Polyunsaturated fatty acids, membrane organization, T cells, and antigen presentation

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.

Polyunsaturated fatty acids promote the expansion of myeloid-derived suppressor cells by activating the JAK/STAT3 pathway

Polyunsaturated fatty acids (PUFAs) exert immunosuppressive effects that could prove beneficial in clinical therapies for certain autoimmune and inflammatory disorders. However, the mechanism of PUFA-mediated immunosuppression is far from understood. Here, we provide evidence that PUFAs enhance the accumulation of myeloid-derived suppressor cells (MDSCs), a negative immune regulator. PUFA-induced MDSCs have a more potent suppressive effect on T-cell responses than do control MDSCs. These observations were found both in cultured mouse bone marrow cells in vitro and in vivo in mice fed diets enriched in PUFAs. The enhanced suppressive activity of MDSCs by PUFAs administration was coupled with a dramatic induction of nicotinamide adenine dinucleo- tide phosphate oxidase subunit p47(phox) and was dependent on reactive oxygen species (ROS) production. Mechanistic studies revealed that PUFAs mediate its effects through JAK-STAT3 signaling. Inhibition of STAT3 phosphorylation by JAK inhibitor JSI-124 almost completely abrogated the effects of PUFAs on MDSCs. Moreover, the effects of PUFAs on MDSCs and the underlying mechanisms were confirmed in tumor-bearing mice. In summary, this study sheds new light on the immune modulatory role of PUFAs, and demonstrates that MDSCs expansion may mediate the effects of PUFAs on the immune system.

Mechanism and function of DHHC S-acyltransferases

Protein S-palmitoylation is a reversible post-translational modification of proteins with fatty acids. In the last 5 years, improved proteomic methods have increased the number of proteins identified as substrates for palmitoylation from tens to hundreds. Palmitoylation regulates protein membrane interactions, activity, trafficking and stability and can be constitutive or regulated by signalling inputs. A family of PATs (protein acyltransferases) is responsible for modifying proteins with palmitate or other long-chain fatty acids on the cytoplasmic face of cellular membranes. PATs share a signature DHHC (Asp-His-His-Cys) cysteine-rich domain that is the catalytic centre of the enzyme. The biomedical importance of members of this family is underscored by their association with intellectual disability, Huntington's disease and cancer in humans, and raises the possibility of DHHC PATs as targets for therapeutic intervention. In the present paper, we discuss recent progress in understanding enzyme mechanism, regulation and substrate specificity.

Cholesterol load of microglia: contribution of membrane architecture changes to neurotoxic power?

Considerable evidence provides a link between hypercholesterolemia and ageing-related neurodegenerative diseases. The present study was aimed to provide a complex view on the effects caused by cholesterol- and cholesterol 5α,6α-epoxide-load in microglia, with particular emphasize put on membrane proteins. Prolonged application of oxysterol significantly enhanced LPS-stimulated association of cytosolic NADPH-oxidase factor p47[phox] with detergent-resistant microdomains (DRMs) in BV-2 cells. Although the treatment with both sterols does not influence the portion of CD36 receptor in DRMs, its apparent surface-cellular expression was altered. Even though sterol-treatment potentiated oxidant production by microglia, as well as their phagocytosis, these effects, however, appeared to be independent of cholesterol profusion in the membrane. In addition, oxysterol-treatment resulted in a loss of DRMs-associated activity of 26S proteasome, the protease critically regulating both protein homeostasis and immune signaling in microglia. Oxysterol relatively ameliorated cytotoxic effects of inflammed microglia on co-cultured PC12 cells. The outcomes of this study suggest that cholesterol and cholesterol oxides can differentially modulate microglia resulting either in impairment of their immune functionalities or enhanced neurotoxic power. Moreover, these findings shed light on possible complexity of this effect, produced by simultaneous affection of the levels, distribution and function of the critical proteins within microglial membrane compartments.

Food components and the immune system: from tonic agents to allergens

The intestinal mucosa is the major site of contact with antigens, and it houses the largest lymphoid tissue in the body. In physiological conditions, microbiota and dietary antigens are the natural sources of stimulation for the gut-associated lymphoid tissues (GALT) and for the immune system as a whole. Germ-free models have provided some insights on the immunological role of gut antigens. However, most of the GALT is not located in the large intestine, where gut microbiota is prominent. It is concentrated in the small intestine where protein absorption takes place. In this review, we will address the involvement of food components in the development and the function of the immune system. Studies in mice have already shown that dietary proteins are critical elements for the developmental shift of the immature neonatal immune profile into a fully developed immune system. The immunological effects of other food components (such as vitamins and lipids) will also be addressed. Most of the cells in the GALT are activated and local pro-inflammatory mediators are abundant. Regulatory elements are known to provide a delicate yet robust balance that maintains gut homeostasis. Usually antigenic contact in the gut induces two major immune responses, oral tolerance and production of secretory IgA. However, under pathological conditions mucosal homeostasis is disturbed resulting in inflammatory reactions such as food hypersensitivity. Food allergy development depends on many factors such as genetic predisposition, biochemical features of allergens, and a growing array of environmental elements. Neuroimmune interactions are also implicated in food allergy and they are examples of the high complexity of the phenomenon. Recent findings on the gut circuits triggered by food components will be reviewed to show that, far beyond their role as nutrients, they are critical players in the operation of the immune system in health and disease.

A novel oral nutraceutical formula of omega-3 and omega-6 fatty acids with vitamins (PLP10) in relapsing remitting multiple sclerosis: a randomised, double-blind, placebo-controlled proof-of-concept clinical trial

OBJECTIVE

To assess whether three novel interventions, formulated based on a systems medicine therapeutic concept, reduced disease activity in patients with relapsing-remitting multiple sclerosis (MS) who were either treated or not with disease-modifying treatment.

DESIGN

A 30-month randomised, double-blind, placebo-controlled, parallel design, phase II proof-of-concept clinical study.

SETTINGS

Cyprus Institute of Neurology and Genetics.

PARTICIPANTS

80 participants were randomised into four groups of 20 each. A total of 41 (51%) patients completed the 30-month trial. The eligibility criteria were an age of 18-65; a diagnosis of relapsing-remitting MS according to the McDonald criteria; a score of 0.0-5.5 on the Expanded Disability Status Scale (EDSS); MRI showing lesions consistent with MS; at least one documented clinical relapse and either receiving or not a disease-modifying treatment within the 24-month period before enrolment in the study. Patients were excluded because of a recent (<30 days) relapse, prior immunosuppressant or monoclonal antibody therapy, pregnancy or nursing, other severe disease compromising organ function, progressive MS, history of recent drug or alcohol abuse, use of any additional food supplements, vitamins or any form of polyunsaturated fatty acids, and a history of severe allergic or anaphylactic reactions or known specific nutritional hypersensitivity.

INTERVENTIONS

The first intervention (A) was composed of Ω-3 and Ω-6 polyunsaturated fatty acids at 1:1 wt/wt. Specifically, the Ω-3 fatty acids were docosahexaenoic acid and eicosapentaenoic acid at 3:1 wt/wt, and the Ω-6 fatty acids were linoleic acid and γ-linolenic acid at 2:1 wt/wt. This intervention also included minor quantities of other specific polyunsaturated, monounsaturated and saturated fatty acids as well as vitamin A and vitamin E (α-tocopherol). The second intervention (B, PLP10) was a combination of A and γ-tocopherol. The third intervention (C) was γ-tocopherol alone. The fourth group of 20 participants received placebo. The interventions were administered per os (by mouth) once daily, 30 min before dinner for 30 months.

MAIN OUTCOME MEASURES

The primary end point was the annualised relapse rate (ARR) of the three interventions versus the placebo at 2 years. The secondary end point was the time to confirmed disability progression at 2 years.

RESULTS

A total of 41 (51%) patients completed the 30-month trial. Overall, for the per-protocol analysis of the 2-year primary end point, eight relapses were recorded in the PLP10 group (n=10; 0.40 ARR) versus 25 relapses in the placebo group (n=12; 1.04 ARR), representing a 64% adjusted relative rate reduction for the PLP10 group (RRR 0.36, 95% CI 0.15 to 0.87, p=0.024). In a subgroup analysis that excluded patients on monoclonal antibody (natalizumab) treatment, the observed adjusted RRR became stronger (72%) over the 2 years (RRR 0.28, 95% CI 0.10 to 0.79, p=0.016). The per-protocol analysis for the secondary outcome at 2 years, the time to disability progression, was significantly longer only for PLP10. The cumulative probability of disability progression at 2 years was 10% in the PLP10 group and 58% in the placebo group (unadjusted log-rank p=0.019). In a subgroup analysis that excluded patients on natalizumab, the cumulative probability of progression was 10% for the 10 patients in the PLP10 group and 70% for the 12 patients in the placebo group, representing a relative 86% decrease in the risk of the sustained progression of disability in the PLP10 group (unadjusted log-rank p=0.006; adjusted HR, 0.11; 95% CI 0.01 to 0.97, p=0.047). No adverse events were reported. Interventions A (10 patients) and C (9 patients) showed no significant efficacy.

CONCLUSIONS

In this small proof-of-concept, randomised, double-blind clinical trial; the PLP10 treatment significantly reduced the ARR and the risk of sustained disability progression without any reported serious adverse events. Larger studies are needed to further assess the safety and efficacy of PLP10.

TRIAL REGISTRATION

International Standard Randomised Controlled Trial, number ISRCTN87818535.

Respiratory hospitalisation of infants supplemented with docosahexaenoic acid as preterm neonates

AIM

To determine the effect of neonatal docosahexaenoic acid (DHA) supplementation in preterm infants on later respiratory-related hospitalisations.

METHODS

We enrolled 657 infants in a multicentre, randomised, controlled trial designed to study the long-term efficacy of higher dose dietary DHA in infants born <33 weeks' gestation. Treatment was with high DHA (∼1%) compared with standard DHA (∼0.3%) in breast milk or formula, given from the first week of life to term equivalent. Parent-reported hospital admissions to 18 months corrected age were recorded. The proportion of children hospitalised for lower respiratory tract (LRT) conditions and the mean number of hospitalisations per infant were determined.

RESULTS

Twenty-three per cent (154/657) of infants were hospitalised for LRT conditions. Seventy-three per cent (173/238) of admissions were for bronchiolitis. There was no significant effect of higher DHA on the proportion of infants admitted for LRT conditions (high DHA 22% vs. standard DHA 25%, adjusted relative risk 0.92, 95% confidence interval (CI) 0.68-1.24, P = 0.57) or in the mean number of admissions per infant (high DHA 0.34, standard DHA 0.38, adjusted ratio of means 0.91, 95% CI 0.63-1.32, P = 0.62). The sexes responded differently to treatment (interaction P = 0.046), with reduced admissions in boys given high DHA, but this was not statistically significant (high DHA 19%, standard DHA 28%, adjusted relative risk 0.69, 95% CI 0.46-1.04, P = 0.08).

CONCLUSIONS

Hospitalisation for LRT problems in the first 18 months for preterm infants was not reduced by neonatal supplementation with 1% DHA.

Hepatic transcriptome analysis of inter-family variability in flesh n-3 long-chain polyunsaturated fatty acid content in Atlantic salmon

Background

Genetic selection of Atlantic salmon families better adapted to alternative feed formulations containing high levels of vegetable ingredients has been suggested to ensure sustainable growth of aquaculture. The present study aimed to identify molecular pathways that could underlie phenotypic differences in flesh n-3 long-chain polyunsaturated fatty acid (LC-PUFA) levels when fish are fed vegetable oil diets. Liver transcriptome was analyzed and compared in four families presenting higher or lower n-3 LC-PUFA contents at two contrasting flesh total lipid levels.

Results

The main effect of n-3 LC-PUFA contents was in the expression of immune response genes (38% of all significantly affected genes), broadly implicated in the modulation of inflammatory processes and innate immune response. Although genetic evaluations of traits used in the breeding program revealed that the chosen families were not balanced for viral disease resistance, this did not fully explain the preponderance of immune response genes in the transcriptomic analysis. Employing stringent statistical analysis no lipid metabolism genes were detected as being significantly altered in liver when comparing families with high and low n-3 LC-PUFA flesh contents. However, relaxing the statistical analysis enabled identification of potentially relevant effects, further studied by RT-qPCR, in cholesterol biosynthesis, lipoprotein metabolism and lipid transport, as well as eicosanoid metabolism particularly affecting the lipoxygenase pathway. Total lipid level in flesh also showed an important effect on immune response and 8% of significantly affected genes related to lipid metabolism, including a fatty acyl elongase (elovl2), an acyl carrier protein and stearoyl-CoA desaturase.

Conclusions

Inter-family differences in n-3 LC-PUFA content could not be related to effects on lipid metabolism, including transcriptional modulation of the LC-PUFA biosynthesis pathway. An association was found between flesh adiposity and n-3 LC-PUFA in regulation of cholesterol biosynthesis, which was most likely explained by variation in tissue n-3 LC-PUFA levels regulating transcription of cholesterol metabolism genes through srebp2. A preponderance of immune response genes significantly affected by n-3 LC-PUFA contents could be potentially associated with disease resistance, possibly involving anti-inflammatory actions of tissue n-3 LC-PUFA through eicosanoid metabolism. This association may have been fortuitous, but it is important to clarify if this trait is included in future salmon breeding programmes.

Trans fatty acid intake is associated with insulin sensitivity but independently of inflammation

High saturated and trans fatty acid intake, the typical dietary pattern of Western populations, favors a proinflammatory status that contributes to generating insulin resistance (IR). We examined whether the consumption of these fatty acids was associated with IR and inflammatory markers. In this cross-sectional study, 127 non-diabetic individuals were allocated to a group without IR and 56 to another with IR, defined as homeostasis model assessment-IR (HOMA-IR) >2.71. Diet was assessed using 24-h food recalls. Multiple linear regression was employed to test independent associations with HOMA-IR. The IR group presented worse anthropometric, biochemical and inflammatory profiles. Energy intake was correlated with abdominal circumference and inversely with adiponectin concentrations (r = -0.227, P = 0.002), while saturated fat intake correlated with inflammatory markers and trans fat with HOMA-IR (r = 0.160, P = 0.030). Abdominal circumference was associated with HOMA-IR (r = 0.430, P < 0.001). In multiple analysis, HOMA-IR remained associated with trans fat intake (β = 1.416, P = 0.039) and body mass index (β = 0.390, P < 0.001), and was also inversely associated with adiponectin (β = -1.637, P = 0.004). Inclusion of other nutrients (saturated fat and added sugar) or other inflammatory markers (IL-6 and CRP) into the models did not modify these associations. Our study supports that trans fat intake impairs insulin sensitivity. The hypothesis that its effect could depend on transcription factors, resulting in expression of proinflammatory genes, was not corroborated. We speculate that trans fat interferes predominantly with insulin signaling via intracellular kinases, which alter insulin receptor substrates.

Exercise and the aging immune system

Aging is associated with a decline in the normal functioning of the immune system that is described by the canopy term "immunosenescence". This contributes to poorer vaccine responses and the increased incidence of infection and malignancy seen in the elderly. Regular exercise has been associated with enhanced vaccination responses, lower numbers of exhausted/senescent T-cells, increased T-cell proliferative capacity, lower circulatory levels of inflammatory cytokines ("inflamm-aging"), increased neutrophil phagocytic activity, lowered inflammatory response to bacterial challenge, greater NK-cell cytotoxic activity and longer leukocyte telomere lengths in aging humans, all of which indicate that habitual exercise is capable of regulating the immune system and delaying the onset of immunosenescence. This contention is supported by the majority of animal studies that report improved immune responses and outcomes to viral infections and malignancies due to exercise training. However, whether or not exercise can reverse, as well as prevent, immunosenescence is a contentious issue, particularly because most longitudinal exercise training studies do not report the same positive effects of exercise on immunity that have been widely reported in studies with a cross-sectional design. In this review, we summarize some of the known effects of exercise on immunosenescence, discuss avenues for future research, and provide potential mechanisms by which exercise may help rejuvinate the aging immune system.

Profiling changes triggered during maturation of dendritic cells: a lipidomic approach

Lipids are important in several biological processes because they act as signalling and regulating molecules, or, locally, as membrane components that modulate protein function. This paper reports the pattern of lipid composition of dendritic cells (DCs), a cell type of critical importance in inflammatory and immune responses. After activation by antigens, DCs undergo drastic phenotypical and functional transformations, in a process known as maturation. To better characterize this process, changes of lipid profile were evaluated by use of a lipidomic approach. As an experimental model of DCs, we used a foetal skin-derived dendritic cell line (FSDC) induced to mature by treatment with lipopolysaccharide (LPS). The results showed that LPS treatment increased ceramide (Cer) and phosphatidylcholine (PC) levels and reduced sphingomyelin (SM) and phosphatidylinositol (PI) content. Mass spectrometric analysis of a total lipid extract and of each class of lipids revealed that maturation promoted clear changes in ceramide profile. Quantitative analysis enabled identification of an increase in the total ceramide content and enhanced Cer at m/z 646.6, identified as Cer(d18:1/24:1), and at m/z 648.6, identified as Cer(d18:1/24:0). The pattern of change of these lipids give an extremely rich source of data for evaluating modulation of specific lipid species triggered during DC maturation.

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

N-3 polyunsaturated fatty acids (PUFAs) from fish oil exert their functional effects by targeting multiple mechanisms. One mechanism to emerge in the past decade is the ability of n-3 PUFA acyl chains to perturb the molecular organization of plasma membrane sphingolipid/cholesterol-enriched lipid raft domains. These domains are nanometer-scale assemblies that coalesce to compartmentalize select proteins for optimal function. Here we review recent evidence on how n-3 PUFAs modify lipid rafts from biophysical and biochemical experiments from several different model systems. A central theme emerges from these studies. N-3 PUFA acyl chains display tremendous conformational flexibility and a low affinity for cholesterol and saturated acyl chains. This unique flexibility of n-3 PUFA acyl chains impacts the organization of inner and outer leaflet lipid rafts by disrupting acyl chain packing and molecular order within rafts. Ultimately, the disruption in raft organization has consequences for protein clustering and thereby signaling. Overall, elucidating the complex mechanisms by which n-3 PUFA acyl chains reorganize membrane architecture will enhance the translation of these fatty acids into the clinic for treating several diseases.

n-3 Polyunsaturated fatty acids exert immunomodulatory effects on lymphocytes by targeting plasma membrane molecular organization

Fish oil, enriched in bioactive n-3 polyunsaturated fatty acids (PUFA), has therapeutic value for the treatment of inflammation-associated disorders. The effects of n-3 PUFAs are pleiotropic and complex; hence, an understanding of their cellular targets and molecular mechanisms of action remains incomplete. Here we focus on recent data indicating n-3 PUFAs exert immunosuppressive effects on the function of effector and regulatory CD4(+) T cells. In addition, we also present emerging evidence that n-3 PUFAs have immunomodulatory effects on B cells. We then focus on one multifaceted mechanism of n-3 PUFAs, which is the alteration of the biophysical and biochemical organization of the plasma membrane. This mechanism is central for downstream signaling, eicosanoid production, transcriptional regulation and cytokine secretion. We highlight recent work demonstrating n-3 PUFA acyl chains in the plasma membrane target the lateral organization of membrane signaling assemblies (i.e. lipid rafts or signaling networks) and de novo phospholipid biosynthesis. We conclude by proposing new functional and mechanistic questions in this area of research that will aid in the development of fish oil as adjuvant therapy for treating unresolved chronic inflammation.

Dietary fatty acids affect the immune system in male mice sensitized to ovalbumin or vaccinated with influenza

PUFA are precursor molecules for eicosanoids such as leukotrienes and prostaglandins and may influence immune function through other mechanisms involving membranes, cell signaling, and gene expression. Immune-modulating properties of diets containing different oils [sunflower oil, rich in linoleic acid; linseed oil, rich in α-linolenic acid; salmon oil, rich in marine (n-3) PUFA; and beef tallow, rich in SFA] were investigated in an influenza-vaccination model, in which the delayed-type hypersensitivity (DTH) response was studied in C57BL/6 mice, and an ovalbumin (OVA)-sensitization model for experimental allergy in BALB/c mice. Six-week-old mice were fed the different diets for 7 wk. The first vaccination or OVA sensitization was given 2 wk after the start of the dietary intervention. In the mice vaccinated with influenza, the DTH response to the vaccine was significantly higher in mice fed the marine (n-3) PUFA diet compared to all other groups, indicating that these PUFA promote a T helper-1 response. In the OVA-sensitized mice, those fed the marine (n-3) PUFA diet had a less severe acute allergic skin response (ASR), suggesting that (n-3) PUFA lessen the T helper-2 response. Mice fed the SFA-rich diet had the most severe ASR, indicating that a diet with high levels of SFA may contribute to increased severity of allergic symptoms. Whereas significant differences in in vivo immune responses were measured, in vitro responses did not differ among the dietary groups. In conclusion, using 2 different models of immune responses demonstrates potential benefits from marine (n-3) PUFA.

Impacts of membrane biophysics in Alzheimer's disease: from amyloid precursor protein processing to aβ Peptide-induced membrane changes

An increasing amount of evidence supports the notion that cytotoxic effects of amyloid-β peptide (Aβ), the main constituent of senile plaques in Alzheimer's disease (AD), are strongly associated with its ability to interact with membranes of neurons and other cerebral cells. Aβ is derived from amyloidogenic cleavage of amyloid precursor protein (AβPP) by β- and γ-secretase. In the nonamyloidogenic pathway, AβPP is cleaved by α-secretases. These two pathways compete with each other, and enhancing the non-amyloidogenic pathway has been suggested as a potential pharmacological approach for the treatment of AD. Since AβPP, α-, β-, and γ-secretases are membrane-associated proteins, AβPP processing and Aβ production can be affected by the membrane composition and properties. There is evidence that membrane composition and properties, in turn, play a critical role in Aβ cytotoxicity associated with its conformational changes and aggregation into oligomers and fibrils. Understanding the mechanisms leading to changes in a membrane's biophysical properties and how they affect AβPP processing and Aβ toxicity should prove to provide new therapeutic strategies for prevention and treatment of AD.

Essential fats for future health. Proceedings of the 9th Unilever Nutrition Symposium, 26-27 May 2010

The 9th Unilever Nutrition Symposium entitled 'Essential fats for future health', held on 26-27 May 2010, aimed to review the dietary recommendations for essential fatty acids (EFA); discuss the scientific evidence for the roles of EFA in cognition, immune function and cardiovascular health; and to identify opportunities for joint efforts by industry, academia, governmental and non-governmental organizations to effectively improve health behaviour. This paper summarizes the main conclusions of the presentations given at the symposium. Linoleic acid (LA) and α-linolenic acid (ALA) are EFA that cannot by synthesized by the human body. Docosahexaenoic acid (DHA) is considered as conditionally essential because of its limited formation from ALA in the human body and its critical role in early normal retinal and brain development and, jointly with eicosapentaenoic acid (EPA), in prevention of cardiovascular disease (CVD). Some evidence for possible beneficial roles of n-3 fatty acids for immune function and adult cognitive function is emerging. A higher consumption of polyunsaturated fatty acids (PUFA; >10%E), including LA, ALA and at least 250-500 mg per day of EPA+DHA, is recommended for prevention of coronary heart disease (CHD). Two dietary interventions suggest that EFA may affect CVD risk factors in children similarly as in adults. To ensure an adequate EFA intake of the population, including children, public health authorities should develop clear messages based on current science; ensure availability of healthy, palatable foods; and collaborate with scientists, the food industry, schools, hospitals, health-care providers and communities to encourage consumers to make healthy choices.

Polyunsaturated fatty acids. Immunomodulators in older adults

The immune system tends to become less efficient as people age, and nutrition plays a significant role in older adults' immune responses. In particular, dietary fatty acids are precursors to important immune system components. Certain fatty acids, predominantly those that are polyunsaturated, also tend to decrease the risk of certain neurological diseases in older adults. This article describes the impact of dietary polyunsaturated fatty acids (PUFA) on older adults' immune system and discusses the roles of age and immune status with regard to PUFA supplements.

Effects of linoleic acid and eicosapentaenoic acid on cell proliferation and lipid-metabolism gene expression in primary duck hepatocytes

Several studies have investigated that linoleic acid (LA) and eicosapentaenoic acid (EPA) affect cell proliferation and lipid catabolic gene expression in mammals. To determine if LA and EPA increase duck cell proliferation and lipid catabolic gene expression, the authors exposed duck primary hepatocyte cultures to LA or EPA. The results showed that both LA and EPA increased cell proliferation in a dose-dependent manner (100 μM). The effect on specific cell-cycle phases was also studied; LA and EPA (100 μM) deceased the proportion of cells in the G0/G1 phase from 83 to 80.8 and 80.3%, respectively, concomitant with an increase in the proportion of S-phase cells (11.5 and 10.5 vs. 8%, respectively). The expression of PPAR-α and PPAR-α target genes, such as acyl-CoA oxidase (ACOX), lipoprotein lipase (LPL), liver fatty acid-binding protein (L-FABP), was examined by quantitative real-time PCR. The results showed that the expression of the PPAR-α, ACOX, and LPL genes increased significantly following LA and EPA exposure, but that the expression of L-FABP remained unchanged. This study provides the first characterization of LA- and EPA-induced cell proliferation and PPAR-α and PPAR-α target gene transcriptional responses in duck primary hepatocyte cultures.

Effects of fatty acid unsaturation numbers on membrane fluidity and α-secretase-dependent amyloid precursor protein processing

Fatty acids may integrate into cell membranes to change physical properties of cell membranes, and subsequently alter cell functions in an unsaturation number-dependent manner. To address the roles of fatty acid unsaturation numbers in cellular pathways of Alzheimer's disease (AD), we systematically investigated the effects of fatty acids on cell membrane fluidity and α-secretase-cleaved soluble amyloid precursor protein (sAPP(α)) secretion in relation to unsaturation numbers using stearic acid (SA, 18:0), oleic acid (OA, 18:1), linoleic acid (LA, 18:2), α-linolenic acid (ALA, 18:3), arachidonic acid (AA, 20:4), eicosapentaenoic acid (EPA, 20:5), and docosahexaenoic acid (DHA, 22:6). Treatments of differentiated human neuroblastoma (SH-SY5Y cells) with AA, EPA and DHA for 24h increased sAPP(α) secretion and membrane fluidity, whereas those treatments with SA, OA, LA and ALA did not. Treatments with AA and DHA did not alter the total expressions of amyloid precursor protein (APP) and α-secretases in SH-SY5Y cells. These results suggested that not all unsaturated fatty acids but only those with 4 or more double bonds, such as AA, EPA and DHA, are able to increase membrane fluidity and lead to increase in sAPP(α) secretion. This study provides insights into dietary strategies for the prevention of AD.

Role of calcium and ROS in cell death induced by polyunsaturated fatty acids in murine thymocytes

We investigated the mechanisms whereby omega-3 and -6 polyunsaturated fatty acids (PUFAs) cause cell death of mouse thymocytes using flow cytometry, focusing on the respective roles of intracellular calcium concentration, [Ca(2+)](i) and reactive oxygen species (ROS). We applied the C-22, 20, and 18 carbon omega-3 (DHA, EPA, ALA) and omega-6 (DTA, ARA, and LNA) fatty acids to isolated thymocytes and monitored cell death using the DNA-binding dye, propidium iodide. When applied at 20 µM concentration, omega-3 fatty acids killed thymocytes over a period of 1 h with a potency of DHA > EPA > ALA. The omega-6 PUFAs were more potent. The C18 omega-6 fatty acid, LNA, was the most potent, followed by DHA and ARA. Cell death was always accompanied by an increase in the levels of [Ca(2+)](i) and ROS. Both increases were in proportion to the potency of the PUFAs in inducing cell death. Removing extracellular calcium did not prevent the elevation in [Ca(2+)](i) nor cell death. However, the intracellular calcium chelator, BAPTA, almost totally reduced both the elevation in [Ca(2+)](i) and cell death, while vitamin E reduced the elevation in ROS and cell death. BAPTA also prevented the elevation in ROS, but vitamin E did not prevent the elevation in [Ca(2+)](i). Thapsigargin, which depletes endoplasmic reticulum calcium, blocked the elevation in [Ca(2+)](i), but CCCP, a mitochondrial calcium uptake inhibitor, did not. These results suggest that the six PUFAs we studied kill thymocytes by causing release of calcium from endoplasmic reticulum, which causes release of ROS from mitochondria which leads to cell death.

Lipid accumulation and dendritic cell dysfunction in cancer

Professional antigen presenting cells, dendritic cells (DC) are responsible for initiation and maintenance of immune responses. Here, we report that a substantial proportion of DCs in tumor-bearing mice and cancer patients have increased levels of triglycerides. Lipid accumulation in DCs was caused by increased uptake of extracellular lipids due to up-regulation of scavenger receptor A. DCs with high lipid content were not able to effectively stimulate allogeneic T cells or present tumor-associated antigens. DCs with high and normal lipid levels did not differ in expression of MHC and co-stimulatory molecules. However, lipid-laden DCs had reduced capacity to process antigens. Pharmacological normalization of lipid levels in DCs with an inhibitor of acetyl-CoA carboxylase restored the functional activity of DCs and substantially enhanced the effects of a cancer vaccine. These findings support the regulation of immune responses in cancer by manipulation of lipid levels in DCs.

Benefits versus risks associated with consumption of fish and other seafood

Fish provide nutrition for much of the world's population, and when not contaminated with chemicals, fish is a very good food. A major benefit of fish is that they are high in polyunsaturated fatty acids (PUFAs), low in saturated fat, and they contain other critical nutrients. Much of the benefit of fish consumption derives from their high levels of long chain omega-3 PUFAs, which are produced by aquatic microorganisms and bioconcentrate in the aquatic food supply. The PUFAs are essential, in that humans and other vertebrates are not able to synthesize them and therefore must obtain them from the diet. The PUFAs particularly concentrate in the nervous system, alter immune system function reduce serum triglyceride levels and have been reported to reduce the risk of sudden death after a myocardial infarction. But the problem is that most fish have at least some degree of chemical contamination with methylmercury, (which binds to muscle) and/or with persistent organic pollutants such as dioxins, polychlorinated biphenyls, polybrominated diphenyl ethers, chlorinated pesticides (which concentrate in fish fat). These chemicals have adverse effects on nervous system function, modulate the immune system, and are associated with elevations in risk of cardiovascular disease. Thus the question of benefits and risk from fish consumption is complex but very important.

Mechanisms underlying the immunomodulatory effects of n-3 PUFA

The enrichment of immune cell membranes with n-3 PUFA is associated with modulation of immune function. The degree of incorporation of n-3 PUFA (and therefore the impact of dietary n-3 PUFA on immune function) appears to depend on a number of factors including species and age. The mechanisms involved are still largely unclear, but recent work has focused on two areas; lipid rafts and eicosanoids. In vitro studies suggest that lipid rafts could play a role in the immunomodulatory effects of n-3 PUFA, but there is still little information regarding the extent to which membrane microdomains in human lymphocytes are modulated by dietary supplementation. The enrichment of cell membranes with n-3 PUFA also modulates the production of eicosanoids, the full extent of which has not yet been realized; this represents a key area for future research.

Differential effects of conjugated linoleic acid isomers on macrophage glycerophospholipid metabolism

Conjugated linoleic acids (CLA) are dietary fatty acids. Whereas cis-9,trans-11-(c9,t11)-CLA can be found in meat and dairy products, trans-9,trans-11-(t9,t11)-CLA is a constituent of vegetable oils. Previous studies showed that these two isomers activate different nuclear receptors and, thus, expression of genes related to lipid metabolism. Here we show that these CLA isomers are differentially elongated and desaturated in primary monocyte-derived macrophages isolated from healthy volunteers by using gas chromatography-mass spectrometry (GC-MS). We further demonstrate that c9,t11-CLA incorporates in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) species and activates de novo glycerophospholipid synthesis by quantitative electrospray ionization-tandem mass spectrometry (ESI-MS/MS). c9,t11-CLA leads to strong shifts of the species profiles to PC 18:2/18:2 and PE 18:2/18:2, which are due to de novo synthesis and fatty acid remodeling. In contrast, t9,t11-CLA is preferentially bound to neutral lipids, including triglycerides and cholesterol esters. Taken together our results show that c9,t11-CLA and t9,t11-CLA have differential effects on PC and PE metabolism. Moreover, these data demonstrate that the structure of fatty acids not only determines their incorporation into lipid classes but also modulates the kinetics of lipid metabolism, particularly PC synthesis.

Developmental and neurobehavioral effects of perinatal exposure to diets with different omega-6:omega-3 ratios in mice

OBJECTIVE

To investigate in mice the effect of diets enriched with soy or sunflower oil with different omega-6:omega-3 ratios on gestation, reproductive success, physical maturation, and the neurobiological development of the pups.

METHODS

Dams were assigned, throughout gestation and lactation, to different groups: a commercial diet (CD), a soy oil-enriched diet (SOD), or a sunflower oil-enriched diet (SFOD). Measurements during gestation were dams' body weights and daily food intakes. Measurements in the offspring were physical parameters (body weight, body length, body mass index, fur appearance, pinna detachment, incisor eruption, eye opening, and puberty onset) and behavioral preweaning tests (surface righting reflex, negative geotaxis, and cliff avoidance).

RESULTS

The SOD and SFOD dams became significantly heavier than the CD dams from gestational days 14 and 19, respectively, to parturition. There were no significant differences in gestational length or food consumption during pregnancy or lactation or in maternal weight during lactation. Diets did not modify litter size, sex ratio, survival index at weaning, or body weight. The SFOD and SOD offspring were significantly shorter than the CD offspring at weaning. The mean offspring physical scores of SOD and SFOD offspring were higher than CD offspring and simple reflexes were earlier in the SOD and SFOD groups. In SFOD offspring, puberty onset was significantly delayed, at postnatal days 26 and 27 in male and female offspring, respectively.

CONCLUSION

This study suggests that the maintenance of an adequate omega-6:omega-3 ratio is necessary for the optimal growth and development of murine offspring. In populations that do not have sufficient provision of polyunsaturated fatty acids in the diet, their consumption would be advisable during gestation and lactation because these improve most neurodevelopmental outcomes included in this study.

Diet-induced docosahexaenoic acid non-raft domains and lymphocyte function

Docosahexaenoic acid (DHA) is an n-3 polyunsaturated fatty acid (PUFA) that generally suppresses the function of T lymphocytes and antigen presenting cells (APCs). An emerging mechanism by which DHA modifies lymphocyte function is through changes in the organization of sphingolipid/cholesterol lipid raft membrane domains. Two contradictory models have been proposed to explain how DHA exerts its effects through changes in raft organization. The biophysical model, developed in model membranes, shows that DHA-containing phospholipids form unique non-raft membrane domains, that are organizationally distinct from lipid rafts, which serve to alter the conformation and/or lateral organization of lymphocyte proteins. In contrast, the cellular model on DHA and rafts shows that DHA suppresses lymphocyte function, in part, by directly incorporating into lipid rafts and altering protein activity. To reconcile opposing biophysical and cellular viewpoints, a major revision to existing models is presented herein. Based largely on quantitative microscopy data, it is proposed that DHA, consumed through the diet, modifies lymphocyte function, in part, through the formation of nanometer scale DHA-rich domains. These nano-scale domains disrupt the optimal raft-dependent clustering of proteins necessary for initial signaling. The data covered in this review highlights the importance of understanding how dietary n-3 PUFAs modify lymphocyte membranes, which is essential toward developing these fatty acids as therapeutic agents for treating inflammatory diseases.

Retinal very long-chain PUFAs: new insights from studies on ELOVL4 protein

Compared with other mammalian tissues, retina is highly enriched in PUFA. Long-chain PUFA (LC-PUFA; C18-C24) are essential FAs that are enriched in the retina and are necessary for maintenance of normal retinal development and function. The retina, brain, and sperm also contain very LC-PUFA (VLC-PUFA; >C24). Although VLC-PUFA were discovered more than two decades ago, very little is known about their biosynthesis and functional roles in the retina. This is due mainly to intrinsic difficulties associated with working on these unusually long polyunsaturated hydrocarbon chains and their existence in small amounts. Recent studies on the FA elongase elongation of very long chain fatty acids-4 (ELOVL4) protein, however, suggest that VLC-PUFA probably play some uniquely important roles in the retina as well as the other tissues. Mutations in the ELOVL4 gene are found in patients with autosomal dominant Stargardt disease. Here, we review the recent literature on VLC-PUFA with special emphasis on the elongases responsible for their synthesis. We focus on a novel elongase, ELOVL4, involved in the synthesis of VLC-PUFA, and the importance of these FAs in maintaining the structural and functional integrity of retinal photoreceptors.

The nutritional and clinical significance of lipid rafts

PURPOSE OF REVIEW

Lipid rafts are potentially modifiable by diet, particularly (but not exclusively) by dietary fatty acids. This review examines the potential for dietary modification of raft structure and function in the immune system, brain and retinal tissue, the gut, and in cancer cells.

RECENT FINDINGS

In-vitro and ex-vivo studies suggest that dietary n-3 polyunsaturated fatty acids (PUFAs) may exert immunosuppressive and anticancer effects through changes in lipid raft organization. In addition, gangliosides and cholesterol may modulate lipid raft organization in a number of tissues, and recent work has highlighted sphingolipids in membrane microdomains as potential targets for inhibition of tumor growth. The roles of fatty acids and gangliosides, especially in relation to lipid rafts, in cognitive development, age-related cognitive decline, psychiatric disorders, and Alzheimer's disease are poorly understood and require further investigation. The roles of lipid rafts in cancer, in microbial pathogenesis, and in insulin resistance are starting to emerge, and indicate compelling evidence for the growing importance of membrane microdomains in health and disease.

SUMMARY

In-vitro and animal studies show that n-3 PUFAs, cholesterol, and gangliosides modulate the structure and composition of lipid rafts, potentially influencing a wide range of biological processes, including immune function, neuronal signaling, cancer cell growth, entry of pathogens through the gut barrier, and insulin resistance in metabolic disorders. The physiological, clinical, and nutritional relevance of these observations remains to be determined.

Oleic- and docosahexaenoic acid-containing phosphatidylethanolamines differentially phase separate from sphingomyelin

A central tenet of the lipid raft model is the existence of non-raft domains. In support of this view, we have established in model membranes that a phosphatidylethanolamine (PE)-containing docosahexaenoic acid (DHA) forms organizationally distinct non-raft domains in the presence of sphingomyelin (SM) and cholesterol (Chol). We have shown that formation of DHA-rich domains is driven by unfavorable molecular interactions between the rigid Chol molecule and the highly flexible DHA acyl chain. However, the molecular interactions between SM and the DHA-containing PE, which could also contribute to the formation of DHA-rich non-raft domains, have not been sufficiently investigated. To address this issue, we use differential scanning calorimetry (DSC) to study the phase behavior of mixtures of SM with either 1-palmitoyl-2-docosahexaenoyl-sn-glycero-3-phosphoethanolamine (16:0-22:6PE) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (16:0-18:1PE), an oleic acid (OA)-containing control, over a wide range of concentrations. Deconvolution of binary DSC scans shows that both 16:0-22:6PE and 16:0-18:1PE phase separate from SM. Analysis of transition temperatures and partial phase diagrams, constructed from the DSC scans for the first time, shows that 16:0-22:6PE displays greater non-ideal mixing with SM compared to 16:0-18:1PE. Our findings support a model in which DHA- and OA-containing PEs differentially phase separate from SM over a wide range of molar ratios to initiate the formation of non-raft domains, which is greatly enhanced by DHA, but not OA, in the presence of cholesterol.

Docosahexaenoic acid modifies the clustering and size of lipid rafts and the lateral organization and surface expression of MHC class I of EL4 cells

An emerging molecular mechanism by which docosahexaenoic acid (DHA) exerts its effects is modification of lipid raft organization. The biophysical model, based on studies with liposomes, shows that DHA avoids lipid rafts because of steric incompatibility between DHA and cholesterol. The model predicts that DHA does not directly modify rafts; rather, it incorporates into nonrafts to modify the lateral organization and/or conformation of membrane proteins, such as the major histocompatibility complex (MHC) class I. Here, we tested predictions of the model at a cellular level by incorporating oleic acid, eicosapentaenoic acid (EPA), and DHA, compared with a bovine serum albumin (BSA) control, into the membranes of EL4 cells. Quantitative microscopy showed that DHA, but not EPA, treatment, relative to the BSA control diminished lipid raft clustering and increased their size. Approximately 30% of DHA was incorporated directly into rafts without changing the distribution of cholesterol between rafts and nonrafts. Quantification of fluorescence colocalization images showed that DHA selectively altered MHC class I lateral organization by increasing the fraction of the nonraft protein into rafts compared with BSA. Both DHA and EPA treatments increased antibody binding to MHC class I compared with BSA. Antibody titration showed that DHA and EPA did not change MHC I conformation but increased total surface levels relative to BSA. Taken together, our findings are not in agreement with the biophysical model. Therefore, we propose a model that reconciles contradictory viewpoints from biophysical and cellular studies to explain how DHA modifies lipid rafts on several length scales. Our study supports the notion that rafts are an important target of DHA's mode of action.

In vivo test of the vertical phase separation hypothesis: the display of major histocompatibility complex (MHC) class I molecules on membranes of B cells from mice fed high-fat diets

The membrane vertical phase separation hypothesis predicts that a decrease in plasma membrane acyl chain order will increase major histocompatibility complex (MHC) class I surface expression. The hypothesis is based on modification of plasma membrane acyl chain order in cell culture and has not been tested in vivo. In the present study, we isolated splenic B cells from C57/BL6 mice fed either a normal diet or high-fat diets enriched in SFA or MUFA and assayed for changes in plasma membrane acyl chain order and MHC class I surface expression. Plasma membranes of B cells from MUFA-fed mice had significantly decreased acyl chain order and increased headgroup order. The decrease in acyl chain order correlated with a significant increase in the acyl chain unsaturation of B cells from the MUFA-fed mice. MHC class I surface levels on B cells were not affected by the MUFA-rich diet. This study suggests that the membrane vertical phase separation hypothesis may have limited application in a physiologically relevant setting.

Partial replacement of dietary (n-6) fatty acids with medium-chain triglycerides decreases the incidence of spontaneous colitis in interleukin-10-deficient mice

Enteral nutrition has a primary therapeutic effect in active Crohn's disease. It is unknown which nutrient(s) account for this action, but a role for both the amount and type of dietary fat has been postulated. Some clinical and experimental data suggest that medium-chain triglycerides (MCT) may reduce intestinal inflammation. We aimed to assess the effect of replacing part of the dietary fat with MCT on the incidence and severity of colitis in interleukin (IL)-10(-/-) mice under specific pathogen-free conditions. Twenty-four IL-10(-/-) 4-wk-old mice were randomized to receive a control diet based on sunflower oil [(n-6) fatty acids (FA)] and an experimental isocaloric, isonitrogenous diet with 50% sunflower and 50% coconut oil (MCT diet). When the mice were 12 wk old, they were killed and the colon was examined for the presence of colitis, lymphocyte subpopulations and apoptosis, ex vivo cytokine production in supernatant of colon explants, toll-like receptor (TLR)-2 and TLR-9 mRNA, and FA profile in colonic tissue homogenates. Colitis incidence was lower in the IL-10(-/-) mice fed the MCT diet (1/12) than in the mice fed the control diet (8/12; P = 0.03). The histological damage score was also lower in the former (P < 0.0005). Feeding the MCT diet resulted in fewer total and apoptotic intraepithelial CD3+ and lamina propria CD3+CD4+ lymphocytes, as well as downregulated production of IL-6 and interferon-gamma, and reduced TLR-9 mRNA. We conclude that partial replacement of dietary (n-6) FA with MCT decreases the incidence of colitis in a model of spontaneous intestinal inflammation and provide experimental arguments for a possible primary therapeutic effect of MCT in human Crohn's disease.

Chemotherapeutic Properties of n-3 Polyunsaturated Fatty Acids - Old Concepts and New Insights

Over the past several decades, data from both experimental animal studies and human clinical trials have shown that dietary n-3 polyunsaturated fatty acids (PUFA) exhibit anti-inflammatory bioactive properties, compared to n-6 PUFA. Collectively, these studies have identified multiple mechanisms by which n-3 PUFA affect immune cell responses. In this review, we discuss the putative targets of anti-inflammatory n-3 PUFA, specifically, cytokine production, antagonism of n-6 PUFA metabolism, binding to nuclear receptors as ligands, and the alteration of signaling protein acylation. In addition, we investigate the effect of n-3 PUFA on the coalescence of lipid rafts, specialized signaling platforms in the plasma membrane.

Effect of dietary fatty acid composition on Th1/Th2 polarization in lymphocytes

BACKGROUND

It has become increasingly clear that polyunsaturated fatty acids (PUFAs) have immunomodulatory effects. However, the intake of these fatty acids used in animal studies often greatly exceeds dietary human intake. Whether differences in the composition of fatty acids that are consumed in amounts consistent with normal dietary intake can influence immune function remains uncertain.

METHODS

We manufactured 3 types of liquid diet, related to modified fatty acid composition (omega-6/omega-3 = 0.25, 2.27 and 42.9), but excluding eicosapentaenoic acid and docosahexaenoic acid, based upon a liquid diet used clinically in humans. We assessed CD3-stimulated cytokine production of splenocytes in female BALB/c mice (n = 4 per group) fed 1 of 3 liquid diets for 4 weeks. We also measured the cytokine production of peripheral blood mononuclear cells stimulated with phorbol myristate acetate and ionomycin in humans at the end of a 4-week period of consumption of 2 different liquid diets (omega-6/omega-3 = 3 and 44).

RESULTS

We found that the ratio of interfero omega-gamma (IFN-gamma) / interleukin-4 (IL-4) was significantly higher in mice fed the omega-3 rich diet than in others. In humans, IFN-gamma / IL-4 was significantly higher after the omega-3 versus the omega-6 enhanced diet.

CONCLUSIONS

Differences in the composition of omega-3 and omega-6 PUFAs induces a shift in the Th1/Th2 balance in both mouse and human lymphocytes, even when ingested in normal dietary amounts. An omega-3 rich diet containing alpha-linolenic acid modulates immune function.

Accumulation of raft lipids in T-cell plasma membrane domains engaged in TCR signalling

Activating stimuli for T lymphocytes are transmitted through plasma membrane domains that form at T-cell antigen receptor (TCR) signalling foci. Here, we determined the molecular lipid composition of immunoisolated TCR activation domains. We observed that they accumulate cholesterol, sphingomyelin and saturated phosphatidylcholine species as compared with control plasma membrane fragments. This provides, for the first time, direct evidence that TCR activation domains comprise a distinct molecular lipid composition reminiscent of liquid-ordered raft phases in model membranes. Interestingly, TCR activation domains were also enriched in plasmenyl phosphatidylethanolamine and phosphatidylserine. Modulating the T-cell lipidome with polyunsaturated fatty acids impaired the plasma membrane condensation at TCR signalling foci and resulted in a perturbed molecular lipid composition. These results correlate the accumulation of specific molecular lipid species with the specific plasma membrane condensation at sites of TCR activation and with early TCR activation responses.

n-3 polyunsaturated fatty acids suppress the localization and activation of signaling proteins at the immunological synapse in murine CD4+ T cells by affecting lipid raft formation

The molecular properties of immunosuppressive n-3 polyunsaturated fatty acids (PUFA) have not been fully elucidated. Using CD4(+) T cells from wild-type control and fat-1 transgenic mice (enriched in n-3 PUFA), we show that membrane raft accumulation assessed by Laurdan (6-dodecanoyl-2-dimethyl aminonaphthalene) labeling was enhanced in fat-1 cells following immunological synapse (IS) formation by CD3-specific Ab expressing hybridoma cells. However, the localization of protein kinase Ctheta, phospholipase Cgamma-1, and F-actin into the IS was suppressed. In addition, both the phosphorylation status of phospholipase Cgamma-1 at the IS and cell proliferation as assessed by CFSE labeling and [(3)H]thymidine incorporation were suppressed in fat-1 cells. These data imply that lipid rafts may be targets for the development of dietary agents for the treatment of autoimmune and chronic inflammatory diseases.

Boron and fish oil have different beneficial effects on strength and trabecular microarchitecture of bone

An experiment was performed to determine whether boron deprivation would adversely affect vertebra (trabecular) bone microarchitecture, and whether any adverse effect would be modified by dietary fatty acid composition. Female rats were fed diets containing 0.1mg (9 micromol) boron/kg in a factorial arrangement with variables of supplemental boron at 0 (boron-deprived) or 3 (boron-adequate) mg (278 micromol)/kg and fat sources of 75 g safflower oil/kg or 65 g fish (menhaden)oil/kg plus 10 g linoleic acid/kg. After 6 weeks, six females per treatment were bred. Dams and pups continued on their respective diets through gestation, lactation, and after weaning. At age 21 weeks, the microarchitecture of the fourth lumbar vertebrae from 12 randomly selected pups from each treatment was determined by microcomputed tomography. Boron deprivation decreased bone volume fraction and increased trabecular separation and structural model index. Boron deprivation decreased trabecular thickness when the dietary oil was safflower. A three-point bending test for bone strength found that boron deprivation decreased the maximum force needed to break the femur. Feeding fish oil instead of safflower oil decreased connectivity density in vertebrae of boron-deficient but not in boron-adequate rats. Fish oil instead of safflower oil increased the maximum force to break and the bending moment of the femur, especially in rats fed adequate boron. The findings confirm that boron and fish oil are beneficial to cortical bone strength, and show that nutritional intakes of boron are beneficial for trabecular bone microarchitecture and influence the beneficial effects of fish oil on bone.

Boron deprivation decreases liver S-adenosylmethionine and spermidine and increases plasma homocysteine and cysteine in rats

Two experiments were conducted with weanling Sprague-Dawley rats to determine whether changes in S-adenosylmethionine utilization or metabolism contribute to the diverse responses to boron deprivation. In both experiments, four treatment groups of 15 male rats were fed ground corn-casein based diets that contained an average of 0.05 mg (experiment 1) or 0.15 mg (experiment 2) boron/kg. In experiment 2, some ground corn was replaced by sucrose and fructose to increase oxidative stress. The dietary variables were supplemental 0 (boron-deprived) or 3 (boron-adequate) mg boron/kg and different fat sources (can affect the response to boron) of 75 g corn oil/kg or 65 g fish (menhaden) oil/kg plus 10 linoleic acid/kg. When euthanized at age 20 (experiment 1) and 18 (experiment 2) weeks, rats fed the low-boron diet were considered boron-deprived because they had decreased boron concentrations in femur and kidney. Boron deprivation regardless of dietary oil increased plasma cysteine and homocysteine and decreased liver S-adenosylmethionine, S-adenosylhomocysteine, and spermidine. Plasma concentration of 8-iso-prostaglandin F2alpha (indicator of oxidative stress) was not affected by boron, but was decreased by feeding fish oil instead of corn oil. Fish oil instead of corn oil decreased S-adenosylmethionine, increased spermidine, and did not affect S-adenosylhomocysteine concentrations in liver. Additionally, fish oil versus corn oil did not affect plasma homocysteine in experiment 1, and slightly increased it in experiment 2. The findings suggest that boron is bioactive through affecting the formation or utilization of S-adenosylmethionine. Dietary fatty acid composition also affects S-adenosylmethionine formation or utilization, but apparently through a mechanism different from that of boron.

Docosahexaenoic and eicosapentaenoic acids increase prion formation in neuronal cells

Background

The transmissible spongiform encephalopathies, otherwise known as prion diseases, occur following the conversion of the cellular prion protein (PrP^C) to an alternatively folded, disease-associated isoform (PrP^Sc). Recent studies suggest that this conversion occurs via a cholesterol-sensitive process, as cholesterol synthesis inhibitors reduced the formation of PrP^Sc and delayed the clinical phase of scrapie infection. Since polyunsaturated fatty acids also reduced cellular cholesterol levels we tested their effects on PrP^Sc formation in three prion-infected neuronal cell lines (ScGT1, ScN2a and SMB cells).

Results

We report that treatment with docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA) or the cholesterol synthesis inhibitor simvastatin reduced the amounts of free cholesterol in membrane extracts from prion-infected neuronal cells. Simvastatin reduced cholesterol production while DHA and EPA promoted the conversion of free cholesterol to cholesterol esters. Crucially, while simvastatin reduced PrP^Sc formation, both DHA and EPA significantly increased the amounts of PrP^Sc in these cells. Unlike simvastatin, the effects of DHA and EPA on PrP^Sc content were not reversed by stimulation of cholesterol synthesis with mevalonate. Treatment of ScGT1 cells with DHA and EPA also increased activation of cytoplasmic phospholipase A₂ and prostaglandin E₂ production. Finally, treatment of neuronal cells with DHA and EPA increased the amounts of PrP^C expressed at the cell surface and significantly increased the half-life of biotinylated PrP^C.

Conclusion

We report that although treatment with DHA or EPA significantly reduced the free cholesterol content of prion-infected cells they significantly increased PrP^Sc formation in three neuronal cell lines. DHA or EPA treatment of infected cells increased activation of phospholipase A₂, a key enzyme in PrP^Sc formation, and altered the trafficking of PrP^C. PrP^C expression at the cell surface, a putative site for the PrP^Sc formation, was significantly increased, and the rate at which PrP^C was degraded was reduced. Cholesterol depletion is seen as a potential therapeutic strategy for prion diseases. However, these results indicate that a greater understanding of the precise relationship between membrane cholesterol distribution, PrP^C trafficking, cell activation and PrP^Sc formation is required before cholesterol manipulation can be considered as a prion therapeutic.