Proresolving lipid mediators resolvin D1, resolvin D2, and maresin 1 are critical in modulating T cell responses

"Only a Life Lived for Others Is Worth Living": Redox Signaling by Oxygenated Phospholipids in Cell Fate Decisions

SIGNIFICANCE

Oxygenated polyunsaturated lipids are known to play multi-functional roles as essential signals coordinating metabolism and physiology. Among them are well-studied eicosanoids and docosanoids that are generated via phospholipase A2 hydrolysis of membrane phospholipids and subsequent oxygenation of free polyunsaturated fatty acids (PUFA) by cyclooxygenases and lipoxygenases. Recent Advances: There is an emerging understanding that oxygenated PUFA-phospholipids also represent a rich signaling language with yet-to-be-deciphered details of the execution machinery-oxygenating enzymes, regulators, and receptors. Both free and esterified oxygenated PUFA signals are generated in cells, and their cross-talk and inter-conversion through the de-acylation/re-acylation reactions is not sufficiently explored.

CRITICAL ISSUES

Here, we review recent data related to oxygenated phospholipids as important damage signals that trigger programmed cell death pathways to eliminate irreparably injured cells and preserve the health of multicellular environments. We discuss the mechanisms underlying the trans-membrane redistribution and generation of oxygenated cardiolipins in mitochondria by cytochrome c as pro-apoptotic signals. We also consider the role of oxygenated phosphatidylethanolamines as proximate pro-ferroptotic signals.

FUTURE DIRECTIONS

We highlight the importance of sequential processes of phospholipid oxygenation and signaling in disease contexts as opportunities to use their regulatory mechanisms for the identification of new therapeutic targets.

Role of the Specialized Proresolving Mediator Resolvin D1 in Systemic Lupus Erythematosus: Preliminary Results

Objective

Systemic lupus erythematosus (SLE) is an autoimmune systemic disease and its pathogenesis has not yet been completely clarified. Patients with SLE show a deranged lipid metabolism, which can contribute to the immunopathogenesis of the disease and to the accelerated atherosclerosis. Resolvin D1 (RvD1), a product of the metabolism of the omega-3 polyunsaturated fatty acid docosahexaenoic acid (DHA), acts as a specialized proresolving mediator which can contribute in restoring the homeostasis in inflamed tissues. The aim of the present pilot study is to evaluate plasma levels of RvD1 in patients with SLE and healthy subjects, investigating its potential role as a biomarker of SLE and assessing its relationship with disease activity and laboratory parameters.

Methods

Thirty patients with SLE and thirty age- and sex-matched healthy subjects (HSs) have been consecutively recruited at Campus Bio-Medico University Hospital. RvD1 plasma levels were measured by ELISA according to the manufacturer's protocol (Cayman Chemical Co.). RvD1 levels were compared using Mann-Whitney test. Discriminatory ability for SLE has been evaluated by the area under the ROC curve.

Results

Lower levels of RvD1, 45.6 (35.5-57.4) pg/ml, in patients with SLE have been found compared to HSs, 65.1 (39.43-87.95) pg/ml (p = 0.0043). The area under the ROC curve (AUC) for RvD1 was 0.71 (95% CI: 0.578-0.82) and the threshold value of RvD1 for the classification of SLE was <58.4 pg/ml, sensitivity 80% (95% CI: 61.4-92.3), and specificity 63.3% (95% CI: 43.9-80.1), likelihood ratio 2.2 (95% CI: 1.3-3.6).

Conclusions

The present preliminary study allows hypothesizing a dysregulation of RvD1 in patients with SLE, confirming the emerging role of bioactive lipids in this disease.

Omega-3 polyunsaturated fatty acids attenuate inflammatory activation and alter differentiation in human adipocytes

BACKGROUND

Omega-3 polyunsaturated fatty acids, specifically the fish-oil-derived eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have been proposed as inflammation-resolving agents via their effects on adipose tissue.

OBJECTIVE

We proposed to determine the effects of EPA and DHA on human adipocyte differentiation and inflammatory activation in vitro.

METHODS

Primary human subcutaneous adipocytes from lean and obese subjects were treated with 100 μM EPA and/or DHA throughout differentiation (differentiation studies) or for 72 h postdifferentiation (inflammatory studies). THP-1 monocytes were added to adipocyte wells for co-culture experiments. Subcutaneous and visceral adipose explants from obese subjects were treated for 72 h with EPA and DHA. Oil Red O staining was performed on live cells. Cells were collected for mRNA analysis by quantitative polymerase chain reaction, and media were collected for protein quantification by enzyme-linked immunosorbent assay.

RESULTS

Incubation with EPA and/or DHA attenuated inflammatory response to lipopolysaccharide (LPS) and monocyte co-culture with reduction in post-LPS mRNA expression and protein levels of IL6, CCL2 and CX3CL1. Expression of inflammatory genes was also reduced in the endogenous inflammatory response in obese adipose. Both DHA and EPA reduced lipid droplet formation and lipogenic gene expression without alteration in expression of adipogenic genes or adiponectin secretion.

CONCLUSIONS

EPA and DHA attenuate inflammatory activation of in vitro human adipocytes and reduce lipogenesis.

Group IID, IIE, IIF and III secreted phospholipase A2s

Among the 11 members of the secreted phospholipase A₂ (sPLA₂) family, group IID, IIE, IIF and III sPLA₂s (sPLA₂-IID, -IIE, -IIF and -III, respectively) are “new” isoforms in the history of sPLA₂ research. Relative to the better characterized sPLA₂s (sPLA₂-IB, -IIA, -V and -X), the enzymatic properties, distributions, and functions of these “new” sPLA₂s have remained obscure until recently. Our current studies using knockout and transgenic mice for a nearly full set of sPLA₂s, in combination with comprehensive lipidomics, have revealed unique and distinct roles of these “new” sPLA₂s in specific biological events. Thus, sPLA₂-IID is involved in immune suppression, sPLA₂-IIE in metabolic regulation and hair follicle homeostasis, sPLA₂-IIF in epidermal hyperplasia, and sPLA₂-III in male reproduction, anaphylaxis, colonic diseases, and possibly atherosclerosis. In this article, we overview current understanding of the properties and functions of these sPLA₂s and their underlying lipid pathways in vivo.

Can inflammation be resolved in Alzheimer's disease?

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive memory loss and dementia. Accumulating evidence suggests that inflammation is involved in the pathogenesis of AD. Epidemiological studies suggest that use of anti-inflammatory drugs is associated with a lower incidence of AD. However, clinical trials with anti-inflammatory drugs have not been successful. Recent studies have shown that inflammation is resolved by a process that is mediated by a group of lipid mediators, so called specialized pro-resolving lipid mediators (SPMs). Unlike anti-inflammatory strategies, which usually involve inhibition of the synthesis of inflammatory mediators, stimulating the resolution of inflammation is aimed at ending inflammation in a similar fashion as under normal physiological conditions. We have previously shown that pathways of resolution are impaired in AD. Moreover, we found that SPMs can improve neuronal survival and increase microglial phagocytosis of amyloid beta (Aβ) in in vitro studies, indicating that stimulating resolution of inflammation may be a potential therapeutic target in AD. In this review, we summarize recent findings regarding resolution of inflammation in AD. We also discuss possible strategies to stimulate the resolution of inflammation in AD, specifically focusing on signaling pathways, including SPMs, their receptors and enzymes involved in their formation.

Bioactive Lipid Species and Metabolic Pathways in Progression and Resolution of Nonalcoholic Steatohepatitis

The prevalence of nonalcoholic steatohepatitis (NASH) is increasing worldwide, yet there are no effective treatments. A decade has passed since the initial lipidomics analyses of liver tissues from patients with nonalcoholic fatty liver disease. We have learned that liver cells from patients with NASH have an abnormal lipid composition and that the accumulation of lipids leads to organelle dysfunction, cell injury and death, and chronic inflammation, called lipotoxicity. We review the lipid species and metabolic pathways that contribute to the pathogenesis of NASH and potential therapeutic targets, including enzymes involved in fatty acid and triglyceride synthesis, bioactive sphingolipids and polyunsaturated-derived eicosanoids, and specialized pro-resolving lipid mediators. We discuss the concept that NASH is a disease that can resolve and the roles of lipid molecules in the resolution of inflammation and regression of fibrosis.

Maresin 1 improves the Treg/Th17 imbalance in rheumatoid arthritis through miR-21

Objective

Treg/Th17 imbalance plays an important role in rheumatoid arthritis (RA). Maresin 1 (MaR1) prompts inflammation resolution and regulates immune responses. We explored the effect of MaR1 on RA progression and investigated the correlation between MaR1 and Treg/Th17 balance.

Methods

Both patients with RA and healthy controls were recruited into the study. Collagen-induced arthritis (CIA) model was constructed to detect the clinical score, histopathological changes and Treg/Th17 ratio. Purified naive CD4+ T-cells were used to study the effect of MaR1 on its differentiation process and microRNA microarray studies were performed to investigate MaR1 downstream microRNAs in this process. MicroRNA transfection experiments were conducted by lentivirus to verify the mechanism of MaR1 on Treg/Th17 balance.

Results

Compared with controls, the MaR1 concentration was higher in the patients with inactive RA and lower in the patients with active RA. Expression of the Treg transcription factor FoxP3 was the highest in inactive RA and the lowest in active RA, while the Th17 transcription factor RORc showed a reverse trend. An inverse correlation was observed between the FoxP3/RORc ratio and Disease Activity Score 28. Intervention of MaR1 in the CIA model reduced joint inflammation and damage, and improved the imbalanced Treg/Th17 ratio. MaR1 increased Treg cells proportion while reduced Th17 cells proportion under specific differentiation conditions. Furthermore, miR-21 was verified as MaR1 downstream microRNA, which was upregulated by MaR1, modulating the Treg/Th17 balance and thus ameliorating the RA progression.

Conclusions

MaR1 is a therapeutic target for RA, likely operating through effects on the imbalanced Treg/Th17 ratio found in the disease.

Key roles for lipid mediators in the adaptive immune response

Chronic inflammation is an underlying feature of many diseases, including chronic obstructive pulmonary disease, rheumatoid arthritis, asthma, and multiple sclerosis. There is an increasing appreciation of the dysregulation of adaptive immunity in chronic inflammatory and allergic diseases. The discovery of specialized pro-resolving lipid mediators (SPMs) that actively promote the resolution of inflammation has opened new avenues for the treatment of chronic inflammatory diseases. Much work has been done focusing on the impact of SPMs on innate immune cells. However, much less is known about the influence of SPMs on the development of antigen-specific adaptive immune responses. This Review highlights the important breakthroughs concerning the effects of SPMs on the key cell types involved in the development of adaptive immunity, namely dendritic cells, T cells, and B cells.

Targeting formyl peptide receptors to facilitate the resolution of inflammation

The formyl peptide receptors (FPRs) are G protein coupled receptors that recognize a broad range of structurally distinct pathogen and danger-associated molecular patterns and mediate host defense to infection and tissue injury. It became evident that the cellular distribution and biological functions of FPRs extend beyond myeloid cells and governing their activation and trafficking. In recent years, significant progress has been made to position FPRs at check points that control the resolution of inflammation, tissue repair and return to homeostasis. Accumulating data indicate a role for FPRs in an ever-increasing range of human diseases, including atherosclerosis, chronic obstructive pulmonary disease, asthma, autoimmune diseases and cancer, in which dysregulated or defective resolution are increasingly recognized as critical component of the pathogenesis. This review summarizes recent advances on how FPRs recognize distinct ligands and integrate opposing cues to govern various responses and will discuss how this knowledge could be harnessed for developing novel therapeutic strategies to counter inflammation that underlies many human diseases.

Bioactive lipids ALIAmides differentially modulate inflammatory responses of distinct subsets of primary human T lymphocytes

Autacoid local injury antagonist amides (ALIAmides) are a family of endogenous bioactive acyl ethanolamides that include the renowned palmitoyl ethanolamide (PEA), oleoyl ethanolamide (OEA), and stearoyl ethanolamide (SEA), and that are involved in several biologic processes such as nociception, lipid metabolism, and inflammation. The role of ALIAmides in the control of inflammatory processes has recently gained much attention and prompted the use of these molecules or their analogs, and the pharmacologic manipulation of their endogenous levels, as plausible therapeutic strategies in the treatment of several chronic inflammatory conditions. Since chronic inflammation is mainly driven by cells of adaptive immunity, particularly T lymphocytes, we aimed at investigating whether such bioactive lipids could directly modulate T-cell responses. We found that OEA, PEA, and eicosatrienoyl ethanolamide (ETEA) could directly inhibit both T-cell responses by reducing their production of TNF-α and IFN-γ from CD8 T cells and TNF-α, IFN-γ and IL-17 from CD4 T cells. Furthermore, neither SEA nor docosatrienoyl ethanolamide (DTEA) could affect cytokine production from both T cell subsets. Interestingly, unlike OEA and ETEA, PEA was also able to enhance de novo generation of forkhead box P3 (FoxP3)-expressing regulatory T cells from CD4-naive T cells. Our findings show for the first time that specific ALIAmides can directly affect different T-cell subsets, and provide proof of their anti-inflammatory role in chronic inflammation, ultimately suggesting that these bioactive lipids could offer novel tools for the management of T-cell dependent chronic inflammatory diseases.-Chiurchiù, V., Leuti, A., Smoum, R., Mechoulam, R., Maccarrone, M. Bioactive lipids ALIAmides differentially modulate inflammatory responses of distinct subsets of primary human T lymphocytes.

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

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

Resolvin D2 Restrains Th1 Immunity and Prevents Alveolar Bone Loss in Murine Periodontitis

Periodontitis is an infectious inflammatory disease of the supporting structures of the teeth. Resolvins are part of a large family of specialized pro-resolving lipid mediators that enhance active resolution of inflammation and return of inflammatory lesions to homeostasis. In this paper, we demonstrate that resolvin D2 (RvD2), a product of docosahexaenoic acid (DHA) metabolism, prevents alveolar bone loss in Porphyromonas gingivalis-induced experimental periodontitis. Investigations of the immune mechanism of RvD2 actions reveal that 6 weeks after infection, the gingiva of RvD2-treated mice exhibit decreased CD4⁺ T-cells as well as lower RANKL expression levels and higher osteoprotegerin expression levels. Systemically, RvD2 prevents chronic secretion of IFN-γ and rapidly restores IFN-α levels, without dampening the P. gingivalis-specific immune response. In the gingiva, immediately after P. gingivalis inoculation, RvD2 regulates the mRNA expression of IFN-γ, IL-1β, TNF-α, and IL-10, hence contributing to maintaining local homeostasis. Moreover, RvD2 treatment reduces local neutrophil numbers, whereas pro-resolving macrophage counts were increased. These findings suggest that RvD2 resolves innate inflammatory responses, inhibiting systemic and gingival Th1-type adaptive responses that are known to mediate alveolar bone loss in this model.

Age and Age-Related Diseases: Role of Inflammation Triggers and Cytokines

Cytokine dysregulation is believed to play a key role in the remodeling of the immune system at older age, with evidence pointing to an inability to fine-control systemic inflammation, which seems to be a marker of unsuccessful aging. This reshaping of cytokine expression pattern, with a progressive tendency toward a pro-inflammatory phenotype has been called "inflamm-aging." Despite research there is no clear understanding about the causes of "inflamm-aging" that underpin most major age-related diseases, including atherosclerosis, diabetes, Alzheimer's disease, rheumatoid arthritis, cancer, and aging itself. While inflammation is part of the normal repair response for healing, and essential in keeping us safe from bacterial and viral infections and noxious environmental agents, not all inflammation is good. When inflammation becomes prolonged and persists, it can become damaging and destructive. Several common molecular pathways have been identified that are associated with both aging and low-grade inflammation. The age-related change in redox balance, the increase in age-related senescent cells, the senescence-associated secretory phenotype (SASP) and the decline in effective autophagy that can trigger the inflammasome, suggest that it may be possible to delay age-related diseases and aging itself by suppressing pro-inflammatory molecular mechanisms or improving the timely resolution of inflammation. Conversely there may be learning from molecular or genetic pathways from long-lived cohorts who exemplify good quality aging. Here, we will discuss some of the current ideas and highlight molecular pathways that appear to contribute to the immune imbalance and the cytokine dysregulation, which is associated with "inflammageing" or parainflammation. Evidence of these findings will be drawn from research in cardiovascular disease, cancer, neurological inflammation and rheumatoid arthritis.

Identification of proresolving and inflammatory lipid mediators in human psoriasis

BACKGROUND

Psoriasis (PSO) is an immune-mediated inflammatory disease associated with metabolic and cardiovascular comorbidities. It is now known that resolution of inflammation is an active process locally controlled by specialized proresolving mediators (SPMs), named resolvins (Rvs), protectins, and maresins.

OBJECTIVE

It is unknown whether these potent lipid mediators (LMs) are involved in PSO pathophysiology and if the skin and blood have disease-specific SPMs phenotype profiles.

METHODS

We used liquid chromatography-tandem mass spectrometry-based LM metabololipidomics to obtain skin and peripheral blood LM profiles from PSO compared to healthy subjects. Some LMs were tested in cell culture experiments with corresponding gene expression and protein concentration analyses.

RESULTS

The levels of several LM were significantly elevated in lesional PSO skin compared to nonlesional and skin from healthy subjects. Particularly, RvD5, protectins Dx, and aspirin-triggered forms of lipoxin were present only in lesional PSO skin, whereas protectin D1 was present in nonlesional PSO skin. To determine specific roles of SPMs on skin-related inflammatory cytokines, RvD1 and RvD5 were incubated with human keratinocytes. RvD1 and RvD5 reduced the expression levels of interleukin 24 and S100A12, whereas only RvD1 significantly abrogated interleukin-24 production by keratinocytes.

CONCLUSIONS

These findings suggest that an imbalance between locally produced proresolution and proinflammatory LMs identified in PSO skin and blood compartments might play a role in PSO pathophysiology. Moreover, some of the PSO-related cytokines can be modified by specific SPMs and involved mechanisms support investigation of targeting novel proresolving lipid mediators as a therapy for PSO.

Maresin-1 suppresses imiquimod-induced skin inflammation by regulating IL-23 receptor expression

The anti-inflammatory effect of omega 3 polyunsaturated fatty acids has been confirmed in various inflammatory disease models. Maresin-1 (MaR1) is a lipid mediator derived from the omega-3 fatty acid docosahexaenoic acid (DHA) that has displayed strong anti-inflammatory effects in various inflammatory disease models. However, the effect of topical MaR1 on cutaneous inflammation remains unclear. Therefore, we initially examined the anti-inflammatory effects of topical Maresin-1 using an imiquimod (IMQ)-induced psoriasis-like mouse model of inflammation. Topical MaR1 reduced the ear swelling response as seen in histological findings. RT-PCR and flow cytometry analyses revealed MaR1 had no inhibitory effect on IL-23, but MaR1 suppressed IL-17A production by γδTCR^mid+ and CD4⁺ cells in the skin. These inhibitory effects were also observed in a subcutaneous IL-23-injected psoriasis model. MaR1 downmodulated IL-23 receptor (IL-23R) expression by suppressing retinoic acid-related orphan receptor γt (RORγt) expression and internalization in a clathrin-dependent manner in γδTCR^mid+ and CD4⁺ cells. These results lead to assumptions that topical MaR1 may be a new therapeutic agent for psoriasis and other IL-17-mediated cutaneous inflammatory diseases.

Metabololipidomic profiling of functional immunoresolvent clusters and eicosanoids in mammalian tissues

Metabolomics enables a systems approach to interrogate the bioactive mediators, their pathways and further metabolites involved in the physiology and pathophysiology of human and animal tissues. New metabololipidomic approaches with mass spectrometry presented in this brief review can now be utilized for the identification and profiling of lipid mediator networks that control inflammation-resolution in human blood and healthy and diseased solid tissues. Coagulation of blood is a protective response that prevents excessive bleeding on injury of blood vessels. Here, we review novel approaches to understand the relationship(s) between coagulation and resolution of inflammation and infection. To determine whether coagulation is involved in host-protective actions by lipid mediators, we used a metabololipidomic-based profiling approach with human whole blood (WB) during coagulation. We identified recently temporal clusters of endogenously produced pro-thrombotic and proinflammatory lipid mediators (eicosanoids), as well as specialized proresolving mediators (SPMs) in this vital process. In addition to the classic eicosanoids (prostaglandins, thromboxanes and leukotrienes), a specific SPM cluster was identified that consists of resolvin E1 (RvE1), RvD1, RvD5, lipoxin B₄, and maresin 1, each of which present at bioactive concentrations (0.1-1 nM). The removal of adenosine from coagulating blood samples significantly enhances SPM amounts and unleashes the biosynthesis of RvD3, RvD4, and RvD6 evident following rapid snap freezing with centrifugation before extraction and LC-MS-MS. The classic cyclooxygenase inhibitors, celecoxib and indomethacin, that block thromboxanes and prostanoids do not block production of the clot-driven SPM cluster. Unbiased mass cytometry analysis demonstrated that the SPM cluster produced in human blood targets leukocytes at the single-cell level, directly activating extracellular signaling in human neutrophils and monocytes. Human whole blood treated with the components of this SPM cluster enhanced both phagocytosis and killing of Escherichia coli by leukocytes. Thus, we identified a pro-resolving lipid mediator circuit and specific SPM cluster that promotes host defense. This new lipid mediator (LM)-SPM metabololipidomic approach now provides accessible metabolomic profiles in healthy and diseased human tissues, including cancer, for precision and personalized medicine.

Perioperative Immunonutrition Modulates Inflammatory Response after Radical Cystectomy: Results of a Pilot Randomized Controlled Clinical Trial

PURPOSE

Poor preoperative nutritional status is associated with a higher complication rate after radical cystectomy in patients with bladder cancer. Given the short interval between diagnosis and radical cystectomy, we compared the effect of short-term specialized immunonutrition to that of a standard oral nutritional supplement on the acute inflammatory response and arginine status in patients treated with radical cystectomy.

MATERIALS AND METHODS

In this prospective, randomized study in 29 men 14 received specialized immunonutrition and 15 received oral nutritional supplement. Each group drank 3 cartons per day for 5 days before and 5 days after radical cystectomy. The Th1-Th2 balance, plasma interleukin-6 and plasma amino acids were measured at baseline, intraoperatively and on postoperative days 2, 14 and 30. Body composition was measured by dual energy x-ray absorptiometry at baseline and on postoperative days 14 and 30. Differences in outcomes were assessed using the generalized linear mixed model.

RESULTS

In the specialized immunonutrition group there was a 54.3% average increase in the Th1-Th2 balance according to the tumor necrosis factor-α-to-interleukin-13 ratio from baseline to intraoperative day, representing a shift toward a Th1 response. In the oral nutritional supplement group the Th1-Th2 balance decreased 4.8%. The change in the Th1-Th2 balance between the specialized immunonutrition and oral nutritional supplement groups significantly differed (p <0.027). Plasma interleukin-6 was 42.8% lower in the specialized immunonutrition group compared to the oral nutritional supplement group on postoperative day 2 (p = 0.020). In the specialized immunonutrition group plasma arginine was maintained from baseline to postoperative day 2 and yet the oral nutritional supplement group showed a 26.3% reduction from baseline to postoperative day 2 (p = 0.0003). The change in appendicular muscle loss between the groups was not statistically significant.

CONCLUSIONS

Th1-to-Th2 ratios, peak interleukin-6 levels and plasma arginine suggest that consuming specialized immunonutrition counteracts the disrupted T-helper balance, lowers the inflammatory response and prevents arginine depletion due to radical cystectomy.

Resolvin D1 blocks H2O2-mediated inhibitory crosstalk between SHP2 and PP2A and suppresses endothelial-monocyte interactions

In recent years, various studies have demonstrated a role for endogenously derived specialized proresolving mediators such as resolvins in the resolution of inflammation. In exploring the signaling mechanisms, in the present study we show that Resolvin D1 (RvD1) reduces LPS-induced endothelial cell (EC)-monocyte interactions via blocking H₂O₂-mediated PP2A inactivation, NFκB activation and ICAM1 and VCAM1 expression. In addition, we found that H₂O₂-mediated SHP2 inhibition leads to tyrosine phosphorylation and inactivation of PP2A by LPS, which in turn, accounts for increased NFκB activation and ICAM1 and VCAM1 expression facilitating EC-monocyte interactions and all these LPS-mediated responses were reduced by RvD1. Furthermore, the suppression of NFκB activation, ICAM1 and VCAM1 expression and EC and monocyte interactions by RvD1 involved its receptors ALX/FPR2 and GPR32 as inhibition or neutralization of these receptors negated its effects. Besides, pertussis toxin completely prevented the effects of RvD1 on inhibition of LPS-induced H₂O₂ production, SHP2 and PP2A inactivation, NFκB activation, ICAM1 and VCAM1 expression and EC and monocyte interactions. Together, these observations suggest that RvD1 via activation of Gi-coupled ALX/FPR2 and GPR32 receptors blocks LPS-induced H₂O₂-mediated SHP2 and PP2A inactivation, NFκB activation, ICAM1 and VCAM1 expression and EC-monocyte interactions, which could be one of the several possible mechanisms underlying the anti-inflammatory actions of this specialized proresolving mediator.

Bioactive Lipid Mediator Profiles in Human Psoriasis Skin and Blood

Psoriasis is a chronic immune-mediated disease that represents a unique model for investigating inflammation at local and systemic levels. Bioactive lipid mediators (LMs) are potent compounds reported to play a role in the development and resolution of inflammation. Currently, it is not known to what extent these LMs are involved in psoriasis pathophysiology and related metabolic dysfunction. Here, we use targeted and untargeted liquid chromatography-tandem mass spectrometry approaches to quantify LMs in skin and peripheral blood from psoriasis patients and compared them with those of healthy individuals. Lesional psoriasis skin was abundant in arachidonic acid metabolites, as 8-, 12- and 15-hydroxyeicosatetraenoic acid, compared with adjacent nonlesional and skin from healthy individuals. Additionally, a linoleic acid-derived LM, 13-hydroxyoctadecadienoic acid, was significantly increased compared with healthy skin (607.9 ng/g vs. 5.4 ng/g, P = 0.001). These psoriasis skin differences were accompanied by plasma decreases in antioxidant markers, including glutathione, and impaired lipolysis characterized by lower concentrations of primary and secondary bile acids. In conclusion, our study shows that psoriasis skin and blood have disease-specific phenotype profiles of bioactive LMs represented by omega-6 fatty acid-oxidized derivatives. These findings provide insights into psoriasis pathophysiology that could potentially contribute to new biomarkers and therapeutics.

Host Lipid Mediators in Leprosy: The Hypothesized Contributions to Pathogenesis

The spectrum of clinical forms observed in leprosy and its pathogenesis are dictated by the host's immune response against Mycobacterium leprae, the etiological agent of leprosy. Previous results, based on metabolomics studies, demonstrated a strong relationship between clinical manifestations of leprosy and alterations in the metabolism of ω3 and ω6 polyunsaturated fatty acids (PUFAs), and the diverse set of lipid mediators derived from PUFAs. PUFA-derived lipid mediators provide multiple functions during acute inflammation, and some lipid mediators are able to induce both pro- and anti-inflammatory responses as determined by the cell surface receptors being expressed, as well as the cell type expressing the receptors. However, little is known about how these compounds influence cellular immune activities during chronic granulomatous infectious diseases, such as leprosy. Current evidence suggests that specialized pro-resolving lipid mediators (SPMs) are involved in the down-modulation of the innate and adaptive immune response against M. leprae and that alteration in the homeostasis of pro-inflammatory lipid mediators versus SPMs is associated with dramatic shifts in the pathogenesis of leprosy. In this review, we discuss the possible consequences and present new hypotheses for the involvement of ω3 and ω6 PUFA metabolism in the pathogenesis of leprosy. A specific emphasis is placed on developing models of lipid mediator interactions with the innate and adaptive immune responses and the influence of these interactions on the outcome of leprosy.

Disease tolerance: concept and mechanisms

Two distinct defense strategies provide a host with survival to infectious diseases: resistance and tolerance. Resistance is dependent on the ability of the host to kill pathogens. Tolerance promotes host health while having a neutral to positive impact of pathogen fitness. Immune responses are almost inevitably defined in terms of pathogen resistance. Recent evidence has shown, however, that several effects attributed to activation of innate and adaptive immune mechanisms, cannot be readily explained with the paradigm of immunity as effectors of microbial destruction. This review focuses on integrating the concept of disease tolerance into recent studies of immune system function related to the regulation and resolution of tissue damage, T cell exhaustion, and tolerance to innocuous antigen.

Bioactive Lipids and Chronic Inflammation: Managing the Fire Within

Inflammation is an immune response that works as a contained fire that is pre-emptively sparked as a defensive process during infections or upon any kind of tissue insult, and that is spontaneously extinguished after elimination or termination of the damage. However, persistent and uncontrolled immune reactions act as a wildfire that promote chronic inflammation, unresolved tissue damage and, eventually, chronic diseases. A wide network of soluble mediators, among which endogenous bioactive lipids, governs all immune processes. They are secreted by basically all cells involved in inflammatory processes and constitute the crucial infrastructure that triggers, coordinates and confines inflammatory mechanisms. However, these molecules are also deeply involved in the detrimental transition from acute to chronic inflammation, be it for persistent or excessive action of pro-inflammatory lipids or for the impairment of the functions carried out by resolving ones. As a matter of fact, bioactive lipids have been linked, to date, to several chronic diseases, including rheumatoid arthritis, atherosclerosis, diabetes, cancer, inflammatory bowel disease, systemic lupus erythematosus, and multiple sclerosis. This review summarizes current knowledge on the involvement of the main classes of endogenous bioactive lipids—namely classical eicosanoids, pro-resolving lipid mediators, lysoglycerophospholipids/sphingolipids, and endocannabinoids—in the cellular and molecular mechanisms that lead to the pathogenesis of chronic disorders.

Resolvin D1 Halts Remote Neuroinflammation and Improves Functional Recovery after Focal Brain Damage Via ALX/FPR2 Receptor-Regulated MicroRNAs

Remote damage is a secondary phenomenon that usually occurs after a primary brain damage in regions that are distant, yet functionally connected, and that is critical for determining the outcomes of several CNS pathologies, including traumatic brain and spinal cord injuries. The understanding of remote damage-associated mechanisms has been mostly achieved in several models of focal brain injury such as the hemicerebellectomy (HCb) experimental paradigm, which helped to identify the involvement of many key players, such as inflammation, oxidative stress, apoptosis and autophagy. Currently, few interventions have been shown to successfully limit the progression of secondary damage events and there is still an unmet need for new therapeutic options. Given the emergence of the novel concept of resolution of inflammation, mediated by the newly identified ω3-derived specialized pro-resolving lipid mediators, such as resolvins, we reported a reduced ability of HCb-injured animals to produce resolvin D1 (RvD1) and an increased expression of its target receptor ALX/FPR2 in remote brain regions. The in vivo administration of RvD1 promoted functional recovery and neuroprotection by reducing the activation of Iba-1+ microglia and GFAP+ astrocytes as well as by impairing inflammatory-induced neuronal cell death in remote regions. These effects were counteracted by intracerebroventricular neutralization of ALX/FPR2, whose activation by RvD1 also down-regulated miR-146b- and miR-219a-1-dependent inflammatory markers. In conclusion, we propose that innovative therapies based on RvD1-ALX/FPR2 axis could be exploited to curtail remote damage and enable neuroprotective effects after acute focal brain damage.

Anti-Inflammatory Effects of Omega-3 Fatty Acids in the Brain: Physiological Mechanisms and Relevance to Pharmacology

Classically, polyunsaturated fatty acids (PUFA) were largely thought to be relatively inert structural components of brain, largely important for the formation of cellular membranes. Over the past 10 years, a host of bioactive lipid mediators that are enzymatically derived from arachidonic acid, the main n-6 PUFA, and docosahexaenoic acid, the main n-3 PUFA in the brain, known to regulate peripheral immune function, have been detected in the brain and shown to regulate microglia activation. Recent advances have focused on how PUFA regulate the molecular signaling of microglia, especially in the context of neuroinflammation and behavior. Several active drugs regulate brain lipid signaling and provide proof of concept for targeting the brain. Because brain lipid metabolism relies on a complex integration of diet, peripheral metabolism, including the liver and blood, which supply the brain with PUFAs that can be altered by genetics, sex, and aging, there are many pathways that can be disrupted, leading to altered brain lipid homeostasis. Brain lipid signaling pathways are altered in neurologic disorders and may be viable targets for the development of novel therapeutics. In this study, we discuss in particular how n-3 PUFAs and their metabolites regulate microglia phenotype and function to exert their anti-inflammatory and proresolving activities in the brain.

Structural elucidation and physiologic functions of specialized pro-resolving mediators and their receptors

The acute inflammatory response is host-protective to contain foreign invaders. Many of today's pharmacopeia that block pro-inflammatory chemical mediators can cause serious unwanted side effects such as immune suppression. Uncontrolled inflammation is now considered a pathophysiologic basis associated with many widely occurring diseases such as cardiovascular disease, neurodegenerative diseases, diabetes, obesity and asthma, as well as the classic inflammatory diseases, e.g. arthritis, periodontal diseases. The inflammatory response is designated to be a self-limited process that produces a superfamily of chemical mediators that stimulate resolution of inflammatory responses. Specialized proresolving mediators (SPM) uncovered in recent years are endogenous mediators that include omega-3-derived families resolvins, protectins and maresins, as well as arachidonic acid-derived (n-6) lipoxins that stimulate and promote resolution of inflammation, clearance of microbes, reduce pain and promote tissue regeneration via novel mechanisms. Here, we review recent evidence from human and preclinical animal studies, together with the structural and functional elucidation of SPM indicating the SPM as physiologic mediators and pharmacologic agonists that stimulate resolution of inflammation and infection. These results suggest that it is time to develop immunoresolvents as agonists for testing resolution pharmacology in nutrition and health as well as in human diseases and during surgery.

Immunoresolvents signaling molecules at intersection between the brain and immune system

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The vagus nerve regulates ILC-3 and macrophage trafficking to the peritoneum.

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Vagotomy reduces peritoneal PCTR concentrations and alters tissue resolution tone.

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Resection of the vagus nerve impairs resolution responses to sterile and infectious insults.

Understanding mechanisms that control immunity is central in the quest to gain insights into the etiopathology of many of the diseases that afflict modern societies. New results implicate the nervous system as a central player in controlling many aspects of both the innate and adaptive arms of the immune response. Furthermore it is now well appreciated that a novel group of autacoids termed as specialized proresolving mediators, which are enzymatically produced from essential fatty acids, orchestrate the immune response promoting the termination of inflammation as well as tissue repair and regeneration. The present brief review discusses evidence for the crosstalk between the nervous system and leukocytes in regulating SPM production. We will also discuss the impact that this has on controlling tissue resolution tone and the resolution of both infectious and sterile inflammation.

Maresin 1 Promotes Inflammatory Resolution, Neuroprotection, and Functional Neurological Recovery After Spinal Cord Injury

Resolution of inflammation is defective after spinal cord injury (SCI), which impairs tissue integrity and remodeling and leads to functional deficits. Effective pharmacological treatments for SCI are not currently available. Maresin 1 (MaR1) is a highly conserved specialized proresolving mediator (SPM) hosting potent anti-inflammatory and proresolving properties with potent tissue regenerative actions. Here, we provide evidence that the inappropriate biosynthesis of SPM in the lesioned spinal cord hampers the resolution of inflammation and leads to deleterious consequences on neurological outcome in adult female mice. We report that, after spinal cord contusion injury in adult female mice, the biosynthesis of SPM is not induced in the lesion site up to 2 weeks after injury. Exogenous administration of MaR1, a highly conserved SPM, propagated inflammatory resolution after SCI, as revealed by accelerated clearance of neutrophils and a reduction in macrophage accumulation at the lesion site. In the search of mechanisms underlying the proresolving actions of MaR1 in SCI, we found that this SPM facilitated several hallmarks of resolution of inflammation, including reduction of proinflammatory cytokines (CXCL1, CXCL2, CCL3, CCL4, IL6, and CSF3), silencing of major inflammatory intracellular signaling cascades (STAT1, STAT3, STAT5, p38, and ERK1/2), redirection of macrophage activation toward a prorepair phenotype, and increase of the phagocytic engulfment of neutrophils by macrophages. Interestingly, MaR1 administration improved locomotor recovery significantly and mitigated secondary injury progression in a clinical relevant model of SCI. These findings suggest that proresolution, immunoresolvent therapies constitute a novel approach to improving neurological recovery after acute SCI.SIGNIFICANCE STATEMENT Inflammation is a protective response to injury or infection. To result in tissue homeostasis, inflammation has to resolve over time. Incomplete or delayed resolution leads to detrimental effects, including propagated tissue damage and impaired wound healing, as occurs after spinal cord injury (SCI). We report that inflammation after SCI is dysregulated in part due to inappropriate synthesis of proresolving lipid mediators. We demonstrate that the administration of the resolution agonist referred to as maresin 1 (MaR1) after SCI actively propagates resolution processes at the lesion site and improves neurological outcome. MaR1 is identified as an interventional candidate to attenuate dysregulated lesional inflammation and to restore functional recovery after SCI.

Effects of fish oils on ex vivo B-cell responses of obese subjects upon BCR/TLR stimulation: a pilot study

The long-chain n-3 polyunsaturated fatty acids (LC-PUFAs) eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) in fish oil have immunomodulatory properties. B cells are a poorly studied target of EPA/DHA in humans. Therefore, in this pilot study, we tested how n-3 LC-PUFAs influence B-cell responses of obese humans. Obese men and women were assigned to consume four 1-g capsules per day of olive oil (OO, n=12), fish oil (FO, n=12) concentrate or high-DHA-FO concentrate (n=10) for 12 weeks in a parallel design. Relative to baseline, FO (n=9) lowered the percentage of circulating memory and plasma B cells, whereas the other supplements had no effect. There were no postintervention differences between the three supplements. Next, ex vivo B-cell cytokines were assayed after stimulation of Toll-like receptors (TLRs) and/or the B-cell receptor (BCR) to determine if the effects of n-3 LC-PUFAs were pathway-dependent. B-cell IL-10 and TNFα secretion was respectively increased with high DHA-FO (n=10), relative to baseline, with respective TLR9 and TLR9+BCR stimulation. OO (n=12) and FO (n=12) had no influence on B-cell cytokines compared to baseline, and there were no differences in postintervention cytokine levels between treatment groups. Finally, ex vivo antibody levels were assayed with FO (n=7) after TLR9+BCR stimulation. Compared to baseline, FO lowered IgM but not IgG levels accompanied by select modifications to the plasma lipidome. Altogether, the results suggest that n-3 LC-PUFAs could modulate B-cell activity in humans, which will require further testing in a larger cohort.

Monocyte-Macrophages and T Cells in Atherosclerosis

Atherosclerosis is an arterial disease process characterized by the focal subendothelial accumulation of apolipoprotein-B-containing lipoproteins, immune and vascular wall cells, and extracellular matrix. The lipoproteins acquire features of damage-associated molecular patterns and trigger first an innate immune response, dominated by monocyte-macrophages, and then an adaptive immune response. These inflammatory responses often become chronic and non-resolving and can lead to arterial damage and thrombosis-induced organ infarction. The innate immune response is regulated at various stages, from hematopoiesis to monocyte changes and macrophage activation. The adaptive immune response is regulated primarily by mechanisms that affect the balance between regulatory and effector T cells. Mechanisms related to cellular cholesterol, phenotypic plasticity, metabolism, and aging play key roles in affecting these responses. Herein, we review select topics that shed light on these processes and suggest new treatment strategies.

Polyunsaturated fatty acids: any role in rheumatoid arthritis?

Background

Polyunsaturated fatty acids (PUFAs) are members of the family of fatty acids and are included in the diet. Particularly, western diet is usually low in n-3 PUFAs and high in n-6 PUFAs. PUFAs play a central role in the homeostasis of immune system: n-6 PUFAs have predominantly pro-inflammatory features, while n-3 PUFAs seem to exert anti-inflammatory and pro-resolving properties. Rheumatoid arthritis (RA) is a chronic inflammatory arthritis in which many inflammatory pathways contribute to joint and systemic inflammation, disease activity, and structural damage. Research on PUFAs could represent an important opportunity to better understand the pathogenesis and to improve the management of RA patients.

Methods

We searched PubMed, Embase, EBSCO-Medline, Cochrane Central Register of Controlled Trials (CENTRAL), CNKI and Wanfang to identify primary research reporting the role of n-3 PUFAs in rheumatoid arthritis both in humans and in animal models up to the end of March 2017.

Results

Data from animal models allows to hypothesize that n-3 PUFAs supplementation may represent an interesting perspective in future research as much in prevention as in treating RA. In humans, several case-control and prospective cohort studies suggest that a high content of n-3 PUFAs in the diet could have a protective role for incident RA in subjects at risk. Moreover, n-3 PUFAs supplementation has been assessed as a valuable therapeutic option also for patients with RA, particularly in order to improve the pain symptoms, the tender joint count, the duration of morning stiffness and the frequency of NSAIDs assumption.

Conclusions

n-3 PUFAs supplementation could represent a promising therapeutic option to better control many features of RA. The impact of n-3 PUFAs on radiographic progression and synovial histopathology has not been yet evaluated, as well as their role in early arthritis and the combination with biologics.

Boosting Inflammation Resolution in Atherosclerosis: The Next Frontier for Therapy

Defective inflammation resolution is the underlying cause of prevalent chronic inflammatory diseases, such as arthritis, asthma, cancer, and neurodegenerative and cardiovascular diseases. Inflammation resolution is governed by several endogenous factors, including fatty acid-derived specialized proresolving mediators and proteins, such as annexin A1. Specifically, specialized proresolving mediators comprise a family of mediators that include arachidonic acid-derived lipoxins, omega-3 fatty acid eicosapentaenoic acid-derived resolvins, docosahexaenoic acid-derived resolvins, protectins, and maresins. Emerging evidence indicates that imbalances between specialized proresolving mediators and proinflammatory mediators are associated with several prevalent human diseases, including atherosclerosis. Mechanisms that drive this imbalance remain largely unknown and will be discussed in this review. Furthermore, the concept of dysregulated inflammation resolution in atherosclerosis has been known for several decades. Recently, there has been an explosion of new work with regard to the therapeutic application of proresolving ligands in experimental atherosclerosis. Therefore, this review will highlight recent advances in our understanding of how inflammation resolution may become defective in atherosclerosis and the potential for proresolving therapeutics in atherosclerosis. Last, we offer insight for future implications of the field.

A cluster of immunoresolvents links coagulation to innate host defense in human blood

Blood coagulation is a protective response that prevents excessive bleeding upon blood vessel injury. We investigated the relationship between coagulation and the resolution of inflammation and infection by lipid mediators (LMs) through metabololipidomics-based profiling of human whole blood (WB) during coagulation. We identified temporal clusters of endogenously produced prothrombotic and proinflammatory LMs (eicosanoids), as well as specialized proresolving mediators (SPMs). In addition to eicosanoids, a specific SPM cluster was identified that consisted of resolvin E1 (RvE1), RvD1, RvD5, lipoxin B₄, and maresin 1, each of which was present at bioactive concentrations (0.1 to 1 nM). Removal of adenosine from the coagulating blood markedly enhanced the amounts of SPMs produced and further increased the biosynthesis of RvD3, RvD4, and RvD6. The cyclooxygenase inhibitors celecoxib and indomethacin, which block the production of thromboxanes and prostanoids, did not block the production of clot-driven SPMs. Unbiased mass cytometry analysis demonstrated that the SPM cluster produced in human blood targeted leukocytes at the single-cell level, directly activating ERK and CREB signaling in neutrophils and CD14⁺ monocytes. Treatment of human WB with the components of this SPM cluster enhanced both the phagocytosis and killing of Escherichia coli by leukocytes. Together, these data identify a proresolving LM circuit, including endogenous molecular brakes and accelerators, which promoted host defense. These temporal LM-SPM clusters can provide accessible metabolomic profiles for precision and personalized medicine.

Maresin 1 Ameliorates Lung Ischemia/Reperfusion Injury by Suppressing Oxidative Stress via Activation of the Nrf-2-Mediated HO-1 Signaling Pathway

Lung ischemia/reperfusion (I/R) injury occurs in various clinical conditions and heavily damaged lung function. Oxidative stress reaction and antioxidant enzymes play a pivotal role in the etiopathogenesis of lung I/R injury. In the current study, we investigated the impact of Maresin 1 on lung I/R injury and explored the possible mechanism involved in this process. MaR 1 ameliorated I/R-induced lung injury score, wet/dry weight ratio, myeloperoxidase, tumor necrosis factor, bronchoalveolar lavage fluid (BALF) leukocyte count, BALF neutrophil ratio, and pulmonary permeability index levels in lung tissue. MaR 1 significantly reduced ROS, methane dicarboxylic aldehyde, and 15-F2t-isoprostane generation and restored antioxidative enzyme (superoxide dismutase, glutathione peroxidase, and catalase) activities. Administration of MaR 1 improved the expression of nuclear Nrf-2 and cytosolic HO-1 in I/R-treated lung tissue. Furthermore, we also found that the protective effects of MaR 1 on lung tissue injury and oxidative stress were reversed by HO-1 activity inhibitor, Znpp-IX. Nrf-2 transcription factor inhibitor, brusatol, significantly decreased MaR 1-induced nuclear Nrf-2 and cytosolic HO-1 expression. In conclusion, these results indicate that MaR 1 protects against lung I/R injury through suppressing oxidative stress. The mechanism is partially explained by activation of the Nrf-2-mediated HO-1 signaling pathway.

Frontline Science: Aspirin-triggered resolvin D1 controls herpes simplex virus-induced corneal immunopathology

Stromal keratitis (SK) is a chronic immunopathological lesion of the eye, caused by HSV-1 infection, and a common cause of vision impairment in humans. The inflammatory lesions in the cornea are primarily caused by neutrophils with the active participation of CD4⁺ T cells. Therefore, the targeting of these immune cell types and their products represents a potentially valuable form of therapy to reduce the severity of disease. Resolvin D1 (RvD1) and its epimer aspirin-triggered RvD1 (AT-RvD1) are lipid mediators derived from docosahexaenoic acid (DHA) and were shown to promote resolution in several inflammatory disease models. In this report, we examined whether AT-RvD1 administration, begun before infection or at a later stage after ocular infection of mice with HSV-1, could control the severity of SK lesions. Treatment with AT-RvD1 significantly diminished the extent of corneal neovascularization and the severity of SK lesions. AT-RvD1-treated mice had fewer numbers of inflammatory cells that included neutrophils as well as Th1 and Th17 cells in the infected cornea. The mechanisms by which AT-RvD1 acts appear to be multiple. These include inhibitory effects on proinflammatory mediators, such as IL-1β, IL-6, IL-12, CXCL1, MCP-1, MIP-2, vascular endothelial growth factor (VEGF)-A, matrix metalloproteinase 9 (MMP-9), and proinflammatory miRNA, such as miR-155, miR-132, and miR-223, which are involved in SK pathogenesis and corneal neovascularization. In addition, AT-RvD1 attenuated STAT1, which plays an important role in Th1 cell differentiation and IFN-γ expression. These findings demonstrate that AT-RvD1 treatment could represent a useful strategy for the management of virus-induced immunopathological lesions.

The role of systemic and topical fatty acids for dry eye treatment

Dry eye is a prevalent condition and one of the main reasons for patients to seek ophthalmic medical care. A low systemic level of omega fatty acids is a risk factor for dry eye disease (DED). There are two groups of essential fatty acids (EFAs): the omega-6 (n-6) family and the omega-3 (n-3) family. Humans evolved on a diet in which the n-6:n-3 ratio was approximately 1:1, however the current Western diet tends to be deficient in n-3 EFAs and this ratio is typically much higher (approaching 17:1). The metabolism of EFAs generates four new families of local acting mediators: lipoxins, resolvins, protectins, and maresins. These molecules have anti-inflammatory and pro-resolution properties. We present a critical overview of animal model studies and human clinical trials that have shown that dietary modification and oral supplementation could be complementary therapeutic strategies for the treatment of dry eye. Furthermore, we discuss preliminary results of the topical application of n-3 and n-6 EFAs because these molecules may act as natural anti-inflammatory agents with positive changes of the entire ocular surface system.

Aspirin-Triggered Resolvin D1-modified materials promote the accumulation of pro-regenerative immune cell subsets and enhance vascular remodeling

Many goals in tissue engineering rely on modulating cellular localization and polarization of cell signaling, including the inhibition of inflammatory infiltrate, facilitation of inflammatory cell egress, and clearance of apoptotic cells. Omega-3 polyunsaturated fatty acid-derived resolvins are gaining increasing recognition for their essential roles in inhibition of neutrophil invasion into inflamed tissue and promotion of macrophage phagocytosis of cellular debris as well as their egress to the lymphatics. Biomaterial-based release of lipid mediators is a largely under-explored approach that provides a method to manipulate local lipid signaling gradients in vivo and direct the recruitment and/or polarization of anti-inflammatory cell subsets to suppress inflammatory signaling and enhance angiogenesis and tissue regeneration. The goal of this study was to encapsulate Aspirin-Triggered Resolvin D1 (AT-RvD1) into a degradable biomaterial in order to elucidate the effects of sustained, localized delivery in a model of sterile inflammation. Flow cytometric and imaging analysis at both 1 and 3days after injury showed that localized AT-RvD1 delivery was able significantly increase the accumulation of anti-inflammatory monocytes and M2 macrophages while limiting the infiltration of neutrophils. Additionally, cytokine profiling and longitudinal vascular analysis revealed a shift towards a pro-angiogenic profile with increased concentrations of VEGF and SDF-1α, and increased arteriolar diameter and tortuosity. These results demonstrate the ability of locally-delivered AT-RvD1 to increase pro-regenerative immune subpopulations and promote vascular remodeling.

STATEMENT OF SIGNIFICANCE

This work is motivated by our efforts to explore the underlying mechanisms of inflammation resolution after injury and to develop biomaterial-based approaches to amplify endogenous mechanisms of resolution and repair. Though specific lipid mediators have been identified that actively promote the resolution of inflammation, biomaterial-based localized delivery of these mediators has been largely unexplored. We loaded Aspirin-Triggered Resolvin D1 into a PLGA scaffold and examined the effects of sustained, localized delivery on the innate immune response. We found that biomaterial delivery of resolvin was able to enhance the accumulation of pro-regenerative populations of immune cells, including anti-inflammatory monocytes, population that has never before been shown to respond to resolvin treatment, and also enhance vascular remodeling in response to tissue injury.

Treating inflammation and infection in the 21st century: new hints from decoding resolution mediators and mechanisms

Practitioners of ancient societies from the time of Hippocrates and earlier recognized and treated the signs of inflammation, heat, redness, swelling, and pain with agents that block or inhibit proinflammatory chemical mediators. More selective drugs are available today, but this therapeutic concept has not changed. Because the acute inflammatory response is host protective to contain foreign invaders, much of today's pharmacopeia can cause serious unwanted side effects, such as immune suppression. Uncontrolled inflammation is now considered pathophysiologic and is associated with many widely occurring diseases such as cardiovascular disease, neurodegenerative diseases, diabetes, obesity, and asthma, as well as classic inflammatory diseases (e.g., arthritis and periodontal diseases). The inflammatory response, when self-limited, produces a superfamily of chemical mediators that stimulate resolution of the response. Specialized proresolving mediators (SPMs), identified in recent years, are endogenous mediators that include the n-3-derived families resolvins, protectins, and maresins, as well as arachidonic acid-derived (n-6) lipoxins, which promote resolution of inflammation, clearance of microbes, reduction of pain, and promotion of tissue regeneration via novel mechanisms. Aspirin and statins have a positive impact on these resolution pathways, producing epimeric forms of specific SPMs, whereas other drugs can disrupt timely resolution. In this article, evidence from recent human and preclinical animal studies is reviewed, indicating that SPMs are physiologic mediators and pharmacologic agonists that stimulate resolution of inflammation and infection. The findings suggest that it is time to challenge current treatment practices-namely, using inhibitors and antagonists alone-and to develop immunoresolvents as agonists to test resolution pharmacology and their role in catabasis for their therapeutic potential.-Serhan, C. N. Treating inflammation and infection in the 21st century: new hints from decoding resolution mediators and mechanisms.

Age-associated DNA methylation changes in naive CD4+ T cells suggest an evolving autoimmune epigenotype in aging T cells

AIM

We sought to define age-associated DNA methylation changes in naive CD4⁺ T cells.

MATERIALS & METHODS

Naive CD4⁺ T cells were collected from 74 healthy individuals (age 19-66 years), and age-related DNA methylation changes were characterized.

RESULTS

We identified 11,431 age-associated CpG sites, 57% of which were hypermethylated with age. Hypermethylated sites were enriched in CpG islands and repressive transcription factor binding sites, while hypomethylated sites showed T cell specific enrichment in active enhancers marked by H3K27ac and H3K4me1. Our data emphasize cancer-related DNA methylation changes with age, and also reveal age-associated hypomethylation in immune-related pathways, such as T cell receptor signaling, FCγR-mediated phagocytosis, apoptosis and the mammalian target of rapamycin signaling pathway. The MAPK signaling pathway was hypermethylated with age, consistent with a defective MAPK signaling in aging T cells.

CONCLUSION

Age-associated DNA methylation changes may alter regulatory mechanisms and signaling pathways that predispose to autoimmunity.

Impairment of systemic DHA synthesis affects macrophage plasticity and polarization: implications for DHA supplementation during inflammation

Docosahexaenoic acid (DHA) is an omega-3 fatty acid obtained from the diet or synthesized from alpha-linolenic acid through the action of fatty acid elongases (ELOVL) and desaturases. DHA plays important roles in the central nervous system as well as in peripheral organs and is the precursor of several molecules that regulate resolution of inflammation. In the present study, we questioned whether impaired synthesis of DHA affected macrophage plasticity and polarization both in vitro and in vivo models. For this we investigated the activation status and inflammatory response of bone marrow-derived M1 and M2 macrophages obtained from mice deficient of Elovl2 (Elovl2^−/−), a key enzyme for DHA synthesis in mammals. Although both wild type and Elovl2^−/− mice were able to generate efficient M1 and M2 macrophages, M1 cells derived from Elovl2^−/− mice showed an increased expression of key markers (iNOS, CD86 and MARCO) and cytokines (IL-6, IL-12 and IL-23). However, M2 macrophages exhibited upregulated M1-like markers like CD80, CD86 and IL-6, concomitantly with a downregulation of their signature marker CD206. These effects were counteracted in cells obtained from DHA-supplemented animals. Finally, white adipose tissue of Elovl2^−/− mice presented an M1-like pro-inflammatory phenotype. Hence, impairment of systemic DHA synthesis delineates an alteration of M1/M2 macrophages both in vitro and in vivo, with M1 being hyperactive and more pro-inflammatory while M2 less protective, supporting the view that DHA has a key role in controlling the balance between pro- and anti-inflammatory processes.

Specialized pro-resolving mediators in cardiovascular diseases

The resolution of inflammation is a highly regulated process enacted by endogenous mediators including specialized pro-resolving lipid mediators (SPMs): the lipoxins, resolvins, protectins and maresins. SPMs activate specific cellular receptors to temper the production of pro-inflammatory mediators, diminish the recruitment of neutrophils, and promote the clearance of dead cells by macrophages. These mediators also enhance host-defense and couple resolution of inflammation to subsequent phases of tissue repair. Given that unresolved inflammation plays a causal role in the development of cardiovascular diseases, an understanding of these endogenous pro-resolving processes is critical for determining why cardiovascular inflammation does not resolve. Here, we discuss the receptor-dependent actions of resolvins and related pro-resolving mediators and highlight their emerging roles in the cardiovascular system. We propose that stimulating resolution could be a novel approach for treating chronic cardiovascular inflammation without promoting immunosuppression.

Resolution of Cancer-Promoting Inflammation: A New Approach for Anticancer Therapy

Inflammation is a protective response that eliminates harmful stimuli and restores tissue homeostasis, whereas the failure to resolve inflammation leads to the development of malignancies. Immune cells in the tumor inflammatory microenvironment endow cancer cells with their specific hallmarks, including mutations, metabolic reprograming, angiogenesis, invasion, and metastasis. Targeting the inflammatory microenvironment with anti-inflammatory drugs (e.g., aspirin) or by enhancing antitumor immunity (e.g., chimeric antigen receptor T cell therapy) has been extensively investigated and has achieved promising results in many cancers. Recently, a novel approach promoting antitumor immunity via a dual anti-inflammatory and pro-resolving strategy was proposed based on the discovery of potent, endogenous, specialized pro-resolving mediators, including lipoxins, resolvins, protectins, and maresins. In this review, we describe the updated principal cellular and molecular mechanisms of inflammation resolution and cancer immunity and discuss the pro-resolution strategy in cancer treatment and prevention.

Prevention of Chronic Post-Thoracotomy Pain in Rats By Intrathecal Resolvin D1 and D2: Effectiveness of Perioperative and Delayed Drug Delivery

Thoracotomy results in a high frequency of chronic postoperative pain. Resolvins are endogenous molecules, synthesized and released by activated immune cells, effective against inflammatory and neuropathic pain. Different resolvins have differential actions on selective neuronal and glial receptors and enzymes. This article examines the ability of intrathecal resolvin D1 and resolvin D2 to reduce chronic post-thoracotomy pain in rats. Thoracotomy, involving intercostal incision and rib retraction, resulted in a decrease in the mechanical force threshold to induce nocifensive behavior, an enlargement of the pain-sensitive area, and an increase in the fraction of rats showing nocifensive behavior, all for at least 5 weeks. The qualitative nature of the behavioral responses to tactile stimulation changed dramatically after thoracotomy, including the appearance of vigorous behaviors, such as turning, shuddering, and squealing, all absent in naive rats. Intrathecal delivery of resolvin D1 (30 ng/30 μL), at surgery or 4 days later, halved the spread of the mechanosensitive area, lowered by 60% the percent of rats with tactile hypersensitivity, and reduced the drop in threshold for a nocifensive response, along with a reduction in the occurrence of vigorous nocifensive responses. Resolvin D2's actions on threshold changes were statistically the same. These findings suggest that intrathecal resolvins, delivered preoperatively or several days later, can prevent chronic postoperative hyperalgesia.

PERSPECTIVE

In studies of rats, the injection of the proresolving compounds of the resolvin-D series into spinal fluid, before or just after thoracotomy surgery, prevents the occurrence of acute and chronic pain. If these chemicals, which have shown no side-effects, were used in humans it might greatly reduce chronic postoperative pain.