Intestinal microbe-dependent ω3 lipid metabolite αKetoA prevents inflammatory diseases in mice and cynomolgus macaques

The omega-3 postbiotic trans-10-cis-15-octadecadienoic acid attenuates contact hypersensitivity in mice through downregulation of vascular endothelial growth factor A

Intestinal bacteria metabolize dietary substances to produce bioactive postbiotics, among which some are recognized for their role in promoting host health. We here explored the postbiotic potential of two omega-3 α-linolenic acid-derived metabolites: trans-10-cis-15-octadecadienoic acid (t10,c15-18:2) and cis-9-cis-15-octadecadienoic acid (c9,c15-18:2). Dietary intake of lipids rich in omega-3 α-linolenic acid elevated levels of t10,c15-18:2 and c9,c15-18:2 in the serum and feces of mice, an effect dependent on the presence of intestinal bacteria. Notably, t10,c15-18:2 mitigated skin inflammation in mice that became hypersensitive after exposure to 2,4-dinitrofluorobenzene, an experimental model for allergic contact dermatitis. In particular, t10,c15-18:2-but not c9,c15-18:2-attenuated ear swelling and edema, characteristic symptoms of contact hypersensitivity. The anti-inflammatory effects of t10,c15-18:2 were due to its ability to suppress the release of vascular endothelial growth factor A from keratinocytes, thereby mitigating the enhanced vascular permeability induced by hapten stimulation. Our study identified retinoid X receptor as a functional receptor that mediates the downregulation of skin inflammation upon treatment with t10,c15-18:2. Our results suggest that t10,c15-18:2 holds promise as an omega-3 fatty acid-derived postbiotic with potential therapeutic implications for alleviating the skin edema seen in allergic contact dermatitis-induced inflammation.

Lactobacillus johnsonii N6.2 phospholipids induce immature-like dendritic cells with a migratory-regulatory-like transcriptional signature

Shifts in the gut microbiota composition, called dysbiosis, have been directly associated with acute and chronic diseases. However, the underlying biological systems connecting gut dysbiosis to systemic inflammatory pathologies are not well understood. Phospholipids (PLs) act as precursors of both, bioactive inflammatory and resolving mediators. Their dysregulation is associated with chronic diseases including cancer. Gut microbial-derived lipids are structurally unique and capable of modulating host's immunity. Lactobacillus johnsonii N6.2 is a Gram-positive gut symbiont with probiotic characteristics. L. johnsonii N6.2 reduces the incidence of autoimmunity in animal models of Type 1 Diabetes and improves general wellness in healthy volunteers by promoting, in part, local and systemic anti-inflammatory responses. By utilizing bioassay-guided fractionation methods with bone marrow-derived dendritic cells (BMDCs), we report here that L. johnsonii N6.2 purified lipids induce a transcriptional signature that resembles that of migratory (mig) DCs. RNAseq-based analysis showed that BMDCs stimulated with L. johnsonii N6.2 total lipids upregulate maturation-mig related genes Cd86, Cd40, Ccr7, Icam1 along with immunoregulatory genes including Itgb8, Nfkbiz, Jag1, Adora2a, IL2ra, Arg1, and Cd274. Quantitative reverse transcription (qRT)-PCR analysis indicated that PLs are the bioactive lipids triggering the BMDCs response. Antibody-blocking of surface Toll-like receptor (TLR)2 resulted in boosted PL-mediated upregulation of pro-inflammatory Il6. Chemical inhibition of the IKKα kinase from the non-canonical NF-κB pathway specifically restricted upregulation of Il6 and Tnf. Phenotypically, PL-stimulated BMDCs displayed an immature like-phenotype with significantly increased surface ICAM-1. This study provides insight into the immunoregulatory capacity of Gram-positive, gut microbial-derived phospholipids on innate immune responses.

Oral-gut axis as a novel biological mechanism linking periodontal disease and systemic diseases: A review

Substantial evidence suggests that periodontal disease increases the risk of developing and progressing extraoral manifestations such as diabetes, atherosclerosis, rheumatoid arthritis, and inflammatory bowel disease. The most probable causative mechanism behind this is the influx of bacteria and/or bacterial products (endotoxin) and inflammatory cytokines into the systemic circulation originating from inflamed periodontal tissues. However, recent studies have revealed that oral bacteria, especially periodontopathic bacteria, play a role in inducing dysbiosis of the gut microbiota resulting induction of gut dysbiosis-related pathology associated with systemic diseases. Conversely, the disruption of gut microbiota has been shown to have a negative impact on the pathogenesis of periodontal disease. Based on our study findings and the available literature, this review presents an overview of the relationship between periodontal disease and systemic health, highlighting the mouth-gut connection.

Exploring the roles of prostanoids, leukotriens, and dietary fatty acids in cutaneous inflammatory diseases: Insights from pharmacological and genetic approaches

Prostanoids and leukotrienes (LTs) are representative of ω6 fatty acid-derived metabolites that exert their actions through specific receptors on the cell surface. These lipid mediators, being unstable in vivo, act locally at their production sites; thus, their physiological functions remain unclear. However, recent pharmacological and genetic approaches using experimental murine models have provided significant insights into the roles of these lipid mediators in various pathophysiological conditions, including cutaneous inflammatory diseases. These lipid mediators act not only through signaling by themselves but also by potentiating the signaling of other chemical mediators, such as cytokines and chemokines. For instance, prostaglandin E2 -EP4 and LTB4 -BLT1 signaling on cutaneous dendritic cells substantially facilitate their chemokine-induced migration ability into the skin and play critical roles in the priming and/or activation of antigen-specific effector T cells in the skin. In addition to these ω6 fatty acid-derived metabolites, various ω3 fatty acid-derived metabolites regulate skin immune cell functions, and some exert potent anti-inflammatory functions. Lipid mediators act as modulators of cutaneous immune responses, and manipulating the signaling from lipid mediators has the potential as a novel therapeutic approach for human skin diseases.

Induction of unique macrophage subset by simultaneous stimulation with LPS and IL-4

Macrophages manifest as various subtypes that play diverse and important roles in immunosurveillance and the maintenance of immunological homeostasis in various tissues. Many in vitro studies divide macrophages into two broad groups: M1 macrophages induced by lipopolysaccharide (LPS), and M2 macrophages induced by interleukin 4 (IL-4). However, considering the complex and diverse microenvironment in vivo, the concept of M1 and M2 is not enough to explain diversity of macrophages. In this study, we analyzed the functions of macrophages induced by simultaneous stimulation with LPS and IL-4 (termed LPS/IL-4-induced macrophages). LPS/IL-4-induced macrophages were a homogeneous population showing a mixture of the characteristics of M1 and M2 macrophages. In LPS/IL-4-induced macrophages, expression of cell-surface M1 markers (I-Ab) was higher than in M1 macrophages, but lower expression of iNOS, and expression of M1-associated genes (Tnfα and Il12p40) were decreased in comparison to expression in M1 macrophages. Conversely, expression of the cell-surface M2 marker CD206 was lower on LPS/IL-4-induced macrophages than on M2 macrophages and expression of M2-associated genes (Arg1, Chi3l3, and Fizz1) varied, with Arg1 being greater than, Fizz1 being lower than, and Chi3l3 being comparable to that in M2 macrophages. Glycolysis-dependent phagocytic activity of LPS/IL-4-induced macrophages was strongly enhanced as was that of M1 macrophages; however, the energy metabolism of LPS/IL-4-induced macrophages, such as activation state of glycolytic and oxidative phosphorylation, was quite different from that of M1 or M2 macrophages. These results indicate that the macrophages induced by LPS and IL-4 had unique properties.

Current insights into skin lipids and their roles in cutaneous health and disease

PURPOSE OF REVIEW

The unique and complex array of cutaneous lipids include essential components of the skin structure and signalling molecules mediating homeostasis and inflammation. Understanding skin lipid biology and metabolism can support our comprehension of health and disease, including systemic conditions with cutaneous involvement.

RECENT FINDINGS

Lipids found on the skin surface, produced by both the host and resident microbes, maintain and regulate the skin microbiome and the epidermal barrier, whilst altered contributions from either source can be detrimental to skin health. The unique lipid composition of the epidermal barrier is essential for its function, and recent studies have expanded our understanding of epidermal ceramide production. This has been supported by improved models available for skin research, including organotypic skin models enabling in-vitro production of complex acylceramides for the first time, and model systems facilitating in-silico exploration of the lipid profile changes observed in clinical samples. Studies have revealed further involvement of lipid mediators such as eicosanoids in cutaneous inflammation, as well as immune regulation in both healthy and diseased skin.

SUMMARY

Skin lipids offer exciting opportunities as therapeutic targets for many conditions, whether through topical interventions or nutritional supplementation.

Mead acid inhibits retinol-induced irritant contact dermatitis via peroxisome proliferator-activated receptor alpha

Retinol is widely used in topical skincare products to ameliorate skin aging and treat acne and wrinkles; however, retinol and its derivatives occasionally have adverse side effects, including the induction of irritant contact dermatitis. Previously, we reported that mead acid (5,8,11-eicosatrienoic acid), an oleic acid metabolite, ameliorated skin inflammation in dinitrofluorobenzene-induced allergic contact hypersensitivity by inhibiting neutrophil infiltration and leukotriene B₄ production by neutrophils. Here, we showed that mead acid also suppresses retinol-induced irritant contact dermatitis. In a murine model, we revealed that mead acid inhibited keratinocyte abnormalities such as keratinocyte hyperproliferation. Consistently, mead acid inhibited p38 MAPK (mitogen-activated protein kinase) phosphorylation, which is an essential signaling pathway in the keratinocyte hyperplasia induced by retinol. These inhibitory effects of mead acid were associated with the prevention of both keratinocyte hyperproliferation and the gene expression of neutrophil chemoattractants, including Cxcl1 and Cxcl2, and they were mediated by a PPAR (peroxisome proliferator-activated receptor)-α pathway. Our findings identified the anti-inflammatory effects of mead acid, the use of which can be expected to minimize the risk of adverse side effects associated with topical retinoid application.

The metabolic nature of inflammatory bowel diseases

Crohn's disease and ulcerative colitis, phenotypically comprising a spectrum of inflammatory bowel diseases (IBDs), spread globally during the westernization of lifestyle and dietary habits over the past few decades. Here, we review experimental and clinical evidence for the metabolic nature of gut inflammation in IBD and delineate distinct parallels to the inflammatory state in metabolic diseases. Experimental evidence indicates that excessive intake of specific macronutrients in a Western diet fuels an inflammatory response in the gut by exploiting sensors of innate immunity and perturbation of gut microbial metabolism. Genetic IBD risk partly affects metabolism and stress signalling of innate immunity, and immunometabolism controls susceptibility to gut inflammation. Epidemiological and clinical studies indicate that specific nutrients in the Western diet pose a risk for the development of IBD and a poor disease course. Translational studies in IBD indicate perturbation of energy metabolism in immune cells and perturbation of gut microbial metabolism, which can be shaped by diet. In turn, dietary restriction by exclusive enteral nutrition induces remission in patients with IBD. Collectively, these studies support a metabolic underpinning of gut inflammation in IBD as described for metabolic inflammation in obesity and related disorders.

The PPARα Regulation of the Gut Physiology in Regard to Interaction with Microbiota, Intestinal Immunity, Metabolism, and Permeability

Peroxisome proliferator-activated receptor alpha (PPARα) is expressed throughout the mammalian gut: in epithelial cells, in the villi of enterocytes and in Paneth cells of intestinal crypts, as well as in some immune cells (e.g., lamina propria macrophages, dendritic cells) of the mucosa. This review examines the reciprocal interaction between PPARα activation and intestinal microbiota. We refer to the published data confirming that microbiota products can influence PPARα signaling and, on the other hand, PPARα activation is able to affect microbiota profile, viability, and diversity. PPARα impact on the broad spectrum of events connected to metabolism, signaling (e.g., NO production), immunological tolerance to dietary antigens, immunity and permeability of the gut are also discussed. We believe that the phenomena described here play a prominent role in gut homeostasis. Therefore, in conclusion we propose future directions for research, including the application of synthetic activators and natural endogenous ligands of PPARα (i.e., endocannabinoids) as therapeutics for intestinal pathologies and systemic diseases assumed to be related to gut dysbiosis.

Macrophages-microenvironment crosstalk in fibrostenotic inflammatory bowel disease: from basic mechanisms to clinical applications

INTRODUCTION

Intestinal fibrosis is a common complication of Inflammatory Bowel Disease (IBD) with no available drugs. The current therapeutic principle is surgical intervention as the core. Intestinal macrophages contribute to both the progression of inflammation and fibrosis. Understanding the role of macrophages in the intestinal microenvironment could bring new hope for fibrosis prevention or even reversal.

AREAS COVERED

This article reviewed the most relevant reports on macrophage in the field of intestinal fibrosis. The authors discussed current opinions about how intestinal macrophages function and interact with surrounding mediators during inflammation resolution and fibrostenotic IBD. Based on biological mechanisms findings, authors summarized related clinical trial outcomes.

EXPERT OPINION

The plasticity of intestinal macrophages allows them to undergo dramatic alterations in their phenotypes or functions when exposed to gastrointestinal environmental stimuli. They exhibit distinct metabolic characteristics, secrete various cytokines, express unique surface markers, and transmit different signals. Nevertheless, the specific mechanism through which the intestinal macrophages contribute to intestinal fibrosis remains unclear. It should further elucidate a novel therapeutic approach by targeting macrophages, especially distinct mechanisms in specific subgroups of macrophages involved in the progression of fibrogenesis in IBD.

Lactic acid bacteria-derived γ-linolenic acid metabolites are PPARδ ligands that reduce lipid accumulation in human intestinal organoids

Gut microbiota regulate physiological functions in various hosts, such as energy metabolism and immunity. Lactic acid bacteria, including Lactobacillus plantarum, have a specific polyunsaturated fatty acid saturation metabolism that generates multiple fatty acid species, such as hydroxy fatty acids, oxo fatty acids, conjugated fatty acids, and trans-fatty acids. How these bacterial metabolites impact host physiology is not fully understood. Here, we investigated the ligand activity of lactic acid bacteria–produced fatty acids in relation to nuclear hormone receptors expressed in the small intestine. Our reporter assays revealed two bacterial metabolites of γ-linolenic acid (GLA), 13-hydroxy-cis-6,cis-9-octadecadienoic acid (γHYD), and 13-oxo-cis-6,cis-9-octadecadienoic acid (γKetoD) activated peroxisome proliferator-activated receptor delta (PPARδ) more potently than GLA. We demonstrate that both γHYD and γKetoD bound directly to the ligand-binding domain of human PPARδ. A docking simulation indicated that four polar residues (T289, H323, H449, and Y473) of PPARδ donate hydrogen bonds to these fatty acids. Interestingly, T289 does not donate a hydrogen bond to GLA, suggesting that bacterial modification of GLA introducing hydroxy and oxo group determines ligand selectivity. In human intestinal organoids, we determined γHYD and γKetoD increased the expression of PPARδ target genes, enhanced fatty acid β-oxidation, and reduced intracellular triglyceride accumulation. These findings suggest that γHYD and γKetoD, which gut lactic acid bacteria could generate, are naturally occurring PPARδ ligands in the intestinal tract and may improve lipid metabolism in the human intestine.

Oral administration of Blautia wexlerae ameliorates obesity and type 2 diabetes via metabolic remodeling of the gut microbiota

The gut microbiome is an important determinant in various diseases. Here we perform a cross-sectional study of Japanese adults and identify the Blautia genus, especially B. wexlerae, as a commensal bacterium that is inversely correlated with obesity and type 2 diabetes mellitus. Oral administration of B. wexlerae to mice induce metabolic changes and anti-inflammatory effects that decrease both high-fat diet–induced obesity and diabetes. The beneficial effects of B. wexlerae are correlated with unique amino-acid metabolism to produce S-adenosylmethionine, acetylcholine, and l-ornithine and carbohydrate metabolism resulting in the accumulation of amylopectin and production of succinate, lactate, and acetate, with simultaneous modification of the gut bacterial composition. These findings reveal unique regulatory pathways of host and microbial metabolism that may provide novel strategies in preventive and therapeutic approaches for metabolic disorders.

Here, the authors inversely associate Blautia wexlerae with obesity and type 2 diabetes mellitus in humans and further show that administration of B. wexlerae to mice decrease both high-fat diet–induced obesity and diabetes via modulating gut microbial metabolism.

Gamma-Linolenic Acid (GLA) Protects against Ionizing Radiation-Induced Damage: An In Vitro and In Vivo Study

Radiation is pro-inflammatory in nature in view of its ability to induce the generation of reactive oxygen species (ROS), cytokines, chemokines, and growth factors with associated inflammatory cells. Cells are efficient in repairing radiation-induced DNA damage; however, exactly how this happens is not clear. In the present study, GLA reduced DNA damage (as evidenced by micronuclei formation) and enhanced metabolic viability, which led to an increase in the number of surviving RAW 264.7 cells in vitro by reducing ROS generation, and restoring the activities of desaturases, COX-1, COX-2, and 5-LOX enzymes, TNF-α/TGF-β, NF-kB/IkB, and Bcl-2/Bax ratios, and iNOS, AIM-2, and caspases 1 and 3, to near normal. These in vitro beneficial actions were confirmed by in vivo studies, which revealed that the survival of female C57BL/6J mice exposed to lethal radiation (survival~20%) is significantly enhanced (to ~80%) by GLA treatment by restoring altered levels of duodenal HMGB1, IL-6, TNF-α, and IL-10 concentrations, as well as the expression of NF-kB, IkB, Bcl-2, Bax, delta-6-desaturase, COX-2, and 5-LOX genes, and pro- and anti-oxidant enzymes (SOD, catalase, glutathione), to near normal. These in vitro and in vivo studies suggest that GLA protects cells/tissues from lethal doses of radiation by producing appropriate changes in inflammation and its resolution in a timely fashion.

Diet-Microbiota Interplay: An Emerging Player in Macrophage Plasticity and Intestinal Health

Inflammatory bowel diseases (IBD) are chronic disorders of the gastrointestinal tract with an increasing prevalence worldwide. Targeted therapies for IBD are limited by several factors, including the therapeutic ceiling and the high incidence of non-responders or loss-of-response. In order to improve therapeutic efficacy, there is critical need to decipher disease pathogenesis, currently not well understood. Macrophages, innate immune cells that exhibit high plasticity, perpetuate inflammatory signalling in IBD through excessive release of inflammatory mediators. In recent years, pioneering research has revealed the importance of the interplay between macrophages and gut microbiota in maintaining intestinal homeostasis. Particular attention is focusing on microbiota-derived metabolites, believed to possess immunomodulatory properties capable of manipulating macrophage plasticity. Microbiota-derived short-chain fatty acids (SCFAs) and indole compounds, along with dietary sourced omega-3 (ω-3) polyunsaturated fatty acids (PUFA), exert anti-inflammatory effects, attributable to interactions with macrophages. Before we can effectively incorporate these metabolites into IBD therapies, a deeper understanding of microbiota-macrophage interactions at a molecular level is necessary. Therefore, the aim of this review is firstly to detail current knowledge regarding how diet and microbiota-derived metabolites modify macrophage plasticity. Later, we discuss the concept of therapeutic strategies directed at microbiota-macrophage interactions, which could be highly valuable for IBD therapies in the future.