Modulation of the endogenous omega-3 fatty acid and oxylipin profile in vivo-A comparison of the fat-1 transgenic mouse with C57BL/6 wildtype mice on an omega-3 fatty acid enriched diet

Oxidative stress leads to the formation of esterified erythro- and threo-dihydroxy-fatty acids in HepG2 cells

Oxidative stress plays a central role in pathophysiology. To assess oxidative stress, sensitive methods are required to monitor the cellular damage caused by reactive oxygen species. Phospholipid-bound isoprostanes, such as 5-iPF2α-VI determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) are currently the best markers for oxidative stress. Here, we describe erythro- and threo-dihydroxy-polyunsaturated fatty acids (PUFA), the hydrolysis products of trans- and cis-epoxy-PUFA, as new biomarkers of oxidative stress in cells. This is demonstrated in four oxidative stress models in HepG2 cells using radical-forming tert-butyl hydroperoxide, glutathione peroxidase 4 inhibiting RSL-3, the redox cycling agent paraquat or rotenone blocking the electron transport chain. LC-MS/MS analysis following the liberation of esterified oxylipins by saponification unveiled in all oxidative stress models a strong formation of erythro- and threo-dihydroxy-PUFA. The levels increased concentration-dependently and correlated to isoprostane 5-iPF2α-VI formation. Among the positional isomers derived from linoleic acid, arachidonic acid and docosahexaenoic acid, those bearing the dihydroxy-group closest to the carboxy terminus were predominantly formed. Thus, the highest concentrations were found of erythro-5,6-DiHETrE and erythro-4,5-DiHDPE, which allowed a more sensitive detection of oxidative stress compared to 5-iPF2α-VI levels. The (erythro-) dihydroxy-PUFA are a new set of markers, which enable a more comprehensive analysis of oxidative stress, particularly when combined with simultaneous LC-MS/MS quantification of trans-epoxy-PUFA and isoprostanes.

Brain Cytochrome P450: Navigating Neurological Health and Metabolic Regulation

Human cytochrome P450 (CYP) enzymes in the brain represent a crucial frontier in neuroscience, with far-reaching implications for drug detoxification, cellular metabolism, and the progression of neurodegenerative diseases. The brain's complex architecture, composed of interconnected cell types and receptors, drives unique neuronal signaling pathways, modulates enzyme functions, and leads to distinct CYP gene expression and regulation patterns compared to the liver. Despite their relatively low levels of expression, brain CYPs exert significant influence on drug responses, neurotoxin susceptibility, behavior, and neurological disease risk. These enzymes are essential for maintaining brain homeostasis, mediating cholesterol turnover, and synthesizing and metabolizing neurochemicals, neurosteroids, and neurotransmitters. Moreover, they are key participants in oxidative stress responses, neuroprotection, and the regulation of inflammation. In addition to their roles in metabolizing psychotropic drugs, substances of abuse, and endogenous compounds, brain CYPs impact drug efficacy, safety, and resistance, underscoring their importance beyond traditional drug metabolism. Their involvement in critical physiological processes also links them to neuroprotection, with significant implications for the onset and progression of neurodegenerative diseases. Understanding the roles of cerebral CYP enzymes is vital for advancing neuroprotective strategies, personalizing treatments for brain disorders, and developing CNS-targeting therapeutics. This review explores the emerging roles of CYP enzymes, particularly those within the CYP1-3 and CYP46 families, highlighting their functional diversity and the pathological consequences of their dysregulation on neurological health. It also examines the potential of cerebral CYP-based biomarkers to improve the diagnosis and treatment of neurodegenerative disorders, offering new avenues for therapeutic innovation.

Fat-1 Ameliorates Metabolic Dysfunction-Associated Fatty Liver Disease and Atherosclerosis through Promoting the Nuclear Localization of PPARα in Hamsters

Fat-1, an enzyme encoded by the fat-1 gene, is responsible for the conversion of endogenous omega-6 polyunsaturated fatty acids into omega-3 polyunsaturated fatty acids in Caenorhabditis elegans. To better investigate whether the expression of Fat-1 will exert a beneficial function in dyslipidemia and metabolic dysfunction-associated fatty liver disease (MAFLD), we established an adeno-associated virus 9 expressing Fat-1. We found that adeno-associated-virus-mediated expression of Fat-1 markedly reduced the levels of plasma triglycerides and total cholesterol but increased high-density lipoprotein levels in male wild-type hamsters on both chow diet and high-fat diet as well as in chow-diet-fed male LDLR-/- hamsters. Fat-1 ameliorated diet-induced MAFLD in wild-type hamsters by enhancing fatty acid oxidation through the hepatic peroxisome proliferator-activated receptor α (PPARα)-dependent pathway. Mechanistically, Fat-1 increased the levels of multiple lipid derivatives as ligands for PPARα and simultaneously facilitated the nuclear localization of PPARα. Our results provide new insights into the multiple therapeutic potentials of Fat-1 to treat dyslipidemia, MAFLD, and atherosclerosis.

Emerging mechanisms of organ crosstalk: The role of oxylipins

There is growing interest in the role of oxylipins in the pathophysiology of several diseases. This is accompanied by a limited but evolving evidence base describing augmented oxylipin concentrations in a range of complications including cardiovascular disease, obesity, liver disease and neurological disorders. Despite this, literature describing oxylipin profiles in blood and multiple organs is inconsistent and the mechanisms by which these profiles are altered, and the relationships between localised tissue and circulating oxylipins are poorly understood. Inflammation and immune response associated with disease requires communication across organs and physiological systems. For example, inflammation and comorbidities associated with obesity extend beyond the adipose tissue and affect the vascular, hepatobiliary and digestive systems amongst others. Communication between organs and physiological systems is implicated in the progression of disease as well as the maintenance of homeostasis. There is emerging evidence for the role of oxylipins as a mechanism of communication in organ crosstalk but the role of these in orchestrating multiple organ and system responses is poorly understood. Herein, we review evidence to support and describe the role of oxylipins in organ crosstalk via the cardiosplenic and gut-link axis. In addition, we review emerging mechanisms of oxylipin regulation, the gut microbiome and modification using nutritional intervention. Finally, we describe future perspectives for addressing challenges in measurement and interpretation of oxylipin research with focus on the host genome as a modifier of oxylipin profiles and response to dietary lipid intervention.

An Optimized Ex Vivo n-3 PUFA Supplementation Strategy for Primary Human Macrophages Shows That DHA Suppresses Prostaglandin E2 Formation

Evidence suggests beneficial effects of long-chain n-3 polyunsaturated fatty acids (PUFAs) in inflammatory diseases. However, the underlying mechanisms are still subject of research. For this purpose, we developed an ex vivo n-3 PUFA supplementation strategy. M2-like macrophages were supplemented for 2-3 days with 20-40 µM docosahexaenoic acid (DHA) during differentiation. Quality parameters include <3% oxylipins for PUFA-preparation, total fatty acids (FAs) <10 mM, and low oxylipins in plasma, n-3 PUFA <0.25 mM for the selection of donors of plasma as well as %n-6 in highly unsaturated fatty acids (HUFAs) ≥70% for donors of cells. Following supplementation, PUFA pattern of cells was shifted toward one described for blood and tissue from subjects with higher n-3 and lower n-6 PUFAs. This was accompanied by a decrease of arachidonic acid-derived oxylipins in a dose- and time-dependent manner in favor of n-3 PUFA ones. Stimulation with LPS resulted in decreased levels of pro-inflammatory prostaglandins in the DHA-supplemented cells, but no changes in cytokines. In vitro supplementation studies with n-3 PUFA need rigorous controls to exclude the background formation of oxylipins. By accounting for these possible confounders the described approach allows the mechanistic investigation of n-3 PUFAs in primary human immune cells, offering an alternative for intervention studies.

Essential Fatty Acids along the Women’s Life Cycle and Promotion of a Well-balanced Metabolism

Abstract:

Linoleic acid (ω-6 LA) and α-linolenic acid (ω-3 ALA) are essential fatty acids (EFA) for human beings. They must be consumed through diet and then extensively metabolized, a process that plays a fundamental role in health and eventually in disease prevention. Given the numerous changes depending on age and sex, EFA metabolic adaptations require further investigations along the women’s life cycle, from onset to decline of the reproductive age. Thus, this review explains women’s life cycle stages and their involvement in diet intake, digestion and absorption, the role of microbiota, metabolism, bioavailability, and EFA fate and major metabolites. This knowledge is crucial to promoting lipid homeostasis according to female physiology through well-directed health strategies. Concerning this, the promotion of breastfeeding, nutrition, and physical activity is cardinal to counteract ALA deficiency, LA/ALA imbalance, and the release of unhealthy derivatives. These perturbations arise after menopause that compromise both lipogenic and lipolytic pathways. The close interplay of diet, age, female organism, and microbiota also plays a central role in regulating lipid metabolism. Consequently, future studies are encouraged to propose efficient interventions for each stage of women's cycle. In this sense, plant-derived foods and products are promising to be included in women’s nutrition to improve EFA metabolism.

Effects of Omega-3 Polyunsaturated Fatty Acids on the Formation of Adipokines, Cytokines, and Oxylipins in Retroperitoneal Adipose Tissue of Mice

Oxylipins and specialized pro-resolving lipid mediators (SPMs) derived from polyunsaturated fatty acids (PUFAs) are mediators that coordinate an active process of inflammation resolution. While these mediators have potential as circulating biomarkers for several disease states with inflammatory components, the source of plasma oxylipins/SPMs remains a matter of debate but may involve white adipose tissue (WAT). Here, we aimed to investigate to what extent high or low omega (n)-3 PUFA enrichment affects the production of cytokines and adipokines (RT-PCR), as well as oxylipins/SPMs (liquid chromatography-tandem mass spectrometry) in the WAT of mice during lipopolysaccharide (LPS)-induced systemic inflammation (intraperitoneal injection, 2.5 mg/kg, 24 h). For this purpose, n-3 PUFA genetically enriched mice (FAT-1), which endogenously synthesize n-3 PUFAs, were compared to wild-type mice (WT) and combined with n-3 PUFA-sufficient or deficient diets. LPS-induced systemic inflammation resulted in the decreased expression of most adipokines and interleukin-6 in WAT, whereas the n-3-sufficient diet increased them compared to the deficient diet. The n-6 PUFA arachidonic acid was decreased in WAT of FAT-1 mice, while n-3 derived PUFAs (eicosapentaenoic acid, docosahexaenoic acid) and their metabolites (oxylipins/SPMs) were increased in WAT by genetic and nutritional n-3 enrichment. Several oxylipins/SPMs were increased by LPS treatment in WAT compared to PBS-treated controls in genetically n-3 enriched FAT-1 mice. Overall, we show that WAT may significantly contribute to circulating oxylipin production. Moreover, n-3-sufficient or n-3-deficient diets alter adipokine production. The precise interplay between cytokines, adipokines, and oxylipins remains to be further investigated.

Stearidonic acid improves eicosapentaenoic acid status: studies in humans and cultured hepatocytes

Background

Ahiflower oil from the seeds of Buglossoides arvensis is rich in α-linolenic acid (ALA) and stearidonic acid (SDA). ALA and SDA are potential precursor fatty acids for the endogenous synthesis of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are n3-long chain polyunsaturated fatty acids (n3-LC-PUFAS), in humans. Since taurine, an amino sulfonic acid, is often associated with tissues rich in n3-LC-PUFAS (e.g., in fatty fish, human retina), taurine may play a role in EPA- and DHA-metabolism.

Objective

To examine the capacity of the plant-derived precursor fatty acids (ALA and SDA) and of the potential fatty acid metabolism modulator taurine to increase n3-LC-PUFAS and their respective oxylipins in human plasma and cultivated hepatocytes (HepG2 cells).

Methods

In a monocentric, randomized crossover study 29 healthy male volunteers received three sequential interventions, namely ahiflower oil (9 g/day), taurine (1.5 g/day) and ahiflower oil (9 g/day) + taurine (1.5 g/day) for 20 days. In addition, cultivated HepG2 cells were treated with isolated fatty acids ALA, SDA, EPA, DHA as well as taurine alone or together with SDA.

Results

Oral ahiflower oil intake significantly improved plasma EPA levels (0.2 vs. 0.6% of total fatty acid methyl esters (FAMES)) in humans, whereas DHA levels were unaffected by treatments. EPA-levels in SDA-treated HepG2 cells were 65% higher (5.1 vs. 3.0% of total FAMES) than those in ALA-treated cells. Taurine did not affect fatty acid profiles in human plasma in vivo or in HepG2 cells in vitro. SDA-rich ahiflower oil and isolated SDA led to an increase in EPA-derived oxylipins in humans and in HepG2 cells, respectively.

Conclusion

The consumption of ahiflower oil improves the circulating levels of EPA and EPA-derived oxylipins in humans. In cultivated hepatocytes, EPA and EPA-derived oxylipins are more effectively increased by SDA than ALA.

n-3 Polyunsaturated Fatty Acids Modulate LPS-Induced ARDS and the Lung-Brain Axis of Communication in Wild-Type versus Fat-1 Mice Genetically Modified for Leukotriene B4 Receptor 1 or Chemerin Receptor 23 Knockout

Specialized pro-resolving mediators (SPMs) and especially Resolvin E1 (RvE1) can actively terminate inflammation and promote healing during lung diseases such as acute respiratory distress syndrome (ARDS). Although ARDS primarily affects the lung, many ARDS patients also develop neurocognitive impairments. To investigate the connection between the lung and brain during ARDS and the therapeutic potential of SPMs and its derivatives, fat-1 mice were crossbred with RvE1 receptor knockout mice. ARDS was induced in these mice by intratracheal application of lipopolysaccharide (LPS, 10 µg). Mice were sacrificed at 0 h, 4 h, 24 h, 72 h, and 120 h post inflammation, and effects on the lung, liver, and brain were assessed by RT-PCR, multiplex, immunohistochemistry, Western blot, and LC-MS/MS. Protein and mRNA analyses of the lung, liver, and hypothalamus revealed LPS-induced lung inflammation increased inflammatory signaling in the hypothalamus despite low signaling in the periphery. Neutrophil recruitment in different brain structures was determined by immunohistochemical staining. Overall, we showed that immune cell trafficking to the brain contributed to immune-to-brain communication during ARDS rather than cytokines. Deficiency in RvE1 receptors and enhanced omega-3 polyunsaturated fatty acid levels (fat-1 mice) affect lung-brain interaction during ARDS by altering profiles of several inflammatory and lipid mediators and glial activity markers.

Prevention of colitis-induced liver oxidative stress and inflammation in a transgenic mouse model with increased omega-3 polyunsaturated fatty acids

Inflammatory bowel disease (IBD) is an immune-mediated gut dysfunction, which might also be associated with an inflammatory phenotype in the liver. It is known that the nutritional intake of omega-3 polyunsaturated fatty acids (n-3 PUFA) is inversely correlated to the severity and occurrence of IBD. In order to investigate whether n-3 PUFA can also reduce liver inflammation and oxidative liver damage due to colon inflammation, we explored the dextran sulfate sodium (DSS)-induced colitis model in wild-type and fat-1 mice with endogenously increased n-3 PUFA tissue content. Besides confirming previous data of alleviated DSS-induced colitis in the fat-1 mouse model, the increase of n-3 PUFA also resulted in a significant reduction of liver inflammation and oxidative damage in colitis-affected fat-1 mice as compared to wild-type littermates. This was accompanied by a remarkable increase of established inflammation-dampening n-3 PUFA oxylipins, namely docosahexaenoic acid-derived 19,20-epoxydocosapentaenoic acid and eicosapentaenoic acid-derived 15-hydroxyeicosapentaenoic acid and 17,18-epoxyeicosatetraenoic acid. Taken together, these observations demonstrate a strong inverse correlation between the anti-inflammatory lipidome derived from n-3 PUFA and the colitis-triggered inflammatory changes in the liver by reducing oxidative liver stress.

Measuring brain docosahexaenoic acid turnover as a marker of metabolic consumption

Docosahexaenoic acid (DHA, 22:6n-3) accretion in brain phospholipids is critical for maintaining the structural fluidity that permits proper assembly of protein complexes for signaling. Furthermore, membrane DHA can by released by phospholipase A₂ and act as substrate for synthesis of bioactive metabolites that regulate synaptogenesis, neurogenesis, inflammation, and oxidative stress. Thus, brain DHA is consumed through multiple pathways including mitochondrial β-oxidation, autoxidation to neuroprostanes, as well as enzymatic synthesis of bioactive metabolites including oxylipins, synaptamide, fatty-acid amides, and epoxides. By using models developed by Rapoport and colleagues, brain DHA loss has been estimated to be 0.07-0.26 μmol DHA/g brain/d. Since β-oxidation of DHA in the brain is relatively low, a large portion of brain DHA loss may be attributed to synthesis of autoxidative and bioactive metabolites. In recent years, we have developed a novel application of compound specific isotope analysis to trace DHA metabolism. By the use of natural abundance in ¹³C-DHA in food supply, we are able to trace brain phospholipid DHA loss in free-living mice with estimates ranging from 0.11 to 0.38 μmol DHA/g brain/d, in reasonable agreement with previous methods. This novel fatty acid metabolic tracing methodology should improve our understanding of the factors that regulate brain DHA metabolism.

Impact of intravenous fish oil on omega-3 fatty acids and their derived lipid metabolites in patients with parenteral nutrition

BACKGROUND

Long-term parenteral nutrition (PN) can lead to intestinal failure-associated liver disease (IFALD). Omega-3 (n-3) polyunsaturated fatty acids (PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were shown to prevent IFALD. EPA-derived and DHA-derived oxylipins could contribute to this protective effect.

METHODS

We analyzed the effect of parenteral fish oil on oxylipins in patients with chronic intestinal failure receiving PN (n = 8). Patients first received no fish oil for 8 weeks and then switched to PN with 25% of fat as fish oil for another 8 weeks. Fatty acid profiles of red blood cells, PUFA-derived oxylipins generated by cyclooxygenase, lipoxygenase (LOX), and cytochrome P450 (CYP) pathways, inflammatory markers, and liver function were assessed before and during fish-oil PN.

RESULTS

EPA plus DHA in erythrocytes (the Omega-3 Index) was high with a median of 11.96% at baseline and decreased to 9.57% without fish oil in PN. Addition of fish oil in PN increased the median Omega-3-Index to 12.75%. EPA-derived and DHA-derived CYP-dependent and LOX-dependent metabolites increased significantly with fish oil in PN, with less pronounced changes in arachidonic acid and its oxylipins. There were no significant changes of inflammation and liver function parameters.

CONCLUSIONS

This study shows that fish oil-containing PN leads to primarily CYP- and LOX-dependent n-3 PUFA-derived inflammation-dampening oxylipins arising from EPA and DHA. Within this short (16-week) study, there were no significant changes in inflammation and clinical readout parameters.

A Review of Oxylipins in Alzheimer's Disease and Related Dementias (ADRD): Potential Therapeutic Targets for the Modulation of Vascular Tone and Inflammation

There is now a convincing body of evidence from observational studies that the majority of modifiable Alzheimer's disease and related dementia (ADRD) risk factors are vascular in nature. In addition, the co-existence of cerebrovascular disease with AD is more common than AD alone, and conditions resulting in brain ischemia likely promote detrimental effects of AD pathology. Oxylipins are a class of bioactive lipid mediators derived from the oxidation of long-chain polyunsaturated fatty acids (PUFAs) which act as modulators of both vascular tone and inflammation. In vascular cognitive impairment (VCI), there is emerging evidence that oxylipins may have both protective and detrimental effects on brain structure, cognitive performance, and disease progression. In this review, we focus on oxylipin relationships with vascular and inflammatory risk factors in human studies and animal models pertinent to ADRD. In addition, we discuss future research directions with the potential to impact the trajectory of ADRD risk and disease progression.

Comprehensive Analysis of Fatty Acid and Oxylipin Patterns in n3-PUFA Supplements

Supplementing long-chain omega-3 polyunsaturated fatty acids (n3-PUFA) improves health. We characterized the pattern of total and non-esterified oxylipins and fatty acids in n3 supplements made of fish, krill, or micro-algae oil by LC-MS. All supplements contained the declared amount of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA); however, their content per capsule and the concentration of other fatty acids varied strongly. Krill oil contained the highest total n3 oxylipin concentration (6000 nmol/g) and the highest degree of oxidation (EPA 0.7%; DHA 1.3%), while micro-algae oil (Schizochytrium sp.) showed the lowest oxidation (<0.09%). These oils contain specifically high amounts of the terminal hydroxylation product of EPA (20-HEPE, 300 nmol/g) and DHA (22-HDHA, 200 nmol/g), which can serve as an authenticity marker for micro-algae oil. Refined micro-algae and fish oil were characterized by NEFA levels of ≤0.1%. Overall, the oxylipin and fatty acid pattern allows gaining new insights into the origin and quality of n3-PUFA oils in supplements.

Maternal omega-3 fatty acids maintained positive maternal lipids and cytokines profile, and improved pregnancy outcomes of C57BL/6 mice

Omega (n)-3 polyunsaturated fatty acids (PUFA) are known to regulate lipid metabolism and inflammation; however, the regulation of maternal lipid metabolism and cytokines profile by n-3 PUFA during different gestation stages, and its impact on fetal sustainability is not known. We investigated the effects of maternal diet varying in n-3 PUFA prior to, and during gestation, on maternal metabolic profile, placental inflammatory cytokines, and fetal outcomes. Female C57BL/6 mice were fed either a high, low or very low (9, 3 or 1% w/w n-3 PUFA) diet, containing n-6:n-3 PUFA of 5:1, 20:1 and 40:1, respectively for two weeks before mating, and throughout pregnancy. Animals were sacrificed prior to mating (NP), and during pregnancy at gestation days 6.5, 12.5 and 18.5. Maternal metabolic profile, placental cytokines and fetal outcomes were determined. Our results show for the first time that a maternal diet high in n-3 PUFA prevented dyslipidemia in NP mice, and maintained the expected lipid profile during pregnancy. However, females fed the very low n-3 PUFA diet became hyperlipidemic prior to pregnancy, and carried this profile into pregnancy. Maternal diet high in n-3 PUFA maintained maternal plasma progesterone and placental pro-inflammatory cytokines profile, and sustained fetal numbers throughout pregnancy, while females fed the low and very-low n-3 PUFA diet had fewer fetuses. Our findings demonstrate the importance of maternal diet before, and during pregnancy, to maintain maternal metabolic profile and fetus sustainability. These findings are important when designing dietary strategies to optimize maternal metabolism during pregnancy for successful pregnancy outcome.

The Ω-3 fatty acid docosahexaenoic acid selectively induces apoptosis in tumor-derived cells and suppress tumor growth in gastric cancer

Despite current achievements and innovations in cancer treatment, conventional chemotherapy has several limitations, such as unsatisfactory long-term survival, cancer drug resistance and toxicity against non-tumoral cells. In the search for safer therapeutic alternatives, docosahexaenoic acid (DHA) has shown promising effects inhibiting tumor growth without significant side effects in several types of cancer, but in gastric cancer (GC) its effects have not been completely described. In this study, we characterized the effects of DHA in GC using in vivo and in vitro models. Among all of the evaluated Ω-3 and Ω-6 fatty acids, DHA showed the highest antiproliferative potency and selectivity against the GC-derived cell line AGS. 10-100 μM DHA decreased AGS cell viability in a concentration-dependent manner but had no effect on non-tumoral GES-1 cells. To evaluate if the effects of DHA were due to apoptosis induction, cells were stained with Annexin V-PI, observing that 75 and 100 μM DHA increased apoptosis in AGS, but not in GES-1 cells. Additionally, levels of several proapoptotic and antiapoptotic regulators were assessed by qPCR, western blot and activity assays, showing similar results. In order to evaluate DHA efficacy in vivo, xenografts in an immunodeficient mouse model (BALB/cNOD-SCID) were used. In these experiments, DHA treatment for six weeks consistently reduced subcutaneous tumor size, ascitic fluid volume and liver metastasis. In summary, we found that DHA has a selective antiproliferative effect on GC, being this effect driven by apoptosis induction. Our investigation provides promising features for DHA as potential therapeutic agent in GC.

Omega-3 fatty acids protect from colitis via an Alox15-derived eicosanoid

An increased omega-3 polyunsaturated fatty acid (n-3 PUFA) tissue status can lead to a significant formation of anti-inflammatory lipid mediators and effective reduction in inflammation and tissue injury in murine colitis. Arachidonic acid lipoxygenases (ALOX) have been implicated in the pathogenesis of inflammatory bowel disease as well as in the formation of pro- and anti-inflammatory lipid mediators. To explore the role of Alox15 in the protective response found in fat1 transgenic mice with endogenously increased n-3 PUFA tissue status fat1 transgenic mice were crossed with Alox15-deficient animals and challenged in the dextran sulfate sodium (DSS)- and the 2,4,6-trinitrobenzene sulphonic acid (TNBS)-induced colitis model. Transgenic fat1 mice rich in endogenous n-3 PUFAs were protected from colitis. However, additional systemic inactivation of the Alox15 gene counteracted this protective effect. To explore the molecular basis for this effect Alox15 lipid metabolites derived from n-3 PUFA were analyzed in the different mice. Alox15 deficiency suppressed the formation of n-3 PUFA-derived 15-hydroxy eicosapentaenoic acid (15-HEPE). In contrast, treating mice with intraperitoneal injections of 15S-HEPE protected wild-type mice from DSS- and TNBS-induced colitis. These data suggest that the anti-colitis effect of increased n-3 PUFA in the transgenic fat1 mouse model is mediated in part via Alox15-derived 15-HEPE formation.

A Walnut Diet in Combination with Enriched Environment Improves Cognitive Function and Affects Lipid Metabolites in Brain and Liver of Aged NMRI Mice

This in vivo study aimed to test if a diet enriched with 6% walnuts alone or in combination with physical activity supports healthy ageing by changing the oxylipin profile in brain and liver, improving motor function, cognition, and cerebral mitochondrial function. Female NMRI mice were fed a 6% walnut diet starting at an age of 12 months for 24 weeks. One group was additionally maintained in an enriched environment, one group without intervention served as control. After three months, one additional control group of young mice (3 weeks old) was introduced. Motor and cognitive functions were measured using Open Field, Y-Maze, Rotarod and Passive Avoidance tests. Lipid metabolite profiles were determined using RP-LC-ESI(-)-MS/MS in brain and liver tissues of mice. Cerebral mitochondrial function was characterized by the determination of ATP levels, mitochondrial membrane potential and mitochondrial respiration. Expression of genes involved with mito- and neurogenesis, inflammation, and synaptic plasticity were determined using qRT-PCR. A 6% walnut-enriched diet alone improved spatial memory in a Y-Maze alternation test (p < 0.05) in mice. Additional physical enrichment enhanced the significance, although the overall benefit was virtually identical. Instead, physical enrichment improved motor performance in a Rotarod experiment (p* < 0.05) which was unaffected by walnuts alone. Bioactive oxylipins like hydroxy-polyunsaturated fatty acids (OH-PUFA) derived from linoleic acid (LA) were significantly increased in brain (p** < 0.01) and liver (p*** < 0.0001) compared to control mice, while OH-PUFA of α-linolenic acid (ALA) could only be detected in the brains of mice fed with walnuts. In the brain, walnuts combined with physical activity reduced arachidonic acid (ARA)-based oxylipin levels (p < 0.05). Effects of walnut lipids were not linked to mitochondrial function, as ATP production, mitochondrial membrane potential and mitochondrial respiration were unaffected. Furthermore, common markers for synaptic plasticity and neuronal growth, key genes in the regulation of cytoprotective response to oxidative stress and neuronal growth were unaffected. Taken together, walnuts change the oxylipin profile in liver and brain, which could have beneficial effects for healthy ageing, an effect that can be further enhanced with an active lifestyle. Further studies may focus on specific nutrient lipids that potentially provide preventive effects in the brain.

Diet during early life defines testicular lipid content and sperm quality in adulthood

Childhood obesity is a serious concern associated with ill health later in life. Emerging data suggest that obesity has long-term adverse effects upon male sexual and reproductive health, but few studies have addressed this issue. We hypothesized that exposure to high-fat diet during early life alters testicular lipid content and metabolism, leading to permanent damage to sperm parameters. After weaning (day 21 after birth), 36 male mice were randomly divided into three groups and fed with a different diet regimen for 200 days: a standard chow diet (CTRL), a high-fat diet (HFD) (carbohydrate: 35.7%, protein: 20.5%, and fat: 36.0%), and a high-fat diet for 60 days, then replaced by standard chow (HFD_t). Biometric and metabolic data were monitored. Animals were then euthanized, and tissues were collected. Epididymal sperm parameters and endocrine parameters were evaluated. Testicular metabolites were extracted and characterized by 1H-NMR and GC-MS. Testicular mitochondrial and antioxidant activity were evaluated. Our results show that mice fed with a high-fat diet, even if only until early adulthood, had lower sperm viability and motility, and higher incidence of head and tail defects. Although diet reversion with weight loss during adulthood prevents the progression of metabolic syndrome, testicular content in fatty acids is irreversibly affected. Excessive fat intake promoted an overaccumulation of proinflammatory n-6 polyunsaturated fatty acids in the testis, which is strongly correlated with negative effects upon sperm quality. Therefore, the adoption of high-fat diets during early life correlates with irreversible changes in testicular lipid content and metabolism, which are related to permanent damage to sperm quality later in life.

Cytochrome P450 Metabolism of Polyunsaturated Fatty Acids and Neurodegeneration

Due to the aging population in the world, neurodegenerative diseases have become a serious public health issue that greatly impacts patients' quality of life and adds a huge economic burden. Even after decades of research, there is no effective curative treatment for neurodegenerative diseases. Polyunsaturated fatty acids (PUFAs) have become an emerging dietary medical intervention for health maintenance and treatment of diseases, including neurodegenerative diseases. Recent research demonstrated that the oxidized metabolites, particularly the cytochrome P450 (CYP) metabolites, of PUFAs are beneficial to several neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease; however, their mechanism(s) remains unclear. The endogenous levels of CYP metabolites are greatly affected by our diet, endogenous synthesis, and the downstream metabolism. While the activity of omega-3 (ω-3) CYP PUFA metabolites and omega-6 (ω-6) CYP PUFA metabolites largely overlap, the ω-3 CYP PUFA metabolites are more active in general. In this review, we will briefly summarize recent findings regarding the biosynthesis and metabolism of CYP PUFA metabolites. We will also discuss the potential mechanism(s) of CYP PUFA metabolites in neurodegeneration, which will ultimately improve our understanding of how PUFAs affect neurodegeneration and may identify potential drug targets for neurodegenerative diseases.

Effect of dietary EPA and DHA on murine blood and liver fatty acid profile and liver oxylipin pattern depending on high and low dietary n6-PUFA

The intake of long-chain n3-polyunsaturated fatty acids (PUFA), which are associated with beneficial health effects, is low in the Western diet, while the portion of dietary n6-PUFA and hence the n6/n3-PUFA ratio is high. Strategies to improve the n3-PUFA status are n3-PUFA supplementation and/or lowering n6-PUFA intake. In the present study, mice were fed with two different sunflower oil-based control diets rich in linoleic (n6-high) or oleic acid (n6-low), either with low n3-PUFA content (∼0.02%) as control or with ∼0.6% eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA). The n6-low diet had only little or no effect on levels of arachidonic acid (ARA) and its free oxylipins in liver tissue. Supplementation with EPA or DHA lowered ARA levels with an effect size of n6-high < n6-low. Blood cell %EPA + DHA reached >8% and >11% in n6-high and n6-low groups, respectively. Elevation of EPA levels and EPA derived oxylipins was most pronounced in n6-low groups in liver tissue, while levels of DHA and DHA derived oxylipins were generally unaffected by the background diet. While the n6-low diet alone had no effect on blood and liver tissue ARA levels or n3-PUFA status, a supplementation of EPA or DHA was more effective in combination with an n6-low diet. Thus, supplementation of long-chain n3-PUFA combined with a reduction of dietary n6-PUFA is the most effective way to improve the endogenous n3-PUFA status.

Harmonized procedures lead to comparable quantification of total oxylipins across laboratories

Oxylipins are potent lipid mediators involved in a variety of physiological processes. Their profiling has the potential to provide a wealth of information regarding human health and disease and is a promising technology for translation into clinical applications. However, results generated by independent groups are rarely comparable, which increases the need for the implementation of internationally agreed upon protocols. We performed an interlaboratory comparison for the MS-based quantitative analysis of total oxylipins. Five independent laboratories assessed the technical variability and comparability of 133 oxylipins using a harmonized and standardized protocol, common biological materials (i.e., seven quality control plasmas), standard calibration series, and analytical methods. The quantitative analysis was based on a standard calibration series with isotopically labeled internal standards. Using the standardized protocol, the technical variance was within ±15% for 73% of oxylipins; however, most epoxy fatty acids were identified as critical analytes due to high variabilities in concentrations. The comparability of concentrations determined by the laboratories was examined using consensus value estimates and unsupervised/supervised multivariate analysis (i.e., principal component analysis and partial least squares discriminant analysis). Interlaboratory variability was limited and did not interfere with our ability to distinguish the different plasmas. Moreover, all laboratories were able to identify similar differences between plasmas. In summary, we show that by using a standardized protocol for sample preparation, low technical variability can be achieved. Harmonization of all oxylipin extraction and analysis steps led to reliable, reproducible, and comparable oxylipin concentrations in independent laboratories, allowing the generation of biologically meaningful oxylipin patterns.

A single meal has the potential to alter brain oxylipin content

Our objective was to determine whether consumption of a single meal has the potential to alter brain oxylipin content. We examined the cerebrum of mice fed a single high-fat/high-sucrose Western meal or a low-fat/low-sucrose control meal, as well as fasted mice. We found no changes in fatty acid composition of cerebrum across the groups. The cerebral oxylipin profile of mice fed a Western meal is distinct from the profile of mice fed a low-fat/low-sucrose meal. Cerebral gene expression of cyclooxygenase 1, cyclooxygenase 2, and epoxide hydrolase 1 were elevated in Western meal-fed mice compared to low-fat/low-sucrose meal-fed mice. Mice that consumed either meal had lower gene expression of cytochrome P450, family 2, subfamily j, polypeptide 12 than fasted mice. Our data in this hypothesis-generating study indicates that the composition of a single meal has the potential to alter brain oxylipins and the gene expression of the enzymes responsible for their production.

Synthesis and function of fatty acids and oxylipins, with a focus on Caenorhabditis elegans

Polyunsaturated fatty acids (PUFAs) exhibit a diverse range of important biological functions in most biological systems. These PUFAs can be oxygenated via enzymatic or free radical-mediated reactions to form bioactive oxygenated lipid mediators termed oxylipins. Eicosanoids are broad class of oxylipins that are transient and locally synthesized signalling molecules, including prostaglandins, leukotrienes, lipoxins and thromboxanes, which mediate various physiological responses, such as inflammation. In addition to arachidonic acid-derived eicosanoids, current developments in lipidomic methodologies have brought attention to vast number of oxylipins produced from other PUFAs, including omega-3. Although, the molecular mechanisms of how PUFAs and oxylipins contribute to majority of the fundamental biological processes are largely unclear, a model organism Caenorhabditis elegans remains a powerful model for exploring lipid metabolism and functions of PUFAs and oxylipins. For instance, the ability of C. elegans to modify fatty acid composition with dietary supplementation and genetic manipulation enables the dissection of the roles of omega-3 and omega-6 PUFAs in many biological processes that include aging, reproduction, and neurobiology. However, much remains to be elucidated concerning the roles of oxylipins, but thus far, C. elegans is well-known for the synthesis of vast set of cytochrome (CYP) eicosanoids. These CYP eicosanoids are extremely susceptible to changes in the relative bioavailability of the different PUFAs, thus providing a better insight into complex mechanisms connecting essential dietary fatty acids to various biological processes. Therefore, this review provides an overview of the synthesis and function of PUFAs and oxylipins in mammals. It also focusses on what is known regarding the production of PUFAs and oxylipins in C. elegans and their functions.

α-Linolenic acid-enriched butter attenuated high fat diet-induced insulin resistance and inflammation by promoting bioconversion of n-3 PUFA and subsequent oxylipin formation

α-Linolenic acid (ALA) is an essential fatty acid and the precursor for long-chain n-3 PUFA. However, biosynthesis of n-3 PUFA is limited in a Western diet likely due to an overabundance of n-6 PUFA. We hypothesized that dietary reduction of n-6/n-3 PUFA ratio is sufficient to promote the biosynthesis of long-chain n-3 PUFA, leading to an attenuation of high fat (HF) diet-induced obesity and inflammation. C57BL/6 J mice were fed a HF diet from ALA-enriched butter (n3Bu, n-6/n-3=1) in comparison with isocaloric HF diets from either conventional butter lacking both ALA and LA (Bu, n-6/n-3=6), or margarine containing a similar amount of ALA and abundant LA (Ma, n-6/n-3=6). Targeted lipidomic analyses revealed that n3Bu feeding promoted the bioconversion of long-chain n-3 PUFA and their oxygenated metabolites (oxylipins) derived from ALA and EPA. The n3Bu supplementation attenuated hepatic TG accumulation and adipose tissue inflammation, resulting in improved insulin sensitivity. Decreased inflammation by n3Bu feeding was attributed to the suppression of NF-κB activation and M1 macrophage polarization. Collectively, our work suggests that dietary reduction of the n-6/n-3 PUFA ratio, as well as total n-3 PUFA consumed, is a crucial determinant that facilitates n-3 PUFA biosynthesis and subsequent lipidomic modifications, thereby conferring metabolic benefits against obesity-induced inflammation and insulin resistance.

MS-based targeted metabolomics of eicosanoids and other oxylipins: Analytical and inter-individual variabilities

Oxylipins, including the well-known eicosanoids, are potent lipid mediators involved in numerous physiological and pathological processes. Therefore, their quantitative profiling has gained a lot of attention during the last years notably in the active field of health biomarker discovery. Oxylipins include hundreds of structurally and stereochemically distinct lipid species which today are most commonly analyzed by (ultra) high performance liquid chromatography-mass spectrometry based ((U)HPLC-MS) methods. To maximize the utility of oxylipin profiling in clinical research, it is crucial to understand and assess the factors contributing to the analytical and biological variability of oxylipin profiles in humans. In this review, these factors and their impacts are summarized and discussed, providing a framework for recommendations expected to enhance the interlaboratory comparability and biological interpretation of oxylipin profiling in clinical research.

Targeting esterified oxylipins by LC-MS - Effect of sample preparation on oxylipin pattern

A major part of oxygenated metabolites of polyunsaturated fatty acids - i.e. eicosanoids and other oxylipins - in biological samples is found in the esterified form. Yet, their biological role is only poorly understood. For quantification of esterified oxylipins in biological samples current protocols mostly apply alkaline hydrolysis with or without prior lipid extraction to release oxylipins into their free form which can be subsequently quantified via liquid chromatography-mass spectrometry. Herein, a detailed protocol for precise and reproducible quantification of esterified oxylipins in plasma is presented comprising i) extraction of lipids and removal of proteins with iso-propanol, ii) base hydrolysis with potassium hydroxide to saponify lipids and iii) solid phase extraction of the liberated oxylipins on C8/anion exchange mixed mode material. Unequal extraction of internal standards and lipid classes during lipid extraction before hydrolysis led to distorted concentrations, emphasizing that the choice of solvent used in this step is important to minimize discrimination. Regarding the hydrolysis conditions, at least 30 min incubation at 60 °C is required with 0.1 M KOH in sample. Drying of the SPE cartridges is a critical parameter since autoxidation processes of PUFA, which are present in high concentrations after cleavage, lead to artificial formation of epoxy fatty acids. With the developed protocol, inter-day, intra-day and inter-operator variance was <21% for most oxylipins including hydroxy-, dihydroxy-, and epoxy-PUFA. The applicability of the developed methodology is demonstrated by investigating the changes in the oxylipin pattern following omega-3 fatty acid feeding to rats.

Dietary omega-3 PUFA improved tubular function after ischemia induced acute kidney injury in mice but did not attenuate impairment of renal function

BACKGROUND

Acute kidney injury (AKI) is an important complication after major surgery and solid organ transplantation. Here, we present a dietary omega-3 polyunsaturated fatty acid (n3-PUFA) supplementation study to investigate whether pre-treatment can reduce ischemia induced AKI in mice.

METHODS

Male 12-14 week old C57BL/6 J mice received a linoleic acid rich sunflower oil based standard diet containing 10 % fat (STD) or the same diet enriched with n3-PUFA (containing 1 % EPA and 1 % DHA) (STD + n3). After 14 days of feeding bilateral 30 min renal ischemia reperfusion injury (IRI) was conducted to induce AKI and mice were sacrificed at 24 h. Serum creatinine and blood urea nitrogen (BUN) as well as liver enzyme elevation were measured. Kidney damage was analyzed by histology and immunohistochemistry. Furthermore, pro-inflammatory cytokines (IL-6, MCP-1) were determined by qPCR. FA and oxylipin pattern were quantified in blood and kidneys by GC-FID and LC-MS/MS, respectively.

RESULTS

n3-PUFA supplementation prior to renal IRI increased systemic and renal levels of n3-PUFA. Consistently, eicosanoids and other oxylipins derived from n3-PUFA including precursors of specialized pro-resolving mediators were elevated while n6-PUFA derived mediators such as pro-inflammatory prostaglandins were decreased. Feeding of n3-PUFA did not attenuate renal function impairment, morphological renal damage and inflammation characterized by IL-6 and MCP-1 elevation or neutrophil infiltration. However, the tubular transport marker alpha-1 microglobulin (A1M) was significantly higher expressed in proximal tubular epithelial cells of STD + n3 compared to STD fed mice. This indicates a better integrity of proximal tubular epithelial cells and thus significant protection of tubular function. In addition, heme oxygenase-1 (HO-1) which protects tubular function was also up-regulated in the treatment group receiving n3-PUFA supplemented chow.

DISCUSSION

We showed that n3-PUFA pre-treatment did not affect overall renal function or renal inflammation in a mouse model of moderate ischemia induced AKI, but tubular transport was improved. In conclusion, dietary n3-PUFA supplementation altered the oxylipin levels significantly but did not protect from renal function deterioration or attenuate ischemia induced renal inflammation.

Characterization of Lipid Profiles after Dietary Intake of Polyunsaturated Fatty Acids Using Integrated Untargeted and Targeted Lipidomics

Illuminating the comprehensive lipid profiles after dietary supplementation of polyunsaturated fatty acids (PUFAs) is crucial to revealing the tissue distribution of PUFAs in living organisms, as well as to providing novel insights into lipid metabolism. Here, we performed lipidomic analyses on mouse plasma and nine tissues, including the liver, kidney, brain, white adipose, heart, lung, small intestine, skeletal muscle, and spleen, with the dietary intake conditions of arachidonic acid (ARA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) as the ethyl ester form. We incorporated targeted and untargeted approaches for profiling oxylipins and complex lipids such as glycerol (phospho) lipids, sphingolipids, and sterols, respectively, which led to the characterization of 1026 lipid molecules from the mouse tissues. The lipidomic analysis indicated that the intake of PUFAs strongly impacted the lipid profiles of metabolic organs such as the liver and kidney, while causing less impact on the brain. Moreover, we revealed a unique lipid modulation in most tissues, where phospholipids containing linoleic acid were significantly decreased in mice on the ARA-supplemented diet, and bis(monoacylglycero)phosphate (BMP) selectively incorporated DHA over ARA and EPA. We comprehensively studied the lipid profiles after dietary intake of PUFAs, which gives insight into lipid metabolism and nutrition research on PUFA supplementation.

Visualizing and Profiling Lipids in the OVLT of Fat-1 and Wild Type Mouse Brains during LPS-Induced Systemic Inflammation Using AP-SMALDI MSI

Lipids, including omega-3 polyunsaturated fatty acids (n-3-PUFAs), modulate brain-intrinsic inflammation during systemic inflammation. The vascular organ of the lamina terminalis (OVLT) is a brain structure important for immune-to-brain communication. We, therefore, aimed to profile the distribution of several lipids (e.g., phosphatidyl-choline/ethanolamine, PC/PE), including n-3-PUFA-carrying lipids (esterified in phospholipids), in the OVLT during systemic lipopolysaccharide(LPS)-induced inflammation. We injected wild type and endogenously n-3-PUFA producing fat-1 transgenic mice with LPS (i.p., 2.5 mg/kg) or PBS. Brain samples were analyzed using immunohistochemistry and high-resolution atmospheric-pressure scanning microprobe matrix-assisted laser desorption/ionization orbital trapping mass spectrometry imaging (AP-SMALDI-MSI) for spatial resolution of lipids. Depending on genotype and treatment, several distinct distribution patterns were observed for lipids [e.g., lyso(L)PC (16:0)/(18:0)] proposed to be involved in inflammation. The distribution patterns ranged from being homogeneously disseminated [LPC (18:1)], absent/reduced signaling within the OVLT relative to adjacent preoptic tissue [PE (38:6)], either treatment- and genotype-dependent or independent low signal intensities [LPC (18:0)], treatment- and genotype-dependent [PC 38:6)] or independent accumulation in the OVLT [PC (38:7)], and accumulation in commissures, e.g., nerve fibers like the optic nerve [LPE (18:1)]. Overall, screening of lipid distribution patterns revealed distinct inflammation-induced changes in the OVLT, highlighting the prominent role of lipid metabolism in brain inflammation. Moreover, known and novel candidates for brain inflammation and immune-to-brain communication were detected specifically within this pivotal brain structure, a window between the periphery and the brain. The biological significance of these newly identified lipids abundant in the OVLT and the adjacent preoptic area remains to be further analyzed.

Effects of Omega-3 Fatty Acids on Immune Cells

Alterations on the immune system caused by omega-3 fatty acids have been described for 30 years. This family of polyunsaturated fatty acids exerts major alterations on the activation of cells from both the innate and the adaptive immune system, although the mechanisms for such regulation are diverse. First, as a constitutive part of the cellular membrane, omega-3 fatty acids can regulate cellular membrane properties, such as membrane fluidity or complex assembly in lipid rafts. In recent years, however, a new role for omega-3 fatty acids and their derivatives as signaling molecules has emerged. In this review, we describe the latest findings describing the effects of omega-3 fatty acids on different cells from the immune system and their possible molecular mechanisms.

Fatty Acid Metabolites as Novel Regulators of Non-shivering Thermogenesis

Fatty acids are essential contributors to adipocyte-based non-shivering thermogenesis by acting as activators of uncoupling protein 1 and serving as fuel for mitochondrial heat production. Novel evidence suggests a contribution to this thermogenic mechanism by their conversion to bioactive compounds. Mammalian cells produce a plethora of oxylipins and endocannabinoids, some of which have been identified to affect the abundance or thermogenic activity of brown and brite adipocytes. These effectors are produced locally or at distant sites and signal toward thermogenic adipocytes via a direct interaction with these cells or indirectly via secondary mechanisms. These interactions are evoked by the activation of receptor-mediated pathways. The endogenous production of these compounds is prone to modulation by the dietary intake of the respective precursor fatty acids. The effect of nutritional interventions on uncoupling protein 1-derived thermogenesis may thus at least in part be conferred by the production of a supportive oxylipin and endocannabinoid profile. The manipulation of this system in future studies will help to elucidate the physiological potential of these compounds as novel, endogenous regulators of non-shivering thermogenesis.