Dietary n-3 polyunsaturated fatty acids promote activation-induced cell death in Th1-polarized murine CD4+ T-cells

Ferroptosis: An important mechanism of disease mediated by the gut-liver-brain axis

AIMS

As a unique iron-dependent non-apoptotic cell death, Ferroptosis is involved in the pathogenesis and development of many human diseases and has become a research hotspot in recent years. However, the regulatory role of ferroptosis in the gut-liver-brain axis has not been elucidated. This paper summarizes the regulatory role of ferroptosis and provides theoretical basis for related research.

MATERIALS AND METHODS

We searched PubMed, CNKI and Wed of Science databases on ferroptosis mediated gut-liver-brain axis diseases, summarized the regulatory role of ferroptosis on organ axis, and explained the adverse effects of related regulatory effects on various diseases.

KEY FINDINGS

According to our summary, the main way in which ferroptosis mediates the gut-liver-brain axis is oxidative stress, and the key cross-talk of ferroptosis affecting signaling pathway network is Nrf2/HO-1. However, there were no specific marker between different organ axes mediate by ferroptosis.

SIGNIFICANCE

Our study illustrates the main ways and key cross-talk of ferroptosis mediating the gut-liver-brain axis, providing a basis for future research.

Eicosapentaenoic acid reduces the proportion of IL-17A-producing T cells in a 3D psoriatic skin model

Psoriasis is a skin disease presenting as erythematous lesions with accentuated proliferation of epidermal keratinocytes, infiltration of leukocytes, and dysregulated lipid metabolism. T cells play essential roles in the disease. n-3 polyunsaturated fatty acids are anti-inflammatory metabolites, which exert an immunosuppressive effect on healthy T cells. However, the precise mechanistic processes of n-3 polyunsaturated fatty acids on T cells in psoriasis are still unrevealed. In this study, we aimed to evaluate the action of eicosapentaenoic acid (EPA) on T cells in a psoriatic skin model produced with T cells. A coculture of psoriatic keratinocytes and polarized T cells was prepared using culture media, which was either supplemented with 10 μM EPA or left unsupplemented. Healthy and psoriatic skin substitutes were produced according to the self-assembly method. In the coculture model, EPA reduced the proportion of IL-17A-positive cells, while increasing that of FOXP3-positive cells, suggesting an increase in the polarization of regulatory T cells. In the 3D psoriatic skin model, EPA normalized the proliferation of psoriatic keratinocytes and diminished the levels of IL-17A. The expression of the proteins of the signal transducer and activator of transcription was influenced following EPA supplementation with downregulation of the phosphorylation levels of signal transducer and activator of transcription 3 in the dermis. Finally, the NFκB signaling pathway was modified in the EPA-supplemented substitutes with an increase in Fas amounts. Ultimately, our results suggest that in this psoriatic model, EPA exerts its anti-inflammatory action by decreasing the proportion of IL-17A-producing T cells.

Vitamin D Repletion and AA/EPA Intake in Children with Type 1 Diabetes: Influences on Metabolic Status

Our study aimed to show a relationship between metabolic control, vitamin D status (25OHD), and arachidonic acid (AA)/eicosapentaenoic acid (EPA) ratio in children with type 1 diabetes (T1D). The secondary aim was to evaluate dietary intake and the presence of ketoacidosis (DKA) at the onset of T1D. Methods: A cohort of 40 children with T1D was recruited, mean age 9.7 years (7.1; 13), with onset of T1D in the last 5 years: some at onset (n: 20, group A) and others after 18.0 ± 5 months (n: 20; group B). Twenty healthy children were compared as control subjects (CS). Dietary intakes were assessed through a diary food frequency questionnaire. Moreover, dried blood spots were used to test AA/EPA ratio by gas chromatography. Results: T1D children had a lower percentage of sugar intake (p < 0.02) than CS. Furthermore, group B introduced a greater amount of AA with the diet (g/day; p < 0.05) than CS (p < 0.01) and group A (p < 0.01). Children with an AA/EPA ratio ≤ 22.5 (1st quartile) required a lower insulin demand and had higher 25OHD levels than those who were in the higher quartiles (p < 0.05). Subjects with DKA (9/40) had levels of 25OHD (p < 0.05) and C-peptide (p < 0.05) lower than those without DKA. Moreover, analyzing the food questionnaire in group A, subjects with DKA showed a lower intake of proteins, sugars, fiber (g/day; p< 0.05), vitamin D, EPA, and DHA (g/day; p < 0.01) compared to subjects without DKA. Non-linear associations between vitamin D intake (p < 0.0001; r2:0.580) and linear between EPA intake and C-peptide (p < 0.05; r: 0.375) were found in all subjects. Conclusions: The study shows a relationship between vitamin D status, AA/EPA ratio, and metabolic state, probably due to their inflammatory and immune mechanisms. A different bromatological composition of the diet could impact the severity of the onset.

Current knowledge of the implication of lipid mediators in psoriasis

The skin is an organ involved in several biological processes essential to the proper functioning of the organism. One of these essential biological functions of the skin is its barrier function, mediated notably by the lipids of the stratum corneum, and which prevents both penetration from external aggression, and transepidermal water loss. Bioactive lipid mediators derived from polyunsaturated fatty acids (PUFAs) constitute a complex bioactive lipid network greatly involved in skin homeostasis. Bioactive lipid mediators derived from n-3 and n-6 PUFAs have well-documented anti- and pro-inflammatory properties and are recognized as playing numerous and complex roles in the behavior of diverse skin diseases, including psoriasis. Psoriasis is an inflammatory autoimmune disease with many comorbidities and is associated with enhanced levels of pro-inflammatory lipid mediators. Studies have shown that a high intake of n-3 PUFAs can influence the development and progression of psoriasis, mainly by reducing the severity and frequency of psoriatic plaques. Herein, we provide an overview of the differential effects of n-3 and n-6 PUFA lipid mediators, including prostanoids, hydroxy-fatty acids, leukotrienes, specialized pro-resolving mediators, N-acylethanolamines, monoacylglycerols and endocannabinoids. This review summarizes current findings on lipid mediators playing a role in the skin and their potential as therapeutic targets for psoriatic patients.

Nutrition and immune system: from the Mediterranean diet to dietary supplementary through the microbiota

The interaction between nutrition and the immune system is very complex. In particular, at every stage of the immune response, specific micronutrients, including vitamins and minerals play a key role and often synergistic, and the deficiency of only one essential nutrient may impair immunity. An individual's overall nutrition status and pattern of dietary intake (comprised of nutrients and non-nutritive bioactive compounds and food) and any supplementation with nutraceuticals including vitamins and minerals, can influence positively or negatively the function of the immune system. This influence can occur at various levels from the innate immune system and adaptive immune system to the microbiome. Although there are conflicting evidence, the current results point out that dietary supplementation with some nutrients such as vitamin D and zinc may modulate immune function. An update on the complex relationship between nutrition, diet, and the immune system through gut microbiota is the aim of this current review. Indeed, we will provide the overview of the link among immune function, nutrition and gut microbiota, paying particular attention at the effect of the Mediterranean diet on the immune system, and finally we will speculate the possible role of the main one functional supplements on immune function.

Role of dietary lipids in food allergy

The prevalence of food allergy is raising in industrialized countries, but the mechanisms behind this increased incidence are not fully understood. Environmental factors are believed to play a role in allergic diseases, including lifestyle influences, such as diet. There is a close relationship between allergens and lipids, with many allergenic proteins having the ability to bind lipids. Dietary lipids exert pro-inflammatory or anti-inflammatory functions on cells of the innate immunity and influence antigen presentation to cells of the adaptive immunity. In addition to modifying the immunostimulating properties of proteins, lipids also alter their digestibility and intestinal absorption, changing allergen bioavailability. This study provides an overview of the role of dietary lipids in food allergy, taking into account epidemiological information, as well as results of mechanistic investigations using in vivo, ex vivo and in vitro models. The emerging link among high-fat diets, obesity, and allergy is also discussed.

Nutritional Modulation of Immune Function: Analysis of Evidence, Mechanisms, and Clinical Relevance

It is well-established that the nutritional deficiency or inadequacy can impair immune functions. Growing evidence suggests that for certain nutrients increased intake above currently recommended levels may help optimize immune functions including improving defense function and thus resistance to infection, while maintaining tolerance. This review will examine the data representing the research on prominent intervention agents n-3 polyunsaturated fatty acids (PUFA), micronutrients (zinc, vitamins D and E), and functional foods including probiotics and tea components for their immunological effects, working mechanisms, and clinical relevance. Many of these nutritive and non-nutritive food components are related in their functions to maintain or improve immune function including inhibition of pro-inflammatory mediators, promotion of anti-inflammatory functions, modulation of cell-mediated immunity, alteration of antigen-presenting cell functions, and communication between the innate and adaptive immune systems. Both animal and human studies present promising findings suggesting a clinical benefit of vitamin D, n-3 PUFA, and green tea catechin EGCG in autoimmune and inflammatory disorders, and vitamin D, vitamin E, zinc, and probiotics in reduction of infection. However, many studies report divergent and discrepant results/conclusions due to various factors. Chief among them, and thus call for attention, includes more standardized trial designs, better characterized populations, greater consideration for the intervention doses used, and more meaningful outcome measurements chosen.

Toxicity of a Soybean Oil Emulsion on Human Lymphocytes and Neutrophils

BACKGROUND

The incorporation of lipid emulsions in parenteral diets is a requirement for energy and essential fatty acid supply to critically ill patients. In this study, the toxicity of a lipid emulsion rich (60%) in triacylglycerol of omega-6 polyunsaturated fatty acids on leukocytes from healthy volunteers was investigated.

METHODS

Eleven volunteers were recruited, and blood samples were collected before infusion of a soybean oil emulsion, immediately afterwards, and 18 hours later. The cells were studied immediately after isolation and again after 24 hours or 48 hours in culture. The following determinations were made: composition and concentration of fatty acids in plasma, lymphocytes and neutrophils, lymphocyte proliferation, levels of cell viability, DNA fragmentation, phosphatidylserine externalization, mitochondrial depolarization, reactive oxygen species production, and neutral lipid accumulation.

RESULTS

Soybean oil emulsion decreased lymphocyte proliferation and provoked neutrophil and lymphocyte apoptosis and necrosis. Evidence is presented herein that soybean oil emulsion is less toxic to neutrophils than to lymphocytes. The mechanism of cell death induced by this oil emulsion was characterized by mitochondrial membrane depolarization and neutral lipid accumulation but did not alter reactive oxygen species production.

CONCLUSIONS

Soybean oil emulsion given as a single dose of 500 mL promotes lymphocyte and neutrophil death that may enhance the susceptibility of the patients to infections.

Effect of tyrosine hydroxylase overexpression in lymphocytes on the differentiation and function of T helper cells

The aim of the present study was to examine the effect of the overexpression of tyrosine hydroxylase (TH), a rate-limiting enzyme for the synthesis of catecholamines (CAs), in lymphocytes on the differentiation and function of T helper (Th) cells. A recombinant TH overexpression plasmid (pEGFP-N1-TH) was constructed and transfected into mesenteric lymphocytes using nucleofection technology. These cells were stimulated with concanavalin A (Con A) for 48 h and then examined for TH expression and CA content, as well as for the percentage of Th1 and Th2 cells, cytokine concentrations and for the levels of signaling molecules. The lymphocytes overexpressing TH also expressed higher mRNA and protein levels of TH, and synthesized more CAs, including norepinephrine (NE), epinephrine (E) and dopamine (DA) than the mock-transfected control cells. TH gene overexpression in the lymphocytes reduced the percentage of interferon-γ (IFN-γ)-producing CD4+ cells and the ratio of CD4+IFN-γ+/CD4+IL-4+ cells, as well as the percentages of CD4+CD26+ and CD4+CD30+ cells and the ratio of CD4+CD26+/CD4+CD30+ cells. TH overexpression also reduced the secretion of IFN-γ and tumor necrosis factor (TNF) from lymphocytes. Moreover, NE inhibited the Con A-induced lymphocyte proliferation and decreased both cyclic adenosine monophosphate (cAMP) levels and p38 mitogen-activated protein kinase (MAPK) expression in the lymphocytes. Our findings thus indicate that TH gene overexpression promotes the polarization and differentiation of CD4+ cells towards Th2 cells, and this effect is mediated by the cAMP and p38 MAPK signaling pathways.

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.

Omega-3 fatty acids, lipid rafts, and T cell signaling

n-3 polyunsaturated fatty acids (PUFA) have been shown in many clinical studies to attenuate inflammatory responses. Although inflammatory responses are orchestrated by a wide spectrum of cells, CD4(+) T cells play an important role in the etiology of many chronic inflammatory diseases such as inflammatory bowel disease and obesity. In light of recent concerns over the safety profiles of non-steroidal anti-inflammatory drugs (NSAIDs), alternatives such as bioactive nutraceuticals are becoming more attractive. In order for these agents to be accepted into mainstream medicine, however, the mechanisms by which nutraceuticals such as n-3 PUFA exert their anti-inflammatory effects must be fully elucidated. Lipid rafts are nanoscale, dynamic domains in the plasma membrane that are formed through favorable lipid-lipid (cholesterol, sphingolipids, and saturated fatty acids) and lipid-protein (membrane-actin cytoskeleton) interactions. These domains optimize the clustering of signaling proteins at the membrane to facilitate efficient cell signaling which is required for CD4(+) T cell activation and differentiation. This review summarizes novel emerging data documenting the ability of n-3 PUFA to perturb membrane-cytoskeletal structure and function in CD4(+) T cells. An understanding of these underlying mechanisms will provide a rationale for the use of n-3 PUFA in the treatment of chronic inflammation.

Regulation of differentiation and function of helper T cells by lymphocyte-derived catecholamines via α₁- and β₂-adrenoceptors

OBJECTIVE

Recently, we have reported that lymphocyte-derived endogenous catecholamines (CAs) facilitate a shift in the T helper (Th)1/Th2 balance towards Th2. The purpose of this study was to explore the involvement of adrenoreceptors (ARs) in Th differentiation and function modulation by lymphocyte-derived CAs.

METHODS

Lymphocytes were separated from the mesenteric lymph nodes of mice, stimulated with concanavalin A (Con A) and treated with pargyline, an inhibitor of CA degradation.

RESULTS

Pargyline downregulated the expression of Th1-relative factors, T-bet, interferon (IFN)-γ and interleukin (IL)-2, but upregulated the expression of Th2-relative factors, GATA-3, IL-4 and IL-10. Pargyline reduced the percentage of IFN-γ-producing CD4+ cells and the CD4+IFN-γ+/CD4+IL-4+ cell ratio, although it did not alter the proportion of IL-4-producing CD4+ cells. In addition, the percentage of CD4+CD26+ T cells and the CD4+CD26+/CD4+CD30+ cell ratio were also reduced in the pargyline-treated group. Furthermore, Con A-activated T cells treated with pargyline produced a lower level of IFN-γ and a higher level of IL-4 than the control group. All these effects were blocked by the α1-AR antagonist corynanthine or the β2-AR antagonist ICI 118551, but not by the α2-AR antagonist yohimbine or β1-AR antagonist atenolol.

CONCLUSIONS

These results imply that lymphocyte-derived CAs promote polarization of differentiation and function towards Th2 cells and that this effect is mediated by α1-AR and β2-AR.

Activation of the mitochondrial ATP-sensitive K+ channel reduces apoptosis of spleen mononuclear cells induced by hyperlipidemia

Background

We have previously demonstrated that increased rates of superoxide generation by extra-mitochondrial enzymes induce the activation of the mitochondrial ATP-sensitive potassium channel (mitoK_ATP) in the livers of hypertriglyceridemic (HTG) mice. The resulting mild uncoupling mediated by mitoK_ATP protects mitochondria against oxidative damage. In this study, we investigate whether immune cells from HTG mice also present increased mitoK_ATP activity and evaluate the influence of this trait on cell redox state and viability.

Methods

Oxygen consumption (Clark-type electrode), reactive oxygen species production (dihydroethidium and H2-DCF-DA probes) and cell death (annexin V, cytocrome c release and Trypan blue exclusion) were determined in spleen mononuclear cells.

Results

HTG mice mononuclear cells displayed increased mitoK_ATP activity, as evidenced by higher resting respiration rates that were sensitive to mitoK_ATP antagonists. Whole cell superoxide production and apoptosis rates were increased in HTG cells. Inhibition of mitoK_ATP further increased the production of reactive oxygen species and apoptosis in these cells. Incubation with HTG serum induced apoptosis more strongly in WT cells than in HTG mononuclear cells. Cytochrome c release into the cytosol and caspase 8 activity were both increased in HTG cells, indicating that cell death signaling starts upstream of the mitochondria but does involve this organelle. Accordingly, a reduced number of blood circulating lymphocytes was found in HTG mice.

Conclusions

These results demonstrate that spleen mononuclear cells from hyperlipidemic mice have more active mitoK_ATP channels, which downregulate mitochondrial superoxide generation. The increased apoptosis rate observed in these cells is exacerbated by closing the mitoK_ATP channels. Thus, mitoK_ATP opening acts as a protective mechanism that reduces cell death induced by hyperlipidemia.

n-3 polyunsaturated fatty acids suppress phosphatidylinositol 4,5-bisphosphate-dependent actin remodelling during CD4+ T-cell activation

n-3 PUFA (polyunsaturated fatty acids), i.e. DHA (docosahexaenoic acid), found in fish oil, exhibit anti-inflammatory properties; however, the molecular mechanisms remain unclear. Since PtdIns(4,5)P2 resides in raft domains and DHA can alter the size of rafts, we hypothesized that PtdIns(4,5)P2 and downstream actin remodelling are perturbed by the incorporation of n-3 PUFA into membranes, resulting in suppressed T-cell activation. CD4+ T-cells isolated from Fat-1 transgenic mice (membranes enriched in n-3 PUFA) exhibited a 50% decrease in PtdIns(4,5)P2. Upon activation by plate-bound anti-CD3/anti-CD28 or PMA/ionomycin, Fat-1 CD4+ T-cells failed to metabolize PtdIns(4,5)P2. Furthermore, actin remodelling failed to initiate in Fat-1 CD4+ T-cells upon stimulation; however, the defect was reversed by incubation with exogenous PtdIns(4,5)P2. When Fat-1 CD4+ T-cells were stimulated with anti-CD3/anti-CD28-coated beads, WASP (Wiskott-Aldrich syndrome protein) failed to translocate to the immunological synapse. The suppressive phenotype, consisting of defects in PtdIns(4,5)P2 metabolism and actin remodelling, were recapitulated in CD4+ T-cells isolated from mice fed on a 4% DHA triacylglycerol-enriched diet. Collectively, these data demonstrate that n-3 PUFA, such as DHA, alter PtdIns(4,5)P2 in CD4+ T-cells, thereby suppressing the recruitment of WASP to the immunological synapse, and impairing actin remodelling in CD4+ T-cells.

Fish oil increases raft size and membrane order of B cells accompanied by differential effects on function

Fish oil (FO) targets lipid microdomain organization to suppress T-cell and macrophage function; however, little is known about this relationship with B cells, especially at the animal level. We previously established that a high FO dose diminished mouse B-cell lipid raft microdomain clustering induced by cross-linking GM1. To establish relevance, here we tested a FO dose modeling human intake on B-cell raft organization relative to a control. Biochemical analysis revealed more docosahexaenoic acid (DHA) incorporated into phosphatidylcholines than phosphatidylethanolamines of detergent-resistant membranes, consistent with supporting studies with model membranes. Subsequent imaging experiments demonstrated that FO increased raft size, GM1 expression, and membrane order upon cross-linking GM1 relative to no cross-linking. Comparative in vitro studies showed some biochemical differences from in vivo measurements but overall revealed that DHA, but not eicosapentaenoic acid (EPA), increased membrane order. Finally, we tested the hypothesis that disrupting rafts with FO would suppress B-cell responses ex vivo. FO enhanced LPS-induced B-cell activation but suppressed B-cell stimulation of transgenic naive CD4(+) T cells. Altogether, our studies with B cells support an emerging model that FO increases raft size and membrane order accompanied by functional changes; furthermore, the results highlight differences in EPA and DHA bioactivity.

n-3 Fatty acids uniquely affect anti-microbial resistance and immune cell plasma membrane organization

It is now well established that dietary lipids are incorporated into macrophage and T-cell membrane microdomains, altering their structure and function. Within cell membranes, there are specific detergent-resistant domains in which key signal transduction proteins are localized. These regions are classified as "lipid rafts". Rafts are composed mostly of cholesterol and sphingolipids and therefore do not integrate well into the fluid phospholipid bilayers causing them to form microdomains. Upon cell activation, rafts compartmentalize signal-transducing molecules, thus providing an environment conducive to signal transduction. In this review, we discuss recent novel data describing the effects of n-3 PUFA on alterations in the activation and functions of macrophages and T-cells. We believe that the modifications in these two disparate immune cell types are linked by fundamentally similar changes in membrane lipid composition and transmembrane signaling functions. We conclude that the outcomes of n-3 PUFA-mediated immune cell alterations may be beneficial (e.g., anti-inflammatory) or detrimental (e.g., loss of microbial immunity) depending upon the cell type interrogated.

Linoleic acid and butyrate synergize to increase Bcl-2 levels in colonocytes

The biological properties of polyunsaturated fatty acid (PUFA) classes have been the source of much contention. For example, n-3 PUFA are chemoprotective, whereas n-6 PUFA may promote tumor development. Since dietary components can have combinatorial effects, we further examined the apoptotic properties of n-3 or n-6 fatty acids when combined with different fiber sources. Mice were fed diets supplemented with either fish oil (FO; enriched in n-3 PUFA) or corn oil (CO; enriched in n-6 PUFA) and nonfermentable (cellulose) or fermentable (pectin) fiber sources. In complementary experiments, immortalized young adult mouse colonic (YAMC) cells were treated with docosahexaenoic acid (DHA; 22:6n-3) or linoleic acid (LA; 18:2n-6) with or without butyrate. Mice fed a FO and pectin diet had significantly (p < 0.05) increased levels of apoptosis in colonocytes compared to all other diets. Similarly, apoptosis was highly induced in DHA and butyrate cotreated YAMC cells. In contrast, in both YAMC and mouse models, LA/CO with butyrate/pectin treatment reduced apoptosis and enhanced expression of bcl-2. The LA and butyrate induced antiapoptotic phenotype was reversed by knocking down bcl-2 using targeted siRNA. In comparison, overexpression of bcl-2 blocked the proapoptotic effect of DHA and butyrate. These data provide new mechanistic insights into the regulation of apoptosis by dietary PUFA and fiber.

Eicosapentaenoic acid disrupts the balance between Tregs and IL-17+ T cells through PPARγ nuclear receptor activation and protects cardiac allografts

Eicosapentaenoic acid (EPA) is one of n-3 polyunsaturated fatty acids that possesses a wide array of anti-inflammatory effects but its effects, on transplantation in general and on Tregs and IL-17(+) T cells in particular, are not well studied. We treated recipient mice of heart transplantation with EPA and examined the effect of EPA on the ratio of Tregs/IL-17(+) T cells in an allogeneic heart transplant model. The hearts from BALB/c (H-2d) mice were transplanted into C57BL/6 (H-2b) mice, and the recipients were administered EPA (500 mg/kg/d, 250 mg/kg/d, or 100 mg/kg/d) from d 1 to 3 post-transplant. The survival of cardiac allografts in mice treated with EPA was significantly protracted. Further examination of donor hearts in EPA-treated group demonstrated that infiltrating Foxp3(+) T cells were increased, IL-17(+) T cells were decreased, and expression of PPARγ was up-regulated. In mixed lymphocytes reaction (MLR), incubation with EPA significantly inhibited the proliferation of IL-17(+) T cells and promoted the proliferation of Tregs, while PPARγ antagonists GW9662 could reverse the results. Our study demonstrated that EPA can effectively protect cardiac allografts and disrupt the balance between Tregs and IL-17(+) T cells in a murine model. This effect is partially mediated by PPARγ nuclear receptor activation.

Regulatory activity of polyunsaturated fatty acids in T-cell signaling

n-3 Polyunsaturated fatty acids (PUFA) are considered to be authentic immunosuppressors and appear to exert beneficial effects with respect to certain immune-mediated diseases. In addition to promoting T-helper 1 (Th1) cell to T-helper 2 (Th2) cell effector T-cell differentiation, n-3 PUFA may also exert anti-inflammatory actions by inducing apoptosis in Th1 cells. With respect to mechanisms of action, effects range from the modulation of membrane receptors to gene transcription via perturbation of a number of second messenger cascades. In this review, the putative targets of anti-inflammatory n-3 PUFA, activated during early and late events of T-cell activation will be discussed. Studies have demonstrated that these fatty acids alter plasma membrane micro-organization (lipid rafts) at the immunological synapse, the site where T-cells and antigen-presenting cells (APC) form a physical contact for antigen initiated T-cell signaling. In addition, the production of diacylglycerol and the activation of different isoforms of protein kinase C (PKC), mitogen-activated protein kinase (MAPK), calcium signaling, and nuclear translocation/activation of transcriptional factors, can be modulated by n-3 PUFA. Advantages and limitations of diverse methodologies to study the membrane lipid raft hypothesis, as well as apparent contradictions regarding the effect of n-3 PUFA on lipid rafts will be critically presented.

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.

Incorporation of a dietary omega 3 fatty acid impairs murine macrophage responses to Mycobacterium tuberculosis

BACKGROUND

Beside their health benefits, dietary omega 3 polyunsaturated fatty acids (n-3 PUFA) might impair host resistance to Mycobacterium tuberculosis (Mtb) by creating an immunosuppressive environment. We hypothesized that incorporation of n-3 PUFA suppresses activation of macrophage antimycobacterial responses and favors bacterial growth, in part, by modulating the IFNgamma-mediated signaling pathway.

METHODOLOGY/PRINCIPAL FINDINGS

Murine macrophage-like J774A.1 cells were incubated with bovine serum albumin (BSA)-conjugated docosahexaenoic acid (DHA; 22:6n-3) or BSA alone, activated with recombinant IFNgamma, and infected with a virulent strain (H37Rv) of M. tuberculosis. The fatty acid composition of macrophage membranes was modified significantly by DHA treatment. DHA-treated macrophages were less effective in controlling intracellular mycobacteria and showed impaired oxidative metabolism and reduced phagolysosome maturation. Incorporation of DHA resulted in defective macrophage activation, as characterized by reduced production of pro-inflammatory cytokines (TNFalpha, IL-6 and MCP-1), and lower expression of co-stimulatory molecules (CD40 and CD86). DHA treatment impaired STAT1 phosphorylation and colocalization of the IFNgamma receptor with lipid rafts, without affecting surface expression of IFNgamma receptor.

CONCLUSIONS/SIGNIFICANCE

We conclude that DHA reduces the ability of J774A.1 cells to control M. tuberculosis in response to activation by IFNgamma, by modulation of IFNgamma receptor signaling and function, suggesting that n-3 PUFA-enriched diets may have a detrimental effect on host immunity to tuberculosis.

n-3 polyunsaturated fatty acids--physiological relevance of dose

n-3 polyunsaturated fatty acids (PUFA) are widely used for chemotheraphy/chemoprevention of chronic diseases. However, the molecular mechanism(s) by which the bioactive n-3 PUFA (eicosapentaenoic acid and docosahexaenoic acid) modulate effector pathways are not fully elucidated. Multiple experimental approaches, including use of animal models, cell lines, and human clinical trials, have been utilized to dissect the complex effectors. It is imperative to link these different experimental approaches together in order to interpret outcomes in the context of human physiology and pathophysiology. Unfortunately, the adoption of a broad array of model systems and a wide range of fatty acid exposures (i.e. doses) has made it difficult to interpret biological outcomes. Therefore, in this mini-review we discuss the impact of (a) molecular structure of bioactive fatty acids, (b) dose relevance relative to human consumption, (c) enrichment of fatty acids in sera and tissues following dietary intake, and (d) limitations of cell/tissue culture studies.

n-3 PUFA improves fatty acid composition, prevents palmitate-induced apoptosis, and differentially modifies B cell cytokine secretion in vitro and ex vivo

n-3 polyunsaturated fatty acids (PUFAs) modify T-cell activation, in part by remodeling lipid composition; however, the relationship between n-3 PUFA and B-cell activation is unknown. Here we tested this relationship in vitro and ex vivo by measuring upregulation of B-cell surface molecules, the percentage of cells activated, and cytokine secreted in response to lipopolysaccharide (LPS) activation. In vitro, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) improved the membrane n-6/n-3 PUFA ratio, and DHA lowered interleukin (IL)-6 secretion; overall, n-3 PUFAs did not suppress B-cell activation compared with BSA, oleate, or elaidate treatment. Palmitate treatment suppressed the percentage of B cells activated through lipoapoptosis, which was differentially prevented by cosupplementing cells with MUFAs and PUFAs. Ex vivo, we tested the hypothesis with mice fed a control or high-fat saturated, hydrogenated, MUFA or n-3 PUFA diets. n-3 PUFAs had no effect on the percentage of B cells activated. Unexpectedly, the n-3 PUFA diet increased B-cell CD69 surface expression, IL-6 and IFNgamma secretion, and it significantly increased body weight gain. Overall, we propose that changes in lipid composition with n-3 PUFA and suppression of lymphocyte activation is not universal. The study highlights that high-fat n-3 PUFA diets can promote pro-inflammatory responses, at least from one cell type.

Are all n-3 polyunsaturated fatty acids created equal?

N-3 Polyunsaturated fatty acids have been shown to have potential beneficial effects for chronic diseases including cancer, insulin resistance and cardiovascular disease. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in particular have been studied extensively, whereas substantive evidence for a biological role for the precursor, alpha-linolenic acid (ALA), is lacking. It is not enough to assume that ALA exerts effects through conversion to EPA and DHA, as the process is highly inefficient in humans. Thus, clarification of ALA's involvement in health and disease is essential, as it is the principle n-3 polyunsaturated fatty acid consumed in the North American diet and intakes of EPA and DHA are typically very low. There is evidence suggesting that ALA, EPA and DHA have specific and potentially independent effects on chronic disease. Therefore, this review will assess our current understanding of the differential effects of ALA, EPA and DHA on cancer, insulin resistance, and cardiovascular disease. Potential mechanisms of action will also be reviewed. Overall, a better understanding of the individual role for ALA, EPA and DHA is needed in order to make appropriate dietary recommendations regarding n-3 polyunsaturated fatty acid consumption.

Dietary curcumin and limonin suppress CD4+ T-cell proliferation and interleukin-2 production in mice

Phytochemicals may reduce chronic inflammation and cancer risk in part by modulating T-cell nuclear factor-kappaB (NF-kappaB) activation. Therefore, we examined the effects of curcumin (Cur) and limonin (Lim) feeding on NF-kappaB-dependent CD4(+) T-cell proliferation. DO11.10 transgenic mice (n = 5-7) were fed diets containing 1% Cur or 0.02% Lim combined with either (n-6) PUFA [5% corn oil (CO)] or (n-3) PUFA [4% fish oil+1% corn oil (FO)] for 2 wk, followed by splenic CD4(+) T-cell isolation and stimulation with ovalbumin peptide 323-339 (OVA) and antigen-presenting cells from mice fed a conventional nonpurified rodent diet. Both Cur and Lim diets suppressed (P < 0.05) NF-kappaB p65 nuclear translocation in activated CD4(+) T-cells. In contrast, activator protein-1 (c-Jun) and nuclear factor of activated T-cells c1 were not affected compared with the CO control diet (no Cur or Lim). CD4(+) T-cell proliferation in response to either mitogenic anti-CD3/28 monoclonal antibodies (mAb) or antigenic stimulation by OVA was also suppressed (P < 0.05) by Cur as assessed by carboxyfluorescein succinimidyl ester staining. In contrast, interleukin-2 production was not directly associated with NF-kappaB status. Interestingly, dietary combination with FO enhanced the suppressive effects (P < 0.05) of Cur or Lim with respect to CD4(+) T-cell proliferation in response to anti-CD3/28 mAb. These results suggest that combination chemotherapy (FO+Cur or Lim) may favorably modulate CD4(+) T-cell-mediated inflammation.

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.

fat-1 transgene expression prevents cell culture-induced loss of membrane n-3 fatty acids in activated CD4+ T-cells

In order to evaluate the effects of fatty acids on immune cell membrane structure and function, it is often necessary to maintain cells in culture. However, cell culture conditions typically reverse alterations in polyunsaturated fatty acid (PUFA) composition achieved by dietary lipid manipulation. Therefore, we hypothesized that T-cells from transgenic mice expressing the Caenorhabditis elegans n-3 desaturase (fat-1) gene would be resistant to the culture-induced loss of n-3 PUFA and, therefore, obviate the need to incorporate fatty acids or homologous serum into the medium. CD4+ T-cells were isolated from (i) control wild type (WT) mice fed a safflower oil-n-6 PUFA enriched diet (SAF) devoid of n-3 PUFA, (ii) fat-1 transgenic mice (enriched with endogenous n-3 PUFA) fed a SAF diet, or (iii) WT mice fed a fish oil (FO) based diet enriched in n-3 PUFA. T-cell phospholipids isolated from WT mice fed FO diet (enriched in n-3 PUFA) and fat-1 transgenic mice fed a SAF diet (enriched in n-6 PUFA) were both enriched in n-3 PUFA. As expected, the mol% levels of both n-3 and n-6 PUFA were decreased in cultures of CD4+ T-cells from FO-fed WT mice after 3d in culture. In contrast, the expression of n-3 desaturase prevented the culture-induced decrease of n-3 PUFA in CD4+ T-cells from the transgenic mice. Carboxyfluorescein succinidyl ester (CFSE) -labeled CD4+ T-cells from fat-1/SAF vs. WT/SAF mice stimulated with anti-CD3 and anti-CD28 for 3d, exhibited a reduced (P<0.05) number of cell divisions. We conclude that fat-1-containing CD4+ T-cells express a physiologically relevant, n-3 PUFA enriched, membrane fatty acid composition which is resistant to conventional cell culture-induced depletion.

Bioactive dietary long-chain fatty acids: emerging mechanisms of action

The plasma membranes of all eukaryotic cells contain heterogeneous self-organising intrinsically unstable liquid ordered domains or lipid assemblies in which key signal transduction proteins are localised. These assemblies are classified as 'lipid rafts' (10-200 nm), which are composed mostly of cholesterol and sphingolipid microdomains and therefore do not integrate well into the fluid phospholipid bilayers. In addition, caveolae represent a subtype of lipid raft macrodomain that form flask-shaped membrane invaginations containing structural proteins, i.e. caveolins. With respect to the diverse biological effects of long-chain PUFA, increasing evidence suggests that n-3 PUFA and perhaps conjugated fatty acids uniquely alter the basic properties of cell membranes. Because of its polyunsaturation, DHA and possibly conjugated linoleic acid are sterically incompatible with sphingolipid and cholesterol and, therefore, appear to alter lipid raft behaviour and protein function. The present review examines the evidence indicating that dietary sources of n-3 PUFA can profoundly alter the biochemical make up of lipid rafts/caveolae microdomains, thereby influencing cell signalling, protein trafficking and cell cytokinetics.

Triglyceride-rich lipoprotein lipolysis increases aggregation of endothelial cell membrane microdomains and produces reactive oxygen species

Triglyceride-rich lipoprotein (TGRL) lipolysis may provide a proinflammatory stimulus to endothelium. Detergent-resistant plasma membrane microdomains (lipid rafts) have a number of functions in endothelial cell inflammation. The mechanisms of TGRL lipolysis-induced endothelial cell injury were investigated by examining endothelial cell lipid rafts and production of reactive oxygen species (ROS). Lipid raft microdomains in human aortic endothelial cells were visualized by confocal microscopy with fluorescein isothiocyanate-labeled cholera toxin B as a lipid raft marker. Incubation of Atto565-labeled TGRL with lipid raft-labeled endothelial cells showed that TGRL colocalized with the lipid rafts, TGRL lipolysis caused clustering and aggregation of lipid rafts, and colocalization of TGRL remnant particles on the endothelial cells aggregated lipid rafts. Furthermore, TGRL lipolysis caused translocation of low-density lipoprotein receptor-related protein, endothelial nitric oxide synthase, and caveolin-1 from raft regions to nonraft regions of the membrane 3 h after treatment with TGRL lipolysis. TGRL lipolysis significantly increased the production of ROS in endothelial cells, and both NADPH oxidase and cytochrome P-450 inhibitors reduced production of ROS. Our studies suggest that alteration of lipid raft morphology and composition and ROS production could contribute to TGRL lipolysis-mediated endothelial cell injury.

Docosahexaenoic acid (DHA) and hepatic gene transcription

The type and quantity of dietary fat ingested contributes to the onset and progression of chronic diseases, like diabetes and atherosclerosis. The liver plays a central role in whole body lipid metabolism and responds rapidly to changes in dietary fat composition. Polyunsaturated fatty acids (PUFA) play a key role in membrane composition and function, metabolism and the control of gene expression. Certain PUFA, like the n-3 PUFA, enhance hepatic fatty acid oxidation and inhibit fatty acid synthesis and VLDL secretion, in part, by regulating gene expression. Our studies have established that key transcription factors, like PPARalpha, SREBP-1, ChREBP and MLX, are regulated by n-3 PUFA, which in turn control levels of proteins involved in lipid and carbohydrate metabolism. Of the n-3 PUFA, 22:6,n-3 has recently been established as a key controller of hepatic lipid synthesis. 22:6,n-3 controls the 26S proteasomal degradation of the nuclear form of SREBP-1. SREBP-1 is a major transcription factor that controls the expression of multiple genes involved fatty acid synthesis and desaturation. 22:6,n-3 suppresses nuclear SREBP-1, which in turn suppresses lipogenesis. This mechanism is achieved, in part, through control of the phosphorylation status of protein kinases. This review will examine both the general features of PUFA-regulated hepatic gene transcription and highlight the unique mechanisms by which 22:6,n-3 impacts gene expression. The outcome of this analysis will reveal that changes in hepatic 22:6,n-3 content has a major impact on hepatic lipid and carbohydrate metabolism. Moreover, the mechanisms involve 22:6,n-3 control of several well-known signaling pathways, such as Akt, Erk1/2, Gsk3beta and PKC (novel or atypical). 22:6,n-3 control of these same signaling pathways in non-hepatic tissues may help to explain the diverse actions of n-3 PUFA on such complex physiological processes as visual acuity and learning.

Mechanisms by which fatty acids regulate leucocyte function

Fatty acids (FAs) have been shown to alter leucocyte function and thus to modulate inflammatory and immune responses. In this review, the effects of FAs on several aspects of lymphocyte, neutrophil and macrophage function are discussed. The mechanisms by which FAs modulate the production of lipid mediators, activity of intracellular signalling pathways, activity of lipid-raft-associated proteins, binding to TLRs (Toll-like receptors), control of gene expression, activation of transcription factors, induction of cell death and production of reactive oxygen and nitrogen species are described in this review. The rationale for the use of specific FAs to treat patients with impaired immune function is explained. Substantial improvement in the therapeutic usage of FAs or FA derivatives may be possible based on an improvement in the understanding of the precise molecular mechanisms of action with respect to the different leucocyte types and outcome with respect to the inflammatory responses.

Immunomodulatory effects of (n-3) fatty acids: putative link to inflammation and colon cancer

Chronic inflammation and colorectal cancer are closely linked. Although the overall mechanisms of inflammation-associated gastrointestinal carcinogenesis are complex, it is clear that antiinflammatory therapy is efficacious against neoplastic progression and malignant conversion. From a dietary perspective, fish oil containing (n-3) polyunsaturated fatty acids (PUFAs) has antiinflammatory properties, but for years the mechanism has remained obscure. Of relevance to the immune system in the intestine, we showed that (n-3) PUFA feeding alters the balance between CD4+ T-helper (Th1 and Th2) subsets by directly suppressing Th1 cell development (i.e., clonal expansion). This is noteworthy because Th1 cells mediate inflammatory diseases and resistance to intracellular pathogens or allergic hypersensitivity, and Th2 cells mediate resistance to extracellular pathogens. Therefore, any changes induced by (n-3) PUFAs in T-cell subset balance and function are important because the outcome is expected to suppress the development of autoimmune diseases and possibly the occurrence of colon cancer. Precisely how the immunomodulatory effects of (n-3) PUFAs influence inflammation-associated colonic tumor development is the subject of an ongoing investigation.

Colon cancer, fatty acids and anti-inflammatory compounds

PURPOSE OF REVIEW

To outline recent findings on the efficacy of n-3 polyunsaturated fatty acids in the prevention/treatment of inflammatory bowel disease and colorectal cancer.

RECENT FINDINGS

Compelling data indicate a functional link between chronic inflammation and colon cancer. With respect to environmental risk factors, there is growing evidence that long-chain n-3 polyunsaturated fatty acids found in fish oil suppress inflammatory bowel diseases and colon cancer risk in humans. Unfortunately, the molecular basis of the effect of n-3 polyunsaturated fatty acids on inflammation/colitis-associated colon cancer risk is still largely obscure. In this review, we focus on recent studies which address three emerging mechanisms of n-3 polyunsaturated fatty acids action: (1) metabolic interconversion into bioactive eicosanoids, (2) modulation of nuclear receptor activation, and (3) alteration of membrane phospholipid composition and functionality of lipid microdomains.

SUMMARY

The consumption of dietary fish oil may prove to be an effective adjuvant therapy in colon cancer. Therefore, it is both appropriate and timely to determine precisely how n-3 polyunsaturated fatty acids modulate cell signaling networks, and reduce the risk of developing colon cancer and inflammatory disorders of the intestine.

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

Dietary supplementation with polyunsaturated fatty acids (PUFAs), especially those of the n-3 class, has immunosuppressive effects on both innate and adaptive immunity through various mechanisms. In this review, we focus on the PUFA modulation of membrane architecture and its consequent effects on both T cell responses and antigen presentation. We first use data from in vitro and in vivo experiments to make the case that the immunosuppressive effects of PUFAs begin with membrane incorporation and modulation of lipid-protein lateral organization. This in turn inhibits downstream signaling mediated by T cell receptors and suppresses T cell activation and proliferation. Next, we review evidence for PUFA-mediated alteration of major histocompatibility complex class I and II surface expression and antigen presentation. We propose that PUFAs influence the expression of major histocompatibility complex by altering its conformation, orientation, lateral organization, and trafficking, with consequences for recognition by effector T cells. Finally, we present data from model membrane studies to explain the physical principles that make PUFA acyl chains unique in modifying membrane lateral organization and protein function. An important concept to emerge from these studies is that PUFA acyl chains and cholesterol molecules are sterically incompatible. By applying this concept to the T cell activation and signaling model, mechanisms emerge by which PUFAs can modulate membrane lipid-protein lateral organization. Our data-based models show that membrane modification of both effectors and targets is an important, often overlooked, mechanism of immunomodulation by PUFAs.

Dietary fish oil inhibits antigen-specific murine Th1 cell development by suppression of clonal expansion

To determine the mechanisms by which dietary fish oil (FO) affects antigen-stimulated Th1 cell development, DO11.10 Rag 2(-/-) T cell receptor transgenic mice were fed a control diet (5% corn oil (CO) or a FO diet (1% CO + 4% FO, (n-3) PUFA) for 2 wk. CD4(+) T cells were cultured under neutral or Th1 polarizing conditions. FO feeding suppressed (P < 0.05) ovalbumin peptide-induced proliferation of nonpolarized CD4(+) T cells. Differentiation in vitro to Th1 cells was not affected by dietary FO, as evidenced by similar percentages of KJ1-26(+), IFN-gamma(+), IL-4(-) Th1 cells in cultures from CO-fed (99%) and FO-fed (97%) mice. However, the absolute number of viable Th1 cells in polarized cultures from FO-fed mice was less than half that observed in CO-fed mice (P < 0.05), indicating that FO inhibits in vitro Th1 clonal expansion. The reduced number of Th1 cells in FO cultures was not a result of increased apoptosis, because similar percentages of apoptotic Th1 cells were observed in cultures from FO- and CO-fed mice. IL-2-induced cell proliferation was significantly decreased in polarized Th1 cells from the FO group; however, the suppressed proliferation was not linked to reduced CD25 surface expression on antigen-stimulated CD4(+) T cells. Adoptively transferred CFSE-labeled DO11.10 CD4(+) cells into immunized mice (Th1 polarizing agents) showed that dietary FO reduced (P < 0.05) the number of cell divisions in vivo. These studies suggest that the attenuated inflammatory response which accompanies FO feeding may be explained, at least in part, by suppression of Th1 clonal expansion.

n-3 PUFA fail to affect in vivo, antigen-driven CD8+T-cell proliferation in the spleen of naïve mice

One of the most frequently reported immunomodulatory actions of n-3 PUFA is their ability to diminish in vitro lymphocyte proliferation. The purpose of this study was to determine if n-3 PUFA intake affects the kinetics or magnitude of the antigen-driven expansion of CD8(+)T-lymphocytes in vivo. In this study we utilized a well-characterized model of T-cell immunity (i.e. infection with the intracellular bacterium, Listeria monocytogenes). Weanling BALB/c mice were fed one of two experimental diets that differed solely in fat source. Our control diet contained lard (180 g/kg) and was devoid of long-chain n-3 PUFA. The experimental diet contained 150 g/kg menhaden fish oil and 30 g/kg corn oil, thus providing approximately 8 % of energy from long-chain n-3 PUFA. After 4 weeks, mice were infected intravenously with 10(6) colony-forming units of actA-deficient L. monocytogenes. Clonal expansion of antigen-specific CD8(+)T-cells in the spleen was measured at 5, 7, 9 and 14 d post-challenge using a class I MHC tetramer loaded with the immunodominant peptide from this pathogen (i.e. K(d):LLO91-99). We report that feeding mice a diet rich in n-3 fatty acids did not significantly impact either the kinetics or magnitude of in vivo, antigen-driven expansion of CD8(+)T-cells. Furthermore, contraction of this T-cell population was not affected by n-3 PUFA treatment. To our knowledge this is the first time MHC tetramers have been used to investigate the influence of n-3 PUFA on in vivo CD8(+)T-cell proliferation.

Dietary eicosapentaenoic acid modulates CTLA-4 expression in murine CD4+ T-cells

We have demonstrated that downregulation of proliferation by CD4(+) T-cells in mice fed n-3 PUFA diets is dependent on the involvement of CD28. Therefore, we hypothesized that the balance of co-stimulatory and downregulatory properties of CD28 and CTLA-4, respectively, would be altered by diet. Mice were fed a control corn oil (CO)-enriched diet devoid of n-3 PUFA, or diets enriched with either docosahexaenoic acid (DHA) or eicosapentaenoic acid (EPA) for 14d. The proliferation of splenic CD4(+) T-cells was suppressed by DHA and EPA following stimulation with anti-CD3 and anti-CD28. Surprisingly, the number of surface CD28 molecules was not reduced in activated CD4(+) T-cells from either group of n-3 PUFA-fed mice. However, in mice fed EPA, CTLA-4 protein levels were enhanced significantly 72 h post-activation (P<0.01). Therefore, we conclude that dietary EPA may suppress CD4(+) T-cell activation by enhancing the downregulatory co-receptor CTLA-4, while not altering the levels of CD28.

Conjugated linoleic acid suppresses NF-kappa B activation and IL-12 production in dendritic cells through ERK-mediated IL-10 induction

Polyunsaturated fatty acids (PUFA) have been shown to modulate immune responses and have therapeutic effects in inflammatory disorders. However, the influence of PUFA on dendritic cells (DC), key cells of the innate immune system in shaping adaptive immune responses, has not yet been defined. In this study, we examine the effects of the cis-9, trans-11 isomer of conjugated linoleic acid (c9, t11-CLA), a dietary PUFA found in meat and dairy products, on murine DC activation. Treatment of DC with c9, t11-CLA suppressed LPS-induced IL-12, enhanced IL-10R expression, and enhanced IL-10 production at the transcriptional and protein level. The suppression of IL-12 by c9, t11-CLA was found to be IL-10 dependent. We investigated the involvement of the MAPK, ERK, and the transcription factor, NF-kappaB, in this IL-10-mediated effect. c9, t11-CLA enhanced ERK activation after LPS stimulation, and inhibition of ERK resulted in abrogation of IL-10 and recovery of IL-12 production. c9, t11-CLA decreased NF-kappaB:DNA binding after LPS stimulation, which was concomitant with delayed translocation of NF-kappaBp65 into the nucleus and an increase in IkappaBalpha. These effects were reversed by addition of a neutralizing anti-IL-10 Ab. Our findings demonstrate that c9, t11-CLA suppresses IL-12 production by LPS-stimulated DC by ERK mediated IL-10-induction. Furthermore, these IL-10-mediated effects are dependent on inhibition of NF-kappaB activation. This is the first study to demonstrate that c9, t11-CLA can enhance transcription and production of the anti-inflammatory cytokine IL-10, while inhibiting the Th1-promoting cytokine IL-12, and may explain certain of its immunosuppressive properties.

The Docosatriene Protectin D1 Is Produced by TH2 Skewing and Promotes Human T Cell Apoptosis via Lipid Raft Clustering

Docosahexaenoic acid, a major omega-3 fatty acid in human brain, synapses, retina, and other neural tissues, displays beneficial actions in neuronal development, cancer, and inflammatory diseases by mechanisms that remain to be elucidated. In this study we found, using lipid mediator informatics employing liquid chromatography-tandem mass spectrometry, that (10,17S)-docosatriene/neuroprotectin D1, now termed protectin D1 (PD1), is generated from docosahexaenoic acid by T helper type 2-skewed peripheral blood mononuclear cells in a lipoxygenase-dependent manner. PD1 blocked T cell migration in vivo, inhibited tumor necrosis factor alpha and interferon-gamma secretion, and promoted apoptosis mediated by raft clustering. These results demonstrated novel anti-inflammatory roles for PD1 in regulating events associated with inflammation and resolution.

Comparative toxicity of oleic and linoleic acid on human lymphocytes

Commercially available lipid emulsions for parenteral nutrition are mainly composed by long chain triacylglycerol containing a high proportion of linoleic acid (LA) or oleic acid (OA). The immunological impact of such therapy is particularly important because parenteral diets are often administered to critically ill patients as a mechanism to supply adequate nutrition during catabolic stress conditions. The comparative toxicity of OA and LA on human lymphocytes and the type of cell death induced by these fatty acids were determined in vitro. Parameters of cell death were investigated by flow cytometry-cell viability, DNA fragmentation, phosphatidylserine externalization, mitochondrial depolarization, neutral lipid accumulation and production of reactive oxygen species-and by fluorescence microscopy-chromatin condensation. Additionally a spectrofluorometric assay was employed to determine the activities of caspase--3, 6 and 8. Evidence is presented herein that OA is less toxic to human lymphocytes than LA. However, both fatty acids promoted apoptosis and necrosis of these cells. The mechanism of cell death induced by OA involved activation of caspase 3 while the mechanism of death induced by LA involved mitochondrial depolarization and ROS production. Importantly, neutral lipid accumulation may be a mechanism to protect lymphocytes against the toxicity induced by OA. OA may offer an immunological less problematic alternative to LA with respect to fatty acid composition of parenteral nutritional emulsions.

Polyunsaturated eicosapentaenoic acid changes lipid composition in lipid rafts

BACKGROUND

Polyunsaturated fatty acids (PUFAs) modulate immune responses particularly by affecting T cell function and are applied clinically as adjuvant immunosuppressants in the treatment of various inflammatory diseases. However, the molecular mechanisms of PUFA-induced immunosuppressive effects are not yet elucidated. Membrane lipid rafts are functional plasma membrane microdomains characterized by a unique lipid environment. Since lipid interactions are crucial for the formation of lipid rafts, the immunomodulatory effects of PUFAs may be due to changes of fatty acid composition in lipid rafts.

AIM OF THE STUDY

We investigated the effects of eicosapentaenoic acid (EPA, 20:5 n - 3) supplementation on modulating lipid composition and fatty acyl substitution in their cytoplasmic and exoplasmic lipid leaflet in lipid rafts.

METHODS

The human Jurkat E6-1 T cells were cultured in EPA-supplemented medium and the cells treated with stearic acid served as a control. Lipid rafts were isolated by discontinuous sucrose density gradient ultracentrifugation. The lipids in raft and soluble fractions from EPA-treated and control T cells were extracted and separated by gas chromatography. Raft phospholipids were analyzed by mass spectrometry.

RESULTS

Our results showed that EPA treatment could alter lipid composition resulting in a considerable increase of unsaturated fatty acyl chains in lipid rafts from EPA-treated T cells compared with control cells. Effective incorporation of EPA to rafts was not only in the exoplasmic but also in the cytoplasmic membrane lipid leaflet. EPA treatment altered the lipid environment in lipid rafts. EPA presented an inhibiting effect on Jurkat T cells proliferation and inhibited IL-2Ralpha expression on the surface of T cells.

CONCLUSIONS

Our data provided evidence for an important modification in lipid composition of membrane lipid rafts and T cell function by EPA supplementation.

Dietary (n-3) polyunsaturated fatty acids modulate murine Th1/Th2 balance toward the Th2 pole by suppression of Th1 development

We showed that dietary long-chain (n-3) PUFAs present in fish oil (FO) affect CD4(+) T cell proliferation and cytokine production in C57BL/6 mice. To test the hypothesis that the anti-inflammatory effect of dietary (n-3) PUFAs could be due to the indirect suppression of T helper (Th)1 cells by cross-regulation of enhanced Th2 activation, mice were fed a wash-out control diet [5% corn oil (CO), (n-6) PUFA] for 1 wk, followed by the control diet or a fish oil diet [1% CO + 4% FO, (n-3) PUFA] for 2 wk. Splenic CD4+ T cells were cultured under both neutral and Th2 polarizing conditions for 2 d. Cells were reactivated and analyzed for interleukin-4 and interferon-gamma by intracellular cytokine staining. Dietary fish oil significantly increased the percentage of Th2 polarized cells and suppressed Th1 cell frequency under neutral conditions. However, under Th2 polarizing conditions, although the suppression of Th1 cells was maintained in FO-fed mice, no effect was observed in Th2 cells. Dietary fish oil increased the Th2/Th1 ratio in the presence of homologous mouse serum under both neutral (P = 0.0009) and Th2 polarizing conditions (P = 0.0185). The FO diet did not significantly affect proliferation under Th2 polarizing conditions. Thus, the anti-inflammatory effects of FO may be explained in part by a shift in the Th1/Th2 balance, due to the direct suppression of Th1 development, and not by enhancement of the propensity of CD4+ T cells to be polarized toward a Th2 phenotype, at least in vitro.

Effects of dietary n-3 polyunsaturated fatty acids on T-cell membrane composition and function

Dietary n-3 PUFA have been shown to attenuate T-cell-mediated inflammation, in part, by suppressing T-cell activation and proliferation. n-3 PUFA have also been shown to promote apoptosis, another important mechanism for the prevention of chronic inflammation by maintaining T-cell homeostasis through the contraction of populations of activated T cells. Recent studies have specifically examined Fas death receptor-mediated activation-induced cell death (AICD), since it is the form of apoptosis associated with peripheral T-cell deletion involved in immunological tolerance and T-cell homeostasis. Data from our laboratory indicate that n-3 PUFA promote AICD in T helper 1 polarized cells, which are the mediators of chronic inflammation. Since Fas and components of the death-inducing signaling complex are recruited to plasma membrane microdomains (rafts), the effect of dietary n-3 PUFA on raft composition and resident protein localization has been the focus of recent investigations. Indeed, there is now compelling evidence that dietary n-3 PUFA are capable of modifying the composition of T-cell membrane microdomains (rafts). Because the lipids found in membrane microdomains actively participate in signal transduction pathways, these results support the hypothesis that dietary n-3 PUFA influence signaling complexes and modulate T-cell cytokinetics in vivo by altering T-cell raft composition.

Does fish oil supplementation in pregnancy reduce the risk of allergic disease in infants?

PURPOSE OF REVIEW

Parallel increases in many inflammatory diseases over the last 40 years suggest that common environmental changes are promoting inflammatory immune responses and/or inhibiting the processes that normally keep these in check. One key change during this period has been declining intakes of anti-inflammatory dietary factors, including omega-3 polyunsaturated fatty acids (n-3 PUFA). As allergic diseases often first manifest in early infancy, prevention strategies need to be targeted early, even in utero. This review will examine recent evidence for the use of fish oil during this early period as a primary prevention strategy for allergic disease.

RECENT FINDINGS

N-3 PUFA have well documented anti-inflammatory effects in vitro and have also been demonstrated to have health benefits in a range of chronic inflammatory diseases, including cardiovascular disease, rheumatoid arthritis and diabetes, supporting their role in modulating inflammation in vivo. Although the effects of fish oil supplementation in established allergic disease are less convincing, there is accumulating evidence that dietary n-3 PUFA may have greater effects before allergic responses are established.

SUMMARY

Supplementation of the maternal diet in pregnancy with n-3 PUFA may provide a non-invasive intervention with significant potential to prevent the development of allergic and possibly other immune-mediated diseases.