Cell type-specific modulation of lipid mediator's formation in murine adipose tissue by omega-3 fatty acids

Cardiac immune cell infiltration associates with abnormal lipid metabolism

CD36 mediates the uptake of long-chain fatty acids (FAs), a major energy substrate for the myocardium. Under excessive FA supply, CD36 can cause cardiac lipid accumulation and inflammation while its deletion reduces heart FA uptake and lipid content and increases glucose utilization. As a result, CD36 was proposed as a therapeutic target for obesity-associated heart disease. However, more recent reports have shown that CD36 deficiency suppresses myocardial flexibility in fuel preference between glucose and FAs, impairing tissue energy balance, while CD36 absence in tissue macrophages reduces efferocytosis and myocardial repair after injury. In line with the latter homeostatic functions, we had previously reported that CD36^-/- mice have chronic subclinical inflammation. Lipids are important for the maintenance of tissue homeostasis and there is limited information on heart lipid metabolism in CD36 deficiency. Here, we document in the hearts of unchallenged CD36^-/- mice abnormalities in the metabolism of triglycerides, plasmalogens, cardiolipins, acylcarnitines, and arachidonic acid, and the altered remodeling of these lipids in response to an overnight fast. The hearts were examined for evidence of inflammation by monitoring the presence of neutrophils and pro-inflammatory monocytes/macrophages using the respective positron emission tomography (PET) tracers, ⁶⁴Cu-AMD3100 and ⁶⁸Ga-DOTA-ECL1i. We detected significant immune cell infiltration in unchallenged CD36^-/- hearts as compared with controls and immune infiltration was also observed in hearts of mice with cardiomyocyte-specific CD36 deficiency. Together, the data show that the CD36^-/- heart is in a non-homeostatic state that could compromise its stress response. Non-invasive immune cell monitoring in humans with partial or total CD36 deficiency could help evaluate the risk of impaired heart remodeling and disease.

Regulation of Adipose Tissue Biology by Long-Chain Fatty Acids: Metabolic Effects and Molecular Mechanisms

Long-chain fatty acids (LCFA) modulate metabolic, oxidative, and inflammatory responses, and the physiological effects of LCFA are determined by chain length and the degree of saturation. Adipose tissues comprise multiple cell types, and play a significant role in energy storage and expenditure. Fatty acid uptake and oxidation are the pathways through which fatty acids participate in the regulation of energy homeostasis, and their dysregulation can lead to the development of obesity and chronic obesity-related disorders, including type 2 diabetes, cardiovascular diseases, and certain types of cancer. Numerous studies have reported that many aspects of adipose tissue biology are influenced by the number and position of double bonds in LCFA, and these effects are mediated by various signaling pathways, including those regulating adipocyte differentiation (adipogenesis), thermogenesis, and inflammation in adipose tissue. This review aims to describe the underlying molecular mechanisms by which different types of LCFA influence adipose tissue metabolism, and to further clarify their relevance to metabolic dysregulation associated with obesity. A better understanding of the effects of LCFA on adipose tissue metabolism may lead to improved nutraceutical strategies to address obesity and obesity-associated diseases.

Crosstalk between ORMDL3, serine palmitoyltransferase, and 5-lipoxygenase in the sphingolipid and eicosanoid metabolic pathways

Leukotrienes (LTs) and sphingolipids are critical lipid mediators participating in numerous cellular signal transduction events and developing various disorders, such as bronchial hyperactivity leading to asthma. Enzymatic reactions initiating production of these lipid mediators involve 5-lipoxygenase (5-LO)-mediated conversion of arachidonic acid to LTs and serine palmitoyltransferase (SPT)-mediated de novo synthesis of sphingolipids. Previous studies have shown that endoplasmic reticulum membrane protein ORM1-like protein 3 (ORMDL3) inhibits the activity of SPT and subsequent sphingolipid synthesis. However, the role of ORMDL3 in the synthesis of LTs is not known. In this study, we used peritoneal-derived mast cells isolated from ORMDL3 KO or control mice and examined their calcium mobilization, degranulation, NF-κB inhibitor-α phosphorylation, and TNF-α production. We found that peritoneal-derived mast cells with ORMDL3 KO exhibited increased responsiveness to antigen. Detailed lipid analysis showed that compared with WT cells, ORMDL3-deficient cells exhibited not only enhanced production of sphingolipids but also of LT signaling mediators LTB₄, 6t-LTB₄, LTC₄, LTB₅, and 6t-LTB₅. The crosstalk between ORMDL3 and 5-LO metabolic pathways was supported by the finding that endogenous ORMDL3 and 5-LO are localized in similar endoplasmic reticulum domains in human mast cells and that ORMDL3 physically interacts with 5-LO. Further experiments showed that 5-LO also interacts with the long-chain 1 and long-chain 2 subunits of SPT. In agreement with these findings, 5-LO knockdown increased ceramide levels, and silencing of SPTLC1 decreased arachidonic acid metabolism to LTs to levels observed upon 5-LO knockdown. These results demonstrate functional crosstalk between the LT and sphingolipid metabolic pathways, leading to the production of lipid signaling mediators.

Mass spectrometry-based determination of lipids and small molecules composing adipose tissue with a focus on brown adipose tissue

Adipose tissue has been the subject of research for a very long time. Many studies perform a comprehensive analysis of different types of adipose tissue with an emphasis on brown adipose tissue. Mass spectrometry-based approaches are particularly useful in the exploration not only of the metabolic composition of adipose tissue but also its function. In the presented review, a complex and critical overview of publications devoted to the analysis of adipose tissue by means of mass spectrometry was performed. Detailed investigation of analytical aspects related to either untargeted or targeted analysis of adipose tissue was performed, leading to the formation of a collection of hints at the available analytical methods. Moreover, a profound analysis of the metabolic composition of brown adipose tissue was performed. Brown adipose tissue metabolome was characterized on structural and functional levels, providing information about its exact metabolic composition but also connecting these molecules and placing them into biochemical pathways. All our work resulted in a very broad picture of the analysis of adipose tissue, starting from the analytical aspects and finishing on the current knowledge about its composition.

Effect of flaxseed oil supplementation on the erythrocyte membrane fatty acid composition and endocannabinoid system modulation in patients with coronary artery disease: a double-blind randomized controlled trial

Background

The endocannabinoid system (ECS) overactivation, associated with increased inflammatory process, may act as a risk factor for coronary artery disease (CAD). Dietary fat may influence the ECS tone. The aim of the present study was to investigate the effect of flaxseed oil on the erythrocyte membrane fatty acid profile and ECS activity by the measurement of serum N-arachydonoil ethanolamine (AEA) and cannabinoid receptor type-1 (CB1), cannabinoid receptor type-2 (CB2), and fatty acid amide hydrolase (FAAH) mRNA expression.

Methods

This clinical trial was performed on 44 patients with CAD. The intervention group received 1.5% fat milk supplemented with flaxseed oil (containing 2.5 g α-linolenic acid or ALA), while the placebo group received 1.5% fat milk for 10 weeks. The fatty acid profile of erythrocyte membrane phospholipids was measured by gas chromatography. The AEA level was determined using an ELISA kit, and real-time PCR was performed to measure CB1, CB2, and FAAH mRNA expression pre- and post-intervention.

Results

Flaxseed oil supplementation resulted in a significant increase in the ALA content and a significant reduction in linoleic acid (LA) content of membrane phospholipids, compared to the placebo group (MD = − 0.35 and 2.89, respectively; P < 0.05). The within group analysis showed that flaxseed oil supplementation caused a significant reduction in both LA and arachidonic acid (MD = − 4.84 and − 4.03, respectively; P < 0.05) and an elevation in the ALA (MD = 0.37, P < 0.001) content of membrane phospholipids compared with the baseline. In the intervention group, a marked reduction was observed in the serum AEA level after 10 weeks of intervention, compared with the placebo group (MD = 0.64, P = 0.016). Changes in CB2 mRNA expression in the flaxseed oil group were significant (fold change = 1.30, P = 0.003), compared with the placebo group.

Conclusion

Flaxseed oil supplementation could attenuate the ECS tone by decreasing the AEA level and increasing CB2 mRNA expression. Therefore, flaxseed oil may be considered a promising agent with cardioprotective properties.

Increased plasma levels of palmitoleic acid may contribute to beneficial effects of Krill oil on glucose homeostasis in dietary obese mice

Omega-3 polyunsatuarted fatty acids (PUFA) are associated with hypolipidemic and anti-inflammatory effects. However, omega-3 PUFA, usually administered as triacylglycerols or ethyl esters, could also compromise glucose metabolism, especially in obese type 2 diabetics. Phospholipids represent an alternative source of omega-3 PUFA, but their impact on glucose homeostasis is poorly explored. Male C57BL/6N mice were fed for 8 weeks a corn oil-based high-fat diet (cHF) alone or cHF-based diets containing eicosapentaenoic acid and docosahexaenoic acid (~3%; wt/wt), admixed either as a concentrate of re-esterified triacylglycerols (ω3TG) or Krill oil containing mainly phospholipids (ω3PL). Lean controls were fed a low-fat diet. Insulin sensitivity (hyperinsulinemic-euglycemic clamps), parameters of glucose homeostasis, adipose tissue function, and plasma levels of N-acylethanolamines, monoacylglycerols and fatty acids were determined. Feeding cHF induced obesity and worsened (~4.3-fold) insulin sensitivity as determined by clamp. Insulin sensitivity was almost preserved in ω3PL but not ω3TG mice. Compared with cHF mice, endogenous glucose production was reduced to 47%, whereas whole-body and muscle glycogen synthesis increased ~3-fold in ω3PL mice that showed improved adipose tissue function and elevated plasma adiponectin levels. Besides eicosapentaenoic and docosapentaenoic acids, principal component analysis of plasma fatty acids identified palmitoleic acid (C16:1n-7) as the most discriminating analyte whose levels were increased in ω3PL mice and correlated negatively with the degree of cHF-induced glucose intolerance. While palmitoleic acid from Krill oil may help improve glucose homeostasis, our findings provide a general rationale for using omega-3 PUFA-containing phospholipids as nutritional supplements with potent insulin-sensitizing effects.

Endocannabinoid system and cardiometabolic risk factors: A comprehensive systematic review insight into the mechanistic effects of omega-3 fatty acids

Increased levels of endocannabinoids, 2-arachidonoylglycerol (2-AG) and arachidonoyl ethanolamide (AEA) have a pathophysiological role in the setting of cardiometabolic diseases. This systematic review was carried out to appraise the effect of omega-3 on cardiometabolic risk factors by highlighting the mediating effect of endocannabinoids. SCOPUS, PubMed, Embase, Google Scholar and ProQuest databases were searched until January 2020. All published English-language animal studies and clinical trials that evaluated the effects of omega-3 on cardiometabolic diseases with a focus on endocannabinoids were included. Of 1407 studies, 16 animal studies and three clinical trials were included for analysis. Eleven animal studies and two human studies showed a marked reduction in 2-AG and AEA levels following intake of omega-3 which correlated with decreased adiposity, weight gain and improved glucose homeostasis. Moreover, endocannabinoids were elevated in three studies that replaced omega-3 with omega-6. Omega-3 showed anti-inflammatory properties due to reduced levels of inflammatory cytokines, regulation of T-cells function and increased levels of eicosapentaenoyl ethanolamide, docosahexaenoyl ethanolamide and oxylipins; however, a limited number of studies examined a correlation between inflammatory cytokines and endocannabinoids following omega-3 administration. In conclusion, omega-3 modulates endocannabinoid tone, which subsequently attenuates inflammation and cardiometabolic risk factors. However, further randomized clinical trials are needed before any recommendations are made to target the ECS using omega-3 as an alternative therapy to drugs for cardiometabolic disease improvement.

Combining Machine Learning and Metabolomics to Identify Weight Gain Biomarkers

Weight gain is a metabolic disorder that often culminates in the development of obesity and other comorbidities such as diabetes. Obesity is characterized by the development of a chronic, subclinical systemic inflammation, and is regarded as a remarkably important factor that contributes to the development of such comorbidities. Therefore, laboratory methods that allow the identification of subjects at higher risk for severe weight-associated morbidity are of utter importance, considering the health, and safety of populations. This contribution analyzed the plasma of 180 Brazilian individuals, equally divided into a eutrophic control group and case group, to assess the presence of biomarkers related to weight gain, aiming at characterizing the phenotype of this population. Samples were analyzed by mass spectrometry and most discriminant features were determined by a machine learning approach using Random Forest algorithm. Five biomarkers related to the pathogenesis and chronicity of inflammation in weight gain were identified. Two metabolites of arachidonic acid were upregulated in the case group, indicating the presence of inflammation, as well as two other molecules related to dysfunctions in the cycle of nitric oxide (NO) and increase in superoxide production. Finally, a fifth case group marker observed in this study may indicate the trigger for diabetes in overweight and obesity individuals. The use of mass spectrometry combined with machine learning analyses to prospect and characterize biomarkers associated with weight gain will pave the way for elucidating potential therapeutic and prognostic targets.

Role of anti-inflammatory interventions in high-fat-diet-induced obesity

Lipotoxicity is defined as deposition of excess fat associated with an inflammatory response. Metabolomic analysis of fatty acids (FAs) can be a marker of silent inflammation. ω3-Enriched diet, celecoxib, and safranal may have a protective anti-inflammatory role. In this work, total FAs extracted from red blood cells and arachidonic acid-to-eicosapentaenoic acid (AA-to-EPA) ratios were assessed using GC-MS assay in single-ion monitoring mode. The study was conducted on 64 male rats divided into eight groups: I, controls; II, rats received high-fat diet (HFD), III, rats received ω-6-enriched HFD; IV, rats received ω-3-enriched HFD; V, rats received celecoxib with HFD; VI, rats received safranal with HFD; VII and VIII, rats received celecoxib and safranal with ω-3 HFD, respectively. GC-MS Gas chromatography Mass spectrometry was performed for analysis of fatty acid methyl ester. Enzyme-linked immunosorbent assay was used to analyze serum interleukin-6 (IL-6) and transforming growth factor-beta 1 (TGF-β1) concentrations. A statistically significant decrease of AA-to-EPA ratio was observed in group VII when compared with the groups receiving HFDs. This group also showed the lowest serum IL-6 level and highest TGF-β1 level. In conclusion, ω3-enriched diet along with drugs (e.g. celecoxib) and herbal medications (e.g. safranal) may have an anti-inflammatory effect in lipotoxicity. GC-MS with single-ion monitoring is valid for the analysis of FAs.

Differential Anti-Adipogenic Effects of Eicosapentaenoic and Docosahexaenoic Acids in Obesity

SCOPE

To assess the associations of plasma eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) with body fat in a population-based sample and explore the mechanism of action based on browning of white adipose tissue (WAT) in high-fat-diet-induced obese (DIO) mice and 3T3-L1 adipocytes.

METHODS AND RESULTS

Plasma EPA and DHA of 1719 adults in the National Health and Nutrition Examination Survey (2003-2004) are determined by gas chromatography mass spectrometry, while total body fat is measured by dual-energy X-ray absorptiometry. DIO mice are fed a high-fat diet supplemented with EPA or DHA (1% wt/wt) for 15 weeks and 3T3-L1 preadipocytes are treated with EPA or DHA during differentiation. Plasma DHA but not EPA is associated with lower body fat mass (p_trend < 0.0001), which persists in overweight/obese subjects (p_trend = 0.02). DHA supplementation reduces inguinal WAT and exhibits a more pronounced thermogenic effect than EPA in DIO mice. In vitro, the browning process is induced after 2-day and 6-day treatment with DHA and EPA, respectively.

CONCLUSION

Plasma DHA but not EPA is inversely associated with body fat mass. The more potent anti-adipogenic effect of DHA than EPA may involve a better capability of inducing browning of WAT for DHA.

Reduced Number of Adipose Lineage and Endothelial Cells in Epididymal fat in Response to Omega-3 PUFA in Mice Fed High-Fat Diet

We found previously that white adipose tissue (WAT) hyperplasia in obese mice was limited by dietary omega-3 polyunsaturated fatty acids (omega-3 PUFA). Here we aimed to characterize the underlying mechanism. C57BL/6N mice were fed a high-fat diet supplemented or not with omega-3 PUFA for one week or eight weeks; mice fed a standard chow diet were also used. In epididymal WAT (eWAT), DNA content was quantified, immunohistochemical analysis was used to reveal the size of adipocytes and macrophage content, and lipidomic analysis and a gene expression screen were performed to assess inflammatory status. The stromal-vascular fraction of eWAT, which contained most of the eWAT cells, except for adipocytes, was characterized using flow cytometry. Omega-3 PUFA supplementation limited the high-fat diet-induced increase in eWAT weight, cell number (DNA content), inflammation, and adipocyte growth. eWAT hyperplasia was compromised due to the limited increase in the number of preadipocytes and a decrease in the number of endothelial cells. The number of leukocytes and macrophages was unaffected, but a shift in macrophage polarization towards a less inflammatory phenotype was observed. Our results document that the counteraction of eWAT hyperplasia by omega-3 PUFA in dietary-obese mice reflects an effect on the number of adipose lineage and endothelial cells.

Differential modulation of white adipose tissue endocannabinoid levels by n-3 fatty acids in obese mice and type 2 diabetic patients

n-3 polyunsaturated fatty acids (n-3 PUFA) might regulate metabolism by lowering endocannabinoid levels. We examined time-dependent changes in adipose tissue levels of endocannabinoids as well as in parameters of glucose homeostasis induced by n-3 PUFA in dietary-obese mice, and compared these results with the effect of n-3 PUFA intervention in type 2 diabetic (T2DM) subjects. Male C57BL/6J mice were fed for 8, 16 or 24 weeks a high-fat diet alone (cHF) or supplemented with n-3 PUFA (cHF + F). Overweight/obese, T2DM patients on metformin therapy were given for 24 weeks corn oil (Placebo; 5 g/day) or n-3 PUFA concentrate as above (Omega-3; 5 g/day). Endocannabinoids were measured by liquid chromatography-tandem mass-spectrometry. Compared to cHF-fed controls, the cHF + F mice consistently reduced 2-arachidonoylglycerol (up to ~2-fold at week 24) and anandamide (~2-fold) in adipose tissue, while the levels of endocannabinoid-related anti-inflammatory molecules N-eicosapentaenoyl ethanolamine (EPEA) and N-docosahexaenoyl ethanolamine (DHEA) increased more than ~10-fold and ~8-fold, respectively. At week 24, the cHF + F mice improved glucose tolerance and fasting blood glucose, the latter being positively correlated with adipose 2-arachidonoylglycerol levels only in obese cHF-fed controls, like fasting insulin and HOMA-IR. In the patients, n-3 PUFA failed to reduce 2-arachidonoylglycerol and anandamide levels in adipose tissue and serum, but they increased both adipose tissue and serum levels of EPEA and DHEA. In conclusion, the inability of n-3 PUFA to reduce adipose tissue and serum levels of classical endocannabinoids might contribute to a lack of beneficial effects of these lipids on glucose homeostasis in T2DM patients.

Distinct effects of dietary ALA, EPA and DHA on rat adipose oxylipins vary by depot location and sex

Dietary EPA and DHA given together alter oxylipins in adipose tissue. To compare the separate effects of individual dietary n-3 PUFA on oxylipins in different adipose depots (gonadal, mesenteric, perirenal, subcutaneous) in males and females, rats were provided diets containing higher levels of α-linolenic acid (ALA), EPA or DHA. Each n-3 PUFA enhanced its respective oxylipins the most, while effects on other n-3 oxylipins varied. For example: in perirenal and subcutaneous depots, more DHA oxylipins were higher with dietary ALA than with EPA; dietary EPA uniquely decreased 14-hydroxy-docosahexaenoic acid, in contrast to increasing many other DHA oxylipins. The n-3 PUFAs also reduced oxylipins from n-6 PUFAs in order of effectiveness: DHA > EPA > ALA. Diet by sex interactions in all depots except the perirenal depot resulted in higher oxylipins in males given DHA, and higher oxylipins in females given the other diets. Diet and sex effects on oxylipins did not necessarily reflect effects on either their tissue phospholipid or neutral lipid PUFA precursors. These varying diet and sex effects on oxylipins in the different adipose sites indicate that they may have distinct effects on adipose function.

Omega-3 fatty acids and adipose tissue biology

This review provides evidence for the importance of white and brown adipose tissue (i.e. WAT and BAT) function for the maintenance of healthy metabolic phenotype and its preservation in response to omega-3 polyunsaturated fatty acids (omega-3 PUFA), namely in the context of diseased states linked to aberrant accumulation of body fat, systemic low-grade inflammation, dyslipidemia and insulin resistance. More specifically, the review deals with (i) the concept of immunometabolism, i.e. how adipose-resident immune cells and adipocytes affect each other and define the immune-metabolic interface; and (ii) the characteristic features of "healthy adipocytes" in WAT, which are relatively small fat cells endowed with a high capacity for mitochondrial oxidative phosphorylation, triacylglycerol/fatty acid (TAG/FA) cycling and de novo lipogenesis (DNL). The intrinsic metabolic features of WAT and their flexible regulations, reflecting the presence of "healthy adipocytes", provide beneficial local and systemic effects, including (i) protection against in situ endoplasmic reticulum stress and related inflammatory response during activation of adipocyte lipolysis; (ii) prevention of ectopic fat accumulation and dyslipidemia caused by increased hepatic VLDL synthesis, as well as prevention of lipotoxic damage of insulin signaling in extra-adipose tissues; and also (iii) increased synthesis of anti-inflammatory and insulin-sensitizing lipid mediators with pro-resolving properties, including the branched fatty acid esters of hydroxy fatty acids (FAHFAs), also depending on the activity of DNL in WAT. The "healthy adipocytes" phenotype can be induced in WAT of obese mice in response to various stimuli including dietary omega-3 PUFA, especially when combined with moderate calorie restriction, and possibly also with other life style (e.g. physical activity) or pharmacological (e.g. thiazolidinediones) interventions. While omega-3 PUFA could exert beneficial systemic effects by improving immunometabolism of WAT without a concomitant induction of BAT, it is currently not clear whether the metabolic effects of the combined intervention using omega-3 PUFA and calorie restriction or thiazolidinediones depend also on the activation of BAT function and/or the induction of brite/beige adipocytes in WAT. It remains to be established why omega-3 PUFA intervention in type 2 diabetic subjects does not improve insulin sensitivity and glucose homeostasis despite inducing various anti-inflammatory mediators in WAT, including the recently discovered docosahexaenoyl esters of hydroxy linoleic acid, the lipokines from the FAHFA family, as well as several endocannabinoid-related anti-inflammatory lipids. To answer the question whether and to which extent omega-3 PUFA supplementation could promote the formation of "healthy adipocytes" in WAT of human subjects, namely in the obese insulin-resistant patients, represents a challenging task that is of great importance for the treatment of some serious non-communicable diseases.

Docosahexaenoic acid (DHA) at the sn-2 position of triacylglycerols increases DHA incorporation in brown, but not in white adipose tissue, of hamsters

We hypothesised that the incorporation of docosahexaenoic acid (DHA) across adipose tissues will be higher when it is ingested as triacylglycerols (TAG) structured at the sn-2 position. Ten-week old male hamsters were allocated to 4 dietary treatments (n = 10): linseed oil (LSO-control group), fish oil (FO), fish oil ethyl esters (FO-EE) and structured DHA at the sn-2 position of TAG (DHA-SL) during 12 weeks. In opposition to the large variations found for fatty acid composition in retroperitoneal white adipose tissue (WAT), brown adipose tissue (BAT) was less responsive to diets. DHA was not found in subcutaneous and retroperitoneal WAT depots but it was successfully incorporated in BAT reaching the highest percentage in DHA-SL. The PCA on plasma hormones (insulin, leptin, adiponectin) and fatty acids discriminated BAT from WATs pointing towards an individual signature on fatty acid deposition, but did not allow for full discrimination of dietary treatments within each adipose tissue.

Marine Lipids on Cardiovascular Diseases and Other Chronic Diseases Induced by Diet: An Insight Provided by Proteomics and Lipidomics

Marine lipids, especially ω-3 polyunsaturated fatty acids (PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have largely been linked to prevention of diet-induced diseases. The anti-inflammatory and hypolipidemic properties of EPA and DHA supplementation have been well-described. However, there is still a significant lack of information about their particular mechanism of action. Furthermore, repeated meta-analyses have not shown conclusive results in support of their beneficial health effects. Modern "omics" approaches, namely proteomics and lipidomics, have made it possible to identify some of the mechanisms behind the benefits of marine lipids in the metabolic syndrome and related diseases, i.e., cardiovascular diseases and type 2 diabetes. Although until now their use has been scarce, these "omics" have brought new insights in this area of nutrition research. The purpose of the present review is to comprehensively show the research articles currently available in the literature which have specifically applied proteomics, lipidomics or both approaches to investigate the role of marine lipids intake in the prevention or palliation of these chronic pathologies related to diet. The methodology adopted, the class of marine lipids examined, the diet-related disease studied, and the main findings obtained in each investigation will be reviewed.

Molecular adaptations underlying the beneficial effects of hydroxytyrosol in the pathogenic alterations induced by a high-fat diet in mouse liver: PPAR-α and Nrf2 activation, and NF-κB down-regulation

SCOPE

Non-alcoholic fatty liver disease (NAFLD) is a condition characterized by an increment in the liver fat content, with a concomitant reduction in the content of n-3-long chain polyunsaturated fatty acids (n-3 LCPUFAs), downregulation of PPAR-α activity, and upregulation of NF-κB activity, effects that induce pro-lipogenic and pro-inflammatory responses. Hydroxytyrosol (HT), a polyphenol with cytoprotective effects present in extra virgin olive oil, improves the cellular antioxidant capacity for activation of transcription factor Nrf2. The objective of this work is to evaluate the molecular adaptations involved in the anti-lipogenic, anti-inflammatory, and anti-oxidant effects of HT supplementation in high-fat diet (HFD)-fed mice.

METHODS AND RESULTS

Male C57BL/6J mice received (i) control diet (10% fat); (ii) control diet + HT (daily doses of 5 mg per kg body weight), (iii) HFD (60% fat); or (iv) HFD + HT for 12 weeks. HFD-fed mice exhibited (i) liver steatosis; (ii) inflammation; (iii) oxidative stress; and (iv) depletion of n-3 LCPUFAs, together with down-regulation of PPAR-α and Nrf2, and up-regulation of NF-κB. HT supplementation attenuated the metabolic alterations produced by HFD, normalizing the activity of Nrf2, reducing the drop in activity of PPAR-α, and attenuating increment of NF-κB activation.

CONCLUSION

Supplementation with HT activating transcription factors PPAR-α and Nrf2, along with the deactivation of NF-κB, may reduce the liver alterations induced in HFD-fed mice.

Polyunsaturated fatty acids and endocannabinoids in health and disease

Polyunsaturated fatty acids (PUFAs) are lipid derivatives of omega-3 (docosahexaenoic acid, DHA, and eicosapentaenoic acid, EPA) or of omega-6 (arachidonic acid, ARA) synthesized from membrane phospholipids and used as a precursor for endocannabinoids (ECs). They mediate significant effects in the fine-tune adjustment of body homeostasis. Phyto- and synthetic cannabinoids also rule the daily life of billions worldwide, as they are involved in obesity, depression and drug addiction. Consequently, there is growing interest to reveal novel active compounds in this field. Cloning of cannabinoid receptors in the 90s and the identification of the endogenous mediators arachidonylethanolamide (anandamide, AEA) and 2-arachidonyglycerol (2-AG), led to the characterization of the endocannabinoid system (ECS), together with their metabolizing enzymes and membrane transporters. Today, the ECS is known to be involved in diverse functions such as appetite control, food intake, energy balance, neuroprotection, neurodegenerative diseases, stroke, mood disorders, emesis, modulation of pain, inflammatory responses, as well as in cancer therapy. Western diet as well as restriction of micronutrients and fatty acids, such as DHA, could be related to altered production of pro-inflammatory mediators (e.g. eicosanoids) and ECs, contributing to the progression of cardiovascular diseases, diabetes, obesity, depression or impairing conditions, such as Alzheimer' s disease. Here we review how diets based in PUFAs might be linked to ECS and to the maintenance of central and peripheral metabolism, brain plasticity, memory and learning, blood flow, and genesis of neural cells.

Omega-3 fatty acids promote fatty acid utilization and production of pro-resolving lipid mediators in alternatively activated adipose tissue macrophages

It is becoming increasingly apparent that mutual interactions between adipocytes and immune cells are key to the integrated control of adipose tissue inflammation and lipid metabolism in obesity, but little is known about the non-inflammatory functions of adipose tissue macrophages (ATMs) and how they might be impacted by neighboring adipocytes. In the current study we used metabolipidomic analysis to examine the adaptations to lipid overload of M1 or M2 polarized macrophages co-incubated with adipocytes and explored potential benefits of omega-3 polyunsaturated fatty acids (PUFA). Macrophages adjust their metabolism to process excess lipids and M2 macrophages in turn modulate lipolysis and fatty acids (FA) re-esterification of adipocytes. While M1 macrophages tend to store surplus FA as triacylglycerols and cholesteryl esters in lipid droplets, M2 macrophages channel FA toward re-esterification and β-oxidation. Dietary omega-3 PUFA enhance β-oxidation in both M1 and M2. Our data document that ATMs contribute to lipid trafficking in adipose tissue and that omega-3 PUFA could modulate FA metabolism of ATMs.

Resolving inflammation by using nutrition therapy: roles for specialized proresolving mediators

PURPOSE OF REVIEW

Inflammation is a unifying component of many of the diseases that afflict Western civilizations. Nutrition therapy and, in particular, essential fatty acid supplementation is one of the approaches that is currently in use for the treatment and management of many inflammatory conditions. The purpose of the present review is to discuss the recent literature in light of the discovery that essential fatty acids are converted by the body to a novel genus of lipid mediators, termed specialized proresolving mediators (SPMs).

RECENT FINDINGS

The SPM genus is composed of four mediator families - the lipoxins, resolvins, protectins, and maresins. These molecules potently and stereoselectively promote the termination of inflammation, tissue repair, and regeneration. Recent studies indicate that in disease, SPM production becomes dysregulated giving rise to a status of failed resolution. Of note, several studies found that omega-3 fatty acid supplementation, at doses within the recommended daily allowance, led to increases in several SPM families that correlate with enhanced white blood cell responses in humans and reduced inflammation in mice.

SUMMARY

Given the potent biological actions of SPM in organ protection and promoting bacterial clearance, nutritional therapies enriched in omega-3 fatty acids hold promise as a potential co-therapy approach when coupled with functional lipid mediator profiling.

Docosahexaenoic Acid-Derived Fatty Acid Esters of Hydroxy Fatty Acids (FAHFAs) With Anti-inflammatory Properties

White adipose tissue (WAT) is a complex organ with both metabolic and endocrine functions. Dysregulation of all of these functions of WAT, together with low-grade inflammation of the tissue in obese individuals, contributes to the development of insulin resistance and type 2 diabetes. n-3 polyunsaturated fatty acids (PUFAs) of marine origin play an important role in the resolution of inflammation and exert beneficial metabolic effects. Using experiments in mice and overweight/obese patients with type 2 diabetes, we elucidated the structures of novel members of fatty acid esters of hydroxy fatty acids-lipokines derived from docosahexaenoic acid (DHA) and linoleic acid, which were present in serum and WAT after n-3 PUFA supplementation. These compounds contained DHA esterified to 9- and 13-hydroxyoctadecadienoic acid (HLA) or 14-hydroxydocosahexaenoic acid (HDHA), termed 9-DHAHLA, 13-DHAHLA, and 14-DHAHDHA, and were synthesized by adipocytes at concentrations comparable to those of protectins and resolvins derived from DHA in WAT. 13-DHAHLA exerted anti-inflammatory and proresolving properties while reducing macrophage activation by lipopolysaccharides and enhancing the phagocytosis of zymosan particles. Our results document the existence of novel lipid mediators, which are involved in the beneficial anti-inflammatory effects attributed to n-3 PUFAs, in both mice and humans.

EPA prevents fat mass expansion and metabolic disturbances in mice fed with a Western diet

The impact of alpha linolenic acid (ALA), EPA, and DHA on obesity and metabolic complications was studied in mice fed a high-fat, high-sucrose (HF) diet. HF diets were supplemented with ALA, EPA, or DHA (1% w/w) and given to C57BL/6J mice for 16 weeks and to Ob/Ob mice for 6 weeks. In C57BL/6J mice, EPA reduced plasma cholesterol (-20%), limited fat mass accumulation (-23%) and adipose cell hypertrophy (-50%), and reduced plasma leptin concentration (-60%) compared with HF-fed mice. Furthermore, mice supplemented with EPA exhibited a higher insulin sensitivity (+24%) and glucose tolerance (+20%) compared with HF-fed mice. Similar effects were observed in EPA-supplemented Ob/Ob mice, although fat mass accumulation was not prevented. By contrast, in comparison with HF-fed mice, DHA did not prevent fat mass accumulation, increased plasma leptin concentration (+128%) in C57BL/6J mice, and did not improve glucose homeostasis in C57BL/6J and Ob/Ob mice. In 3T3-L1 adipocytes, DHA stimulated leptin expression whereas EPA induced adiponectin expression, suggesting that improved leptin/adiponectin balance may contribute to the protective effect of EPA. In conclusion, supplementation with EPA, but not ALA and DHA, could preserve glucose homeostasis in an obesogenic environment and limit fat mass accumulation in the early stage of weight gain.