Cyclooxygenase-2-derived prostaglandin D(2) is an early anti-inflammatory signal in experimental colitis

Role of epigenetics and the transcription factor Sp1 in the expression of the D prostanoid receptor 1 in human cartilage

D prostanoid receptor 1 (DP1), a prostaglandin D2 receptor, plays a central role in the modulation of inflammation and cartilage metabolism. We have previously shown that activation of DP1 signaling downregulated catabolic responses in cultured chondrocytes and was protective in mouse osteoarthritis (OA). However, the mechanisms underlying its transcriptional regulation in cartilage remained poorly understood. In the present study, we aimed to characterize the human DP1 promoter and the role of DNA methylation in DP1 expression in chondrocytes. In addition, we analyzed the expression level and methylation status of the DP1 gene promoter in normal and OA cartilage. Deletion and site-directed mutagenesis analyses identified a minimal promoter region (-250/-120) containing three binding sites for specificity protein 1 (Sp1). Binding of Sp1 to the DP1 promoter was confirmed using electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assays. Treatment with the Sp1 inhibitor mithramycin A reduced DP1 promoter activity and DP1 mRNA expression. Inhibition of DNA methylation by 5-Aza-2'-deoxycytidine upregulated DP1 expression, and in vitro methylation reduced the DP1 promoter activity. Neither the methylation status of the DP1 promoter nor the DP1 expression level were different between normal and OA cartilage. In conclusion, our results suggest that the transcription factor Sp1 and DNA methylation are important determinants of DP1 transcription regulation. They also suggest that the methylation status and expression level of DP1 are not altered in OA cartilage. These findings will improve our understanding of the regulatory mechanisms of DP1 transcription and may facilitate the development of intervention strategies involving DP1.

Crosstalk between omega-6 oxylipins and the enteric nervous system: Implications for gut disorders?

The enteric nervous system (ENS) continues to dazzle scientists with its ability to integrate signals, from the outside as well as from the host, to accurately regulate digestive functions. Composed of neurons and enteric glial cells, the ENS interplays with numerous neighboring cells through the reception and/or the production of several types of mediators. In particular, ENS can produce and release n-6 oxylipins. These lipid mediators, derived from arachidonic acid, play a major role in inflammatory and allergic processes, but can also regulate immune and nervous system functions. As such, the study of these n-6 oxylipins on the digestive functions, their cross talk with the ENS and their implication in pathophysiological processes is in full expansion and will be discussed in this review.

Oxidized linoleic acid metabolites regulate neuronal morphogenesis in vitro

Linoleic acid (LA, 18:2n-6) is an essential nutrient for optimal infant growth and brain development. The effects of LA in the brain are thought to be mediated by oxygenated metabolites of LA known as oxidized LA metabolites (OXLAMs), but evidence is lacking to directly support this hypothesis. This study investigated whether OXLAMs modulate key neurodevelopmental processes including axon outgrowth, dendritic arborization, cell viability and synaptic connectivity. Primary cortical neuron-glia co-cultures from postnatal day 0-1 male and female rats were exposed for 48h to the following OXLAMs: 1) 13-hydroxyoctadecadienoic acid (13-HODE); 2) 9-hydroxyoctadecadienoic acid (9-HODE); 3) 9,10-dihydroxyoctadecenoic acid (9,10-DiHOME); 4) 12(13)-epoxyoctadecenoic acid (12(13)-EpOME); 5) 9,10,13-trihydroxyoctadecenoic acid (9,10,13-TriHOME); 6) 9-oxo-octadecadienoic acid (9-OxoODE); and 7) 12,13-dihydroxyoctadecenoic acid (12,13-DiHOME). Axonal outgrowth, evaluated by Tau-1 immunostaining, was increased by 9-HODE, but decreased by 12,13-DiHOME in male but not female neurons. Dendrite arborization, evaluated by MAP2B-eGFP expression, was affected by 9-HODE, 9-OxoODE, and 12(13)-EpOME in male neurons and, by 12(13)-EpOME in female neurons. Neither cell viability nor synaptic connectivity were significantly altered by OXLAMs. Overall, this study shows select OXLAMs modulate neuron morphology in a sex-dependent manner, with male neurons being more susceptible.

Staphylococcus aureus controls eicosanoid and specialized pro-resolving mediator production via lipoteichoic acid

Staphylococcus aureus causes severe infections associated with inflammation, such as sepsis or osteomyelitis. Inflammatory processes are regulated by distinct lipid mediators (LMs) but how their biosynthetic pathways are orchestrated in S. aureus infections is elusive. We show that S. aureus strikingly not only modulates pro-inflammatory, but also inflammation-resolving LM pathways in murine osteomyelitis and osteoclasts as well as in human monocyte-derived macrophages (MDMs) with different phenotype. Targeted LM metabololipidomics using ultra-performance liquid chromatography-tandem mass spectrometry revealed massive generation of LM with distinct LM signature profiles in acute and chronic phases of S. aureus-induced murine osteomyelitis in vivo. In human MDM, S. aureus elevated cyclooxygenase-2 (COX-2) and microsomal prostaglandin E₂  synthase-1 (mPGES-1), but impaired the levels of 15-lipoxygenase-1 (15-LOX-1), with respective changes in LM signature profiles initiated by these enzymes, that is, elevated PGE₂ and impaired specialized pro-resolving mediators, along with reduced M2-like phenotypic macrophage markers. The cell wall component, lipoteichoic acid (LTA), mimicked the impact of S. aureus elevating COX-2/mPGES-1 expression via NF-κB and p38 MAPK signalling in MDM, while the impairment of 15-LOX-1 correlates with reduced expression of Lamtor1. In conclusion, S. aureus dictates LM pathways via LTA resulting in a shift from anti-inflammatory M2-like towards pro-inflammatory M1-like LM signature profiles.

Lipids in Liver Failure Syndromes: A Focus on Eicosanoids, Specialized Pro-Resolving Lipid Mediators and Lysophospholipids

Lipids are organic compounds insoluble in water with a variety of metabolic and non-metabolic functions. They not only represent an efficient energy substrate but can also act as key inflammatory and anti-inflammatory molecules as part of a network of soluble mediators at the interface of metabolism and the immune system. The role of endogenous bioactive lipid mediators has been demonstrated in several inflammatory diseases (rheumatoid arthritis, inflammatory bowel disease, atherosclerosis, cancer). The liver is unique in providing balanced immunotolerance to the exposure of bacterial components from the gut transiting through the portal vein and the lymphatic system. This balance is abruptly deranged in liver failure syndromes such as acute liver failure and acute-on-chronic liver failure. In these syndromes, researchers have recently focused on bioactive lipid mediators by global metabonomic profiling and uncovered the pivotal role of these mediators in the immune dysfunction observed in liver failure syndromes explaining the high occurrence of sepsis and subsequent organ failure. Among endogenous bioactive lipids, the mechanistic actions of three classes (eicosanoids, pro-resolving lipid mediators and lysophospholipids) in the pathophysiological modulation of liver failure syndromes will be the topic of this narrative review. Furthermore, the therapeutic potential of lipid-immune pathways will be described.

Facilitation of colonic T cell immune responses is associated with an exacerbation of dextran sodium sulfate-induced colitis in mice lacking microsomal prostaglandin E synthase-1

Background

Microsomal prostaglandin E synthase-1 (mPGES-1) is a key enzyme that acts downstream of cyclooxygenase and plays a major role in inflammation by converting prostaglandin (PG) H₂ to PGE₂. The present study investigated the effect of genetic deletion of mPGES-1 on the development of immunologic responses to experimental colitis induced by dextran sodium sulfate (DSS), a well-established model of inflammatory bowel disease (IBD).

Methods

Colitis was induced in mice lacking mPGES-1 (mPGES-1^−/− mice) and wild-type (WT) mice by administering DSS for 7 days. Colitis was assessed by body weight loss, diarrhea, fecal bleeding, and histological features. The colonic expression of mPGES-1 was determined by real-time PCR, western blotting, and immunohistochemistry. The impact of mPGES-1 deficiency on T cell immunity was determined by flow cytometry and T cell depletion in vivo.

Results

After administration of DSS, mPGES-1^−/− mice exhibited more severe weight loss, diarrhea, and fecal bleeding than WT mice. Histological analysis further showed significant exacerbation of colonic inflammation in mPGES-1^−/− mice. In WT mice, the colonic expression of mPGES-1 was highly induced on both mRNA and protein levels and colonic PGE₂ increased significantly after DSS administration. Additionally, mPGES-1 protein was localized in the colonic mucosal epithelium and infiltrated inflammatory cells in underlying connective tissues and the lamina propria. The abnormalities consistent with colitis in mPGES-1^−/− mice were associated with higher expression of colonic T-helper (Th)17 and Th1 cytokines, including interleukin 17A and interferon-γ. Furthermore, lack of mPGES-1 increased the numbers of Th17 and Th1 cells in the lamina propria mononuclear cells within the colon, even though the number of suppressive regulatory T cells also increased. CD4⁺ T cell depletion effectively reduced symptoms of colitis as well as colonic expression of Th17 and Th1 cytokines in mPGES-1^−/− mice, suggesting the requirement of CD4⁺ T cells in the exacerbation of DSS-induced colitis under mPGES-1 deficiency.

Conclusions

These results demonstrate that mPGES-1 is the main enzyme responsible for colonic PGE₂ production and deficiency of mPGES-1 facilitates the development of colitis by affecting the development of colonic T cell–mediated immunity. mPGES-1 might therefore impact both the intestinal inflammation and T cell–mediated immunity associated with IBD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41232-021-00188-1.

Harnessing Inflammation Resolution in Arthritis: Current Understanding of Specialized Pro-resolving Lipid Mediators' Contribution to Arthritis Physiopathology and Future Perspectives

The concept behind the resolution of inflammation has changed in the past decades from a passive to an active process, which reflects in novel avenues to understand and control inflammation-driven diseases. The time-dependent and active process of resolution phase is orchestrated by the endogenous biosynthesis of specialized pro-resolving lipid mediators (SPMs). Inflammation and its resolution are two forces in rheumatic diseases that affect millions of people worldwide with pain as the most common experienced symptom. The pathophysiological role of SPMs in arthritis has been demonstrated in pre-clinical and clinical studies (no clinical trials yet), which highlight their active orchestration of disease control. The endogenous roles of SPMs also give rise to the opportunity of envisaging these molecules as novel candidates to improve the life quality of rhematic diseases patients. Herein, we discuss the current understanding of SPMs endogenous roles in arthritis as pro-resolutive, protective, and immunoresolvent lipids.

PGI2 Inhibits Intestinal Epithelial Permeability and Apoptosis to Alleviate Colitis

BACKGROUND & AIMS

Inflammatory bowel diseases (IBDs) that encompass both ulcerative colitis and Crohn's disease are a major public health problem with an etiology that has not been fully elucidated. There is a need to improve disease outcomes and preventive measures by developing new effective and lasting treatments. Although polyunsaturated fatty acid metabolites play an important role in the pathogenesis of several disorders, their contribution to IBD is yet to be understood.

METHODS

Polyunsaturated fatty acids metabolite profiles were established from biopsy samples obtained from Crohn's disease, ulcerative colitis, or control patients. The impact of a prostaglandin I₂ (PGI₂) analog on intestinal epithelial permeability was tested in vitro using Caco-2 cells and ex vivo using human or mouse explants. In addition, mice were treated with PGI₂ to observe dextran sulfate sodium (DSS)-induced colitis. Tight junction protein expression, subcellular location, and apoptosis were measured in the different models by immunohistochemistry and Western blotting.

RESULTS

A significant reduction of PGI₂ in IBD patient biopsies was identified. PGI₂ treatment reduced colonic inflammation, increased occludin expression, decreased caspase-3 cleavage and intestinal permeability, and prevented colitis development in DSS-induced mice. Using colonic explants from mouse and human control subjects, the staurosporine-induced increase in paracellular permeability was prevented by PGI₂. PGI₂ also induced the membrane location of occludin and reduced the permeability observed in colonic biopsies from IBD patients.

CONCLUSIONS

The present study identified a PGI₂ defect in the intestinal mucosa of IBD patients and demonstrated its protective role during colitis.

Baccharis dracunculifolia (Asteraceae) essential oil displays anti-inflammatory activity in models of skin inflammation

ETHNOPHARMACOLOGICAL RELEVANCE

Baccharis dracunculifolia (Asteraceae) is a commonly used plant in traditional medicine known as "alecrim-do-campo". Popularly it has been used as an immunostimulant, antibiotic, anti-inflammatory among other applications. So far, only a few studies have investigated the B. dracunculifolia anti-inflammatory effect and none has investigated the effectiveness of essential oil on skin diseases.

AIM OF THE STUDY

The study aimed at evaluating the topical anti-inflammatory activity of B. dracunculifolia essential oil (BdEO) in mice models of acute and chronic skin inflammation.

MATERIALS AND METHODS

BdEO was obtained from leaves and it was analyzed with Gas Chromatograph. Topical anti-inflammatory activity of BdEO (0.1, 0.3 and 1.0 mg/ear) was evaluated in Arachidonic Acid or TPA-induced acute and chronic skin inflammation in mice. Parameters such edema, cell migration and keratinocytes proliferation were evaluated. In addition, safety and a possible mechanism of action for BdEO essential oil were also investigated.

RESULTS

Our results indicate that mainly terpenoids compounds compose BdEO. In addition, topical treatment with BdEO inhibited inflammatory parameters in both acute and chronic models of skin inflammation. This protective effect was associated with reduced edema formation, smaller cellular influx into the inflamed tissue and reduction of keratinocytes hyperproliferation. Although BdEO appears to exert its anti-inflammatory effect through a corticosteroid pathway, no local or systemic side effects were observed.

CONCLUSION

Taken together, the present results showed that the essential oil obtained by hydrodistillation from B. dracunculifolia leaf samples exhibit remarkable topical anti-inflammatory properties. Therefore, our study demonstrated evidence for BdEO topical anti-inflammatory efficacy and safety, suggesting that it could be considered for developing of a new phytotherapeutic formulation as treatment for skin diseases.

Role of Lipocalin-Type Prostaglandin D Synthase in Experimental Osteoarthritis

OBJECTIVE

Lipocalin-type prostaglandin D synthase (L-PGDS) catalyzes the formation of prostaglandin D₂ (PGD₂ ), which has important roles in inflammation and cartilage metabolism. We undertook this study to investigate the role of L-PGDS in the pathogenesis of osteoarthritis (OA) using an experimental mouse model.

METHODS

Experimental OA was induced in wild-type (WT) and L-PGDS-deficient (L-PGDS^-/- ) mice (n = 10 per genotype) by destabilization of the medial meniscus (DMM). Cartilage degradation was evaluated by histology. The expression of matrix metalloproteinase 13 (MMP-13) and ADAMTS-5 was assessed by immunohistochemistry. Bone changes were determined by micro-computed tomography. Cartilage explants from L-PGDS^-/- and WT mice (n = 6 per genotype) were treated with interleukin-1α (IL-1α) ex vivo in order to evaluate proteoglycan degradation. Moreover, the effect of intraarticular injection of a recombinant adeno-associated virus type 2/5 (rAAV2/5) encoding L-PGDS on OA progression was evaluated in WT mice (n = 9 per group).

RESULTS

Compared to WT mice, L-PGDS^-/- mice had exacerbated cartilage degradation and enhanced expression of MMP-13 and ADAMTS-5 (P < 0.05). Furthermore, L-PGDS^-/- mice displayed increased synovitis and subchondral bone changes (P < 0.05). Cartilage explants from L-PGDS^-/- mice showed enhanced proteoglycan degradation following treatment with IL-1α (P < 0.05). Intraarticular injection of rAAV2/5 encoding L-PGDS attenuated the severity of DMM-induced OA-like changes in WT mice (P < 0.05). The L-PGDS level was increased in OA tissues of WT mice (P < 0.05).

CONCLUSION

Collectively, these findings suggest a protective role of L-PGDS in OA, and therefore enhancing levels of L-PGDS may constitute a promising therapeutic strategy.

Bioactive lipids, inflammation and chronic diseases

Endogenous bioactive lipids are part of a complex network that modulates a plethora of cellular and molecular processes involved in health and disease, of which inflammation represents one of the most prominent examples. Inflammation serves as a well-conserved defence mechanism, triggered in the event of chemical, mechanical or microbial damage, that is meant to eradicate the source of damage and restore tissue function. However, excessive inflammatory signals, or impairment of pro-resolving/anti-inflammatory pathways leads to chronic inflammation, which is a hallmark of chronic pathologies. All main classes of endogenous bioactive lipids - namely eicosanoids, specialized pro-resolving lipid mediators, lysoglycerophopsholipids and endocannabinoids - have been consistently involved in the chronic inflammation that characterises pathologies such as cancer, diabetes, atherosclerosis, asthma, as well as autoimmune and neurodegenerative disorders and inflammatory bowel diseases. This review gathers the current knowledge concerning the involvement of endogenous bioactive lipids in the pathogenic processes of chronic inflammatory pathologies.

Emerging roles of metabolites of ω3 and ω6 essential fatty acids in the control of intestinal inflammation

The gastrointestinal tract is continuously exposed to the external environment, which contains numerous non-self antigens, including food materials and commensal micro-organisms. For the maintenance of mucosal homeostasis, the intestinal epithelial layer and mucosal immune system simultaneously provide the first line of defense against pathogens and are tightly regulated to prevent their induction of inflammatory responses to non-pathogenic antigens. Defects in mucosal homeostasis lead to the development of inflammatory and associated intestinal diseases, such as Crohn’s disease, ulcerative colitis, food allergy and colorectal cancer. The recent discovery of novel dietary ω3 and ω6 lipid-derived metabolites—such as resolvin, protectin, maresin, 17,18-epoxy-eicosatetraenoic acid and microbe-dependent 10-hydroxy-cis-12-octadecenoic acid—and their potent biologic effects on the regulation of inflammation have initiated a new era of nutritional immunology. In this review, we update our understanding of the role of lipid metabolites in intestinal inflammation.

Natural polyphenols for the prevention of irritable bowel syndrome: molecular mechanisms and targets; a comprehensive review

Irritable bowel syndrome (IBS) is a well diagnosed disease, thoroughly attributed to series of symptoms criteria that embrace a broad range of abdominal complainers. Such criteria help to diagnosis the disease and can guide controlled clinical trials to seek new therapeutic agents. Accordingly, a verity of mechanisms and pathophysiological conditions including inflammation, oxidative stress, lipid peroxidation and different life styles are involved in IBS. Predictably, diverse therapeutic approaches are available and prescribed by clinicians due to major manifestations (i.e., diarrhea-predominance, constipation-predominance, abdominal pain and visceral hypersensitivity), psychological disturbances, and patient preferences between herbal treatments versus pharmacological therapies, dietary or microbiological approaches. Herein, we gathered the latest scientific data between 1973 and 2019 from databases such as PubMed, Google Scholar, Scopus and Cochrane library on relevant studies concerning beneficial effects of herbal treatments for IBS, in particular polyphenols. This is concluded that polyphenols might be applicable for preventing IBS and improving the IBS symptoms, mainly through suppressing the inflammatory signaling pathways, which nowadays are known as novel platform for the IBS management. Graphical abstract.

Distinct and overlapping functions of glutathione peroxidases 1 and 2 in limiting NF-κB-driven inflammation through redox-active mechanisms

Glutathione peroxidase 2 (GPx2) is one of the five selenoprotein GPxs having a selenocysteine in the active center. GPx2 is strongly expressed in the gastrointestinal epithelium, as is another isoform, GPx1, though with a different localization pattern. Both GPxs are redox-active enzymes that are important for the reduction of hydroperoxides.

Studies on GPx2-deficient mice and human HT-29 cells with a stable knockdown (kd) of GPx2 revealed higher basal and IL-1β-induced expression of NF-κB target genes in vivo and in vitro. The activation of the IKK–IκBα–NF-κB pathway was increased in cultured GPx2 kd cells. Basal signaling was only restored by re-expressing active GPx2 in GPx2 kd cells but not by redox-inactive GPx2. As it is still not clear if the two isoforms GPx1 and GPx2 have different functions, kd cell lines for either GPx1 or GPx2 were studied in parallel. The inhibitory effect of GPx2 on NF-κB signaling and its target gene expression was stronger than that of GPx1, whereas cyclooxygenase (COX)- and lipoxygenase (LOX)-derived lipid mediator levels increased more strongly in GPx1 kd than in GPx2 kd cells. Under unstimulated conditions, the levels of the COX-derived prostaglandins PGE₂ and PGD₂ were enhanced in GPx2 as well as in GPx1 kd compared to control cells. Specifically, in GPx1 kd cells IL-1β stimulation led to a dramatic shift of the PGE₂/PGD₂ ratio towards pro-inflammatory PGE₂.

Taken together, GPx2 and GPx1 have overlapping functions in controlling inflammatory lipid mediator synthesis and, most probably, exert their anti-inflammatory effects by preventing excessive PGE₂ production. In view of the high activity of COX and LOX pathways during inflammatory bowel disease our data therefore provide new insights into the mechanisms of the protective function of GPx1 and GPx2 during colitis as well as inflammation-driven carcinogenesis.

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Loss of GPx2 results in higher basal and IL-1β-induced NF-κB activation.

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Suppressive effects of GPx2 on NF-κB are mediated in a redox-dependent manner.

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Both GPx isoforms modulate the lipid mediator profile in response to IL-1β.

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COX-derived prostaglandins increase more strongly in GPx1 than in GPx2 kd cells.

Therapeutic Potential of Hematopoietic Prostaglandin D2 Synthase in Allergic Inflammation

Worldwide, there is a rise in the prevalence of allergic diseases, and novel efficient therapeutic approaches are still needed to alleviate disease burden. Prostaglandin D₂ (PGD₂) has emerged as a central inflammatory lipid mediator associated with increased migration, activation and survival of leukocytes in various allergy-associated disorders. In the periphery, the hematopoietic PGD synthase (hPGDS) acts downstream of the arachidonic acid/COX pathway catalysing the isomerisation of PGH₂ to PGD₂, which makes it an interesting target to treat allergic inflammation. Although much effort has been put into developing efficient hPGDS inhibitors, no compound has made it to the market yet, which indicates that more light needs to be shed on potential PGD₂ sources and targets to determine which particular condition and patient will benefit most and thereby improve therapeutic efficacy. In this review, we want to revisit current knowledge about hPGDS function, expression in allergy-associated cell types and their contribution to PGD₂ levels as well as beneficial effects of hPGDS inhibition in allergic asthma, rhinitis, atopic dermatitis, food allergy, gastrointestinal allergic disorders and anaphylaxis.

Host- and Microbe-Dependent Dietary Lipid Metabolism in the Control of Allergy, Inflammation, and Immunity

The intestine is the largest immune organ in the body, provides the first line of defense against pathogens, and prevents excessive immune reactions to harmless or beneficial non-self-materials, such as food and intestinal bacteria. Allergic and inflammatory diseases in the intestine occur as a result of dysregulation of immunological homeostasis mediated by intestinal immunity. Several lines of evidence suggest that gut environmental factors, including nutrition and intestinal bacteria, play important roles in controlling host immune responses and maintaining homeostasis. Among nutritional factors, ω3 and ω6 essential polyunsaturated fatty acids (PUFAs) profoundly influence the host immune system. Recent advances in lipidomics technology have led to the identification of lipid mediators derived from ω3- and ω6-PUFAs. In particular, lipid metabolites from ω3-PUFAs (e.g., eicosapentaenoic acid and docosahexaenoic acid) have recently been shown to exert anti-allergic and anti-inflammatory responses; these metabolites include resolvins, protectins, and maresins. Furthermore, a new class of anti-allergic and anti-inflammatory lipid metabolites of 17,18-epoxyeicosatetraenoic acid has recently been identified in the control of allergic and inflammatory diseases in the gut and skin. Although these lipid metabolites were found to be endogenously generated in the host, accumulating evidence indicates that intestinal bacteria also participate in lipid metabolism and thus generate bioactive unique lipid mediators. In this review, we discuss the production machinery of lipid metabolites in the host and intestinal bacteria and the roles of these metabolites in the regulation of host immunity.

Eicosanoids in the gastrointestinal tract

Eicosanoids play important roles in modulating inflammation throughout the body. The gastrointestinal (GI) tract, in part because of its intimate relationship with the gut microbiota, is in a constant state of low-grade inflammation. Eicosanoids like PGs, lipoxins and leukotrienes play essential roles in maintenance of mucosal integrity. On the other hand, in some circumstances, these mediators can become major drivers of inflammatory processes when the lining of the GI tract is breached. Drugs such as nonsteroidal anti-inflammatories, by altering the production of various eicosanoids, can dramatically impact the ability of the GI tract to respond appropriately to injury. Disorders such as inflammatory bowel disease appear to be driven in part by altered production of eicosanoids. Several classes of drugs have been developed that target eicosanoids. LINKED ARTICLES: This article is part of a themed section on Eicosanoids 35 years from the 1982 Nobel: where are we now? To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.8/issuetoc.

Targeting biosynthetic networks of the proinflammatory and proresolving lipid metabolome

Nonsteroidal anti-inflammatory drugs interfere with the metabolism of arachidonic acid to proinflammatory prostaglandins and leukotrienes by targeting cyclooxygenases (COXs), 5-lipoxygenase (LOX), or the 5-LOX-activating protein (FLAP). These and related enzymes act in conjunction with marked crosstalk within a complex lipid mediator (LM) network where also specialized proresolving LMs (SPMs) are formed. Here, we present how prominent LM pathways can be differentially modulated in human proinflammatory M1 and proresolving M2 macrophage phenotypes that, upon exposure to Escherichia coli, produce either abundant prostaglandins and leukotrienes (M1) or SPMs (M2). Targeted liquid chromatography-tandem mass spectrometry-based metabololipidomics was applied to analyze and quantify the specific LM profiles. Besides expected on-target actions, we found that: 1) COX or 15-LOX-1 inhibitors elevate inflammatory leukotriene levels, 2) FLAP and 5-LOX inhibitors reduce leukotrienes in M1 but less so in M2 macrophages, 3) zileuton blocks resolution-initiating SPM biosynthesis, whereas FLAP inhibition increases SPM levels, and 4) that the 15-LOX-1 inhibitor 3887 suppresses SPM formation in M2 macrophages. Conclusively, interference with discrete LM biosynthetic enzymes in different macrophage phenotypes considerably affects the LM metabolomes with potential consequences for inflammation-resolution pharmacotherapy. Our data may allow better appraisal of the therapeutic potential of these drugs to intervene with inflammatory disorders.-Werner, M., Jordan, P. M., Romp, E., Czapka, A., Rao, Z., Kretzer, C., Koeberle, A., Garscha, U., Pace, S., Claesson, H.-E., Serhan, C. N., Werz, O., Gerstmeier, J. Targeting biosynthetic networks of the proinflammatory and proresolving lipid metabolome.

Involvement of EP2 and EP4 Receptors in Eosinophilic Esophagitis: A Pilot Study

BACKGROUND

The prostaglandin D₂ receptor DP2 has been implicated in eosinophil infiltration and the development of eosinophilic esophagitis (EoE).

AIMS AND METHODS

In this study, we investigated an involvement of PGE₂ (EP1-EP4) and PGD₂ (DP1) receptors in EoE by measuring their expression in peripheral blood eosinophils and esophageal mucosal biopsies of EoE patients and by performing migration and adhesion assays with eosinophils from healthy donors.

RESULTS

Expression of EP2 and EP4, but not EP1 and EP3, was decreased in blood eosinophils of patients with EoE vs. control subjects. Adhesion of eosinophils to esophageal epithelial cells was decreased by EP2 receptor agonist butaprost and EP4 agonist ONO-AE1-329, whereas DP1 agonist BW245C increased adhesion. In chemotaxis assays with supernatant from human esophageal epithelial cells, only ONO-AE1-329 but not butaprost or BW245C inhibited the migration of eosinophils. Expression of EP and DP receptors in epithelial cells and eosinophils was detected in sections of esophageal biopsies from EoE patients by immunohistochemistry. qPCR of biopsies from EoE patients revealed that gene expression of EP4 and DP1 was the highest among PGE₂ and PGD₂ receptors. Esophageal epithelial cells in culture showed high gene expression for EP2 and EP4. Activation of EP2 and EP4 receptors decreased barrier integrity of esophageal epithelial cells in impedance assays.

CONCLUSIONS

Activation of EP2 and EP4 receptors may inhibit eosinophil recruitment to the esophageal mucosa. However, their activation could negatively affect esophageal barrier integrity suggesting that eosinophilic rather than epithelial EP2 and EP4 have a protective role in EoE.

Colonic epithelial mTORC1 promotes ulcerative colitis through COX-2-mediated Th17 responses

The functional role of colonic epithelium in the pathogenesis of ulcerative colitis (UC) remains unclear. Here, we reveal a novel mechanism by which colonic epithelia recruit T helper-17 (Th17) cells during the onset of UC. mTOR complex 1 (mTORC1) was hyper-activated in colonic epithelia of UC mice. While colonic epithelial TSC1 (mTORC1 negative regulator) disruption induced constitutive mTORC1 activation in the colon epithelia and aggravated UC, RPTOR (essential mTORC1 component) depletion inactivated mTORC1 and ameliorated UC. TSC1 deficiency enhanced, whereas RPTOR ablation reduced the expression of cyclooxygenase 2 (COX-2), interleukin-1 (IL-1), IL-6, and IL-23, as well as Th17 infiltration in the colon. Importantly, inhibition of COX-2 reversed the elevation in the expression of these proinflammatory mediators induced by TSC1 deficiency, and subsequently reduced the symptoms and pathological characteristics of UC in mouse models. Mechanistically, mTORC1 activates COX-2 transcription via phosphorylating STAT3 and enhancing it's binding to the COX-2 promoter. Consistently, enhanced mTORC1 activity and COX2 expression, as well as strong positive correlation between each other, were observed in colonic epithelial tissues of UC patients. Collectively, our study demonstrates an essential role of epithelial mTORC1 in UC pathogenesis and establishes a novel link between colonic epithelium, Th17 responses, and UC development.

Niacin ameliorates ulcerative colitis via prostaglandin D2-mediated D prostanoid receptor 1 activation

Niacin, as an antidyslipidemic drug, elicits a strong flushing response by release of prostaglandin (PG) D₂. However, whether niacin is beneficial for inflammatory bowel disease (IBD) remains unclear. Here, we observed niacin administration‐enhanced PGD₂ production in colon tissues in dextran sulfate sodium (DSS)‐challenged mice, and protected mice against DSS or 2,4,6‐trinitrobenzene sulfonic acid (TNBS)‐induced colitis in D prostanoid receptor 1 (DP1)‐dependent manner. Specific ablation of DP1 receptor in vascular endothelial cells, colonic epithelium, and myeloid cells augmented DSS/TNBS‐induced colitis in mice through increasing vascular permeability, promoting apoptosis of epithelial cells, and stimulating pro‐inflammatory cytokine secretion of macrophages, respectively. Niacin treatment improved vascular permeability, reduced apoptotic epithelial cells, promoted epithelial cell update, and suppressed pro‐inflammatory gene expression of macrophages. Moreover, treatment with niacin‐containing retention enema effectively promoted UC clinical remission and mucosal healing in patients with moderately active disease. Therefore, niacin displayed multiple beneficial effects on DSS/TNBS‐induced colitis in mice by activation of PGD₂/DP1 axis. The potential efficacy of niacin in management of IBD warrants further investigation.

CD200 selectively upregulates prostaglandin E2 and D2 synthesis in LPS-treated bone marrow-derived macrophages

The CD200/CD200R signalling pathway downregulates the synthesis of proinflammatory mediators and induces the synthesis of antiinflammatory mediators in macrophages and microglia. However, very little is known about the effect of this immunosuppressive pathway on the synthesis of lipid mediators. Therefore, we determined the synthesis of 35 lipids spanning 5 different lipid families in bone marrow-derived macrophages, which were treated with interleukin (IL) 4, IL10, lipopolysaccharide (LPS), or interferon γ (IFNγ) in absence and presence of CD200. Out of these conditions the only significant effect of CD200 was an increased synthesis of prostaglandin (PG) E₂ and D₂ in the presence of LPS. Accordingly, mRNA levels of cyclooxygenase-2, microsomal PGE₂ synthase-1 and hematopoietic PGD synthase were upregulated by CD200 in presence of LPS. During Complete Freund's Adjuvant (CFA-) induced inflammation mPGES-1 was expressed in monocyte-derived macrophages and its expression was stronger in CD200R-positive than in CD200R-negative macrophages.

Eosinophils Contribute to Intestinal Inflammation via Chemoattractant Receptor-homologous Molecule Expressed on Th2 Cells, CRTH2, in Experimental Crohn's Disease

BACKGROUND AND AIMS

Prostaglandin [PG] D2 activates two receptors, DP and CRTH2. Antagonism of CRTH2 has been shown to promote anti-allergic and anti-inflammatory effects. We investigated whether CRTH2 may play a role in Crohn's disease [CD], focusing on eosinophils which are widely present in the inflamed mucosa of CD patients and express both receptors.

METHODS

Using the 2,4,6-trinitrobenzenesulfonic acid [TNBS]-induced colitis model, involvement of CRTH2 in colitis was investigated by pharmacological antagonism, immunohistochemistry, Western blotting, immunoassay, and leukocyte recruitment. Chemotactic assays were performed with isolated human eosinophils. Biopsies and serum samples of CD patients were examined for presence of CRTH2 and ligands, respectively.

RESULTS

High amounts of CRTH2-positive cells, including eosinophils, are present in the colonic mucosa of mice with TNBS colitis and in human CD. The CRTH2 antagonist OC-459, but not the DP antagonist MK0524, reduced inflammation scores and decreased TNF-α, IL-1β, and IL-6 as compared with control mice. OC-459 inhibited recruitment of eosinophils into the colon and also inhibited CRTH2-induced chemotaxis of human eosinophils in vitro. Eosinophil-depleted ΔdblGATA knockout mice were less sensitive to TNBS-induced colitis, whereas IL-5 transgenic mice with lifelong eosinophilia were more severely affected than wild types. In addition, we show that serum levels of PGD2 and Δ(12)-PGJ2 were increased in CD patients as compared with control individuals.

CONCLUSIONS

CRTH2 plays a pro-inflammatory role in TNBS-induced colitis. Eosinophils contribute to the severity of the inflammation, which is improved by a selective CRTH2 antagonist. CRTH2 may, therefore, represent an important target in the pharmacotherapy of CD.

Genome-wide analysis of DNA methylation and gene expression defines molecular characteristics of Crohn's disease-associated fibrosis

BACKGROUND

Fibrosis of the intestine is a common and poorly understood complication of Crohn's disease (CD) characterized by excessive deposition of extracellular matrix and accompanied by narrowing and obstruction of the gut lumen. Defining the molecular characteristics of this fibrotic disorder is a vital step in the development of specific prediction, prevention, and treatment strategies. Previous epigenetic studies indicate that alterations in DNA methylation could explain the mechanism by which mesenchymal cells adopt the requisite pro-fibrotic phenotype that promotes fibrosis progression. However, to date, genome-wide analysis of the DNA methylome of any type of human fibrosis is lacking. We employed an unbiased approach using deep sequencing to define the DNA methylome and transcriptome of purified fibrotic human intestinal fibroblasts (HIF) from the colons of patients with fibrostenotic CD.

RESULTS

When compared with normal fibroblasts, we found that the majority of differential DNA methylation was within introns and intergenic regions and not associated with CpG islands. Only a low percentage occurred in the promoters and exons of genes. Integration of the DNA methylome and transcriptome identified regions in three genes that inversely correlated with gene expression: wingless-type mouse mammary tumor virus integration site family, member 2B (WNT2B) and two eicosanoid synthesis pathway enzymes (prostacyclin synthase and prostaglandin D2 synthase). These findings were independently validated by RT-PCR and bisulfite sequencing. Network analysis of the data also identified candidate molecular interactions relevant to fibrosis pathology.

CONCLUSIONS

Our definition of a genome-wide fibrosis-specific DNA methylome provides new gene networks and epigenetic states by which to understand mechanisms of pathological gene expression that lead to fibrosis. Our data also provide a basis for development of new fibrosis-specific therapies, as genes dysregulated in fibrotic Crohn's disease, following functional validation, can serve as new therapeutic targets.

PPARγ and the Innate Immune System Mediate the Resolution of Inflammation

The resolution of inflammation is an active and dynamic process, mediated in large part by the innate immune system. Resolution represents not only an increase in anti-inflammatory actions, but also a paradigm shift in immune cell function to restore homeostasis. PPARγ, a ligand activated transcription factor, has long been studied for its anti-inflammatory actions, but an emerging body of literature is investigating the role of PPARγ and its ligands (including thiazolidinediones, prostaglandins, and oleanolic acids) in all phases of resolution. PPARγ can shift production from pro- to anti-inflammatory mediators by neutrophils, platelets, and macrophages. PPARγ and its ligands further modulate platelet and neutrophil function, decreasing trafficking, promoting neutrophil apoptosis, and preventing platelet-leukocyte interactions. PPARγ alters macrophage trafficking, increases efferocytosis and phagocytosis, and promotes alternative M2 macrophage activation. There are also roles for this receptor in the adaptive immune response, particularly regarding B cells. These effects contribute towards the attenuation of multiple disease states, including COPD, colitis, Alzheimer's disease, and obesity in animal models. Finally, novel specialized proresolving mediators-eicosanoids with critical roles in resolution-may act through PPARγ modulation to promote resolution, providing another exciting area of therapeutic potential for this receptor.

Activation of the prostaglandin D2 metabolic pathway in Crohn's disease: involvement of the enteric nervous system

Background

Recent works provide evidence of the importance of the prostaglandin D2 (PGD2) metabolic pathway in inflammatory bowel diseases. We investigated the expression of PGD2 metabolic pathway actors in Crohn’s disease (CD) and the ability of the enteric nervous system (ENS) to produce PGD2 in inflammatory conditions.

Methods

Expression of key actors involved in the PGD2 metabolic pathway and its receptors was analyzed using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) in colonic mucosal biopsies of patients from three groups: controls, quiescent and active CD patients. To determine the ability of the ENS to secrete PGD2 in proinflammatory conditions, Lipocalin-type prostaglandin D synthase (L-PGDS) expression by neurons and glial cells was analyzed by immunostaining. PGD2 levels were determined in a medium of primary culture of ENS and neuro-glial coculture model treated by lipopolysaccharide (LPS).

Results

In patients with active CD, inflamed colonic mucosa showed significantly higher COX2 and L-PGDS mRNA expression, and significantly higher PGD2 levels than healthy colonic mucosa. On the contrary, peroxysome proliferator-activated receptor Gamma (PPARG) expression was reduced in inflamed colonic mucosa of CD patients with active disease. Immunostaining showed that L-PGDS was expressed in the neurons of human myenteric and submucosal plexi. A rat ENS primary culture model confirmed this expression. PGD2 levels were significantly increased on primary culture of ENS treated with LPS. This production was abolished by AT-56, a specific competitive L-PGDS inhibitor. The neuro-glial coculture model revealed that each component of the ENS, ECG and neurons, could contribute to PGD2 production.

Conclusions

Our results highlight the activation of the PGD2 metabolic pathway in Crohn’s disease. This study supports the hypothesis that in Crohn’s disease, enteric neurons and glial cells form a functional unit reacting to inflammation by producing PGD2.

Eosinophil-mediated signalling attenuates inflammatory responses in experimental colitis

OBJECTIVE

Eosinophils reside in the colonic mucosa and increase significantly during disease. Although a number of studies have suggested that eosinophils contribute to the pathogenesis of GI inflammation, the expanding scope of eosinophil-mediated activities indicate that they also regulate local immune responses and modulate tissue inflammation. We sought to define the impact of eosinophils that respond to acute phases of colitis in mice.

DESIGN

Acute colitis was induced in mice by administration of dextran sulfate sodium, 2,4,6-trinitrobenzenesulfonic acid or oxazolone to C57BL/6J (control) or eosinophil deficient (PHIL) mice. Eosinophils were also depleted from mice using antibodies against interleukin (IL)-5 or by grafting bone marrow from PHIL mice into control mice. Colon tissues were collected and analysed by immunohistochemistry, flow cytometry and reverse transcription PCR; lipids were analysed by mass spectroscopy.

RESULTS

Eosinophil-deficient mice developed significantly more severe colitis, and their colon tissues contained a greater number of neutrophils, than controls. This compensatory increase in neutrophils was accompanied by increased levels of the chemokines CXCL1 and CXCL2, which attract neutrophils. Lipidomic analyses of colonic tissue from eosinophil-deficient mice identified a deficiency in the docosahexaenoic acid-derived anti-inflammatory mediator 10, 17- dihydroxydocosahexaenoic acid (diHDoHE), namely protectin D1 (PD1). Administration of an exogenous PD1-isomer (10S, 17S-DiHDoHE) reduced the severity of colitis in eosinophil-deficient mice. The PD1-isomer also attenuated neutrophil infiltration and reduced levels of tumour necrosis factor-α, IL-1β, IL-6 and inducible NO-synthase in colons of mice. Finally, in vitro assays identified a direct inhibitory effect of PD1-isomer on neutrophil transepithelial migration.

CONCLUSIONS

Eosinophils exert a protective effect in acute mouse colitis, via production of anti-inflammatory lipid mediators.

[Dual role for prostaglandin D2 in intestinal epithelial homeostasis]

Prostaglandin D2 (PGD2) and derivatives are lipid mediators involved in the control of the intestinal epithelial barrier homeostasis. Their involvement in the pathophysiology of chronic inflammatory bowel disease (IBD) is still debated. Several results highlight the duality of PGD2 as an anti- or pro-inflammatory mediator. This duality seems to be related to a differential expression of its receptors by intestinal epithelial cells and the surrounding immunocompetent cells. The enteric glial cells from the enteric nervous system (ENS) express the lipocalin-type-prostaglandin D synthase and secrete PGD2 and 15d-PGJ2. The protective role of the ENS in the homeostatic control of the epithelial intestinal barrier and its involvement in the pathogenesis of IBD have already been demonstrated. Thus, these lipid mediators seem to be new actors of the neuro-glio-epithelial unit and could play a crucial role maintaining gut barrier integrity.

Resveratrol Pretreatment Ameliorates TNBS Colitis in Rats

Inflammatory bowel disease (IBD) is a chronic intestinal inflammatory disease in humans constituting a major health concern today whose prevalence has been increasing over the world. Production of reactive oxygen species (ROS) and disturbed capacity of antioxidant defense in IBD subjects have been reported. Antioxidants may play a significant role in IBD treatment. This study aimed at evaluating ameliorative effects of intraperitoneal resveratrol pretreatment on trinitrobenzene sulphonic acid (TNBS)-induced colitis in rats. Thirty five Wistar-Albino female rats were divided equally into five groups. Inflammation was induced by the intrarectal administration of TNBS under anesthesia. Intraperitoneal administration of resveratrol (RSV) at a concentration of 10mg/kg/day for 5 days before the induction of colitis significantly reduced microscopy score and malondialdehyde (MDA) levels and increased glutathione peroxidase (GSH Px) activity compared to TNBS and vehicle groups. Also an insignificant increase in catalase (CAT) activity was observed in the RSV treated group compared to TNBS and vehicle groups. In this paper, the most recent patent on the identification and treatment of IBD was indicated. In conclusion, antioxidant RSV proved to have a beneficial effect on TNBS colitis in rats. In light of these advantageous results, the RSV can be considered as adjuvant agent in IBD treatments.

Proresolution effects of hydrogen sulfide during colitis are mediated through hypoxia-inducible factor-1α

During a course of colitis, production of the gaseous mediator hydrogen sulfide (H2S) is markedly up-regulated at sites of mucosal damage and contributes significantly to healing and resolution of inflammation. The signaling mechanisms through which H2S promotes resolution of colitis are unknown. We hypothesized that the beneficial effects of H2S in experimental colitis are mediated via stabilization of hypoxia-inducible factor (HIF)-1α. The hapten dinitrobenzene sulfonic acid was used to induce colitis in rats and mice. This resulted in an elevated expression of the H2S-producing enzyme, cystathionine γ-lyase (CSE), and HIF-1α at sites of mucosal ulceration, and the expression of these 2 enzymes followed a similar pattern throughout the course of colitis. This represented a functionally important relationship because the loss of CSE-derived H2S production led to decreased HIF-1α stabilization and exacerbation of colitis. Furthermore, application of an H2S-releasing molecule, diallyl disulfide (DADS), stabilized colonic HIF-1α expression, up-regulated hypoxia-responsive genes, and reduced the severity of disease during peak inflammation. Importantly, the ability of DADS to promote the resolution of colitis was abolished when coadministered with an inhibitor of HIF-1α in vivo (PX-478). DADS was also able to maintain HIF-1α expression at a later point in colitis, when HIF-1α levels would have normally returned to control levels, and to enhance resolution. Finally, we found that HIF-1α stabilization inhibited colonic H2S production and may represent a negative feedback mechanism to prevent prolonged HIF-1α stabilization. Our findings demonstrate an important link between H2S and HIF-1α in the resolution of inflammation and injury during colitis and provide mechanistic insights into the therapeutic value of H2S donors.

Prostaglandin D2 regulates human colonic ion transport via the DP1 receptor

AIMS

Prostaglandin D2 is released by mast cells and is important in allergies. Its role in gastrointestinal function is not clearly defined. This study aimed to determine the effect of exogenous PGD2 on ion transport in ex vivo normal human colonic mucosa.

MATERIALS AND METHODS

Mucosal sheets were mounted in Ussing chambers and voltage clamped to zero electric potential. Ion transport was quantified as changes in short-circuit current. In separate experiments epithelial monolayers or colonic crypts, isolated by calcium chelation, were treated with PGD2 and cAMP levels determined by ELISA or calcium levels were determined by fluorimetry.

KEY FINDINGS

PGD2 caused a sustained, concentration-dependent rise in short-circuit current by increasing chloride secretion (EC50=376nM). This effect of PGD2 is mediated by the DP1 receptor, as the selective DP1 receptor antagonist BW A686C inhibited PGD2-induced but not PGE2-induced rise in short-circuit current. PGD2 also increased intracellular cAMP in isolated colonic crypts with no measurable influence on cytosolic calcium. PGD2 induces chloride secretion in isolated human colonic mucosa in a concentration-dependent manner with concomitant elevation of cytoplasmic cAMP in epithelial cells.

SIGNIFICANCE

The involvement of DP2 receptor subtypes has not previously been considered in regulation of ion transport in human intestine. Since inflammatory stimuli may induce production of eicosanoids, selective regulation of these pathways may be pivotal in determining therapeutic strategies and in understanding disease.

A deficiency in the prostaglandin D2 receptor CRTH2 exacerbates adjuvant-induced joint inflammation

Although the cyclooxygenase metabolites PGs are known to be involved in the progression of arthritis, the role of PGD2 remains unclear. In this study, we evaluated the contribution of signaling mediated through a PGD2 receptor, chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2), in the progression of adjuvant-induced joint inflammation. Injection of CFA into the ankle joint stimulated PGD2 production and induced paw swelling in both CRTH2-naive (WT) and CRTH2(-/-) mice. CRTH2(-/-) mice presented more severe arthritic manifestations than did WT mice. Through bone marrow transplantation experiments between WT and CRTH2(-/-) mice, we showed that CRTH2 deficiency in bone marrow-derived immune cells is involved in disease progression. Morphological studies showed that CRTH2 deficiency accelerated the infiltration of macrophages into the inflamed paw. Consistent with this finding, we observed that treatment with the macrophage inactivator GdCl3 or the macrophage-depleting agent liposomal clodronate improved arthritis symptoms in CRTH2(-/-) mice. Adoptive transfer of CRTH2(-/-) macrophages exacerbated joint inflammation in WT mice. In addition, CRTH2 deficiency accelerated, whereas CRTH2 agonism inhibited, the expression of a macrophage-activating cytokine (GM-CSF) and a chemokine receptor (CXCR2) in CFA-treated peritoneal macrophages. Together, these observations demonstrate that PGD2-CRTH2 signaling plays a protective role in joint inflammation by attenuating the infiltration of macrophages.

Crucial role of macrophage selenoproteins in experimental colitis

Inflammation is a hallmark of inflammatory bowel disease (IBD) that involves macrophages. Given the inverse link between selenium (Se) status and IBD-induced inflammation, our objective was to demonstrate that selenoproteins in macrophages were essential to suppress proinflammatory mediators, in part, by the modulation of arachidonic acid metabolism. Acute colitis was induced using 4% dextran sodium sulfate in wild-type mice maintained on Se-deficient (<0.01 ppm Se), Se-adequate (0.08 ppm; sodium selenite), and two supraphysiological levels in the form of Se-supplemented (0.4 ppm; sodium selenite) and high Se (1.0 ppm; sodium selenite) diets. Selenocysteinyl transfer RNA knockout mice (Trsp(fl/fl)LysM(Cre)) were used to examine the role of selenoproteins in macrophages on disease progression and severity using histopathological evaluation, expression of proinflammatory and anti-inflammatory genes, and modulation of PG metabolites in urine and plasma. Whereas Se-deficient and Se-adequate mice showed increased colitis and exhibited poor survival, Se supplementation at 0.4 and 1.0 ppm increased survival of mice and decreased colitis-associated inflammation with an upregulation of expression of proinflammatory and anti-inflammatory genes. Metabolomic profiling of urine suggested increased oxidation of PGE2 at supraphysiological levels of Se that also correlated well with Se-dependent upregulation of 15-hydroxy-PG dehydrogenase (15-PGDH) in macrophages. Pharmacological inhibition of 15-PGDH, lack of selenoprotein expression in macrophages, and depletion of infiltrating macrophages indicated that macrophage-specific selenoproteins and upregulation of 15-PGDH expression were key for Se-dependent anti-inflammatory and proresolving effects. Selenoproteins in macrophages protect mice from dextran sodium sulfate-colitis by enhancing 15-PGDH-dependent oxidation of PGE2 to alleviate inflammation, suggesting a therapeutic role for Se in IBD.

Opposing roles of prostaglandin D2 receptors in ulcerative colitis

Proresolution functions were reported for PGD2 in colitis, but the role of its two receptors, D-type prostanoid (DP) and, in particular, chemoattractant receptor homologous molecule expressed on Th2 cells (CRTH2), is less well defined. We investigated DP and CRTH2 expression and function during human and murine ulcerative colitis (UC). Expression of receptors was measured by flow cytometry on peripheral blood leukocytes and by immunohistochemistry and immunoblotting in colon biopsies of patients with active UC and healthy individuals. Receptor involvement in UC was evaluated in a mouse model of dextran sulfate sodium colitis. DP and CRTH2 expression changed in leukocytes of patients with active UC in a differential manner. In UC patients, DP showed higher expression in neutrophils but lower in monocytes as compared with control subjects. In contrast, CRTH2 was decreased in eosinophils, NK, and CD3(+) T cells but not in monocytes and CD3(+)/CD4(+) T cells. The decrease of CRTH2 on blood eosinophils clearly correlated with disease activity. DP correlated positively with disease activity in eosinophils but inversely in neutrophils. CRTH2 internalized upon treatment with PGD2 and 11-dehydro TXB2 in eosinophils of controls. Biopsies of UC patients revealed an increase of CRTH2-positive cells in the colonic mucosa and high CRTH2 protein content. The CRTH2 antagonist CAY10595 improved, whereas the DP antagonist MK0524 worsened inflammation in murine colitis. DP and CRTH2 play differential roles in UC. Although expression of CRTH2 on blood leukocytes is downregulated in UC, CRTH2 is present in colon tissue, where it may contribute to inflammation, whereas DP most likely promotes anti-inflammatory actions.

The universe of arachidonic acid metabolites in inflammatory bowel disease: can we tell the good from the bad?

PURPOSE OF REVIEW

This review summarizes recent developments in the role of soluble mediators of inflammation, particularly arachidonic acid metabolites, in inflammatory bowel disease (IBD).

RECENT FINDINGS

The role of prostaglandin E2 in immune regulation has been better defined. Prostaglandin E2 promotes not only immune tolerance and epithelial homeostasis but also the proinflammatory Th17 pathway. Prostaglandin D2 has been established as promoting the resolution of inflammation in the gastrointestinal mucosa. The 12-lipoxygenase product hepoxilin A3 mediates the migration of neutrophils from the mucosa into the lumen.

SUMMARY

Recent studies of soluble mediators, especially arachidonic acid metabolites, have defined their proinflammatory and anti-inflammatory roles in IBD.

Lung inflammation and thymic atrophy after bleomycin are controlled by the prostaglandin D2 receptor DP1

Acute lung injury (ALI) can be accompanied by secondary systemic manifestations. In a model of ALI induced by bleomycin (bleo), we examined the response of D prostanoid receptor 1 (DP1)-deficient mice (DP1(-/-)) to better understand these processes. DP1 deficiency aggravated the toxicity of bleo as indicated by enhanced body weight loss, mortality, and lung inflammation including bronchoalveolar permeability and neutrophilia. Thymic atrophy was also observed after bleo and was strongly exacerbated in DP1(-/-) mice. This resulted from the enhanced depletion of immature T lymphocytes in the thymus of DP1(-/-) mice, a phenomenon usually related to increased glucocorticoid release in blood. Serum corticosterone was more elevated in DP1(-/-) mice after bleo than in wild-type (wt) mice. Thymocytes of DP1(-/-) mice were not more sensitive to dexamethasone in vitro, and systemic delivery of dexamethasone or peritoneal inflammation after LPS induced a similar thymic atrophy in wt and DP1(-/-) mice, indicating that pulmonary DP1 was critical to the control of thymic atrophy after bleo. DP1(-/-) mice showed increased lung and/or blood mediators involved in neutrophil recruitment and/or glucocorticoid production/thymic atrophy (osteopontin, leukemia inhibitory factor, and keratinocyte-derived chemokine) after bleo. Finally, local pulmonary DP1 activation or inhibition in wt mice abrogated or amplified thymic atrophy after bleo, respectively. Altogether, our data reveal that ALI can perturb the systemic T-cell pool by inducing thymic atrophy and that both pathological processes are controlled by the pulmonary DP1 receptor. This new pathway represents a potential therapeutic target in ALI.

Amniotic fluid stem cells improve survival and enhance repair of damaged intestine in necrotising enterocolitis via a COX-2 dependent mechanism

OBJECTIVE

Necrotising enterocolitis (NEC) remains one of the primary causes of morbidity and mortality in neonates and alternative strategies are needed. Stem cells have become a therapeutic option for other intestinal diseases, which share some features with NEC. We tested the hypothesis that amniotic fluid stem (AFS) cells exerted a beneficial effect in a neonatal rat model of NEC.

DESIGN

Rats intraperitoneally injected with AFS cells and their controls (bone marrow mesenchymal stem cells, myoblast) were analysed for survival, behaviour, bowel imaging (MRI scan), histology, bowel absorption and motility, immunofluorescence for AFS cell detection, degree of gut inflammation (myeloperoxidase and malondialdehyde), and enterocyte apoptosis and proliferation.

RESULTS

AFS cells integrated in the bowel wall and improved rat survival and clinical conditions, decreased NEC incidence and macroscopic gut damage, improved intestinal function, decreased bowel inflammation, increased enterocyte proliferation and reduced apoptosis. The beneficial effect was achieved via modulation of stromal cells expressing cyclooxygenase 2 in the lamina propria, as shown by survival studies using selective and non-selective cyclooxygenase 2 inhibitors. Interestingly, AFS cells differentially expressed genes of the Wnt/β-catenin pathway, which regulate intestinal epithelial stem cell function and cell migration and growth factors known to maintain gut epithelial integrity and reduce mucosal injury.

CONCLUSIONS

We demonstrated here for the first time that AFS cells injected in an established model of NEC improve survival, clinical status, gut structure and function. Understanding the mechanism of this effect may help us to develop new cellular or pharmacological therapies for infants with NEC.

Cryptogenic multifocal ulcerating stenosing enteritis associated with homozygous deletion mutations in cytosolic phospholipase A2-α

OBJECTIVE

Cryptogenic multifocal ulcerating stenosing enteritis (CMUSE) is an extremely rare, but devastating, disease of unknown aetiology. We investigated the genetic basis of this autosomal recessive condition in a pair of affected siblings who have 40-year histories of catastrophic gastrointestinal and extraintestinal disease.

DESIGN

Genome-wide single-nucleotide polymorphism homozygosity mapping in the two affected family members combined with whole-exome sequencing of one affected sibling. This was followed by confirmatory Sanger sequencing of the likely disease-causing sequence variant and functional studies in affected and unaffected family members.

RESULTS

Insertion/deletion variation analysis revealed the presence of a homozygous 4 bp deletion (g.155574_77delGTAA) in the PLA2G4A gene, located in the splice donor site directly after exon 17 (the penultimate exon) of the gene in both affected siblings. This introduces a frameshift of 10 amino acids before a premature stop codon (p.V707fsX10), which is predicted to result in the loss of 43 amino acids (residues 707-749) at the C-terminus of cytosolic phospholipase A2-α (cPLA(2)α). cPLA(2)α protein expression was undetectable in the gut of both siblings, with platelet aggregation and thromboxane A(2) production, as functional assays for cPLA(2)α activity, grossly impaired.

CONCLUSIONS

We have identified mutations in PLA2G4A as a cause of CMUSE in two affected siblings. Further studies are needed to determine if mutations in this gene are also responsible for disease of a similar phenotype in other cases.

Opposing immunomodulatory roles of prostaglandin D2 during the progression of skin inflammation

The effects of PGD2 are extremely context dependent. It can have pro- or anti-inflammatory effects in clinically important pathological conditions. A greater mechanistic insight into the determinants of PGD2 activity during inflammation is thus required. In this study, we investigated the role of PGD2 in croton oil-induced dermatitis using transgenic (TG) mice overexpressing hematopoietic PGD synthase. Administration of croton oil caused tissue swelling and vascular leakage in the mouse ear. Compared with wild-type animals, TG mice produced more PGD2 and showed decreased inflammation in the early phase, but more severe manifestations during the late phase. Data obtained from bone marrow transplantation between wild-type and TG mice indicated that PGD2 produced by tissue resident cells in the TG mice attenuated early-phase inflammation, whereas PGD2 produced from hematopoietic lineage cells exacerbated late-phase inflammation. There are two distinct PGD2 receptors: D-prostanoid receptor (DP) and chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2). In TG mice, treatment with a DP antagonist exacerbated inflammation in the early phase, whereas treatment with a CRTH2 antagonist attenuated inflammation during the late phase. In vitro experiments showed that DP agonism enhanced vascular endothelial barrier formation, whereas CRTH2 agonism stimulated neutrophil migration. Collectively, these results show that when hematopoietic PGD synthase is overexpressed, tissue resident cell-derived PGD2 suppresses skin inflammation via DP in the early phase, but hematopoietic lineage cell-derived PGD2 stimulates CRTH2 and promotes inflammation during the late phase. DP-mediated vascular barrier enhancement or CRTH2-mediated neutrophil activation may be responsible for these effects. Thus, PGD2 represents opposite roles in inflammation, depending on the disease phase in vivo.

Diphenyl diselenide prevents hepatic alterations induced by paraquat in rats

This study aimed to investigate the beneficial effect of diphenyl diselenide (PhSe)₂ on paraquat (PQ) induced alterations in rats liver. Adult male Wistar rats received (PhSe)₂ at 10 mg kg(-1), by oral administration (p.o.), during five consecutive days. Twenty-four hours after the last (PhSe)₂ dose, rats received PQ at 15 mg kg(-1), in a single intraperitoneally injection (i.p.). Seventy-two hours after PQ exposure, animals were sacrificed by decapitation for blood and liver samples obtainment. Histological alterations induced by PQ exposure, such as inflammatory cells infiltration and edema, were prevented by (PhSe)₂ administration. Moreover, (PhSe)₂ prevented hepatic lipid peroxidation (LPO) induced by PQ and was effective in reducing the myeloperoxidase (MPO) activity in liver, which was enhanced by PQ exposure. (PhSe)₂ also was effective in protecting against the reduction in ascorbic acid and non-protein thiols (NPSH) levels induced by PQ. The inhibition of glutathione S-transferase (GST) activity, in rats exposed to PQ, was normalized by (PhSe)₂ pre-treatment, whereas the inhibition of catalase (CAT) activity was not prevented by (PhSe)₂. The serum alkaline phosphatase (ALP) inhibition, induced by PQ administration, was also prevented by (PhSe)₂ pre-treatment. Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities were not modified by PQ and/or (PhSe)₂ administration. Therefore, (PhSe)₂ pre-treatment was effective in protecting against the hepatic alterations induced by PQ in rats. This protective effect can involve the antioxidant and anti-inflammatory properties of (PhSe)₂.

Altered colonic mucosal Polyunsaturated Fatty Acid (PUFA) derived lipid mediators in ulcerative colitis: new insight into relationship with disease activity and pathophysiology

Objectives

Ulcerative colitis (UC) is a relapsing inflammatory disorder of unconfirmed aetiology, variable severity and clinical course, characterised by progressive histological inflammation and with elevation of eicosanoids which have a known pathophysiological role in inflammation. Therapeutic interventions targetting eicosanoids (5-aminosalicylates (ASA)) are effective first line and adjunctive treatments in mild-moderate UC for achieving and sustaining clinical remission. However, the variable clinical response to 5-ASA and frequent deterioration in response to cyclo-oxygenase (COX) inhibitors, has prompted an in depth simultaneous evaluation of multiple lipid mediators (including eicosanoids) within the inflammatory milieu in UC. We hypothesised that severity of inflammation is associated with alteration of lipid mediators, in relapsing UC.

Design

Study was case-control design. Mucosal lipid mediators were determined by LC-MS/MS lipidomics analysis on mucosal biopsies taken from patients attending outpatients with relapsing UC. Univariate and multivariate statistical analyses were used to investigate the association of mucosal lipid mediators, with the disease state and severity graded histologically.

Results

Levels of PGE₂, PGD₂, TXB₂, 5-HETE, 11-HETE, 12-HETE and 15-HETE are significantly elevated in inflamed mucosa and correlate with severity of inflammation, determined using validated histological scoring systems.

Conclusions

Our approach of capturing inflammatory mediator signature at different stages of UC by combining comprehensive lipidomics analysis and computational modelling could be used to classify and predict mild-moderate inflammation; however, predictive index is diminished in severe inflammation. This new technical approach could be developed to tailor drug treatments to patients with active UC, based on the mucosal lipid mediator profile.

Polyunsaturated fatty acid metabolism signature in ischemia differs from reperfusion in mouse intestine

Polyunsaturated fatty acid (PUFA) metabolites are bioactive autoacoids that play an important role in the pathogenesis of a vast number of pathologies, including gut diseases. The induction and the resolution of inflammation depend on PUFA metabolic pathways that are favored. Therefore, understanding the profile of n-6 (eicosanoids)/n-3 (docosanoids) PUFA-derived metabolites appear to be as important as gene or protein array approaches, to uncover the molecules potentially implicated in inflammatory diseases. Using high sensitivity liquid chromatography tandem mass spectrometry, we characterized the tissue profile of PUFA metabolites in an experimental model of murine intestinal ischemia reperfusion. We identified temporal and quantitative differences in PUFA metabolite production, which correlated with inflammatory damage. Analysis revealed that early ischemia induces both pro-inflammatory and anti-inflammatory eicosanoid production. Primarily, LOX- (5/15/12/8-HETE, LTB4, LxA4) and CYP- (5, 6-EET) metabolites were produced upon ischemia, but also PGE3, and PDx. This suggests that different lipids simultaneously play a role in the induction and counterbalance of ischemic inflammatory response from its onset. COX-derived metabolites were more present from 2 to 5 hours after reperfusion, fitting with the concomitant inflammatory peaks. All metabolites were decreased 48 hours post-reperfusion except for to the pro-resolving RvE precursor 18-HEPE and the PPAR-γαμμα agonist, 15d-PGJ2. Data obtained through the pharmacological blockade of transient receptor potential vanilloid-4, which can be activated by 5, 6-EET, revealed that the endogenous activation of this receptor modulates post-ischemic intestinal inflammation. Altogether, these results demonstrate that different lipid pathways are involved in intestinal ischemia-reperfusion processes. Some metabolites, which expression is severely changed upon intestinal ischemia-reperfusion could provide novel targets and may facilitate the development of new pharmacological treatments.