Biophysical and biochemical mechanisms by which dietary N-3 polyunsaturated fatty acids from fish oil disrupt membrane lipid rafts

Eicosapentaenoic acid and docosahexaenoic acid have distinct membrane locations and lipid interactions as determined by X-ray diffraction

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) differentially influence lipid oxidation, signal transduction, fluidity, and cholesterol domain formation, potentially due in part to distinct membrane interactions. We used small angle X-ray diffraction to evaluate the EPA and DHA effects on membrane structure. Membrane vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and cholesterol (C) (0.3C:POPC mole ratio) were prepared and treated with vehicle, EPA, or DHA (1:10 mol ratio to POPC). Electron density profiles generated from the diffraction data showed that EPA increased membrane hydrocarbon core electron density over a broad area, up to ± 20 Å from the membrane center, indicating an energetically favorable extended orientation for EPA likely stabilized by van der Waals interactions. By contrast, DHA increased electron density in the phospholipid head group region starting at ± 12 Å from the membrane center, presumably due to DHA-surface interactions, with coincident reduction in electron density in the membrane hydrocarbon core centered ± 7-9 Å from the membrane center. The membrane width (d-space) decreased by 5 Å in the presence of vehicle as the temperature increased from 10 °C to 30 °C due to increased acyl chain trans-gauche isomerizations, which was unaffected by addition of EPA or DHA. The influence of DHA on membrane structure was modulated by temperature changes while the interactions of EPA were unaffected. The contrasting EPA and DHA effects on membrane structure indicate distinct molecular locations and orientations that may contribute to observed differences in biological activity.

Eicosapentaenoic acid inhibits oxidation of high density lipoprotein particles in a manner distinct from docosahexaenoic acid

The omega-3 fatty acid eicosapentaenoic acid (EPA) reduces oxidation of ApoB-containing particles in vitro and in patients with hypertriglyceridemia. EPA may produce these effects through a potent antioxidant mechanism, which may facilitate LDL clearance and slow plaque progression. We hypothesize that EPA antioxidant effects may extend to ApoA-containing particles like HDL, potentially preserving certain atheroprotective functions. HDL was isolated from human plasma and incubated at 37 °C in the absence (vehicle) or presence of EPA and/or DHA; 5.0 or 10.0 μM each. Samples were then subjected to copper-induced oxidation (10 μM). HDL oxidation was inhibited similarly by EPA and DHA up to 1 h. EPA (10 μM) maintained significant HDL oxidation inhibition of 89% (0.622 ± 0.066 μM MDA; p < .001) at 4 h, with continued inhibition of 64% at 14 h, vs. vehicle (5.65 ± 0.06 to 2.01 ± 0.10 μM MDA; p < .001). Conversely, DHA (10 μM) antioxidant benefit was lost by 4 h. At a lower concentration (5 μM), EPA antioxidant activity remained at 81% (5.53 ± 0.15 to 1.03 ± 0.10 μM MDA; p < .001) at 6 h, while DHA lost all antioxidant activity by 4 h. The antioxidant activity of EPA was preserved when combined with an equimolar concentration of DHA (5 μM each). EPA pretreatment prevented HDL oxidation in a dose-dependent manner that was preserved over time. These results suggest unique lipophilic and electron stabilization properties for EPA as compared to DHA with respect to inhibition of HDL oxidation. These antioxidant effects of EPA may enhance certain atheroprotective functions for HDL.

Anti-Inflammatory Effects of Omega-3 Fatty Acids in the Brain: Physiological Mechanisms and Relevance to Pharmacology

Classically, polyunsaturated fatty acids (PUFA) were largely thought to be relatively inert structural components of brain, largely important for the formation of cellular membranes. Over the past 10 years, a host of bioactive lipid mediators that are enzymatically derived from arachidonic acid, the main n-6 PUFA, and docosahexaenoic acid, the main n-3 PUFA in the brain, known to regulate peripheral immune function, have been detected in the brain and shown to regulate microglia activation. Recent advances have focused on how PUFA regulate the molecular signaling of microglia, especially in the context of neuroinflammation and behavior. Several active drugs regulate brain lipid signaling and provide proof of concept for targeting the brain. Because brain lipid metabolism relies on a complex integration of diet, peripheral metabolism, including the liver and blood, which supply the brain with PUFAs that can be altered by genetics, sex, and aging, there are many pathways that can be disrupted, leading to altered brain lipid homeostasis. Brain lipid signaling pathways are altered in neurologic disorders and may be viable targets for the development of novel therapeutics. In this study, we discuss in particular how n-3 PUFAs and their metabolites regulate microglia phenotype and function to exert their anti-inflammatory and proresolving activities in the brain.

Protective Effects of ω-3 PUFA in Anthracycline-Induced Cardiotoxicity: A Critical Review

It has been demonstrated that ω-3 polyunsaturated fatty acids (ω-3 PUFA) may exert a beneficial role as adjuvants in the prevention and treatment of many disorders, including cardiovascular diseases and cancer. Particularly, several in vitro and in vivo preclinical studies have shown the antitumor activity of ω-3 PUFA in different kinds of cancers, and several human studies have shown that ω-3 PUFA are able to decrease the risk of a series of cardiovascular diseases. Several mechanisms have been proposed to explain their pleiotropic beneficial effects. ω-3 PUFA have also been shown to prevent harmful side-effects (including cardiotoxicity and heart failure) induced by conventional and innovative anti-cancer drugs in both animals and patients. The available literature regarding the possible protective effects of ω-3 PUFA against anthracycline-induced cardiotoxicity, as well as the mechanisms involved, will be critically discussed herein. The study will analyze the critical role of different levels of ω-3 PUFA intake in determining the results of the combinatory studies with anthracyclines. Suggestions for future research will also be considered.

Changes in Plasma and Tissue Long-Chain Polyunsaturated Fatty Acid (LC-PUFA) Content in the Eel Anguilla japonica After External and Internal Osmotic Stress

We investigated the effect of external and internal osmotic stress on the profile of long-chain polyunsaturated fatty acids (LC-PUFA) in euryhaline eels Anguilla japonica. Freshwater (FW) fish were transferred to seawater (SW) for external osmotic stress or subjected to internal stress through injection with hypertonic saline. FW eels injected with isotonic saline served as controls. Plasma osmolality, Na⁺ concentration, and gill Na⁺/K⁺ -ATPase activity increased, but hematocrit decreased compared with controls in eels exposed to external or internal osmotic stress. The expression of two major transporter genes for SW adaptation, the Na⁺ -K⁺ -2Cl - co-transporter 1a (NKCC1a) in the gill and NKCC2b in the intestine, was up-regulated only in SW-transferred eels, suggesting a direct impact of SW on the gill and intestine via SW ingestion. Total LC-PUFA contents and DHA (22:6 n-3) increased in the gill and liver of SW-transferred eels and in the intestine of hypertonic saline-injected eels. However, total LC-PUFA content in plasma decreased after both external and internal osmotic stimuli. In contrast, the gene expression of two key enzymes involved in the LC-PUFA biosynthesis, Δ6 fatty acid desaturase and elongase, did not change in the gill, intestine and liver of osmotically stressed eels. These results indicate that LC-PUFA is possibly involved in osmoregulation and the increased LC-PUFA contents of osmoregulatory organs might be a result of LC-PUFA transport via circulation, rather than through de novo biosynthesis.

Murine diet-induced obesity remodels cardiac and liver mitochondrial phospholipid acyl chains with differential effects on respiratory enzyme activity

Cardiac phospholipids, notably cardiolipin, undergo acyl chain remodeling and/or loss of content in aging and cardiovascular diseases, which is postulated to mechanistically impair mitochondrial function. Less is known about how diet-induced obesity influences cardiac phospholipid acyl chain composition and thus mitochondrial responses. Here we first tested if a high fat diet remodeled murine cardiac mitochondrial phospholipid acyl chain composition and consequently disrupted membrane packing, supercomplex formation and respiratory enzyme activity. Mass spectrometry analyses revealed that mice consuming a high fat diet displayed 0.8-3.3 fold changes in cardiac acyl chain remodeling of cardiolipin, phosphatidylcholine, and phosphatidylethanolamine. Biophysical analysis of monolayers constructed from mitochondrial phospholipids of obese mice showed impairment in the packing properties of the membrane compared to lean mice. However, the high fat diet, relative to the lean controls, had no influence on cardiac mitochondrial supercomplex formation, respiratory enzyme activity, and even respiration. To determine if the effects were tissue specific, we subsequently conducted select studies with liver tissue. Compared to the control diet, the high fat diet remodeled liver mitochondrial phospholipid acyl chain composition by 0.6-5.3-fold with notable increases in n-6 and n-3 polyunsaturation. The remodeling in the liver was accompanied by diminished complex I to III respiratory enzyme activity by 3.5-fold. Finally, qRT-PCR analyses demonstrated an upregulation of liver mRNA levels of tafazzin, which contributes to cardiolipin remodeling. Altogether, these results demonstrate that diet-induced obesity remodels acyl chains in the mitochondrial phospholipidome and exerts tissue specific impairments of respiratory enzyme activity.

n-3 Polyunsaturated Fatty Acids and Cardiovascular Disease: Principles, Practices, Pitfalls, and Promises - A Contemporary Review

Amidst voluminous literature, inconsistencies and opposing results have confused rather than clarified cardiologists' ability to assess the potential benefits of n-3 polyunsaturated fatty acids (n-3 PUFA). In perspective, there are common themes that emerge from n-3 PUFA studies, even as imperfect as they may be. The approach taken was to identify and unite these themes into a manageable, cohesive, evidence-based, yet useful synthesis. In all reviews and meta-analyses, the selection of component studies and assumptions influences outcomes. This overarching principle must be combined with the totality of the data, particularly when evidence is incompletely understood and gaps in knowledge must be bridged. Both the older literature and the most recent rigorous meta-analyses indicate that n-3 PUFA are highly pleiotropic agents with many documented positive physiological effects. Concordance among preclinical, observational, randomized clinical trials and meta-analyses is impressive. These agents have modest, statistically significant benefits which accrue over time. Given their favorable safety profile, a risk reduction of about 10% justifies their potential use in cardiovascular disease.

ω3-Polyunsaturated fatty acids for heart failure: Effects of dose on efficacy and novel signaling through free fatty acid receptor 4

Heart failure (HF) affects 5.7 million in the U.S., and despite well-established pharmacologic therapy, the 5-year mortality rate remains near 50%. Furthermore, the mortality rate for HF has not declined in years, highlighting the need for new therapeutic options. Omega-3 polyunsaturated fatty acids (ω3-PUFAs), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are important regulators of cardiovascular health. However, questions of efficacy and mechanism of action have made the use of ω3-PUFAs in all cardiovascular disease (CVD) controversial. Here, we review recent studies in animal models of HF indicating that ω3-PUFAs, particularly EPA, are cardioprotective, with the results indicating a threshold for efficacy. We also examine clinical studies suggesting that ω3-PUFAs improve outcomes in patients with HF. Due to the relatively small number of clinical studies of ω3-PUFAs in HF, we discuss EPA concentration-dependency on outcomes in clinical trials of CVD to gain insight into the perceived questionable efficacy of ω3-PUFAs clinically, with the results again indicating a threshold for efficacy. Ultimately, we suggest that the main failing of ω3-PUFAs in clinical trials might be a failure to reach a therapeutically effective concentration. We also examine mechanistic studies suggesting that ω3-PUFAs signal through free fatty acid receptor 4 (Ffar4), a G-protein coupled receptor (GPR) for long-chain fatty acids (FA), thereby identifying an entirely novel mechanism of action for ω3-PUFA mediated cardioprotection. Finally, based on mechanistic animal studies suggesting that EPA prevents interstitial fibrosis and diastolic dysfunction, we speculate about a potential benefit for EPA-Ffar4 signaling in heart failure preserved with ejection fraction.

ω3 Polyunsaturated Fatty Acids as Immunomodulators in Colorectal Cancer: New Potential Role in Adjuvant Therapies

Diet composition may affect the onset and progression of chronic degenerative diseases, including cancer, whose pathogenesis relies on inflammatory processes. Growing evidence indicates that diet and its components critically contribute to human health, affecting the immune system, secretion of adipokines, and metabolic pathways. Colorectal cancer (CRC) is one of the leading causes of death worldwide. Antineoplastic drugs are widely used for CRC treatment, but drug resistance and/or off-target toxicity limit their efficacy. Dietary ω3 polyunsaturated fatty acids (PUFA) have been gaining great interest in recent years as possible anti-inflammatory and anticancer agents, especially in areas such as the large bowel, where the pro-inflammatory context promotes virtually all steps of colon carcinogenesis. Growing epidemiological, experimental, and clinical evidence suggests that ω3 PUFA may play a role in several stages of CRC management exhibiting antineoplastic activity against human CRC cells, improving the efficacy of radiation and chemotherapy, ameliorating cancer-associated secondary complications, and preventing CRC recurrence. These effects are most likely related to the immunomodulatory activities of ω3 PUFA that are able to influence several aspects of the inflammatory process ranging from inflammasome activation, leukocyte recruitment, production of immune mediators to differentiation, and activation of immune cells. In this review, we will focus on the potential use of ω3 PUFA as adjuvant agents together with chemo/radiotherapy, highlighting the immunomodulatory effects most likely responsible for their beneficial effects in different stages of CRC management.

Dietary α-linolenic acid supplementation alters skeletal muscle plasma membrane lipid composition, sarcolemmal FAT/CD36 abundance, and palmitate transport rates

The cellular processes influenced by consuming polyunsaturated fatty acids remains poorly defined. Within skeletal muscle, a rate-limiting step in fatty acid oxidation is the movement of lipids across the sarcolemmal membrane, and therefore, we aimed to determine the effects of consuming flaxseed oil high in α-linolenic acid (ALA), on plasma membrane lipid composition and the capacity to transport palmitate. Rats fed a diet supplemented with ALA (10%) displayed marked increases in omega-3 polyunsaturated fatty acids (PUFAs) within whole muscle and sarcolemmal membranes (approximately five-fold), at the apparent expense of arachidonic acid (-50%). These changes coincided with increased sarcolemmal palmitate transport rates (+20%), plasma membrane fatty acid translocase (FAT/CD36; +20%) abundance, skeletal muscle triacylglycerol content (approximately twofold), and rates of whole body fat oxidation (~50%). The redistribution of FAT/CD36 to the plasma membrane could not be explained by increased phosphorylation of signaling pathways implicated in regulating FAT/CD36 trafficking events (i.e., phosphorylation of ERK1/2, CaMKII, AMPK, and Akt), suggesting the increased n-3 PUFA composition of the plasma membrane influenced FAT/CD36 accumulation. Altogether, the present data provide evidence that a diet supplemented with ALA increases the transport of lipids into resting skeletal muscle in conjunction with increased sarcolemmal n-3 PUFA and FAT/CD36 contents.

Mitigation of indomethacin-induced gastrointestinal damages in fat-1 transgenic mice via gate-keeper action of ω-3-polyunsaturated fatty acids

Non-steroidal anti-inflammatory drugs (NSAIDs) damage the gastrointestinal (GI) epithelial cell membranes by inducing several signals through lipid raft organization after membrane incorporation, whereas ω-3 polyunsaturated fatty acids (PUFAs) relieve inflammation, reduce oxidative stress, and provide cytoprotection, consequent to lipid raft disorganization. Therefore, we hypothesized that ω-3 PUFAs can protect the GI from NSAID-induced damages by initiating the gatekeeper action of cell membranes, subsequent to anti-inflammatory and anti-oxidative actions. Administration of indomethacin (IND) leads to the formation of lipid rafts and activation of caveolin-1; however, no such observations were made upon co-administration of eicosapentaenoic acid (EPA) and IND. In addition, the EPA-induced lipid raft disorganization, caveolin-1 inactivation, and cellular cytotoxicity were inhibited when target cells were knocked-out using G-protein coupled receptor 120 (GPR 120). EPA significantly attenuated IND-induced oxidative damage and apoptosis. IND administration induced significant ulceration, bleeding, and oedema in the stomach or small intestine of wild-type (WT) mice; however, such severe damages to the GI significantly decreased in fat-1 transgenic (TG) mice (P < 0.001), which exhibited decreased cyclooxygenase-2 expression and apoptosis, decreased interleukin-1β and FAS concentrations, and increased heme oxygenase-1 concentration. Our study indicates that the gatekeeper function of ω-3 PUFAs improves GI safety when administered with NSAID.

Red blood cell PUFAs reflect the phospholipid PUFA composition of major organs

Numerous clinical trials examining the use of omega-3 long chain polyunsaturated fatty acids (n-3 LCPUFAs) on various health outcomes have been conducted, and fish oil remains one of the most widely used nutritional supplements. More recently, studies have begun to utilize the omega-3 index, defined as the sum of EPA+DHA in red blood cells (RBCs), as both a biomarker of n-3 LCPUFA exposure and a potential risk factor for coronary heart disease (CHD). Considerably less research evaluates whether RBC phospholipid fatty acids reflect the phospholipid fatty acid composition of other tissues across increasing intakes of n-3 LCPUFAs. We fed mice diets containing increasing amounts of EPA+DHA, equivalent to current recommendations by the American Heart Association on a percent of energy basis, and analyzed the phospholipid fatty acid composition of various tissues in relation to RBCs. We observed that RBCs, heart, muscle, spleen, lung, and adipose tissues all respond to dietary supplementation with EPA+DHA with increasing n-3 LCPUFA and decreasing n-6 LCPUFA levels. Furthermore, the n-3 LCPUFA profiles of all measured tissues had strong (r>0.7) and significant (p<0.001) correlations to RBCs. Interestingly, we also observed changes in saturated fatty acid (SFA) and monounsaturated fatty acid (MUFA) levels across various tissues in response to increased EPA+DHA intakes despite there being no change in dietary SFA and MUFA. Specifically, there were increases in RBC SFA and spleen MUFA and decreases in heart MUFA. These demonstrate that the RBC, including the omega-3 index, may serve as a marker for the relative levels of n-3 and n-6 LCPUFAs in phospholipids of certain tissues.

Role of Polyunsaturated Fatty Acids and Their Metabolites on Stem Cell Proliferation and Differentiation

The nervous system is highly enriched with long-chain polyunsaturated fatty acids (PUFAs). Essential fatty acids, namely, ω-6 (n - 6) and ω-3 (n - 3) PUFA, and their metabolites are critical components of cell structure and function and could therefore influence stem cell fate. The available supporting experimental data reveal that n - 6 and n - 3 PUFA and their metabolites can act through multiple mechanisms to promote the proliferation and differentiation of various stem cell types. PUFAs and their mediators regulate several processes within the brain, such as neurotransmission, cell survival and neuroinflammation, and thereby mood and cognition. PUFA levels and the signaling pathways that they regulate are altered in various neurological disorders, including Alzheimer's disease and major depression. Therefore, elucidating the role of PUFAs and their metabolites in stem cell fate regulation is important for stem cell biology as well as stem cell therapy. PUFA-based interventions to generate a positive environment for stem cell proliferation or differentiation might be a promising and practical approach to controlling stem cell fate for clinical applications.

n-3 polyunsaturated fatty acids suppress CD4(+) T cell proliferation by altering phosphatidylinositol-(4,5)-bisphosphate [PI(4,5)P2] organization

The mechanisms by which n-3 polyunsaturated fatty acids (n-3 PUFA), abundant in fish oil, exert their anti-inflammatory effects have not been rigorously defined. We have previously demonstrated that n-3 PUFA decrease the amount of phosphatidylinositol-(4,5)-bisphosphate, [PI(4,5)P2], in CD4(+) T cells, leading to suppressed actin remodeling upon activation. Since discrete pools of PI(4,5)P2 exist in the plasma membrane, we determined whether n-3 PUFA modulate spatial organization of PI(4,5)P2 relative to raft and non-raft domains. We used Förster resonance energy transfer (FRET) to demonstrate that lipid raft mesodomains in the plasma membrane of CD4(+) T cells enriched in n-3 PUFA display increased co-clustering of Lck(N10) and LAT(ΔCP), markers of lipid rafts. CD4(+) T cells enriched in n-3 PUFA also exhibited a depleted plasma membrane non-raft PI(4,5)P2 pool as detected by decreased co-clustering of Src(N15), a non-raft marker, and PH(PLC-δ), a PI(4,5)P2 reporter. Incubation with exogenous PI(4,5)P2 rescued the effects on the non-raft PI(4,5)P2 pool, and reversed the suppression of T cell proliferation in CD4(+) T cells enriched with n-3 PUFA. Furthermore, CD4(+) T cells isolated from mice fed a 4% docosahexaenoic acid (DHA)-enriched diet exhibited a decrease in the non-raft pool of PI(4,5)P2, and exogenous PI(4,5)P2 reversed the suppression of T cell proliferation. Finally, these effects were not due to changes to post-translational lipidation, since n-3 PUFA did not alter the palmitoylation status of signaling proteins. These data demonstrate that n-3 PUFA suppress T cell proliferation by altering plasma membrane topography and the spatial organization of PI(4,5)P2.

α-Tocopherol Is Well Designed to Protect Polyunsaturated Phospholipids: MD Simulations

The presumptive function for alpha-tocopherol (αtoc) in membranes is to protect polyunsaturated lipids against oxidation. Although the chemistry of the process is well established, the role played by molecular structure that we address here with atomistic molecular-dynamics simulations remains controversial. The simulations were run in the constant particle NPT ensemble on hydrated lipid bilayers composed of SDPC (1-stearoyl-2-docosahexaenoylphosphatidylcholine, 18:0-22:6PC) and SOPC (1-stearoyl-2-oleoylphosphatidylcholine, 18:0-18:1PC) in the presence of 20 mol % αtoc at 37°C. SDPC with SA (stearic acid) for the sn-1 chain and DHA (docosahexaenoic acid) for the sn-2 chain is representative of polyunsaturated phospholipids, while SOPC with OA (oleic acid) substituted for the sn-2 chain serves as a monounsaturated control. Solid-state (2)H nuclear magnetic resonance and neutron diffraction experiments provide validation. The simulations demonstrate that high disorder enhances the probability that DHA chains at the sn-2 position in SDPC rise up to the bilayer surface, whereby they encounter the chromanol group on αtoc molecules. This behavior is reflected in the van der Waals energy of interaction between αtoc and acyl chains, and illustrated by density maps of distribution for acyl chains around αtoc molecules that were constructed. An ability to more easily penetrate deep into the bilayer is another attribute conferred upon the chromanol group in αtoc by the high disorder possessed by DHA. By examining the trajectory of single molecules, we found that αtoc flip-flops across the SDPC bilayer on a submicrosecond timescale that is an order-of-magnitude greater than in SOPC. Our results reveal mechanisms by which the sacrificial hydroxyl group on the chromanol group can trap lipid peroxyl radicals within the interior and near the surface of a polyunsaturated membrane. At the same time, water-soluble reducing agents that regenerate αtoc can access the chromanol group when it locates at the surface.

EPA, not DHA, prevents fibrosis in pressure overload-induced heart failure: potential role of free fatty acid receptor 4

Heart failure with preserved ejection fraction (HFpEF) is half of all HF, but standard HF therapies are ineffective. Diastolic dysfunction, often secondary to interstitial fibrosis, is common in HFpEF. Previously, we found that supra-physiologic levels of ω3-PUFAs produced by 12 weeks of ω3-dietary supplementation prevented fibrosis and contractile dysfunction following pressure overload [transverse aortic constriction (TAC)], a model that resembles aspects of remodeling in HFpEF. This raised several questions regarding ω3-concentration-dependent cardioprotection, the specific role of EPA and DHA, and the relationship between prevention of fibrosis and contractile dysfunction. To achieve more clinically relevant ω3-levels and test individual ω3-PUFAs, we shortened the ω3-diet regimen and used EPA- and DHA-specific diets to examine remodeling following TAC. The shorter diet regimen produced ω3-PUFA levels closer to Western clinics. Further, EPA, but not DHA, prevented fibrosis following TAC. However, neither ω3-PUFA prevented contractile dysfunction, perhaps due to reduced uptake of ω3-PUFA. Interestingly, EPA did not accumulate in cardiac fibroblasts. However, FFA receptor 4, a G protein-coupled receptor for ω3-PUFAs, was sufficient and required to block transforming growth factor β1-fibrotic signaling in cultured cardiac fibroblasts, suggesting a novel mechanism for EPA. In summary, EPA-mediated prevention of fibrosis could represent a novel therapy for HFpEF.

Modulation of Breast Cancer Risk Biomarkers by High-Dose Omega-3 Fatty Acids: Phase II Pilot Study in Postmenopausal Women

Associational studies suggest higher intakes/blood levels of the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) relative to the omega-6 arachidonic acid (AA) are associated with reduced breast cancer risk. We performed a pilot study of high-dose EPA + DHA in postmenopausal women to assess feasibility before initiating a phase IIB prevention trial. Postmenopausal women with cytologic evidence of hyperplasia in their baseline random periareolar fine needle aspiration (RPFNA) took 1,860 mg EPA +1500 mg DHA ethyl esters daily for 6 months. Blood and breast tissue were sampled at baseline and study conclusion for exploratory biomarker assessment, with P values uncorrected for multiple comparisons. Feasibility was predefined as 50% uptake, 80% completion, and 70% compliance. Trial uptake by 35 study entrants from 54 eligible women was 65%, with 97% completion and 97% compliance. Favorable modulation was suggested for serum adiponectin (P = 0.0027), TNFα (P = 0.016), HOMA 2B measure of pancreatic β cell function (P = 0.0048), and bioavailable estradiol (P = 0.039). Benign breast tissue Ki-67 (P = 0.036), macrophage chemoattractant protein-1 (P = 0.033), cytomorphology index score (P = 0.014), and percent mammographic density (P = 0.036) were decreased with favorable effects in a proteomics array for several proteins associated with mitogen signaling and cell-cycle arrest; but no obvious overall effect on proteins downstream of mTOR. Although favorable risk biomarker modulation will need to be confirmed in a placebo-controlled trial, we have demonstrated feasibility for development of high-dose EPA and DHA ethyl esters for primary prevention of breast cancer.

The Deleterious Effects of Oxidative and Nitrosative Stress on Palmitoylation, Membrane Lipid Rafts and Lipid-Based Cellular Signalling: New Drug Targets in Neuroimmune Disorders

Oxidative and nitrosative stress (O&NS) is causatively implicated in the pathogenesis of Alzheimer's and Parkinson's disease, multiple sclerosis, chronic fatigue syndrome, schizophrenia and depression. Many of the consequences stemming from O&NS, including damage to proteins, lipids and DNA, are well known, whereas the effects of O&NS on lipoprotein-based cellular signalling involving palmitoylation and plasma membrane lipid rafts are less well documented. The aim of this narrative review is to discuss the mechanisms involved in lipid-based signalling, including palmitoylation, membrane/lipid raft (MLR) and n-3 polyunsaturated fatty acid (PUFA) functions, the effects of O&NS processes on these processes and their role in the abovementioned diseases. S-palmitoylation is a post-translational modification, which regulates protein trafficking and association with the plasma membrane, protein subcellular location and functions. Palmitoylation and MRLs play a key role in neuronal functions, including glutamatergic neurotransmission, and immune-inflammatory responses. Palmitoylation, MLRs and n-3 PUFAs are vulnerable to the corruptive effects of O&NS. Chronic O&NS inhibits palmitoylation and causes profound changes in lipid membrane composition, e.g. n-3 PUFA depletion, increased membrane permeability and reduced fluidity, which together lead to disorders in intracellular signal transduction, receptor dysfunction and increased neurotoxicity. Disruption of lipid-based signalling is a source of the neuroimmune disorders involved in the pathophysiology of the abovementioned diseases. n-3 PUFA supplementation is a rational therapeutic approach targeting disruptions in lipid-based signalling.

N-3 polyunsaturated fatty acids modulate B cell activity in pre-clinical models: Implications for the immune response to infections

B cell antigen presentation, cytokine production, and antibody production are targets of pharmacological intervention in inflammatory and infectious diseases. Here we review recent pre-clinical evidence demonstrating that pharmacologically relevant levels of n-3 polyunsaturated fatty acids (PUFA) derived from marine fish oils influence key aspects of B cell function through multiple mechanisms. N-3 PUFAs modestly diminish B cell mediated stimulation of classically defined naïve CD4(+) Th1 cells through the major histocompatibility complex (MHC) class II pathway. This is consistent with existing data showing that n-3 PUFAs suppress the activation of Th1/Th17 cells through direct effects on helper T cells and indirect effects on antigen presenting cells. Mechanistically, n-3 PUFAs lower antigen presentation and T cell signaling by disrupting the formation of lipid microdomains within the immunological synapse. We then review data to show that n-3 PUFAs boost B cell activation and antibody production in the absence and presence of antigen stimulation. This has potential benefits for several clinical populations such as the aged and obese that have poor humoral immunity. The mode of action by which n-3 PUFA boost B cell activation and antibody production remains unclear, but may involve Th2 cytokines, enhanced production of specialized proresolving lipid mediators, and targeting of protein lateral organization in lipid microdomains. Finally, we highlight evidence to show that different n-3 PUFAs are not biologically equivalent, which has implications for the development of future interventions to target B cell activity.

Whatever happened to the epoxyeicosatrienoic Acid-like endothelium-derived hyperpolarizing factor? The identification of novel classes of lipid mediators and their role in vascular homeostasis

SIGNIFICANCE

Cytochrome P450 (CYP) epoxygenases metabolize arachidonic acid (AA) to generate epoxyeicosatrienoic acids (EETs). The latter are biologically active and reported to act as an endothelium-derived hyperpolarizing factor as well as to affect angiogenic and inflammatory signaling pathways.

RECENT ADVANCES

In addition to AA, the CYP enzymes also metabolize the ω-3 polyunsaturated fatty acids (PUFAs) eicosapentaenoic acid and docosahexaenoic acid to generate bioactive lipid epoxide mediators. The latter can be more potent than the EETs, but their actions are under investigated. The ω3-epoxides, like the EETs, are metabolized by the soluble epoxide hydrolase (sEH) to corresponding diols, and epoxide hydrolase inhibition increases epoxide levels and demonstrates anti-hypertensive as well as anti-inflammatory effects.

CRITICAL ISSUES

It seems that the overall consequences of CYP activation largely depend on enzyme substrate preference and the endogenous ω-3/ω-6 PUFA ratio.

FUTURE DIRECTIONS

More studies combining PUFA profiling with cell signaling and disease studies are required to determine the spectrum of molecular pathways affected by the different ω-6 and ω-3 PUFA epoxides and diols. Such information may help improve dietary studies aimed at promoting health via ω-3 PUFA supplementation and/or sEH inhibition.

N-3 Polyunsaturated Fatty Acids, Lipid Microclusters, and Vitamin E

Increased consumption of long-chain marine n-3 polyunsaturated fatty acids (PUFA) has potential health benefits for the general population and for select clinical populations. However, several key limitations remain in making adequate dietary recommendations on n-3 PUFAs in addition to translating the fatty acids into clinical trials for select diseases. One major constraint is an incomplete understanding of the underlying mechanisms of action of n-3 PUFAs. In this review, we highlight studies to show n-3 PUFA acyl chains reorganize the molecular architecture of plasma membrane sphingolipid-cholesterol-enriched lipid rafts and potentially sphingolipid-rich cholesterol-free domains and cardiolipin-protein scaffolds in the inner mitochondrial membrane. We also discuss the possibility that the effects of n-3 PUFAs on membrane organization could be regulated by the presence of vitamin E (α-tocopherol), which is necessary to protect highly unsaturated acyl chains from oxidation. Finally, we propose the integrated hypothesis, based predominately on studies in lymphocytes, cancer cells, and model membranes, that the mechanism by which n-3 PUFAs disrupt signaling microclusters is highly dependent on the type of lipid species that incorporate n-3 PUFA acyl chains. The current evidence suggests that n-3 PUFA acyl chains disrupt lipid raft formation by incorporating primarily into phosphatidylethanolamines but can also incorporate into other lipid species of the lipidome.

Concise review: Regulation of stem cell proliferation and differentiation by essential fatty acids and their metabolites

Stem cell therapy holds great promise for regenerative medicine and the treatment of numerous diseases. A key issue of stem cell therapy is the control of stem cell fate, but safe and practical methods are limited. Essential fatty acids, namely ω-6 (n-6) and ω-3 (n-3) polyunsaturated fatty acids (PUFA), and their metabolites are critical components of cell structure and function, and could therefore influence stem cell fate. The available evidence demonstrates that n-6 and n-3 PUFA and their metabolites can act through multiple mechanisms to promote the proliferation and differentiation of various stem cell types. Therefore, elucidating the role of PUFA and their metabolites in stem cell fate regulation is both a challenge and an opportunity for stem cell biology as well as stem cell therapy. PUFA-based interventions to create a favorable environment for stem cell proliferation or differentiation may thus be a promising and practical approach to controlling stem cell fate for clinical applications.

Prostaglandins and n-3 polyunsaturated fatty acids in the regulation of the hypothalamic-pituitary axis

The hypothalamic-pituitary (H-P) axis integrates complex physiological and environmental signals and responds to these cues by modulating the synthesis and secretion of multiple pituitary hormones to regulate peripheral tissues. Prostaglandins are a component of this regulatory system, affecting multiple hormone synthesis and secretion pathways in the H-P axis. The implications of these actions are that physiological processes or disease states that alter prostaglandin levels in the hypothalamus or pituitary can impinge on H-P axis function. Considering the role of prostaglandins in mediating inflammation, the potential for neuroinflammation to affect H-P axis function in this manner may be significant. In addition, the mitigating effects of n-3 polyunsaturated fatty acids (n-3 PUFA) on the inflammation-associated synthesis of prostaglandins and their role as substrates for pro-resolving lipid mediators may also include effects in the H-P axis. One context in which neuroinflammation may play a role is in the etiology of diet-induced obesity, which also correlates with altered pituitary hormone levels. This review will survey evidence for the actions of prostaglandins and other lipid mediators in the H-P axis, and will address the potential for obesity-associated inflammation and n-3 PUFA to impinge on these mechanisms.

Nanofluidity of fatty acid hydrocarbon chains as monitored by benchtop time-domain nuclear magnetic resonance

The functional properties of lipid-rich assemblies such as serum lipoproteins, cell membranes, and intracellular lipid droplets are modulated by the fluidity of the hydrocarbon chain environment. Existing methods for monitoring hydrocarbon chain fluidity include fluorescence, electron spin resonance, and nuclear magnetic resonance (NMR) spectroscopy; each possesses advantages and limitations. Here we introduce a new approach based on benchtop time-domain (1)H NMR relaxometry (TD-NMR). Unlike conventional NMR spectroscopy, TD-NMR does not rely on the chemical shift resolution made possible by homogeneous, high-field magnets and Fourier transforms. Rather, it focuses on a multiexponential analysis of the time decay signal. In this study, we investigated a series of single-phase fatty acid oils, which allowed us to correlate (1)H spin-spin relaxation time constants (T2) with experimental measures of sample fluidity, as obtained using a viscometer. Remarkably, benchtop TD-NMR at 40 MHz was able to resolve two to four T2 components in biologically relevant fatty acids, assigned to nanometer-scale domains in different segments of the hydrocarbon chain. The T2 values for each domain were exquisitely sensitive to hydrocarbon chain structure; the largest values were observed for pure fatty acids or mixtures with the highest cis-double bond content. Moreover, the T2 values for each domain exhibited positive linear correlations with fluidity. The TD-NMR T2 and fluidity measurements appear to be monitoring the same underlying phenomenon: variations in hydrocarbon chain packing. The results from this study validate the use of benchtop TD-NMR T2 as a nanofluidity meter and demonstrate its potential for probing nanofluidity in other systems of biological interest.

Eicosapentaenoic and docosahexaenoic acid ethyl esters differentially enhance B-cell activity in murine obesity

EPA and DHA are not biologically equivalent; however, their individual activity on B cells is unknown. We previously reported fish oil enhanced murine B-cell activity in obesity. To distinguish between the effects of EPA and DHA, we studied the ethyl esters of EPA and DHA on murine B-cell function as a function of time. We first demonstrate that EPA and DHA maintained the obese phenotype, with no improvements in fat mass, adipose inflammatory cytokines, fasting insulin, or glucose clearance. We then tested the hypothesis that EPA and DHA would increase the frequency of splenic B cells. EPA and DHA differentially enhanced the frequency and/or percentage of select B-cell subsets, correlating with increased natural serum IgM and cecal IgA. We next determined the activities of EPA and DHA on ex vivo production of cytokines upon lipopolysaccharide stimulation of B cells. EPA and DHA, in a time-dependent manner, enhanced B-cell cytokines with DHA notably increasing IL-10. At the molecular level, EPA and DHA differentially enhanced the formation of ordered microdomains but had no effect on Toll-like receptor 4 mobility. Overall, the results establish differential effects of EPA and DHA in a time-dependent manner on B-cell activity in obesity, which has implications for future clinical studies.

Reversal of myofibroblastic activation by polyunsaturated fatty acids in valvular interstitial cells from aortic valves. Role of RhoA/G-actin/MRTF signalling

Valvular interstitial cells (VICs), the fibroblast-like cellular constituents of aortic heart valves, maintain structural integrity of valve tissue. Activation into contractile myofibroblasts occurs under pathological situations and under standard cell culture conditions of isolated VICs. Reversal of this phenotype switch would be of major importance in respect to fibrotic valve diseases. In this investigation, we found that exogenous polyunsaturated fatty acids (PUFAs) decreased contractility and expression of myofibroblastic markers like α-smooth muscle actin (αSMA) in cultured VICs from porcine aortic valves. The most active PUFAs, docosahexaenoic acid (DHA) and arachidonic acid (AA) reduced the level of active RhoA and increased the G/F-actin ratio. The G-actin-regulated nuclear translocation of myocardin-related transcription factors (MRTFs), co-activators of serum response factor, was also reduced by DHA and AA. The same effects were observed after blocking RhoA directly with C3 transferase. In addition, increased contractility after induction of actin polymerisation with jasplakinolide and concomitant expression of αSMA were ameliorated by active PUFAs. Furthermore, reduced αSMA expression under PUFA exposure was observed in valve tissue explants demonstrating physiological relevance. In conclusion, RhoA/G-actin/MRTF signalling is operative in VICs, and this pathway can be partially blocked by certain PUFAs whereby the activation into the myofibroblastic phenotype is reversed.

How polyunsaturated fatty acids modify molecular organization in membranes: insight from NMR studies of model systems

Marine long chain n-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic (EPA) and docosahexaenoic acid (DHA), are bioactive molecules with clinical applications for the treatment of several diseases. In order to effectively translate these molecules into clinical trials, it is essential to establish the underlying mechanisms for n-3 PUFA. This review focuses on efforts to understand how EPA and DHA, upon incorporation into plasma membrane phospholipids, remodel the molecular organization of cholesterol-enriched lipid microdomains. We first give an overview of results from studies on cells. Paradoxical data generated from mouse studies indicate that EPA and DHA incorporate into lipid microdomains, yet in spite of their high disorder increase molecular order within the domain. We then spotlight the utility of solid state (2)H NMR spectroscopy of model bilayers as a tool for elucidating underlying mechanisms by which n-3 PUFA-containing phospholipids can regulate molecular organization of lipid microdomains. Evidence is presented demonstrating that n-3 PUFA exert differential structural effects when incorporated into phosphatidylethanolamines (PE) compared to phosphatidylcholines (PC), which explains some of the conflicting results observed in vivo. Recent studies that reveal differences between the interactions of EPA and DHA with lipid microdomains, potentially reflecting a differential in bioactivity, are finally described. Overall, we highlight the notion that NMR experiments on model membranes suggest a complex model by which n-3 PUFA reorganize lipid microdomains in vivo.

Regulation of the cancer cell membrane lipid composition by NaCHOleate: effects on cell signaling and therapeutical relevance in glioma

This review summarizes the cellular bases of the effects of NaCHOleate (2-hydroxyoleic acid; 2OHOA; Minerval) against glioma and other types of tumors. NaCHOleate, activates sphingomyelin synthase (SGMS) increasing the levels of cell membrane sphingomyelin (SM) and diacylglycerol (DAG) together with reductions of phosphatidylethanolamine (PE) and phosphatidylcholine (PC). The increases in the membrane levels of NaCHOleate itself and of DAG induce a translocation and overexpression of protein kinase C (PKC) and subsequent reductions of Cyclin D, cyclin-dependent kinases 4 and 6 (CDKs 4 and 6), hypophosphorylation of the retinoblastoma protein, inhibition of E2F1 and knockdown of dihydrofolate reductase (DHFR) impairing DNA synthesis. In addition in some cancer cells, the increases in SM are associated with Fas receptor (FasR) capping and ligand-free induction of apoptosis. In glioma cell lines, the increases in SM are associated with the inhibition of the Ras/MAPK and PI3K/Akt pathways, in association with p27Kip1 overexpression. Finally, an analysis of the Repository of Molecular Brain Neoplasia Data (REMBRANDT) database for glioma patient survival shows that the weight of SM-related metabolism gene expression in glioma patients' survival is similar to glioma-related genes. Due to its low toxicity and anti-tumoral effect in cell and animal models its status as an orphan drug for glioma treatment by the European Medicines Agency (EMA) was recently acknowledged and a phase 1/2A open label, non-randomized study was started in patients with advanced solid tumors including malignant glioma. This article is part of a Special Issue entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Protective action of n-3 fatty acids on benzo[a]pyrene-induced apoptosis through the plasma membrane remodeling-dependent NHE1 pathway

Plasma membrane is an early target of polycyclic aromatic hydrocarbons (PAH). We previously showed that the PAH prototype, benzo[a]pyrene (B[a]P), triggers apoptosis via DNA damage-induced p53 activation (genotoxic pathway) and via remodeling of the membrane cholesterol-rich microdomains called lipid rafts, leading to changes in pH homeostasis (non-genotoxic pathway). As omega-3 (n-3) fatty acids can affect membrane composition and function or hamper in vivo PAH genotoxicity, we hypothesized that addition of physiologically relevant levels of polyunsaturated n-3 fatty acids (PUFAs) might interfere with B[a]P-induced toxicity. The effects of two major PUFAs, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), were tested on B[a]P cytotoxicity in the liver epithelial cell line F258. Both PUFAs reduced B[a]P-induced apoptosis. Surprisingly, pre-treatment with DHA increased the formation of reactive B[a]P metabolites, resulting in higher levels of B[a]P-DNA adducts. EPA had no apparent effect on B[a]P metabolism or related DNA damage. EPA and DHA prevented B[a]P-induced apoptotic alkalinization by affecting Na(+)/H(+) exchanger 1 activity. Thus, the inhibitory effects of omega-3 fatty acids on B[a]P-induced apoptosis involve a non-genotoxic pathway associated with plasma membrane remodeling. Our results suggest that dietary omega-3 fatty acids may have marked effects on the biological consequences of PAH exposure.

Fish oil improves motor function, limits blood-brain barrier disruption, and reduces Mmp9 gene expression in a rat model of juvenile traumatic brain injury

The effects of an oral fish oil treatment regimen on sensorimotor, blood-brain barrier, and biochemical outcomes of traumatic brain injury (TBI) were investigated in a juvenile rat model. Seventeen-day old Long-Evans rats were given a 15mL/kg fish oil (2.01g/kg EPA, 1.34g/kg DHA) or soybean oil dose via oral gavage 30min prior to being subjected to a controlled cortical impact injury or sham surgery, followed by daily doses for seven days. Fish oil treatment resulted in less severe hindlimb deficits after TBI as assessed with the beam walk test, decreased cerebral IgG infiltration, and decreased TBI-induced expression of the Mmp9 gene one day after injury. These results indicate that fish oil improved functional outcome after TBI resulting, at least in part from decreased disruption of the blood-brain barrier through a mechanism that includes attenuation of TBI-induced expression of Mmp9.

Targeting Intracellular Cholesterol is a Novel Therapeutic Strategy for Cancer Treatment

Substantial data from cell culture and animal studies evidence the preventive effect of statins, cholesterol lowering-drugs, in regulation of cancer cell proliferation and metastasis. Various clinical studies also support this correlation between use of statin and the reduction of cancer incidence. However, in some cases, statins have failed to decrease the risk of cancer. Since, instead of serum cholesterol, intracellular cholesterol may play a crucial role in the regulation of tumorigenesis and metastasis. The mechanism by which cholesterol is stored within cancer cells may differ among cancer types and also in different individuals. This paper discusses the molecular detail to speculate the statin-sensitive cancer. It also highlights that statins may work better as anticancer therapy if it is used with the combination of a specific microRNA (miR).

Membrane lipid modifications and therapeutic effects mediated by hydroxydocosahexaenoic acid on Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative pathology with relevant unmet therapeutic needs. Both natural aging and AD have been associated with a significant decline in the omega-3 polyunsaturated fatty acid docosahexaenoic acid (DHA), and accordingly, administration of DHA has been proposed as a possible treatment for this pathology. However, recent clinical trials in mild-to-moderately affected patients have been inconclusive regarding the real efficacy of DHA in halting this disease. Here, we show that the novel hydroxyl-derivative of DHA (2-hydroxydocosahexaenoic acid - OHDHA) has a strong therapeutic potential to treat AD. We demonstrate that OHDHA administration increases DHA levels in the brain of a transgenic mouse model of AD (5xFAD), as well as those of phosphatidylethanolamine (PE) species that carry long polyunsaturated fatty acids (PUFAs). In 5xFAD mice, administration of OHDHA induced lipid modifications that were paralleled with a reduction in amyloid-β (Αβ) accumulation and full recovery of cognitive scores. OHDHA administration also reduced Aβ levels in cellular models of AD, in association with alterations in the subcellular distribution of secretases and reduced Aβ-induced tau protein phosphorylation as well. Furthermore, OHDHA enhanced the survival of neuron-like differentiated cells exposed to different insults, such as oligomeric Aβ and NMDA-mediated neurotoxicity. These results were supported by model membrane studies in which incorporation of OHDHA into lipid-raft-like vesicles was shown to reduce the binding affinity of oligomeric and fibrillar Aβ to membranes. Finally, the OHDHA concentrations used here did not produce relevant toxicity in zebrafish embryos in vivo. In conclusion, we demonstrate the pleitropic effects of OHDHA that might prove beneficial to treat AD, which suggests that an upstream event, probably the modulation of the membrane lipid composition and structure, influences cellular homeostasis reversing the neurodegenerative process. This Article is Part of a Special Issue Entitled: Membrane Structure and Function: Relevance in the Cell's Physiology, Pathology and Therapy.

Omega 3 fatty acids chemosensitize multidrug resistant colon cancer cells by down-regulating cholesterol synthesis and altering detergent resistant membranes composition

Background

The activity of P-glycoprotein (Pgp) and multidrug resistance related protein 1 (MRP1), two membrane transporters involved in multidrug resistance of colon cancer, is increased by high amounts of cholesterol in plasma membrane and detergent resistant membranes (DRMs). It has never been investigated whether omega 3 polyunsatured fatty acids (PUFAs), which modulate cholesterol homeostasis in dyslipidemic syndromes and have chemopreventive effects in colon cancer, may affect the response to chemotherapy in multidrug resistant (MDR) tumors.

Methods

We studied the effect of omega 3 PUFAs docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) in human chemosensitive colon cancer HT29 cells and in their MDR counterpart, HT29-dx cells.

Results

MDR cells, which overexpressed Pgp and MRP1, had a dysregulated cholesterol metabolism, due to the lower expression of ubiquitin E3 ligase Trc8: this produced lower ubiquitination rate of 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCoAR), higher cholesterol synthesis, higher cholesterol content in MDR cells. We found that DHA and EPA re-activated Trc8 E3 ligase in MDR cells, restored the ubiquitination rate of HMGCoAR to levels comparable with chemosensitive cells, reduced the cholesterol synthesis and incorporation in DRMs. Omega 3 PUFAs were incorporated in whole lipids as well as in DRMs of MDR cells, and altered the lipid composition of these compartments. They reduced the amount of Pgp and MRP1 contained in DRMs, decreased the transporters activity, restored the antitumor effects of different chemotherapeutic drugs, restored a proper tumor-immune system recognition in response to chemotherapy in MDR cells.

Conclusions

Our work describes a new biochemical effect of omega 3 PUFAs, which can be useful to overcome chemoresistance in MDR colon cancer cells.

ω-3 fatty acids in the prevention of cognitive decline in humans

The brain is a lipid-rich organ where docosahexaenoic acid (DHA) is enriched and where eicosapentaenoic acid (EPA) may have anti-inflammatory effects. The potential role for n-3 (ω-3) fatty acids such as DHA and EPA in the prevention of cognitive decline, including Alzheimer's disease (AD) has attracted major interest for the past 20 y. This review presents our understanding of recent observational, interventional, and experimental studies, with the aim of providing some answers to the following question: Can n-3 FA intake modulate cognitive function during aging? In longitudinal observation studies we mainly observe inverse relations between fish intake or serum concentrations of DHA and cognitive impairment. Intervention studies of EPA and DHA supplementation in healthy old individuals have been negative so far (i.e., after up to 2 years of treatment, no differences in cognitive decline between treated and nontreated participants have been observed). In studies that provided EPA and DHA to adults with mild cognitive impairment or age-related cognitive impairment the data seem to be positive. However, when patients with established AD were supplemented with EPA and DHA it appears no benefit was gained. For studies on healthy individuals, a major concern is that the treatment periods may have been too short. There might also be subgroup effects because of the carriage of apolipoprotein Eε4 alleles or risk factor burden. Experimental studies appear to be consistently positive (i.e., n-3 FA supplementation in rodents over a substantial portion of their lives reduces amyloid-β deposition and hippocampal neuron loss and improves cognitive functioning). We are getting closer to providing evidence-based recommendations on fish and fish oil intake to facilitate memory function during old age. In the meantime it is advised to follow the general CDC dietary recommendations of 2-3 fish meals per week or the equivalent intake of long chain n-3 fatty acids, particularly DHA.

Immunomodulation by dietary long chain omega-3 fatty acids and the potential for adverse health outcomes

Recommendations to consume fish for prevention of cardiovascular disease (CVD), along with the U.S. Food and Drug Administration-approved generally recognized as safe (GRAS) status for long chain omega-3 fatty acids, may have had the unanticipated consequence of encouraging long-chain omega-3 (ω-3) fatty acid [(eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] supplementation and fortification practices. While there is evidence supporting a protective role for EPA/DHA supplementation in reducing sudden cardiac events, the safety and efficacy of supplementation with LCω-3PUFA in the context of other disease outcomes is unclear. Recent studies of bacterial, viral, and fungal infections in animal models of infectious disease demonstrate that LCω-3PUFA intake dampens immunity and alters pathogen clearance and can result in reduced survival. The same physiological properties of EPA/DHA that are responsible for the amelioration of inflammation associated with chronic cardiovascular pathology or autoimmune states, may impair pathogen clearance during acute infections by decreasing host resistance or interfere with tumor surveillance resulting in adverse health outcomes. Recent observations that high serum LCω-3PUFA levels are associated with higher risk of prostate cancer and atrial fibrillation raise concern for adverse outcomes. Given the widespread use of supplements and fortification of common food items with LCω-3PUFA, this review focuses on the immunomodulatory effects of the dietary LCω-3PUFAs, EPA and DHA, the mechanistic basis for potential negative health outcomes, and calls for biomarker development and validation as rational first steps towards setting recommended dietary intake levels.

Dietary fish oil and DHA down-regulate antigen-activated CD4+ T-cells while promoting the formation of liquid-ordered mesodomains

We have demonstrated previously that n-3 PUFA endogenously produced by fat-1 transgenic mice regulate CD4+ T-cell function by affecting the formation of lipid rafts, liquid-ordered mesodomains in the plasma membrane. In the present study, we tested the effects of dietary sources of n-3 PUFA, i.e. fish oil (FO) or purified DHA, when compared with an n-6 PUFA-enriched maize oil control diet in DO11.10 T-cell receptor transgenic mice. Dietary n-3 PUFA were enriched in CD4+ T-cells, resulting in the increase of the n-3:n-6 ratio. Following antigen-specific CD4+ T-cell activation by B-lymphoma cells pulsed with the ovalbumin 323-339 peptide, the formation of liquid-ordered mesodomains at the immunological synapse relative to the whole CD4+ T-cell, as assessed by Laurdan labelling, was increased (P< 0·05) in the FO-fed group. The FO diet also suppressed (P< 0·05) the co-localisation of PKCθ with ganglioside GM1 (monosialotetrahexosylganglioside), a marker for lipid rafts, which is consistent with previous observations. In contrast, the DHA diet down-regulated (P< 0·05) PKCθ signalling by moderately affecting the membrane liquid order at the immunological synapse, suggesting the potential contribution of the other major n-3 PUFA components of FO, including EPA.

Low brain DHA content worsens sensorimotor outcomes after TBI and decreases TBI-induced Timp1 expression in juvenile rats

The effects of dietary modulation of brain DHA content on outcomes after TBI were examined in a juvenile rat model. Long-Evans rats with normal or diet-induced decreases in brain DHA were subjected to a controlled cortical impact or sham surgery on postnatal day 17. Rats with the greatest decreases in brain DHA had the poorest sensorimotor outcomes after TBI. Ccl2, Gfap, and Mmp 9 mRNA levels, and MMP-2 and -9 enzymatic activities were increased after TBI regardless of brain DHA level. Lesion volume was not affected by brain DHA level. In contrast, TBI-induced Timp1 expression was lower in rats on the Deficient diet and correlated with brain DHA level. These data suggest that decreased brain DHA content contributes to poorer sensorimotor outcomes after TBI through a mechanism involving modulation of Timp1 expression.

Omega-3 polyunsaturated fatty acid (PUFA) status in major depressive disorder with comorbid anxiety disorders

BACKGROUND

Although lower levels of omega-3 polyunsaturated fatty acids (PUFAs) are found in major depressive disorder, less is known about PUFA status and anxiety disorders.

METHOD

Medication-free participants with DSM-IV-defined major depressive disorder (MDD), with (n = 18) and without (n = 41) comorbid DSM-IV anxiety disorders, and healthy volunteers (n = 62) were recruited from October 2006 to May 2010 for mood disorder studies at the New York State Psychiatric Institute. Participants were 18-73 years of age (mean age, 35.8 ± 12.6 years). Depression and anxiety severity was assessed using depression and anxiety subscales from the 17-item Hamilton Depression Rating Scale. Plasma PUFAs eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) and the ratio of arachidonic acid (AA; 22:4n-6) to EPA (AA:EPA) were quantified. This secondary analysis employed analysis of variance with a priori planned contrasts to test for diagnostic group differences in log-transformed PUFA levels (logDHA, logEPA, and logAA:EPA).

RESULTS

Plasma levels of logDHA (F(2,118) = 4.923, P = .009), logEPA (F(2,118) = 6.442, P = .002), and logAA:EPA (F(2,118) = 3.806, P = .025) differed across groups. Participants with MDD had lower logDHA (t(118) = 2.324, P = .022) and logEPA (t(118) = 3.175, P = .002) levels and higher logAA:EPA levels (t(118) = -2.099, P = .038) compared with healthy volunteers. Lower logDHA (t(118) = 2.692, P = .008) and logEPA (t(118) = 2.524, P = .013) levels and higher logAA:EPA levels (t(118) = -2.322, P = .022) distinguished anxious from nonanxious MDD. Depression severity was not associated with PUFA plasma levels; however, anxiety severity across the entire sample correlated negatively with logDHA (r(p) = -0.22, P = .015) and logEPA (r(p) = -0.25, P = .005) levels and positively with logAA:EPA levels (r(p) = 0.18, P = .043).

CONCLUSIONS

The presence and severity of comorbid anxiety were associated with the lowest EPA and DHA levels. Further studies are needed to elucidate whether omega-3 PUFA supplementation may preferentially alleviate MDD with more severe anxiety.

Curcumin and docosahexaenoic acid block insulin-induced colon carcinoma cell proliferation

Diets high in fish and curcumin are associated with a decreased risk of CRC. Insulin resistance and obesity are associated with increased CRC risk and higher reoccurrence rates. We utilized cell culture to determine if dietary compounds could reduce insulin-induced cell proliferation comparing the response in normal and metastatic colon epithelial cells. We treated model normal murine colon epithelial cells (YAMC) and adenocarcinoma cells (MC38) with docosahexaenoic acid (DHA) or curcumin alone and then co-treatments of the diet-derived compound and insulin were combined. Cell proliferation was stimulated with insulin (1 ug/mL) to model insulin resistance in obesity. Despite the presence of insulin, proliferation was reduced in the MC38 cells treated with 10 μM curcumin (p<0.001) and 50 μM DHA (p<0.001). Insulin stimulated MAPK and MEK phosphorylation was inhibited by DHA and curcumin in MC38 cancer cells. Here we show that curcumin and DHA can block insulin-induced colon cancer cell proliferation in vitro via a MEK mediated mechanism.

Models of plasma membrane organization can be applied to mitochondrial membranes to target human health and disease with polyunsaturated fatty acids

Bioactive n-3 polyunsaturated fatty acids (PUFA), abundant in fish oil, have potential for treating symptoms associated with inflammatory and metabolic disorders; therefore, it is essential to determine their fundamental molecular mechanisms. Recently, several labs have demonstrated the n-3 PUFA docosahexaenoic acid (DHA) exerts anti-inflammatory effects by targeting the molecular organization of plasma membrane microdomains. Here we briefly review the evidence that DHA reorganizes the spatial distribution of microdomains in several model systems. We then emphasize how models on DHA and plasma membrane microdomains can be applied to mitochondrial membranes. We discuss the role of DHA acyl chains in regulating mitochondrial lipid-protein clustering, and how these changes alter several aspects of mitochondrial function. In particular, we summarize effects of DHA on mitochondrial respiration, electron leak, permeability transition, and mitochondrial calcium handling. Finally, we conclude by postulating future experiments that will augment our understanding of DHA-dependent membrane organization in health and disease.

Lycopene suppresses proinflammatory response in lipopolysaccharide-stimulated macrophages by inhibiting ROS-induced trafficking of TLR4 to lipid raft-like domains

We recently showed that lycopene inhibited lipopolysaccharide (LPS)-induced productions of nitric oxide (NO) and interleukin-6 (IL-6) in murine RAW264.7 macrophages by mechanisms related to inhibition of ERK and nuclear factor-κB. Since the assembly of Toll-like receptor 4 (TLR4) in lipid rafts is a key element in LPS induced signaling, we investigated whether this process would be influenced by lycopene. We found that pretreatment of RAW264.7 cells with lycopene inhibited LPS-induced recruitment of TLR4 into fractions - enriched with lipid raft marker. By the methods of immunoprecipitation and immunoblotting, we also found that lycopene inhibited the subsequent formation of the complex of TLR4 with its adaptors including myeloid differentiation primary-response protein 88 and TIR domain-containing adaptor-inducing IFN-β. We also found that the lycopene induced inhibition was associated with reduced formation of reactive oxygen species (ROS), which was an upstream mechanism for the effects of lycopene, because treating the cells with the antioxidant N-acetyl-l-cysteine and NADPH oxidase inhibitor diphenyleneiodonium chloride significantly inhibited LPS-induced recruitment of TLR4 into lipid raft-like domains as well as the production of proinflammatory molecule NO and IL-6. Thus, our findings suggest that lycopene may prevent LPS-induced TLR4 assembly into lipid rafts through reducing intracellular ROS level.

Genotype-induced changes in biophysical properties of frontal cortex lipid raft from APP/PS1 transgenic mice

Alterations in the lipid composition of lipid rafts have been demonstrated both in human brain and transgenic mouse models, and it has been postulated that aberrant lipid composition in lipid rafts is partly responsible for neuronal degeneration. In order to assess the impact of lipid changes on lipid raft functional properties, we have aimed at determining relevant physicochemical modifications in lipid rafts purified from frontal cortex of wild type (WT) and APP/PS1 double transgenic mice. By means of steady-state fluorescence anisotropy analyses using two lipid soluble fluorescent probes, TMA-DPH (1-[(4-trimethyl-amino)phenyl]-6-phenyl-1,3,5-hexatriene) and DPH (1,6-diphenyl-1,3,5-hexatriene), we demonstrate that cortical lipid rafts from WT and APP/PS1 animals exhibit different biophysical behaviors, depending on genotype but also on age. Thus, aged APP/PS1 animals exhibited slightly more liquid-ordered lipid rafts than WT counterparts. Membrane microviscosity η_app analyses demonstrate that WT lipid rafts are more fluid than APP/PS1 animals of similar age, both at the aqueous interface and hydrophobic core of the membrane. η_app in APP/PS1 animals was higher for DPH than for TMA-DPH under similar experimental conditions, indicating that the internal core of the membrane is more viscous than the raft membrane at the aqueous interface. The most dramatic changes in biophysical properties of lipid rafts were observed when membrane cholesterol was depleted with methyl-β-cyclodextrin. Overall, our results indicate that APP/PS1 genotype strongly affects physicochemical properties of lipid raft. Such alterations appear not to be homogeneous across the raft membrane axis, but rather are more prominent at the membrane plane. These changes correlate with aberrant proportions of sphingomyelin, cholesterol, and saturated fatty acids, as well as polyunsaturated fatty acids, measured in lipid rafts from frontal cortex in this familial model of Alzheimer's Disease.

DHA-enriched fish oil targets B cell lipid microdomains and enhances ex vivo and in vivo B cell function

DHA is a n-3 LCPUFA in fish oil that generally suppresses T lymphocyte function. However, the effect of fish oil on B cell function remains relatively understudied. Given the important role of B cells in gut immunity and increasing human fish oil supplementation, we sought to determine whether DFO leads to enhanced B cell activation in the SMAD-/- colitis-prone mouse model, similar to that observed with C57BL/6 mice. This study tested the hypothesis that DHA from fish oil is incorporated into the B cell membrane to alter lipid microdomain clustering and enhance B cell function. Purified, splenic B cells from DFO-fed mice displayed increased DHA levels and diminished GM1 microdomain clustering. DFO enhanced LPS-induced B cell secretion of IL-6 and TNF-α and increased CD40 expression ex vivo compared with CON. Despite increased MHCII expression in the unstimulated ex vivo B cells from DFO-fed mice, we observed no difference in ex vivo OVA-FITC uptake in B cells from DFO or CON mice. In vivo, DFO increased lymphoid tissue B cell populations and surface markers of activation compared with CON. Finally, we investigated whether these ex vivo and in vivo observations were consistent with systemic changes. Indeed, DFO-fed mice had significantly higher plasma IL-5, IL-13, and IL-9 (Th2-biasing cytokines) and cecal IgA compared with CON. These results support the hypothesis and an emerging concept that fish oil enhances B cell function in vivo.

DHA-fluorescent probe is sensitive to membrane order and reveals molecular adaptation of DHA in ordered lipid microdomains

Docosahexaenoic acid (DHA) disrupts the size and order of plasma membrane lipid microdomains in vitro and in vivo. However, it is unknown how the highly disordered structure of DHA mechanistically adapts to increase the order of tightly packed lipid microdomains. Therefore, we studied a novel DHA-Bodipy fluorescent probe to address this issue. We first determined if the DHA-Bodipy probe localized to the plasma membrane of primary B and immortal EL4 cells. Image analysis revealed that DHA-Bodipy localized into the plasma membrane of primary B cells more efficiently than EL4 cells. We then determined if the probe detected changes in plasma membrane order. Quantitative analysis of time-lapse movies established that DHA-Bodipy was sensitive to membrane molecular order. This allowed us to investigate how DHA-Bodipy physically adapted to ordered lipid microdomains. To accomplish this, we employed steady-state and time-resolved fluorescence anisotropy measurements in lipid vesicles of varying composition. Similar to cell culture studies, the probe was highly sensitive to membrane order in lipid vesicles. Moreover, these experiments revealed, relative to controls, that upon incorporation into highly ordered microdomains, DHA-Bodipy underwent an increase in its fluorescence lifetime and molecular order. In addition, the probe displayed a significant reduction in its rotational diffusion compared to controls. Altogether, DHA-Bodipy was highly sensitive to membrane order and revealed for the first time that DHA, despite its flexibility, could become ordered with less rotational motion inside ordered lipid microdomains. Mechanistically, this explains how DHA acyl chains can increase order upon formation of lipid microdomains in vivo.