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The fish oil constituent docosahexaenoic acid (DHA, 22:6 n-3) is a signaling lipid with anti-inflammatory properties. The molecular mechanisms underlying the biological effect of DHA are poorly understood. Here, we report the design, synthesis, and application of a complementary pair of bio-orthogonal, photoreactive probes based on the polyunsaturated scaffold DHA and its oxidative metabolite 17-hydroxydocosahexaenoic acid (17-HDHA). In these probes, an alkyne serves as a handle to introduce a fluorescent reporter group or a biotin-affinity tag via copper(I)-catalyzed azide-alkyne cycloaddition. This pair of chemical probes was used to map specific targets of the omega-3 signaling lipids in primary human macrophages. Prostaglandin reductase 1 (PTGR1) was identified as an interaction partner that metabolizes 17-oxo-DHA, an oxidative metabolite of 17-HDHA. 17-oxo-DHA reduced the formation of pro-inflammatory lipids 5-HETE and LTB4 in human macrophages and neutrophils. Our results demonstrate the potential of comparative photoaffinity protein profiling for the discovery of metabolic enzymes of bioactive lipids and highlight the power of chemical proteomics to uncover new biological insights.

Background&Aims: GPR120 (encoded by FFAR4 gene) is a receptor for long chain fatty acids, activated by ω-3 PUFAs, and expressed in many cell types. Its role in the context of colorectal cancer (CRC) is still puzzling with many controversial evidences. Here, we explored the involvement of epithelial GPR120 in the CRC development. Methods: Both in vitro and in vivo experiments were conducted to mimic the conditional deletion of the receptor from gut epithelium. Intestinal permeability and integrity of mucus layer were assessed by using Evans blue dye and immunofluorescence for MUC-2 protein, respectively. Microbiota composition, presence of lipid mediators and short chain fatty acids were analyzed in the stools of conditional GPR120 and wild type (WT) mice. Incidence and grade of tumors were evaluated in all groups of mice before and after colitis-associated cancer. Finally, GPR120 expression was analyzed in 9 human normal tissues, 9 adenomas, and 17 primary adenocarcinomas. Results: Our work for the first time highlight the role of the receptor in the progression of colorectal cancer. We observed that the loss of epithelial GPR120 in the gut results into increased intestinal permeability, microbiota translocation and dysbiosis, which turns into hyperproliferation of epithelial cells, likely through the activation of β -catenin signaling. Therefore, the loss of GPR120 represents an early event of CRC, but avoid its progression as invasive cancer. Conclusion: these results demonstrate that the epithelial GPR120 receptor is essential to maintain the mucosal barrier integrity and to prevent CRC developing. Therefore, our data pave the way to GPR120 as an useful marker for the phenotypic characterization of CRC lesions and as new potential target for CRC prevention.

Inflammation is a tightly regulated process. During the past decade it has become clear that the resolution of inflammation is an active process and its dysregulation can contribute to chronic inflammation. Several cells and soluble mediators, including lipid mediators, regulate the course of inflammation and its resolution. It is, however, unclear which signals and cells are involved in initiating the resolution process. Macrophages are tissue resident cells and key players in regulating tissue inflammation through secretion of soluble mediators, including lipids. We hypothesize that persistent inflammatory stimuli can initiate resolution pathways in macrophages. In this study, we detected 21 lipids in LPS-stimulated human monocyte-derived macrophages by liquid chromatography coupled to tandem mass spectrometry. Cyclooxygenase-derived Prostaglandins were observed in the first six hours of stimulation. Interestingly, a switch towards 15-lipoxygenase products, such as the pro-resolving lipid precursors 15-HEPE and 17-HDHA was observed after 24 h. The RNA and protein expression of cyclooxygenase and 15-lipoxygenase were in line with this trend. Treatment with 17-HDHA increased IL-10 production of monocyte-derived macrophages and decreased LTB4 production by neutrophils, indicating the anti-inflammatory property of this lipid. These data reveal that monocyte-derived macrophages contribute to the resolution of inflammation in time by the production of pro-resolving lipids after an initial inflammatory stimulus.

Critical conditions such as sepsis following infection or traumatic injury disturb the complex state of homeostasis that may lead to uncontrolled inflammation resulting in organ failure, shock and death. They are associated with endogenous mediators that control the onset of acute inflammatory response, but the central problem remains the complete resolution of inflammation. Omega-3 enriched lipid emulsions (Ω-3+ LEs) were used in experimental studies and clinical trials to establish homeostasis, yet with little understanding about their role on the resolution of inflammation and tissue regeneration. Here, we demonstrate that Ω-3 lipid emulsions (LEs) orchestrate inflammation-resolution/regeneration mechanism during sterile peritonitis and murine polymicrobial sepsis. Ω-3+ LEs recessed neutrophil infiltration, reduced pro-inflammatory mediators, reduced the classical monocyte and enhanced the non-classical monocytes/macrophages recruitment and finally increased the efferocytosis in sepsis. The actions of Ω-3+ LE were 5-lipoxygenase (5-LOX) and 12/15-lipoxygenase (12/15-LOX) dependent. Ω-3+ LEs shortened the resolution interval by 56%, stimulated the endogenous biosynthesis of resolution mediators lipoxin A4, protectin DX and maresin 1 and contributed to tissue regeneration. Ω-3+ LEs protected against hypothermia and weight loss and enhanced survival in murine polymicrobial sepsis. We highlighted a role of Ω-3+ LEs in regulating key mechanisms within the resolution terrain during murine sepsis. This might form the basis for a rational design of sepsis specific clinical nutrition.

Recovery after stroke is a multicellular process encompassing neurons, resident immune cells, and brain-invading cells. Stroke alters the gut microbiome, which in turn has considerable impact on stroke outcome. However, the mechanisms underlying gut–brain interaction and implications for long-term recovery are largely elusive. Here, we tested the hypothesis that short-chain fatty acids (SCFAs), key bioactive microbial metabolites, are the missing link along the gut–brain axis and might be able to modulate recovery after experimental stroke. SCFA supplementation in the drinking water of male mice significantly improved recovery of affected limb motor function. Usingin vivowide-field calcium imaging, we observed that SCFAs induced altered contralesional cortex connectivity. This was associated with SCFA-dependent changes in spine and synapse densities. RNA sequencing of the forebrain cortex indicated a potential involvement of microglial cells in contributing to the structural and functional remodeling. Further analyses confirmed a substantial impact of SCFAs on microglial activation, which depended on the recruitment of T cells to the infarcted brain. Our findings identified that microbiota-derived SCFAs modulate poststroke recovery via effects on systemic and brain resident immune cells.SIGNIFICANCE STATEMENTPrevious studies have shown a bidirectional communication along the gut–brain axis after stroke. Stroke alters the gut microbiota composition, and in turn, microbiota dysbiosis has a substantial impact on stroke outcome by modulating the immune response. However, until now, the mediators derived from the gut microbiome affecting the gut-immune-brain axis and the molecular mechanisms involved in this process were unknown. Here, we demonstrate that short-chain fatty acids, fermentation products of the gut microbiome, are potent and proregenerative modulators of poststroke neuronal plasticity at various structural levels. We identified that this effect was mediated via circulating lymphocytes on microglial activation. These results identify short-chain fatty acids as a missing link along the gut–brain axis and as a potential therapeutic to improve recovery after stroke.

Introduction Disturbances in onset and resolution of inflammation in chronic obstructive pulmonary disease (COPD) are incompletely understood. Dietary polyunsaturated fatty acids (PUFAs) can be converted into lipid mediators here collectively named oxylipins. These include classical eicosanoids, but also pro-resolving mediators. A balanced production of pro-inflammatory and pro-resolving oxylipins is of importance for adequate inflammatory responses and subsequent return to homeostasis. Objectives Here we investigated if PUFA metabolism is disturbed in COPD patients. Methods Free PUFA and oxylipin levels were measured in induced sputum samples from the Bergen COPD cohort and COPD exacerbation study using liquid chromatography-mass spectrometry. Additionally, effects of whole cigarette smoke on PUFA metabolism in air-liquid interface cultures of primary bronchial epithelial cells were assessed. Results Significantly lower levels of free alpha-linolenic acid, linoleic acid and eicosapentaenoic acid (EPA) were detected in sputum from stable COPD patients compared to controls. During acute exacerbation (AE), levels of free arachidonic acid and docosapentaenoic acid were higher than in stable COPD patients. Furthermore, levels of omega-3 EPA- and docosahexaenoic acid-derived oxylipins were lower in sputum from stable COPD patients compared to controls. Cyclooxygenase-2-converted mediators were mostly increased during AE. In vitro studies additionally showed that cigarette smoke exposure may also directly contribute to altered epithelial PUFA metabolism, and indirectly by causing airway epithelial remodelling. Conclusions Our findings show significant differences in PUFA metabolism in COPD patients compared to controls, further changed during AE. Airway epithelial remodelling may contribute to these changes. These findings provide new insight in impaired inflammatory resolution in COPD.

Our body contains a wide variety of fatty acids that differ in chain length, the degree of unsaturation, and location of the double bonds. As the various fatty acids play distinct roles in health and disease, methods that can specifically determine the fatty acid profile are needed for fundamental and clinical studies. Here we describe a method for the separation and quantification of fatty acids ranging from 8 to 24 carbon chain lengths in blood samples using gas chromatography-mass spectrometry following derivatization using pentafluorobenzyl bromide. This method quantitatively monitors fatty acid composition in a manner that satisfies the requirements for comprehensiveness, sensitivity, and accuracy.