy in Tuberculosis

Host-directed therapies (HDTs) enhance the host response to tuberculosis (TB) infection to reduce disease severity. For instance, the manipulation of lipid mediator production diminishes the hyperactive immune response which is a known pathological feature of TB that generates lung tissue damage. Non-steroidal anti-inflammatory drugs (NSAIDs) and omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFA) are examples of such HDTs. In this mini-review, we recapitulate the literature available on the effects of NSAIDs and n-3 LCPUFA in TB as well as the immunological pathways underpinning these effects. Many NSAIDs have a great deal of data describing their effects and safety and in many jurisdictions are inexpensive, and sold over the counter in neighborhood convenience stores and supermarkets. The potential benefits of NSAIDs in TB are well-documented in pre-clinical studies. The reduction of pro-inflammatory lipid mediator production by inhibiting cyclooxygenase (COX) pathways with NSAIDs has been found to improve lung histopathology, bacterial control, and survival. Additionally, n-3 LCPUFA and its novel bioactive metabolites produced by COX and lipoxygenase (LOX) have been identified as safe and effective pro-resolving and antibacterial pharmaconutrients. Nevertheless, heterogeneous results have been reported in pre-clinical TB studies. Recently, the importance of the correct timing of NSAIDs and n-3 LCPUFA administration in TB has also been highlighted. This mini-review will provide a better understanding of the potential contribution of these therapies toward reducing inflammatory lung damage and improving bactericidal activity, especially during later stages of TB infection. It further highlights that clinical trials are required to confirm benefit and safety in TB patients.

Specialized proresolving mediators in infection and lung injury

Specialized proresolving mediators (SPMs) are endogenous lipid metabolites of long-chain polyunsaturated fatty acids that are involved in promoting the resolution of inflammation. Many disease conditions characterized by excessive inflammation have impaired or altered SPM biosynthesis, which may lead to chronic, unresolved inflammation. Exogenous administration of SPMs in infectious conditions has been shown to be effective at improving infection clearance and survival in preclinical models. SPMs have also shown tremendous promise in the context of inflammatory lung conditions, such as acute respiratory distress syndrome and chronic obstructive pulmonary disease, mostly in preclinical settings. To date, SPMs have not been studied in the context of the novel Coronavirus, severe acute respiratory syndrome Coronavirus-2 (SARS-CoV-2), however their preclinical efficacy in combatting infections and improving acute respiratory distress suggest they may be a valuable resource in the fight against Coronavirus disease-19 (COVID-19). Overall, while the research on SPMs is still evolving, they may offer a novel therapeutic option for inflammatory conditions.

Elevated Levels of Anti-Inflammatory Eicosanoids and Monocyte Heterogeneity in Mycobacterium tuberculosis Infection and Disease

Eicosanoids modulate both innate and adaptive immune responses in Mycobacterium tuberculosis (Mtb) infection and have been suggested as possible Host Directed Therapy (HDT) targets, but more knowledge of eicosanoid dynamics in Mtb infection is required. We investigated the levels and ratios of eicosanoid mediators and their cellular sources, monocyte subsets and CD4 T cells in Tuberculosis (TB) patients with various clinical states of Mtb infection. Patients consenting to prospective enrolment in a TB quality registry and biorepository, 16 with pulmonary TB (before and at-end-of treatment), 14 with extrapulmonary TB and 17 latently infected (LTBI) were included. Plasma levels of Prostaglandin E2 (PGE2), Lipoxin A4 (LXA4), and Leukotriene B4 (LTB4) were measured by enzyme-linked immunosorbent assay. Monocyte subsets and CD4 T cells and their expression of Cyclooxygenase-2 (COX-2), Prostaglandin receptor EP2 (EP2), and 5-Lipoxygenase (5-LOX) were analyzed by flow cytometry with and without Purified Protein Derivate (PPD)-stimulation. Pulmonary TB patients had elevated levels of the anti-inflammatory mediator LXA4 at diagnosis compared to LTBI (p < 0.01), while levels of PGE2 and LTB4 showed no difference between clinical states of Mtb infection. LTB4 was the only mediator to be reduced upon treatment (p < 0.05), along with the ratio LTB4/LXA4 (p < 0.01). Pulmonary TB patients had higher levels of total monocytes at diagnosis compared to end-of-treatment and LTBI (both p < 0.05), and a relative increase in the classical monocyte subset. All monocyte subsets had low basal expression of COX-2 and 5-LOX, which were markedly increased upon PPD stimulation. By contrast, the expression of EP2 was reduced upon stimulation. CD4 T cells expressed low basal COX-2 activity that increased modestly upon stimulation, whereas their basal expression of 5-LOX was considerable. In conclusion, the level of eicosanoids in plasma seem to vary between clinical states of Mtb infection. Mediators in the eicosanoid system are present in monocytes and CD4 T cells. The expression of eicosanoids in monocytes are responsive to mycobacterial stimulation independent of Mtb disease state, but subsets are heterogeneous with regard to eicosanoid-mediator expression. Further exploration of eicosanoid mediators as targets for HDT in TB are warranted.

Specialized pro-resolving mediator network: an update on production and actions

Today, persistent and uncontrolled inflammation is appreciated to play a pivotal role in many diseases, such as cardiovascular diseases, neurodegenerative diseases, metabolic syndrome and many other diseases of public health concern (e.g. Coronavirus Disease 2019 (COVID-19) and periodontal disease). The ideal response to initial challenge in humans is a self-limited inflammatory response leading to complete resolution. The resolution phase is now widely recognized as a biosynthetically active process, governed by a superfamily of endogenous chemical mediators that stimulate resolution of inflammatory responses, namely specialized proresolving mediators (SPMs). Because resolution is the natural ideal response, the SPMs have gained attention. SPMs are mediators that include ω-6 arachidonic acid-derived lipoxins, ω-3 eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)-derived resolvins, protectins and maresins, cysteinyl-SPMs, as well as n-3 docosapentaenoic acid (DPA)-derived SPMs. These novel immunoresolvents, their biosynthetic pathways and receptors have proven to promote resolution of inflammation, clearance of microbes, reduce pain and promote tissue regeneration via specific cellular and molecular mechanisms. As of 17 August, 2020, PubMed.gov reported >1170 publications for resolvins, confirming their potent protective actions from many laboratories worldwide. Since this field is rapidly expanding, we provide a short update of advances within 2-3 years from human and preclinical animal studies, together with the structural-functional elucidation of SPMs and identification of novel SPM receptors. These new discoveries indicate that SPMs, their pathways and receptors could provide a basis for new approaches for treating inflammation-associated diseases and for stimulating tissue regeneration via resolution pharmacology and precision nutrition.

Maresin 1 resolves aged-associated macrophage inflammation to improve bone regeneration

Inflammaging is associated with poor tissue regeneration observed in advanced age. Specifically, protracted inflammation after acute injury has been associated with decreased bone fracture healing and increased rates of nonunion in elderly patients. Here, we investigated the efficacy of using Maresin 1 (MaR1), an omega-3 fatty acid-derived pro-resolving agent, to resolve inflammation after tibial fracture injury and subsequently improving aged bone healing. Aged (24-month-old mice) underwent tibial fracture surgery and were either treated with vehicle or MaR1 3 days after injury. Fracture calluses were harvested 7 days, 14 days, 21 days, and 28 days after injury to investigate inflammatory response, cartilage development, bone deposition, and mechanical integrity, respectively. Healing bones from MaR1-treated mice displayed decreased cartilage formation and increased bone deposition which resulted in increased structural stiffness and increased force to fracture in the later stages of repair. In the early stages, MaR1 treatment decreased the number of pro-inflammatory macrophages within the fracture callus and decreased the level of inflammatory biomarkers in circulation. In tissue culture models, MaR1 treatment of bone marrow-derived macrophages from aged mice protected cells form a pro-inflammatory phenotype and induced an anti-inflammatory fate. Furthermore, the secretome of MaR1-treated bone marrow-derived macrophages was identified as osteoinductive, enhancing osteoblast differentiation of bone marrow stromal cells. Our findings here identify resolution of inflammation, and MaR1 itself, to be a point of intervention to improve aged bone healing.

Alzheimer's Disease and Specialized Pro-Resolving Lipid Mediators: Do MaR1, RvD1, and NPD1 Show Promise for Prevention and Treatment?

Alzheimer's disease (AD) is a common neurodegenerative disease and a major contributor to progressive cognitive impairment in an aging society. As the pathophysiology of AD involves chronic neuroinflammation, the resolution of inflammation and the group of lipid mediators that actively regulate it-i.e., specialized pro-resolving lipid mediators (SPMs)-attracted attention in recent years as therapeutic targets. This review focuses on the following three specific SPMs and summarizes their relationships to AD, as they were shown to effectively address and reduce the risk of AD-related neuroinflammation: maresin 1 (MaR1), resolvin D1 (RvD1), and neuroprotectin D1 (NPD1). These three SPMs are metabolites of docosahexaenoic acid (DHA), which is contained in fish oils and is thus easily available to the public. They are expected to become incorporated into promising avenues for preventing and treating AD in the future.

Pneumonia caused by Mycobacterium tuberculosis

Tuberculosis (TB) is one of the top ten leading causes of death worldwide. The causative agent of TB is Mycobacterium tuberculosis. Acute tuberculous pneumonia (TP) is an acute form of pulmonary TB. However, acute TP and non-tuberculous community-acquired pneumonia can be easily confused, resulting in deterioration of TP due to delayed treatment. Therefore, rapid and accurate diagnosis of acute TP is crucial in order to stop the transmission of TB. Moreover, development of new diagnostic tools (technologies and approaches), and flexible application of different therapy schemes will help to reduce the incidence of TP and promote the goal of ending the TB epidemic.

Maresin 1 alleviates dextran sulfate sodium-induced ulcerative colitis by regulating NRF2 and TLR4/NF-kB signaling pathway

OBJECTIVE

Ulcerative colitis (UC) is one of the most common gastrointestinal diseases, characterized as a chronic, relapsing inflammation that causes damage to the colonic mucosa. Maresin 1 (MaR1), a specialized proresolving mediator, has powerful anti-inflammatory activity that prevents the occurrence of various inflammatory diseases. The aim of this study was to explore the role and potential mechanism of MaR1 in DSS-induced ulcerative colitis.

METHODS

In the present study, we established dextran sulfate sodium (DSS)-induced ulcerative colitis rat model in vivo. Rats with colitis received tail vein injection of MaR1, with or without intraperitoneal injection of ML385. The changes of body weight, colon length, disease activity index (DAI), colonic histopathology, inflammatory cytokines, the activity of myeloperoxidase (MPO) and reactive oxygen species (ROS), and infiltration of macrophages expressing F4/80 were analyzed for the evaluation of colitis severity. In addition, protein expressions were detected using western blot.

RESULTS

MaR1 significantly reduced inflammatory cytokines production, and restored body weight, DAI and colonic histopathology. Besides, MaR1 improved the expression of tight junction (TJ) proteins and reduced the infiltration of neutrophil and macrophages, as well as a decreased activity of MPO and ROS. Meanwhile, MaR1 activated Nrf2 signaling and decreased toll-like receptor 4(TLR4)/nuclear factor-κB(NF-κB) activation. Furthermore, ML385, an inhibitor of Nrf2, significantly reversed the protective effect of MaR1.

CONCLUSION

MaR1 play a protective role in DSS-induced colitis by activating Nrf2 signaling and inactivating Nrf2-mediated TLR4/NF-κB signaling pathway, which mediate proinflammatory mediators and intestinal TJ proteins in rats, providing novel insights into the therapeutic strategy of colitis.