Metabolic Inactivation of Resolvin E1 and Stabilization of Its Anti-inflammatory Actions

Resolvins D5 and D1 undergo phase II metabolism by uridine 5'-diphospho-glucuronosyltransferases

Specialized pro-resolving mediators (SPMs) are oxidized lipid mediators that have been shown to resolve inflammation in cellular and animal models as well as humans. SPMs and their biological precursors are even commercially available as dietary supplements. It has been understood for more than forty years that pro-inflammatory oxidized lipid mediators, including prostaglandins and leukotrienes, are rapidly inactivated via metabolism. Studies on the metabolism of SPMs are, however, limited. Herein, we report that resolvin D5 (RvD5) and resolvin D1 (RvD1), well-studied SPMs, are readily metabolized by human liver microsomes (HLM) to glucuronide conjugated metabolites. We further show that this transformation is catalyzed by specific uridine 5'-diphospho-glucuronosyltransferase (UGT) isoforms. Additionally, we demonstrate that RvD5 and RvD1 metabolism by HLM is influenced by non-steroidal anti-inflammatory drugs (NSAIDs), which can act as UGT inhibitors through cyclooxygenase-independent mechanisms. The results from these studies highlight the importance of considering metabolism, as well as factors that influence metabolic enzymes, when seeking to quantify SPMs in vivo.

Gut microbial dysbiosis and inflammation: Impact on periodontal health

Periodontitis is widely acknowledged as the most prevalent type of oral inflammation, arising from the dynamic interplay between oral pathogens and the host's immune responses. It is also recognized as a contributing factor to various systemic diseases. Dysbiosis of the oral microbiota can significantly alter the composition and diversity of the gut microbiota. Researchers have delved into the links between periodontitis and systemic diseases through the "oral-gut" axis. However, whether the associations between periodontitis and the gut microbiota are simply correlative or driven by causative mechanistic interactions remains uncertain. This review investigates how dysbiosis of the gut microbiota impacts periodontitis, drawing on existing preclinical and clinical data. This study highlights potential mechanisms of this interaction, including alterations in subgingival microbiota, oral mucosal barrier function, neutrophil activity, and abnormal T-cell recycling, and offers new perspectives for managing periodontitis, especially in cases linked to systemic diseases.

Omega-3 polyunsaturated fatty acid derived lipid mediators: a comprehensive update on their application in anti-cancer drug discovery

INTRODUCTION

ω-3 Polyunsaturated fatty acids (PUFAs) have a range of health benefits, including anticancer activity, and are converted to lipid mediators that could be adapted into pharmacological strategies. However, the stability of these mediators must be improved, and they may require formulation to achieve optimal tissue concentrations.

AREAS COVERED

Herein, the author reviews the literature around chemical stabilization and formulation of ω-3 PUFA mediators and their application in anticancer drug discovery.

EXPERT OPINION

Aryl-urea bioisosteres of ω-3 PUFA epoxides that killed cancer cells targeted the mitochondrion by a novel dual mechanism: as protonophoric uncouplers and as inhibitors of electron transport complex III that activated ER-stress and disrupted mitochondrial integrity. In contrast, aryl-ureas that contain electron-donating substituents prevented cancer cell migration. Thus, aryl-ureas represent a novel class of agents with tunable anticancer properties. Stabilized analogues of other ω-3 PUFA-derived mediators could also be adapted into anticancer strategies. Indeed, a cocktail of agents that simultaneously promote cell killing, inhibit metastasis and angiogenesis, and that attenuate the pro-inflammatory microenvironment is a novel future anticancer strategy. Such regimen may enhance anticancer drug efficacy, minimize the development of anticancer drug resistance and enhance outcomes.

Lipoxin A4 yields an electrophilic 15-oxo metabolite that mediates FPR2 receptor-independent anti-inflammatory signaling

The enzymatic oxidation of arachidonic acid is proposed to yield trihydroxytetraene species (termed lipoxins) that resolve inflammation via ligand activation of the formyl peptide receptor, FPR2. While cell and murine models activate signaling responses to synthetic lipoxins, primarily 5S,6R,15S-trihydroxy-7E,9E,11Z,13E-eicosatetraenoic acid (lipoxin A4, LXA4), there are expanding concerns about the biological formation, detection and signaling mechanisms ascribed to LXA4 and related di- and tri-hydroxy ω-6 and ω-3 fatty acids. Herein, the generation and actions of LXA4 and its primary 15-oxo metabolite were assessed in control, LPS-activated and arachidonic acid supplemented RAW 264.7 macrophages. Despite protein expression of all enzymes required for LXA4 synthesis, both LXA4 and its 15-oxo-LXA4 metabolite were undetectable. Moreover, synthetic LXA4 and the membrane permeable 15-oxo-LXA4 methyl ester that is rapidly de-esterified to 15-oxo-LXA4, displayed no ligand activity for the putative LXA4 receptor FPR2, as opposed to the FPR2 ligand WKYMVm. Alternatively, 15-oxo-LXA4, an electrophilic α,β-unsaturated ketone, alkylates nucleophilic amino acids such as cysteine to modulate redox-sensitive transcriptional regulatory protein and enzyme function. 15-oxo-LXA4 activated nuclear factor (erythroid related factor 2)-like 2 (Nrf2)-regulated gene expression of anti-inflammatory and repair genes and inhibited nuclear factor (NF)-κB-regulated pro-inflammatory mediator expression. LXA4 did not impact these macrophage anti-inflammatory and repair responses. In summary, these data show an absence of macrophage LXA4 formation and receptor-mediated signaling actions. Rather, if LXA4 were present in sufficient concentrations, this, and other more abundant mono- and poly-hydroxylated unsaturated fatty acids can be readily oxidized to electrophilic α,β-unsaturated ketone products that modulate the redox-sensitive cysteine proteome via G-protein coupled receptor-independent mechanisms.

Specialized pro-resolving mediators in vascular inflammation and atherosclerotic cardiovascular disease

Timely resolution of the acute inflammatory response (or inflammation resolution) is an active, highly coordinated process that is essential to optimal health. Inflammation resolution is regulated by specific endogenous signalling molecules that function as 'stop signals' to terminate the inflammatory response when it is no longer needed; to actively promote healing, regeneration and tissue repair; and to limit pain. Specialized pro-resolving mediators are a superfamily of signalling molecules that initiate anti-inflammatory and pro-resolving actions. Without an effective and timely resolution response, inflammation can become chronic, a pathological state that is associated with many widely occurring human diseases, including atherosclerotic cardiovascular disease. Uncovering the mechanisms of inflammation resolution failure in cardiovascular diseases and identifying useful biomarkers for non-resolving inflammation are unmet needs. In this Review, we discuss the accumulating evidence that supports the role of non-resolving inflammation in atherosclerosis and the use of specialized pro-resolving mediators as therapeutic tools for the treatment of atherosclerotic cardiovascular disease. We highlight open questions about therapeutic strategies and mechanisms of disease to provide a framework for future studies on the prevention and treatment of atherosclerosis.

Biomimetic Nanocarriers of Pro-Resolving Lipid Mediators for Resolution of Inflammation in Atherosclerosis

Atherosclerosis (ATH) is a systemic disease characterized by a chronic inflammatory process and lipid deposition in the arterial walls. The chronic inflammation within ATH lesions results, at least in part, from the failed resolution of inflammation. This process is controlled actively by specialized pro-resolving lipid mediators (SPMs), namely lipoxins, resolvins, protectins, and maresins. Herein, biomimetic nanocarriers are produced comprising a cocktail of SPMs-loaded lipid nanoemulsions (LN) covered with macrophage membranes (Bio-LN/SPMs). Bio-LN/SPMs retain on their surface the macrophage receptors involved in cellular interactions and the "marker of self" CD47, which impede their recognition and uptake by other macrophages. The binding of Bio-LN/SPMs to the surface of endothelial cells (EC) and smooth muscle cells (SMC) is facilitated by the receptors on the macrophage membranes and partly by SPMs receptors. In addition, Bio-LN/SPMs prove functional by reducing monocyte adhesion and transmigration to/through activated EC and by stimulating macrophage phagocytic activity. After intravenous administration, Bio-LN/SPMs accumulate in the aorta of ApoE-deficient mice at the level of atherosclerotic lesions. Also, the safety assessment testing reveals no side effects or immunotoxicity of Bio-LN/SPMs. Thus, the newly developed Bio-LN/SPMs represent a reliable targeted nanomedicine for the resolution of inflammation in atherosclerosis.

Metabolization of Resolvin E4 by ω-Oxidation in Human Neutrophils: Synthesis and Biological Evaluation of 20-Hydroxy-Resolvin E4 (20-OH-RvE4)

Resolvin E4 (RvE4) belongs to the resolvin family of specialized pro-resolving mediators (SPMs). The resolvins are endogenously formed mediators with both potent pro-resolving and anti-inflammatory biological activities and have attracted considerable attention in both inflammation research and drug discovery. Hence, further metabolism of the resolvins is of interest. Gaining knowledge about the structure-function of further metabolites of the resolvins is important due to their interest in drug-discovery efforts. For the first time, the total synthesis and biological evaluations of the ω-20 hydroxylated metabolite of RvE4, named herein 20-OH-RvE4, are presented. RvE4 was converted to 20-OH-RvE4 by human polymorphonuclear leukocytes. LC-MS/MS analysis and UV spectrophotometry reveal that the synthetic 20-OH-RvE4 matched RvE4-converted product 20-OH-RvE4 by human neutrophils. Cellular studies have revealed that RvE4 is formed from eicosapentaenoic acid in physiologic hypoxia by human neutrophils and macrophages, and we herein established that 20-OH-RvE4 is a secondary metabolite formed by the ω-oxidation of RvE4 in human neutrophils. A direct comparison of the biological actions between RvE4 and its metabolic product suggested that 20-OH-RvE4 displayed reduced bioactions in stimulating the efferocytosis of human senescent erythrocytes by human M2-like macrophages. At concentrations down to 0.1 nM, RvE4 increased macrophage erythrophagocytosis, an important pro-resolving function that was diminished due to metabolic transformation. The results provided herein contribute to a novel molecular insight on the further local metabolization of RvE4, the newest member among the SPM superfamily.

Microglia Exhibit Distinct Heterogeneity Rather than M1/M2 Polarization within the Early Stage of Acute Ischemic Stroke

The classification of microglial M1/M2 polarization in the acute phase of ischemic stroke remains controversial, which has limited further advances in neuroprotective strategy. To thoroughly assess the microglial phenotypes, we made the middle cerebral artery occlusion model in mice to simulate the acute pathological processes of ischemic stroke from normal conditions to acute cerebral ischemia and then to the early reperfusion period. The temporal changes in gene profiles, cell subtypes, and microglial function were comprehensively analyzed using single-cell RNA sequencing. We identified 37,614 microglial cells and divided them into eight distinct subpopulations. Mic_home, Mic_pre1, and Mic_pre2 subpopulations were three clusters mainly composed of cells from the control samples, in which Mic_home was a homeostatic subpopulation characterized by high expression of Hpgd and Tagap, and Mic_pre1 and Mic_pre2 were two clusters with preliminary inflammatory activation characteristics marked by P2ry13 and Wsb1 respectively. Mic_M1L1 and Mic_M1L2 subpopulations exhibited M1-like polarization manifested by the upregulation of inflammatory genes after ischemic stroke, while the intrinsic heterogeneity on the level of inflammatory responses and neurotrophic support properties was observed. Moreover, we identified three unique clusters of cells with low inflammation levels. Mic_np1, Mic_np2, and Mic_np3 were characterized by high expression of Arhgap45, Rgs10, and Pkm respectively. However, these cells did not show significant M2-like characteristics and their classic microglia function was also attenuated. These subpopulations exhibited higher activation of neuropeptide functional pathways. At last, we performed cell-cell communication analysis and identified major couplings contributing to the interaction between microglia and other cell populations. In summary, our study elucidated the temporal heterogeneity of microglia in the acute phase of ischemic stroke, which may facilitate the identification of effective neuroprotective targets to curb ischemic damage at an early stage.

Resolvins and cysteinyl-containing pro-resolving mediators activate resolution of infectious inflammation and tissue regeneration

This review is a synopsis of the main points from the opening presentation by the authors in the Resolution of Inflammation session at the 8th European Workshop on Lipid Mediators held at the Karolinska Institute, Stockholm, Sweden, June 29th, 2022. Specialized pro-resolving mediators (SPM) promote tissue regeneration, control infections and resolution of inflammation. These include resolvins, protectins, maresins and the newly identified conjugates in tissue regeneration (CTRs). We reported mechanisms of CTRs in activating primordial regeneration pathways in planaria using RNA-sequencing. Also, the 4S,5S-epoxy-resolvin intermediate in the biosynthesis of resolvin D3 and resolvin D4 was prepared by total organic synthesis. Human neutrophils convert this to resolvin D3 and resolvin D4, while human M2 macrophages transformed this labile epoxide intermediate to resolvin D4 and a novel cysteinyl-resolvin that is a potent isomer of RCTR1. The novel cysteinyl-resolvin significantly accelerates tissue regeneration with planaria and inhibits human granuloma formation.

Polyunsaturated Fatty Acids: Conversion to Lipid Mediators, Roles in Inflammatory Diseases and Dietary Sources

Polyunsaturated fatty acids (PUFAs) are important components of the diet of mammals. Their role was first established when the essential fatty acids (EFAs) linoleic acid and α-linolenic acid were discovered nearly a century ago. However, most of the biochemical and physiological actions of PUFAs rely on their conversion to 20C or 22C acids and subsequent metabolism to lipid mediators. As a generalisation, lipid mediators formed from n-6 PUFAs are pro-inflammatory while those from n-3 PUFAs are anti-inflammatory or neutral. Apart from the actions of the classic eicosanoids or docosanoids, many newly discovered compounds are described as Specialised Pro-resolving Mediators (SPMs) which have been proposed to have a role in resolving inflammatory conditions such as infections and preventing them from becoming chronic. In addition, a large group of molecules, termed isoprostanes, can be generated by free radical reactions and these too have powerful properties towards inflammation. The ultimate source of n-3 and n-6 PUFAs are photosynthetic organisms which contain Δ-12 and Δ-15 desaturases, which are almost exclusively absent from animals. Moreover, the EFAs consumed from plant food are in competition with each other for conversion to lipid mediators. Thus, the relative amounts of n-3 and n-6 PUFAs in the diet are important. Furthermore, the conversion of the EFAs to 20C and 22C PUFAs in mammals is rather poor. Thus, there has been much interest recently in the use of algae, many of which make substantial quantities of long-chain PUFAs or in manipulating oil crops to make such acids. This is especially important because fish oils, which are their main source in human diets, are becoming limited. In this review, the metabolic conversion of PUFAs into different lipid mediators is described. Then, the biological roles and molecular mechanisms of such mediators in inflammatory diseases are outlined. Finally, natural sources of PUFAs (including 20 or 22 carbon compounds) are detailed, as well as recent efforts to increase their production.

Dysregulation of Resolvin E1 Metabolism and Signaling in a Light-Damage Model of Age-Related Macular Degeneration

Resolvin E1 (RvE1) is an eicosapentaenoic acid-derived lipid mediator involved in the resolution of inflammation. Here, we investigated whether RvE1 alterations may occur in an animal model of age-related macular degeneration (AMD). To this end, Sprague Dawley albino rats underwent light damage (LD), and retinas and serum were analyzed immediately or seven days after treatment. Western blot of retinas showed that the RvE1 receptor ChemR23 and the RvE1 metabolic enzymes 5-LOX and COX-2 were unchanged immediately after LD, but they were significantly up-regulated seven days later. Instead, the RvE1 receptor BLT1 was not modulated by LD, and neither was the RvE1 degradative enzyme 15-PGDH. Moreover, ChemR23, 5-LOX, COX-2 and BLT1 were found to be more expressed in the inner retina under all experimental conditions, as observed through ImageJ plot profile analysis. Of note, amacrine cells highly expressed BLT1, while ChemR23 was highly expressed in the activated microglia of the outer retina. ELISA assays also showed that LD rats displayed significantly higher circulating levels and reduced retinal levels of RvE1 compared to controls. Altogether, our data indicate that RvE1 metabolism and signaling are modulated in the LD model, suggesting a potentially relevant role of this pathway in AMD.

Intranasal Administration of Resolvin E1 Produces Antidepressant-Like Effects via BDNF/VEGF-mTORC1 Signaling in the Medial Prefrontal Cortex

Intracerebroventricular infusion of resolvin E1 (RvE1), a bioactive metabolite derived from eicosapentaenoic acid, exerts antidepressant-like effects in a mouse model of lipopolysaccharide (LPS)-induced depression; these effects are blocked by systemic injection of rapamycin, a mechanistic target of rapamycin complex 1 (mTORC1) inhibitor. Additionally, local infusion of RvE1 into the medial prefrontal cortex (mPFC) or dorsal hippocampal dentate gyrus (DG) produces antidepressant-like effects. To evaluate the potential of RvE1 for clinical use, the present study examined whether treatment with RvE1 via intranasal (i.n.) route, a non-invasive route for effective drug delivery to the brain, produces antidepressant-like effects in LPS-challenged mice using tail suspension and forced swim tests. Intranasal administration of RvE1 significantly attenuated LPS-induced immobility, and these antidepressant-like effects were completely blocked by an AMPA receptor antagonist or L-type voltage-dependent Ca2+ channel blocker. The antidepressant-like effects of both i.n. and intra-mPFC administrations of RvE1 were blocked by intra-mPFC infusion of a neutralizing antibody (nAb) for brain-derived neurotrophic factor (BDNF) or vascular endothelial growth factor (VEGF). Intra-mPFC infusion of rapamycin completely blocked the antidepressant-like effects of both i.n. and intra-mPFC administrations of RvE1 as well as those of intra-mPFC infusion of BDNF and VEGF. Moreover, i.n. RvE1 produced antidepressant-like effects via mTORC1 activation in the mPFC of a mouse model of repeated prednisolone-induced depression. Intra-dorsal DG infusion of BDNF and VEGF nAbs, but not rapamycin, blocked the antidepressant-like effects of i.n. RvE1. These findings suggest that i.n. administration of RvE1 produces antidepressant-like effects through activity-dependent BDNF/VEGF release in the mPFC and dorsal DG, and mTORC1 activation in the mPFC, but not in the dorsal DG. Thus, RvE1 can be a promising candidate for a novel rapid-acting antidepressant.

Small molecule inhibitors of 15-PGDH exploit a physiologic induced-fit closing system

15-prostaglandin dehydrogenase (15-PGDH) is a negative regulator of tissue stem cells that acts via enzymatic activity of oxidizing and degrading PGE2, and related eicosanoids, that support stem cells during tissue repair. Indeed, inhibiting 15-PGDH markedly accelerates tissue repair in multiple organs. Here we have used cryo-electron microscopy to solve the solution structure of native 15-PGDH and of 15-PGDH individually complexed with two distinct chemical inhibitors. These structures identify key 15-PGDH residues that mediate binding to both classes of inhibitors. Moreover, we identify a dynamic 15-PGDH lid domain that closes around the inhibitors, and that is likely fundamental to the physiologic 15-PGDH enzymatic mechanism. We furthermore identify two key residues, F185 and Y217, that act as hinges to regulate lid closing, and which both inhibitors exploit to capture the lid in the closed conformation, thus explaining their sub-nanomolar binding affinities. These findings provide the basis for further development of 15-PGDH targeted drugs as therapeutics for regenerative medicine.

Specialized Pro-Resolving Mediators as Resolution Pharmacology for the Control of Pain and Itch

Specialized pro-resolving mediators (SPMs), including resolvins, protectins, and maresins, are endogenous lipid mediators that are synthesized from omega-3 polyunsaturated fatty acids during the acute phase or resolution phase of inflammation. Synthetic SPMs possess broad safety profiles and exhibit potent actions in resolving inflammation in preclinical models. Accumulating evidence in the past decade has demonstrated powerful analgesia of exogenous SPMs in rodent models of inflammatory, neuropathic, and cancer pain. Furthermore, endogenous SPMs are produced by sham surgery and neuromodulation (e.g., vagus nerve stimulation). SPMs produce their beneficial actions through multiple G protein-coupled receptors, expressed by immune cells, glial cells, and neurons. Notably, loss of SPM receptors impairs the resolution of pain. I also highlight the emerging role of SPMs in the control of itch. Pharmacological targeting of SPMs or SPM receptors has the potential to lead to novel therapeutics for pain and itch as emerging approaches in resolution pharmacology.

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

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

Current experimental methods to investigate the impact of specialized pro-resolving lipid mediators on Sjögren's syndrome

Sjögren's syndrome is a chronic inflammatory autoimmune disease characterized by diminished secretory function of the exocrine glands. Although extensive investigation has been done to understand Sjögren's syndrome, the causes of the disease are as yet unknown and treatments remain largely ineffective, with established therapeutic interventions being limited to use of saliva substitutes with modest effectiveness. A primary feature of Sjögren's syndrome is uncontrolled inflammation of exocrine tissues and previous studies have demonstrated that lipid-based specialized pro-resolving mediators reduce inflammation and restores tissue integrity in salivary glands. However, these studies are limited to a single specialized pro-resolving lipid mediator's family member resolvin D1 or RvD1 and its aspirin-triggered epimer, AT-RvD1. Consequently, additional studies are needed to explore the potential benefits of other members of the specialized pro-resolving lipid mediator's family and related molecules (e.g., additional resolvin subtypes as well as lipoxins, maresins and protectins). In support of this goal, the current review aims to briefly describe the range of current experimental methods to investigate the impact of specialized pro-resolving lipid mediators on Sjögren's syndrome, including both strengths and weaknesses of each approach where this information is known. With this article, the possibilities presented by specialized pro-resolving lipid mediators will be introduced to a wider audience in immunology and practical advice is given to researchers who may wish to take up this work.

Potential Mechanisms by Which Hydroxyeicosapentaenoic Acids Regulate Glucose Homeostasis in Obesity

Dysregulation of glucose metabolism in response to diet-induced obesity contributes toward numerous complications, such as insulin resistance and hepatic steatosis. Therefore, there is a need to develop effective strategies to improve glucose homeostasis. In this review, we first discuss emerging evidence from epidemiological studies and rodent experiments that increased consumption of EPA (either as oily fish, or dietary/pharmacological supplements) may have a role in preventing impairments in insulin and glucose homeostasis. We then review the current evidence on how EPA-derived metabolites known as hydroxyeicosapentaenoic acids (HEPEs) may be a major mode of action by which EPA exerts its beneficial effects on glucose and lipid metabolism. Notably, cell culture and rodent studies show that HEPEs prevent fat accumulation in metabolic tissues through peroxisome proliferator activated receptor (PPAR)-mediated mechanisms. In addition, activation of the resolvin E1 pathway, either by administration of EPA in the diet or via intraperitoneal administration of resolvin E1, improves hyperglycemia, hyperinsulinemia, and liver steatosis through multiple mechanisms. These mechanisms include shifting immune cell phenotypes toward resolution of inflammation and preventing dysbiosis of the gut microbiome. Finally, we present the next steps for this line of research that will drive future precision randomized clinical trials with EPA and its downstream metabolites. These include dissecting the variables that drive heterogeneity in the response to EPA, such as the baseline microbiome profile and fatty acid status, circadian rhythm, genetic variation, sex, and age. In addition, there is a critical need to further investigate mechanisms of action for HEPEs and to establish the concentration of HEPEs in differing tissues, particularly in response to consumption of oily fish and EPA-enriched supplements.

Major structure-activity relationships of resolvins, protectins, maresins and their analogues

Resolvins, protectins and maresins are a series of polyunsaturated fatty acid-derived molecules which play important roles in the resolution of inflammation. They are termed specialized proresolving mediators and facilitate a return to homeostasis following an inflammatory response. These molecules are currently the focus of intensive investigation, primarily for their ability to suppress inflammation in chronic disease states. Researchers have employed different synthetic approaches to assess whether various structural modifications of these compounds could provide access to future therapeutics. This review summarizes the modifications made thus far and focuses on the key structure-activity relationships which have been uncovered for resolvins, protectins, maresins and their analogues.

A newly synthesized 17-epi-NeuroProtectin D1/17-epi-Protectin D1: Authentication and functional regulation of Inflammation-Resolution

The production of specialized pro-resolving mediators (SPMs) during the resolution phase in the inflammatory milieu is key to orchestrating the resolution of the acute inflammatory response. 17-epi-neuroprotectin D1/17-epi-protectin D1 (17-epi-NPD1/17-epi-PD1: 10R,17R-dihydroxy-4Z,7Z,11E,13E,15Z,19Z-docosahexaenoic acid) is an SPM of the protectin family, biosynthesized from docosahexaenoic acid (DHA), that exhibits both potent anti-inflammatory and neuroprotective functions. Here, we carried out a new commercial-scale synthesis of 17-epi-NPD1/17-epi-PD1 that enabled the authentication and confirmation of its potent bioactions in vivo and determination of its ability to activate human leukocyte phagocytosis. We provide evidence that this new synthetic 17-epi-NPD1/17-epi-PD1 statistically significantly increases human macrophage uptake of E. coli in vitro and confirm that it limits neutrophilic infiltration in vivo in a murine model of peritonitis. The physical properties of the new synthetic 17-epi-NPD1/17-epi-PD1, namely its ultra-violet absorbance, chromatography, and tandem mass spectrometry fragmentation pattern, matched those of the originally synthesized 17-epi-NPD1/17-epi-PD1. In addition, we verified the structure and complete stereochemical assignment of this new synthetic 17-epi-NPD1/17-epi-PD1 using nuclear magnetic resonance (NMR) spectroscopy. Together, these results authenticate this 17-epi-NPD1/17-epi-PD1 for its structure and potent pro-resolving functions.

Tackling inflammation in atherosclerosis: Are we there yet and what lies beyond?

Atherosclerosis is a lipid-driven disease of the artery characterized by chronic non-resolving inflammation. Despite availability of excellent lipid-lowering therapies, atherosclerosis remains the leading cause of disability and death globally. The demonstration that suppressing inflammation prevents the adverse clinical manifestations of atherosclerosis in recent clinical trials has led to heightened interest in anti-inflammatory therapies. In this review, we briefly highlight some key anti-inflammatory and pro-resolution pathways, which could be targeted to modulate pathogenesis and stall atherosclerosis progression. We also highlight key challenges that must be overcome to turn the concept of inflammation targeting therapies into clinical reality for atherosclerotic heart disease.

The antidepressant-like effect of resolvin E1 in repeated prednisolone-induced depression model mice

Resolvin E1 (RvE1) is an anti-inflammatory lipid mediator derived from eicosapentaenoic acid. We previously demonstrated that intracerebroventricular (i.c.v.) and intra-medial prefrontal cortex (mPFC) infusions of RvE1 produce antidepressant-like effects in a lipopolysaccharide-induced depression mouse model. To further confirm the antidepressant-like effect of RvE1, the present study examined whether RvE1 ameliorated depression-like behavior induced by repeated injections of prednisolone (PSL), a synthetic glucocorticoid, in male ICR mice. We first ascertained whether repeated subcutaneous treatment with PSL (50 mg/kg, once a day) affected locomotor activity and anxiety-like behavior in the open field test (OFT; after a 5-day PSL treatment) and induced depression-like behavior in the tail suspension test (TST; after a 6-day PSL treatment) and forced swim test (FST; after a 7-day PSL treatment). Repeated PSL injections significantly increased immobility in the FST, which was not ameliorated by acute desipramine treatment (30 mg/kg, i.p.), but not in the TST, without affecting locomotor activity and anxiety-like behavior in the OFT. Subsequently, we investigated the therapeutic effects of i.c.v. (1 ng) and intra-mPFC (50 pg/side) infusions of RvE1 in the repeated PSL-induced depression mouse model using the OFT and FST after 5- and 6-day PSL treatments, respectively. The repeated PSL-induced increase in immobility in the FST was significantly attenuated by both i.c.v. and intra-mPFC infusions of RvE1 without affecting the locomotor activity and anxiety-like behavior. In addition, a single i.c.v. infusion of RvE1 immediately before the first or fourth injection of PSL also attenuated PSL-induced depression-like behavior in the FST, suggesting the preventive effect of RvE1. These results indicate that RvE1 produces antidepressant-like effects in a mouse model of repeated PSL-induced depression.

E-series resolvin metabolome, biosynthesis and critical role of stereochemistry of specialized pro-resolving mediators (SPMs) in inflammation-resolution: Preparing SPMs for long COVID-19, human clinical trials, and targeted precision nutrition

The COVID-19 pandemic has raised international awareness of the importance of rigorous scientific evidence and the havoc caused by uncontrolled excessive inflammation. Here we consider the evidence on whether the specialized pro-resolving mediators (SPMs) are ready to meet this challenge as well as targeted metabololipidomics of the resolution-inflammation metabolomes. Specific stereochemical mechanisms in the biosynthesis of SPMs from omega-3 essential fatty acids give rise to unique local-acting lipid mediators. SPMs possess stereochemically defined potent bioactive structures that are high-affinity ligands for cognate G protein-coupled surface receptors that evoke the cellular responses required for efficient resolution of acute inflammation. The SPMs biosynthesized from the major omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are coined Resolvins (resolution phase interaction products; E series and D-series), Protectins and Maresins (macrophage mediators in resolving inflammation). Their biosynthesis and stereochemical assignments are established and confirmed (>1,441 resolvin publications in PubMed.gov) as well as their functional roles on innate immune cells and adaptive immune cells (both lymphocyte T-cell subsets and B-cells). The resolution of a protective acute inflammatory response is governed mainly by phagocytes that actively clear apoptotic cells, debris, blood clots and pathogens. These resolution phase functions of the acute inflammatory response are enhanced by SPMs, which together prepare the inflammatory loci for homeostasis and stimulate tissue regeneration via activating stem cells and the biosynthesis of novel cys-SPMs (e.g. MCTRs, PCTRs and RCTRs). These cys-SPMs also activate regeneration, are organ protective and stimulate resolution of local inflammation. Herein, we review the biosynthesis and functions of the E-series resolvins, namely resolvin E1 (the first n-3 resolvin identified), resolvin E2, resolvin E3 and resolvin E4 biosynthesized from their precursor eicosapentaenoic acid (EPA), and the critical role of total organic synthesis in confirming SPM complete stereochemistry, establishing their potent functions in resolution of inflammation, and novel structures. The physical properties of each biologically derived SPM, i.e., ultra-violet (UV) absorbance, chromatographic behavior, and tandem mass spectrometry (MS2) fragmentation, were matched to SPMs biosynthesized and prepared by stereospecific total organic synthesis. We briefly review this approach, also used with the endogenous D-series resolvins, protectins and maresins confirming their potent functions in resolution of inflammation, that paves the way for their rigorous evaluation in human tissues and clinical trials. The assignment of complete stereochemistry for each of the E and D series Resolvins, Protectins and Maresins was a critical and required step that enabled human clinical studies as in SPM profiling in COVID-19 infections and experimental animal disease models that also opened the promise of resolution physiology, resolution pharmacology and targeted precision nutrition as new areas for monitoring health and disease mechanisms.

Regulation of T-Cell Immune Responses by Pro-Resolving Lipid Mediators

Both the initiation and the resolution of inflammatory responses are governed by the sequential activation, migration, and control/suppression of immune cells at the site of injury. Bioactive lipids play a major role in the fine-tuning of this dynamic process in a timely manner. During inflammation and its resolution, polymorphonuclear cells (PMNs) and macrophages switch from producing pro-inflammatory prostaglandins and leukotrienes to specialized pro-resolving lipid mediators (SPMs), namely, lipoxins, resolvins, protectins, and maresins, which are operative at the local level to limit further inflammation and tissue injury and restore homeostasis. Accumulating evidences expand now the role and actions of these lipid mediators from innate to adaptive immunity. In particular, SPMs have been shown to contribute to the control of chronic inflammation, and alterations in their production and/or function have been associated with the persistence of several pathological conditions, including autoimmunity, in human and experimental models. In this review, we focus on the impact of pro-resolving lipids on T cells through their ability to modulate T-cell responses. In particular, the effects of the different families of SPMs to restrain effector T-cell functions while promoting regulatory T cells will be reviewed, along with the underlying mechanisms. Furthermore, the emerging concept of SPMs as new biological markers for disease diagnostic and progression and as putative therapeutic tools to regulate the development and magnitude of inflammatory and autoimmune diseases is discussed.

Specialized pro-resolving receptors are expressed in salivary glands with Sjögren's syndrome

Our previous studies demonstrated that resolvin D1 (RvD1) and its aspirin-trigged (AT) form AT-RvD1, are effective in decreasing inflammation while restoring saliva flow rates in a Sjögren's syndrome (SS)-like mouse model before and after disease onset. Resolvins are specialized pro-resolving mediators (SPM) that actively regulate inflammation. However, we only have extensive data within the salivary glands for RvD1 and AT-RvD1, both of which bind to the receptor ALX/FPR2. As such, the presence of other SPM receptors is unknown within salivary glands. Therefore, the goal of this study was to determine the expression of SPM receptors in non-SS and SS patients. For this purpose, six human minor salivary glands from female subjects were analyzed by H&E using the Chisholm and Mason classification to determine the degree of lymphocytic infiltration. Next, confocal immunofluorescence analysis was performed to determine the presence and distribution of different SPM receptors in mucous acini and striated ducts. We observed diffuse presence of lymphocytic infiltration and clinical data were consistent with SS diagnosis in three patients. Moreover, confocal immunofluorescence analysis indicated the presence of the receptors ALX/FPR2, BLT1 and CMKLR1 in the mucous acini and striated ducts of both non-SS and SS patients. GPR32 was absent in SS and non-SS minor salivary glands. In summary, our results showed that various SPM receptors are expressed in non-SS and SS minor salivary glands, all of which may pose as potential targets for promoting pro-epithelial and anti-inflammatory/pro-resolution signaling on SS patients.

Therapeutic potential of pro-resolving mediators in diabetic kidney disease

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

Resolution of inflammation: An organizing principle in biology and medicine

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

Specialized Proresolving Mediators for Therapeutic Interventions Targeting Metabolic and Inflammatory Disorders

Uncontrolled inflammation is considered the pathophysiological basis of many prevalent metabolic disorders, such as nonalcoholic fatty liver disease, diabetes, obesity, and neurodegenerative diseases. The inflammatory response is a self-limiting process that produces a superfamily of chemical mediators, called specialized proresolving mediators (SPMs). SPMs include the ω-3-derived family of molecules, such as resolvins, protectins, and maresins, as well as arachidonic acid-derived (ω-6) lipoxins that stimulate and promote resolution of inflammation, clearance of microbes, and alleviation of pain and promote tissue regeneration via novel mechanisms. SPMs function by binding and activating G protein-coupled receptors, such as FPR2/ALX, GPR32, and ERV1, and nuclear orphan receptors, such as RORα. Recently, several studies reported that SPMs have the potential to attenuate lipid metabolism disorders. However, the understanding of pharmacological aspects of SPMs, including tissue-specific biosynthesis, and specific SPM receptors and signaling pathways, is currently limited. Here, we summarize recent advances in the role of SPMs in resolution of inflammatory diseases with metabolic disorders, such as nonalcoholic fatty liver disease and obesity, obtained from preclinical animal studies. In addition, the known SPM receptors and their intracellular signaling are reviewed as targets of resolution of inflammation, and the currently available information on the therapeutic effects of major SPMs for metabolic disorders is summarized.

Specialized Pro-Resolving Mediators Mitigate Cancer-Related Inflammation: Role of Tumor-Associated Macrophages and Therapeutic Opportunities

Inflammation is a fundamental physiological response orchestrated by innate immune cells to restore tissue homeostasis. Specialized pro-resolving mediators (SPMs) are involved in active resolution of inflammation but when inflammation is incomplete, chronic inflammation creates a favorable environment that fuels carcinogenesis and cancer progression. Conventional cancer therapy also strengthens cancer-related inflammation by inducing massive tumor cell death that activate surrounding immune-infiltrating cells such as tumor-associated macrophages (TAMs). Macrophages are key actors of both inflammation and its active resolution due to their plastic phenotype. In line with this high plasticity, macrophages can be hijacked by cancer cells to support tumor progression and immune escape, or therapy resistance. Impaired resolution of cancer-associated inflammation supported by TAMs may thus reinforces tumor progression. From this perspective, recent evidence suggests that stimulating macrophage's pro-resolving functions using SPMs can promote inflammation resolution in cancer and improve anticancer treatments. Thus, TAMs' re-education toward an antitumor phenotype by using SPMs opens a new line of attack in cancer treatment. Here, we review SPMs' anticancer capacities with special attention regarding their effects on TAMs. We further discuss how this new therapeutic approach could be envisioned in cancer therapy.

μSPE followed by HPLC-MS/MS for the determination of series D and E resolvins in biological matrices

The critical role of acute inflammatory processes is recognized in many chronic diseases; a key point in molecular mechanisms of acute inflammation resolution is represented by a new group of pro-resolving lipid mediators that include distinct families of molecules: lipoxins, resolvins, protectins and maresins, collectively termed "specialized pro-resolving mediators" (SPMs). In particular, resolvins are active in the picogram to nanogram dose range, whereby they can directly modulate a plethora of anti-inflammatory responses. The presented method proposes an analytical protocol able to extract and to quantify 6 different resolvins from 3 different matrices (plasma, cells and exudates). The method, validated according to the EMA guideline for bioanalysis, exhibited good precision (1%-20%) and accuracy (2%-20%). In particular, the combination of two different sample preparation techniques, Liquid-Liquid Extraction (LLE) and micro-Solid Phase Extraction (μSPE), applied for the first on this class of molecules, used for the extraction and clean-up respectively, led to high enrichment factor (20 fold) and consequently a high sensitivity (LOQ between 1 and 38 pg mL^-1); moreover the validation data proved the versatility of μSPE as clean-up tool as it was capable to manage huge enrichment factor without negatively affect accuracy and precision of analysis.

Resolvins as potential candidates for the treatment of major depressive disorder

In contrast with the delayed onset of therapeutic responses and relatively low efficacy of currently available monoamine-based antidepressants, a single subanesthetic dose of ketamine, an N-methyl-D-aspartate receptor antagonist, produces rapid and sustained antidepressant actions even in patients with treatment-resistant depression. However, since the clinical use of ketamine as an antidepressant is limited owing to its adverse effects, such as psychotomimetic/dissociative effects and abuse potential, there is an unmet need for novel rapid-acting antidepressants with fewer side effects. Preclinical studies have revealed that the antidepressant actions of ketamine are mediated via the release of brain-derived neurotrophic factor and vascular endothelial growth factor, with the subsequent activation of mechanistic target of rapamycin complex 1 (mTORC1) in the medial prefrontal cortex. Recently, we demonstrated that resolvins (RvD1, RvD2, RvE1, RvE2 and RvE3), endogenous lipid mediators generated from n-3 polyunsaturated fatty acids (docosahexaenoic and eicosapentaenoic acids), exert antidepressant effects in a rodent model of depression, and that the antidepressant effects of RvD1, RvD2, and RvE1 necessitate mTORC1 activation. In this review, we first provide an overview of the mechanisms underlying the antidepressant effects of ketamine and other rapid-acting agents. We then discuss the possibility of using resolvins as novel therapeutic candidates for depression.

Omega-3 Polyunsaturated Fatty Acids: Versatile Roles in Blood Pressure Regulation

Significance: Hypertension is characterized as the imbalance of vasoconstriction and vasodilatation. Hypertension is influenced by genetic variation and environmental risk factors, such as unhealthy diet. Clinical trial results suggest that increasing intake of foods rich in n-3 polyunsaturated fatty acids (PUFAs) is beneficial for hypertension. Recent Advances: We summarized recent clinical trials regarding supplementation with n-3 PUFAs to reduce blood pressure (BP) in untreated hypertensive and normotensive subjects and systematically discussed the antihypertension mechanisms of n-3 PUFAs/n-3 oxylipins, including reducing oxidative stress, altering functions of membrane-related proteins, and competing with n-6 PUFAs/n-6 oxylipins in regulating vasodilator release. Critical Issues: Previous studies considered n-3 PUFAs as single molecules with beneficial roles in hypertension. Recently, researchers have paid more attention to the metabolism of n-3 PUFAs and explored molecular mechanisms of n-3 PUFAs and oxylipins derived from n-3 PUFAs in hypertension interventions. Future Directions: Based on the metabolism of n-3 PUFAs/n-3 oxylipins and mechanisms in BP control, we suggested that supplementation of n-3 PUFAs combined with agents targeting PUFA metabolism or the related signal pathways may amplify their effects to treat hypertension and other cardiovascular diseases. Antioxid. Redox Signal. 34, 800-810.

Stereoselective Synthesis and Structural Confirmation of the Specialized Pro-Resolving Mediator Resolvin E4

Herein, we report the stereoselective and convergent synthesis of resolvin E4, a newly identified specialized pro-resolving mediator. This synthesis proves the absolute configuration and exact olefin geometry. Key elements of the successful strategy include a highly stereoselective MacMillan organocatalytic oxyamination, a Midland Alpine borane reduction, and the use of a 1,4-pentadiyne unit as a linchpin building block. The application of reaction telescoping in several of the synthetic transformations enabled the preparation of the resolvin E4 methyl ester in 10% yield over 10 steps (longest linear sequence). The physical property (UV–Vis and LC–MS/MS) data of synthetic resolvin E4 matched those obtained from biologically produced material.

Synthesis of Resolvin E1 and Its Conformationally Restricted Cyclopropane Congeners with Potent Anti-Inflammatory Effect

RvE1 (1) is an endogenous lipid mediator with very potent anti-inflammatory activity, which is due to the inhibition of neutrophil chemotaxis and inflammatory cytokine production and the promotion of macrophage phagocytosis. On the basis of the conformational analysis of RvE1, we designed its four cyclopropane congeners (2a-d), in which the conformationally flexible terminal C1-C4 moiety of RvE1 was rigidified by introducing stereoisomeric cyclopropanes. The four congeners and also RvE1 were efficiently synthesized via a common synthetic route. The evaluation of the anti-inflammatory effects of the compounds in mice resulted in the identification of trans-β-CP-RvE1 (2d), which was significantly more active than RvE1, as a potential lead for anti-inflammatory drugs of a novel mechanism of action.

A New E-Series Resolvin: RvE4 Stereochemistry and Function in Efferocytosis of Inflammation-Resolution

The resolution of the acute inflammatory response is governed by phagocytes actively clearing apoptotic cells and pathogens. Biosynthesis of the specialized pro-resolving mediators (SPMs) is pivotal in the resolution of inflammation via their roles in innate immune cells. Resolvin E4 (RvE4: 5S,15S-dihydroxy-eicosapentaenoic acid) is a newly uncovered member of the E-series resolvins biosynthesized from eicosapentaenoic acid (EPA) recently elucidated in physiologic hypoxia. This new resolvin was termed RvE4 given its ability to increase efferocytosis of apoptotic cells by macrophages. Herein, we report on the total organic synthesis of RvE4 confirming its unique structure, complete stereochemistry assignment and function. This synthetic RvE4 matched the physical properties of biogenic RvE4 material, i.e. ultra-violet (UV) absorbance, chromatographic behavior, and tandem mass spectrometry (MS²) fragmentation, as well as bioactivity. We confirmed RvE4 potent responses with human M2 macrophage efferocytosis of human apoptotic neutrophils and senescent red blood cells. Together, these results provide direct evidence for the assignment of the complete stereochemistry of RvE4 as 5S,15S-dihydroxy-6E,8Z,11Z,13E,17Z-eicosapentaenoic acid and its bioactions in human phagocyte response.

Pro-resolving lipid mediators: regulators of inflammation, metabolism and kidney function

Obesity, diabetes mellitus, hypertension and cardiovascular disease are risk factors for chronic kidney disease (CKD) and kidney failure. Chronic, low-grade inflammation is recognized as a major pathogenic mechanism that underlies the association between CKD and obesity, impaired glucose tolerance, insulin resistance and diabetes, through interaction between resident and/or circulating immune cells with parenchymal cells. Thus, considerable interest exists in approaches that target inflammation as a strategy to manage CKD. The initial phase of the inflammatory response to injury or metabolic dysfunction reflects the release of pro-inflammatory mediators including peptides, lipids and cytokines, and the recruitment of leukocytes. In self-limiting inflammation, the evolving inflammatory response is coupled to distinct processes that promote the resolution of inflammation and restore homeostasis. The discovery of endogenously generated lipid mediators - specialized pro-resolving lipid mediators and branched fatty acid esters of hydroxy fatty acids - which promote the resolution of inflammation and attenuate the microvascular and macrovascular complications of obesity and diabetes mellitus highlights novel opportunities for potential therapeutic intervention through the targeting of pro-resolution, rather than anti-inflammatory pathways.

Spinal neuronal excitability and neuroinflammation in a model of chemotherapeutic neuropathic pain: targeting the resolution pathways

Background

Neuroinflammation is a critical feature of sensitisation of spinal nociceptive processing in chronic pain states. We hypothesised that the resolvin pathways, a unique endogenous control system, may ameliorate aberrant spinal processing of somatosensory inputs associated with chemotherapy-induced neuropathic pain (CINP).

Method

The paclitaxel (PCX) model of CINP was established in male Sprague-Dawley rats and compared to control rats (n = 23 and 22, respectively). Behavioural pain responses were measured, and either single unit electrophysiological recordings of dorsal horn wide dynamic range (WDR) neurones were performed, or mRNA microarray analysis of the dorsal horn of the spinal cord was undertaken.

Results

PCX rats exhibited significant changes in behavioural responses to mechanical and cold stimuli. A higher proportion of WDR neurones in PCX rats were polymodal (generating post-discharge following a non-noxious mechanical stimulus, responding to non-noxious cold and exhibiting spontaneous activity) compared to control (p < 0.05). Microarray analysis revealed changes in proinflammatory pathways (Tlr, Tnfrsf1a, Nlrp1a, Cxcr1, Cxcr5, Ccr1, Cx3cr1) and anti-inflammatory lipid resolvin pathways (Alox5ap, Cyp2j4 and Ptgr1) compared to control (p < 0.05). Ingenuity pathway analysis predicted changes in glutamatergic and astrocyte signaling in the PCX group. Activation of the resolvin system via the spinal administration of aspirin-triggered resolvin D1 (AT-RvD1) markedly inhibited (73 ± 7% inhibition) normally non-noxious mechanically (8 g) evoked responses of WDR neurones only in PCX rats, whilst leaving responses to noxious mechanically induced stimuli intact. Inhibitory effects of AT-RvD1were comparable in magnitude to spinal morphine (84 ± 4% inhibition).

Conclusion

The PCX model of CINP was associated with mechanical allodynia, altered neuronal responses and dysregulation of pro- and anti-inflammatory signalling in the spinal dorsal horn. The resolvin AT-RvD1 selectively inhibited low weight mechanical-evoked responses of WDR neurones in PCX rats, but not in controls. Our data support the targeting of spinal neuroinflammation via the activation of the resolvin system as a new therapeutic approach for CINP.

A unique radioprotective effect of resolvin E1 reduces irradiation-induced damage to the inner ear by inhibiting the inflammatory response

Background

In addition to the direct effects of irradiation, the induced inflammatory response may play an important role in the damage to the inner ear caused by radiotherapy for the treatment of head and neck cancers. Resolvin E1 (RvE1) has anti-inflammatory activity, acting by reducing neutrophil infiltration and proinflammatory cytokine expression. Therefore, in this study we sought to confirm whether the inflammation induced by irradiation was involved in damage to the inner ear after radiotherapy and to investigate the protective effect and underlying mechanism of RvE1 using mouse models.

Methods

A dose of RvE1 was delivered by intraperitoneal injection to mice before irradiation. Changes in the auditory brainstem response (ABR), relative balance ability, inner ear morphology and the expression levels of inflammatory factors in the inner ear were analyzed on days 7 and 14 after irradiation and compared among different experimental groups.

Results

Changes of ABR and relative balance ability showed the inner functions of experimental mice presented severe damage after irradiation, but the damage was significantly alleviated after RvE1 pretreatment compared to irradiation alone. Morphological analysis of the inner ear showed severe damage to the cochlea and vestibule after irradiation. In contrast, damage to the cochlea and vestibule was significantly reduced in the RvE1-pretreated group compared to that in the irradiation alone group. Along with these functional and morphological changes, the mRNA expression level of anti-inflammatory factors interleukin-2 was significantly increased, while those of proinflammatory factors interleukin-6 and tumor necrosis factor-α were significantly decreased in the inner ear of mice after RvE1 pretreatment compared to irradiation alone.

Conclusions

We believe that inflammation induced by irradiation is involved in the damage to the inner ear caused by radiotherapy, and that RvE1 reduces the damage caused by irradiation to the inner ear by regulating the induced inflammatory response.

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.

The Role of Specialized Pro-Resolving Mediators in Cystic Fibrosis Airways Disease

Cystic Fibrosis (CF) is a recessive genetic disease due to mutations of the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene encoding the CFTR chloride channel. The ion transport abnormalities related to CFTR mutation generate a dehydrated airway surface liquid (ASL) layer, which is responsible for an altered mucociliary clearance, favors infections and persistent inflammation that lead to progressive lung destruction and respiratory failure. The inflammatory response is normally followed by an active resolution phase to return to tissue homeostasis, which involves specialized pro-resolving mediators (SPMs). SPMs promote resolution of inflammation, clearance of microbes, tissue regeneration and reduce pain, but do not evoke unwanted immunosuppression. The airways of CF patients showed a decreased production of SPMs even in the absence of pathogens. SPMs levels in the airway correlated with CF patients' lung function. The prognosis for CF has greatly improved but there remains a critical need for more effective treatments that prevent excessive inflammation, lung damage, and declining pulmonary function for all CF patients. This review aims to highlight the recent understanding of CF airway inflammation and the possible impact of SPMs on functions that are altered in CF airways.

Neuromodulation, Specialized Proresolving Mediators, and Resolution of Pain

The current crises in opioid abuse and chronic pain call for the development of nonopioid and nonpharmacological therapeutics for pain relief. Neuromodulation-based approaches, such as spinal cord stimulation, dorsal root ganglion simulation, and nerve stimulation including vagus nerve stimulation, have shown efficacy in achieving pain control in preclinical and clinical studies. However, the mechanisms by which neuromodulation alleviates pain are not fully understood. Accumulating evidence suggests that neuromodulation regulates inflammation and neuroinflammation-a localized inflammation in peripheral nerves, dorsal root ganglia/trigeminal ganglia, and spinal cord/brain-through neuro-immune interactions. Specialized proresolving mediators (SPMs) such as resolvins, protectins, maresins, and lipoxins are lipid molecules produced during the resolution phase of inflammation and exhibit multiple beneficial effects in resolving inflammation in various animal models. Recent studies suggest that SPMs inhibit inflammatory pain, postoperative pain, neuropathic pain, and cancer pain in rodent models via immune, glial, and neuronal modulations. It is noteworthy that sham surgery is sufficient to elevate resolvin levels and may serve as a model of resolution. Interestingly, it has been shown that the vagus nerve produces SPMs and vagus nerve stimulation (VNS) induces SPM production in vitro. In this review, we discuss how neuromodulation such as VNS controls pain via immunomodulation and neuro-immune interactions and highlight possible involvement of SPMs. In particular, we demonstrate that VNS via auricular electroacupuncture effectively attenuates chemotherapy-induced neuropathic pain. Furthermore, auricular stimulation is able to increase resolvin levels in mice. Thus, we propose that neuromodulation may control pain and inflammation/neuroinflammatioin via SPMs. Finally, we discuss key questions that remain unanswered in our understanding of how neuromodulation-based therapies provide short-term and long-term pain relief.

Molecular Dynamics Simulations Provide Insight into the Loading Efficiency of Proresolving Lipid Mediators Resolvin D1 and D2 in Cell Membrane-Derived Nanovesicles

Resolvins D1 and D2 (RvDs) are structural isomers and metabolites of docosahexaenoic acid, an omega-3 fatty acid, enzymatically produced in our body in response to acute inflammation or microbial invasion. Resolvins have been shown to play an essential role in the resolution of inflammation, tissue repair, and return to homeostasis and thus are actively pursued as potential therapeutics in treating inflammatory disorders and infectious diseases. However, effective in vivo delivery of RvDs continues to be a challenging task. Recent studies demonstrated that RvD1 or RvD2 loaded in cell membrane-derived nanovesicles significantly increased therapeutic efficacy in treating murine peritonitis and ischemic stroke, respectively. The mechanistic details of how the subtle structural difference between RvD1 and RvD2 alters their molecular interactions with the membrane lipids of the nanovesicles and thus affects the loading efficiency remain unknown. Here, we report the encapsulation profiles of the neutral and ionized species of both RvD1 and RvD2 determined with the cell membrane-derived nanovesicles at pH values 5.4 and 7.4, respectively. Also, we performed microsecond time-scale all-atom molecular dynamics (MD) simulations in explicit water to elucidate the molecular interactions of both neutral and ionized species of RvD1 and RvD2 with the lipid bilayer using a model membrane system, containing 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and cholesterol. We found that the differences in the position and chirality of hydroxyl groups in RvD1 and RvD2 affected their location, orientation, and conformations within the bilayer. Surprisingly, the deprotonation of their carboxyl group caused their orientation and conformation to change from a fully extended one that is oriented in parallel to the membrane plane to a J-shaped bent conformation that is oriented perpendicular to the bilayer plane. Our studies offer valuable insight into the molecular interactions of RvD1/D2 with the lipid bilayer in atomistic details and provide a mechanistic explanation for the observed differences in the encapsulation profiles of RvD1 and RvD2, which may facilitate the rational design of nanovesicle-based therapeutics for treating inflammatory diseases.

Therapeutic potentials and modulatory mechanisms of fatty acids in bone

Bone metabolism is a lifelong process that includes bone formation and resorption. Osteoblasts and osteoclasts are the predominant cell types associated with bone metabolism, which is facilitated by other cells such as bone marrow mesenchymal stem cells (BMMSCs), osteocytes and chondrocytes. As an important component in our daily diet, fatty acids are mainly categorized as long-chain fatty acids including polyunsaturated fatty acids (LCPUFAs), monounsaturated fatty acids (LCMUFAs), saturated fatty acids (LCSFAs), medium-/short-chain fatty acids (MCFAs/SCFAs) as well as their metabolites. Fatty acids are closely associated with bone metabolism and associated bone disorders. In this review, we summarized the important roles and potential therapeutic implications of fatty acids in multiple bone disorders, reviewed the diverse range of critical effects displayed by fatty acids on bone metabolism, and elucidated their modulatory roles and mechanisms on specific bone cell types. The evidence supporting close implications of fatty acids in bone metabolism and disorders suggests fatty acids as potential therapeutic and nutritional agents for the treatment and prevention of metabolic bone diseases.

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

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

Specialized pro-resolving mediators in diabetes: novel therapeutic strategies

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

Rapid Metabolization of Protectin D1 by β-Oxidation of Its Polar Head Chain

Protectin D1 [neuroprotectin D1 (NPD1), PD1] has been proposed to play a key role in the resolution of inflammation. Aside from its ω-monohydroxylated metabolite, little has been reported on its metabolic fate. Upon NPD1 incubation in HepG2 cells, liquid chromatography-tandem mass spectrometry (LC-MS/MS) revealed the formation of two main metabolites, identified as 2,3-dinor-NPD1 and 2,3,4,5-tetranor-NPD1 by comparison with standards obtained through demanding total chemical syntheses. These data represent the first evidence of β-oxidation occurring in specialized proresolving mediators and show that the biotransformation of NPD1 by human hepatoma cells is extremely rapid and faster than that of leukotriene (LTE₄). Unlike LTE₄, the main metabolic process occurs from the polar head chain of NPD1. It may limit NPD1 systemic circulation and prevent its urinary excretion, making difficult its detection and quantitation in vivo. Interestingly, tetranor-NPD1, but not dinor-NPD1, maintained the bioactivity of the parent NPD1, inhibiting neutrophil chemotaxis in vitro and neutrophil tissue infiltration in vivo.

Effect of omega-3 fatty acid supplementation on resolvin (RvE1)-mediated suppression of inflammation in a mouse model of asthma

Objective: ResolvinE1 (RvE1), an endogenous lipid mediator derived from omega 3 fatty acids contributes to resolution of allergic inflammatory responses. We investigated effects of RvE1 (R) and omega 3 fatty acids (O) on airway reactivity and inflammation using allergic mice. Methods: Mice were divided into control (nonasthmatic; CON) and allergen sensitized-challenged (asthmatic; SEN) groups, and were sensitized i.p. on days 1, 6 with 0.2 μg ovalbumin (OVA) followed by 5% OVA aerosol challenges on days 11-13. RvE1 was administered i.p. postallergen challenge, while omega 3 fatty acids (fish oil) were administered via oral gavage once daily (days 1-13). Whole body plethysmography and bronchoalveolar lavage (BAL) studies were performed on day 14. Results: RvE1 attenuated airway responsiveness to methacholine (48 mg/ml) in treated asthmatic mice vs. nontreated (150 ± 27.88% in SEN vs. 54 ± 7.52% in SEN + R, p < .05). No difference was observed with omega-3 supplementation (115 ± 19.28% in SEN + O) or treatment with both RvE1 and omega 3 fatty acids (39 ± 12.37% in SEN + R + O vs. 54 ± 7.52% in SEN + R). Differential BAL cell analysis showed that RvE1 decreased eosinophils and neutrophils in SEN mice (p < .005) while no difference was observed with omega-3 fatty acids. SEN + R + O group had similar results as RvE1 treated mice, suggesting that only RvE1 attenuated inflammation. Conclusions: RvE1 attenuated airway responsiveness and inflammation in asthmatic mice. Omega-3 fatty acids, although a precursor for RvE1 formation, had no additive effects on RvE1 decreases in airway inflammation and airway reactivity. Our data suggests that omega-3 supplementation has little effect on airway inflammation and reactivity in our model of asthma.

Identification of specialized pro-resolving mediator clusters from healthy adults after intravenous low-dose endotoxin and omega-3 supplementation: a methodological validation

Specialized pro-resolving mediator(s) (SPMs) are produced from the endogenous ω-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and accelerate resolution of acute inflammation. We identified specific clusters of SPM in human plasma and serum using LC-MS/MS based lipid mediator (LM) metabololipidomics in two separate laboratories for inter-laboratory validation. The human plasma cluster consisted of resolvin (Rv)E1, RvD1, lipoxin (LX)B₄, 18-HEPE, and 17-HDHA, and the human serum cluster consisted of RvE1, RvD1, AT-LXA₄, 18-HEPE, and 17-HDHA. Human plasma and serum SPM clusters were increased after ω-3 supplementation (triglyceride dietary supplements or prescription ethyl esters) and low dose intravenous lipopolysaccharide (LPS) challenge. These results were corroborated by parallel determinations with the same coded samples in a second, separate laboratory using essentially identical metabololipidomic operational parameters. In these healthy subjects, two ω-3 supplementation protocols (Study A and Study B) temporally increased the SPM cluster throughout the endotoxin-challenge time course. Study A and Study B were randomized and Study B also had a crossover design with placebo and endotoxin challenge. Endotoxin challenge temporally regulated lipid mediator production in human serum, where pro-inflammatory eicosanoid (prostaglandins and thromboxane) concentrations peaked by 8 hours post-endotoxin and SPMs such as resolvins and lipoxins initially decreased by 2 h and were then elevated at 24 hours. In healthy adults given ω-3 supplementation, the plasma concentration of the SPM cluster (RvE1, RvD1, LXB₄, 18-HEPE, and 17-HDHA) peaked at two hours post endotoxin challenge. These results from two separate laboratories with the same samples provide evidence for temporal production of specific pro-resolving mediators with ω-3 supplementation that together support the role of SPM in vivo in inflammation-resolution in humans.

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

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

Immunoresolvents in asthma and allergic diseases: Review and update

Asthma and allergic diseases are inflammatory conditions developed by excessive reaction of the immune system against normally harmless environmental substances. Although acute inflammation is necessary to eradicate the damaging agents, shifting to chronic inflammation can be potentially detrimental. Essential fatty-acids-derived immunoresolvents, namely, lipoxins, resolvins, protectins, and maresins, are anti-inflammatory compounds that are believed to have protective and beneficial effects in inflammatory disorders, including asthma and allergies. Accordingly, impaired biosynthesis and defective production of immunoresolvents could be involved in the development of chronic inflammation. In this review, recent evidence on the anti-inflam]matory effects of immunoresolvents, their enzymatic biosynthesis routes, as well as their receptors are discussed.