The effect of highly purified eicosapentaenoic and docosahexaenoic acids on monocyte phagocytosis in man

Modulatory Effect of Dietary Polyunsaturated Fatty Acids on Immunity, Represented by Phagocytic Activity

Lately, dietary polyunsaturated fatty acids (PUFAs) have shown substantial importance in human and animal nutrition, especially those of the n-3 group. Development and optimal functioning of the immune system are directed affected by diet. These dietary fatty acids have an important impact on the health and immune competence of various species including human beings. They are essential for the modulation of immune responses in health and disease. Fatty acid composition of immune cells can be modulated by the action of dietary fats and the outcomes in the composition can produce functional effects on reactivity and functioning of immune cells in a short period. There are several mechanisms involved in impacting dietary fatty acids on immune function; however, lipid mediator synthesis from PUFAs is of great importance in terms of inflammation. The objectives of this article are reviewing studies on the impact of PUFA in the diet on phagocytosis of chickens, murine, rats, ruminants, and humans. It also sheds light on the possible mechanism by which this immunomodulation occurs.

Peroxisomes in Immune Response and Inflammation

The immune response is essential to protect organisms from infection and an altered self. An organism’s overall metabolic status is now recognized as an important and long-overlooked mediator of immunity and has spurred new explorations of immune-related metabolic abnormalities. Peroxisomes are essential metabolic organelles with a central role in the synthesis and turnover of complex lipids and reactive species. Peroxisomes have recently been identified as pivotal regulators of immune functions and inflammation in the development and during infection, defining a new branch of immunometabolism. This review summarizes the current evidence that has helped to identify peroxisomes as central regulators of immunity and highlights the peroxisomal proteins and metabolites that have acquired relevance in human pathologies for their link to the development of inflammation, neuropathies, aging and cancer. This review then describes how peroxisomes govern immune signaling strategies such as phagocytosis and cytokine production and their relevance in fighting bacterial and viral infections. The mechanisms by which peroxisomes either control the activation of the immune response or trigger cellular metabolic changes that activate and resolve immune responses are also described.

The Differential Effects of Eicosapentaenoic Acid and Docosahexaenoic Acid on Cardiometabolic Risk Factors: A Systematic Review

A large body of evidence supports the cardioprotective effects of the long-chain omega-3 polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). There is increasing interest in the independent effects of EPA and DHA in the modulation of cardiometabolic risk factors. This systematic review aims to appraise the latest available evidence of the differential effects of EPA and DHA on such risk factors. A systematic literature review was conducted up to May 2017. Randomised controlled trials were included if they met strict eligibility criteria, including EPA or DHA > 2 g/day and purity ≥ 90%. Eighteen identified articles were included, corresponding to six unique studies involving 527 participants. Both EPA and DHA lowered triglyceride concentration, with DHA having a greater triglyceride-lowering effect. Whilst total cholesterol levels were largely unchanged by EPA and DHA, DHA increased high-density lipoprotein (HDL) cholesterol concentration, particularly HDL₂, and increased low-density lipoprotein (LDL) cholesterol concentration and LDL particle size. Both EPA and DHA inhibited platelet activity, whilst DHA improved vascular function and lowered heart rate and blood pressure to a greater extent than EPA. The effects of EPA and DHA on inflammatory markers and glycaemic control were inconclusive; however both lowered oxidative stress. Thus, EPA and DHA appear to have differential effects on cardiometabolic risk factors, but these need to be confirmed by larger clinical studies.

New Parenteral Lipid Emulsions for Clinical Use

Routine use of parenteral lipid emulsions (LE) in clinical practice began in 1961, with the development of soybean oil (SO) - based LE. Although clinically safe, experimental reports indicated that SO-based LE could exert a negative influence on immunological functions. Those findings were related to its absolute and relative excess of omega-6 polyunsaturated fatty acids (PUFA) and the low amount of omega-3 PUFA and also to its high PUFA content with an increased peroxidation risk. This motivated the development of new LE basically designed along the reduction of omega-6 PUFA and the omega-3 PUFA addition in order to obtain balanced levels of the omega-6/omega-3 ratio. The new LE for clinical use (available in Europe and South America) are differentiated by their content in polyunsaturated (omega-6 and omega-3), monounsaturated, and saturated fatty acids (FA), as well as FA source of their origin, including soy, coconut, olive, and fish oil. This article presents the new LE nutrition and energy functions but also its biochemical, metabolic, and immunomodulating aspects, according to their FA content. LE at 20% when infused from 1.0 to 2.0 g/kg body weight/day rates, either alone or in association with amino acids and glucose, are safe and well tolerated in routine clinical practice. LE combining SO with medium-chain triglycerides and/or olive oil have less omega-6 PUFA and are better metabolized, with less inflammatory and immunosuppressive effects than in relation to pure SO-based LE. The omega-3 PUFA used alone or as component of a new and complex LE (soy, MCT, olive and fish oil) has demonstrated anti-inflammatory and immunomodulatory effects.

The impact of an omega-3 fatty acid rich lipid emulsion on fatty acid profiles in critically ill septic patients

BACKGROUND

Death from sepsis in the intensive therapy unit (ITU) is frequently preceded by the development of multiple organ failure as a result of uncontrolled inflammation. Treatment with omega-3 (n-3) fatty acids (FAs), principally eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), has been demonstrated to attenuate the effects of uncontrolled inflammation and may be clinically beneficial in reducing mortality from organ dysfunction. Fish oil (FO) is a source of EPA and DHA.

METHODS

A randomized trial investigating the effects of parenteral (intravenous) nutrition providing FO (0.092g EPA+DHA/kg body weight/day) was conducted. Sixty consecutive ITU patients diagnosed with sepsis were randomised to receive either once daily parenteral FO and standard medical care or standard medical care only.

RESULTS

Forty one patients (21 received fish oil; 20 controls) consented to blood sampling and blood was taken on days 0, 1, 2, 3, 5, 7, 10 and 13; because of deaths, patient discharge and withdrawal of consent, the number of blood samples available for analysis diminished with time. FA composition of plasma phosphatidylcholine (PC), plasma non-esterified FAs (NEFAs) and peripheral blood mononuclear cells (PBMCs) was determined by gas chromatography. EPA and DHA were rapidly incorporated into all 3 lipid pools investigated. There was a reduction in the arachidonic acid (AA) to EPA+DHA ratio in plasma PC and NEFAs. Fewer patients died in the FO group (13.3% (n=4)) compared with the control group (26.7% (n=8)) but this difference was not significant. A reduction in the AA/(EPA+DHA) ratio in PBMCs and plasma PC was associated with significantly improved survival. Plasma PC, plasma NEFA and PBMC FA profiles are rapidly altered by FO infusion in critically ill septic patients.

CONCLUSION

The provision of high dose n-3 FAs resulted in a rapid and significant increase in EPA and DHA and a reduction in AA/(EPA+DHA) ratio. This latter reduction is associated with improved survival.

It is all about fluidity: Fatty acids and macrophage phagocytosis

Phagocytosis is an early and fundamental step for the effective clearance of disease causing agents. The ability to engulf and kill pathogens is considered as a major effector function of macrophages. In their phagocytic role macrophages are part of the first line of innate immune defense. A number of studies investigating fatty acid effects on macrophage phagocytosis have been conducted over many years. In vitro-data consistently report that alterations in macrophage membrane fatty acid composition are linked to an altered phagocytic capacity, i.e. an increase in membrane unsaturated fatty acid content is associated with an increase in engulfment and killing rate. The mode of action of fatty acids seems to be the modulation of the physical nature of the macrophage plasma membrane. It appears that the saturated-to-unsaturated fatty acid ratio of macrophage membrane phospholipids is of importance in determining macrophage phagocytic capacity. Available in vivo-data are less clear. At present, there is a lack of systematic studies elucidating key factors such as fatty acid efficacy, effective dose or dosing intervals. Without this knowledge the targeted modulation of macrophage phagocytosis in vivo by fatty acids is still a distant possibility.

Immunomodulation of microglia by docosahexaenoic acid and eicosapentaenoic acid

PURPOSE OF REVIEW

The omega-3 fatty acids (ω-3 FAs) docosahexaenoic acid and eicosapentaenoic acid are dietary components which have been ascribed many different health benefits. Inflammation is present in, and contributes to, pathological conditions in the central nervous system (CNS). Microglia are the primary cells with immune function in the CNS, and inflammation mediated by activated microglia is present in pathological conditions. In this review, we present and discuss findings on the modulation of microglial activities by ω-3 FAs in vivo as well as in vitro, and propose mechanisms for their effects.

RECENT FINDINGS

The majority of studies show that ω-3 FAs have anti-inflammatory effects on microglia. However, phagocytosis is an activity associated with inflammation and is increased by ω-3 FAs. This can be understood in the light of recent research on the resolution of inflammation. Resolution is induced by proresolving factors, which are metabolites of ω-3 FAs. Proresolving factors are anti-inflammatory and have been shown to increase phagocytosis. Other mechanisms of the anti-inflammatory actions of ω-3 FAs involve the peroxisome proliferator-activated receptor-γ, ω-3 FA incorporation into the cell membrane, and inhibition of ion currents.

SUMMARY

Immunomodulation by ω-3 FAs is mediated by several pathways that are interconnected and is a potential therapy for disorders in the CNS.

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.

Effect of docosahexaenoic acid on macrophage functions of rats

Docosahexaenoic acid (DHA) is an omega-3 fatty acid which has been demonstrated to exhibit anti-inflammatory effects. The objective of this study was to determine the effect of DHA on phagocytic and chemotactic activities of peritoneal macrophages obtained from rats. DHA was dissolved in 1 ml of corn oil at dose of 36 mg/kg/day and given via oral gavage for 4 weeks. Control rats received 1 ml/day corn oil as vehicle. At the end of the treatment period, peritoneal macrophages were isolated and chemotactic and phagocytic activities were assayed. Chemotactic and phagocytic activities were reduced in rats fed with DHA. These results demonstrated the effect of DHA in modulating immune activities of rat peritoneal macrophages.

The effect of feeding structured triacylglycerols enriched in eicosapentaenoic or docosahexaenoic acids on murine splenocyte fatty acid composition and leucocyte phagocytosis

The effects of altering the type of n-3 polyunsaturated fatty acid (PUFA) in the mouse diet on the ability of monocytes and neutrophils to perform phagocytosis were investigated. Male weanling mice were fed for 7 d on one of nine diets which contained 178 g lipid/kg and which differed in the type of n-3 PUFA and in the position of these in dietary triacylglycerol (TAG). The control diet contained 4·4 g α-linolenic acid/100 g total fatty acids. In the other diets, eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) replaced a proportion (50 or 100 %) of the α-linolenic acid, and were in the sn-2 or the sn-1(3) position of dietary TAG. There were significant increases in the content of n-3 PUFA in spleen-cell phospholipids when EPA or DHA was fed. These increases were largely independent of the position of EPA or DHA in dietary TAG except when EPA was fed at the highest level, when the incorporation was greater when it was fed in the sn-2 than in the sn-1(3) position. There was no significant effect of dietary DHA on monocyte or neutrophil phagocytic activity. Dietary EPA dose-dependently decreased the number of monocytes and neutrophils performing phagocytosis. However, when EPA was fed in the sn-2 position, the ability of active monocytes or neutrophils to engulf bacteria was increased in a dose-dependent fashion. This did not occur when EPA was fed in the sn-1(3) position. Thus, there appears to be an influence of the position of EPA, but not of DHA, in dietary TAG on its incorporation into cell phospholipids and on the activity of phagocytic cells.

Effect of docosahexaenoic acid-rich fish oil supplementation on human leukocyte function

BACKGROUND

The effect of a docosahexaenoic acid (DHA)-rich fish oil (FO) supplementation on human leukocyte function was investigated.

METHODS

Ten male volunteers were supplemented with 3g/day FO containing 26% eicosapentaenoic acid (EPA, 20:5, n-3) and 54% DHA (22:6, n-3) for 2 months.

RESULTS

FO supplementation changed the fatty acid (FA) composition of leukocytes resulting in an increase of n-3/n-6 ratio from 0.18 to 0.62 in lymphocytes and from 0.15 to 0.70 in neutrophils. DHA-rich FO stimulated an increase in phagocytic activity by 62% and 145% in neutrophils and monocytes, respectively. Neutrophil chemotactic response was increased by 128%. The rate of production of reactive oxygen species by neutrophils was also increased, as it was with lymphocyte proliferation. These changes were partially reversed after a 2-month wash out period. With respect to cytokine production by lymphocytes, interleukin (IL)-4 release was not altered, whereas secretions of IL-10, interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha were raised. These results are in contrast to those described by others using EPA-rich FO supplementation. Lymphocyte pleiotropic gene expression was analyzed by a macroarray technique. Of the analyzed genes (588 in total), 77 were modified by the supplementation. FO supplementation resulted in up-regulation of 6 genes (GATA binding protein 2, IL-6 signal transducer, transforming growth factor alpha, TNF, heat shock 90kDa protein 1-alpha and heat shock protein 70kDa 1A) and a down regulation of 71 genes (92.2% of total genes changed). The largest functional group of altered genes was that related to signaling pathways (22% of the total modified genes).

CONCLUSIONS

Therefore, although EPA and DHA are members of n-3 FA family, changes in the proportion of DHA and EPA exert different effects on neutrophil, monocyte and lymphocyte function, which may be a result of specific changes in gene expression.

n-3 polyunsaturated fatty acids, inflammation, and inflammatory diseases

Inflammation is part of the normal host response to infection and injury. However, excessive or inappropriate inflammation contributes to a range of acute and chronic human diseases and is characterized by the production of inflammatory cytokines, arachidonic acid-derived eicosanoids (prostaglandins, thromboxanes, leukotrienes, and other oxidized derivatives), other inflammatory agents (e.g., reactive oxygen species), and adhesion molecules. At sufficiently high intakes, long-chain n-3 polyunsaturated fatty acids (PUFAs), as found in oily fish and fish oils, decrease the production of inflammatory eicosanoids, cytokines, and reactive oxygen species and the expression of adhesion molecules. Long-chain n-3 PUFAs act both directly (e.g., by replacing arachidonic acid as an eicosanoid substrate and inhibiting arachidonic acid metabolism) and indirectly (e.g., by altering the expression of inflammatory genes through effects on transcription factor activation). Long-chain n-3 PUFAs also give rise to a family of antiinflammatory mediators termed resolvins. Thus, n-3 PUFAs are potentially potent antiinflammatory agents. As such, they may be of therapeutic use in a variety of acute and chronic inflammatory settings. Evidence of their clinical efficacy is reasonably strong in some settings (e.g., in rheumatoid arthritis) but is weak in others (e.g., in inflammatory bowel diseases and asthma). More, better designed, and larger trials are required to assess the therapeutic potential of long-chain n-3 PUFAs in inflammatory diseases. The precursor n-3 PUFA alpha-linolenic acid does not appear to exert antiinflammatory effects at achievable intakes.

The independent effects of eicosapentaenoic acid and docosahexaenoic acid on cardiovascular risk factors in humans

PURPOSE OF REVIEW

This review details the independent effects of purified eicosapentaenoic acid and docosahexaenoic acid on cardiovascular risk factors in humans. We report data from the recent literature and our own controlled clinical trials which compared the independent effects of these fatty acids in individuals at increased risk of cardiovascular disease, namely overweight hyperlipidaemic men and treated-hypertensive, type 2 diabetic men and women. We discuss the biological effects of these fatty acids and the potential mechanisms through which they may affect cardiovascular disease risk factors.

RECENT FINDINGS

A cardioprotective effect for omega3 fatty acids is supported by prospective studies demonstrating an inverse association between fish intake and coronary heart disease mortality. Data from secondary prevention trials support a reduction in ventricular fibrillation as a primary mechanism for the decreased incidence of myocardial infarction. Clinical trials and experimental studies have shown that omega3 fatty acids have many other potentially important antiatherogenic and antithrombotic effects. Omega-3 fatty acids lower blood pressure and heart rate, improve dyslipidaemia, reduce inflammation, and improve vascular and platelet function. These favourable effects have until recently been primarily attributed to the omega3 fatty acid eicosapentaenoic acid, which is present in large amounts in fish oil. Controlled studies in humans now demonstrate that docosahexaenoic acid, although often present in lower quantities, has equally important anti-arrhythmic, anti-thrombotic and anti-atherogenic effects.

SUMMARY

Available evidence strongly suggests that eicosapentaenoic acid and docosahexaenoic acid have differing haemodynamic and anti-atherogenic properties. The effects of the two fatty acids may also differ depending on the target population.

n-3 fatty acids, inflammation, and immunity--relevance to postsurgical and critically ill patients

Excessive or inappropriate inflammation and immunosuppression are components of the response to surgery, trauma, injury, and infection in some individuals and these can lead, progressively, to sepsis and septic shock. The hyperinflammation is characterized by the production of inflammatory cytokines, arachidonic acid-derived eicosanoids, and other inflammatory mediators, while the immunosuppression is characterized by impairment of antigen presentation and of T helper cell type-1 responses. Long-chain n-3 FA from fish oil decrease the production of inflammatory cytokines and eicosanoids. They act both directly (by replacing arachidonic acid as an eicosanoid substrate and by inhibiting arachidonic acid metabolism) and indirectly (by altering the expression of inflammatory genes through effects on transcription factor activation). Thus, long-chain n-3 FA are potentially useful anti-inflammatory agents and may be of benefit in patients at risk of developing sepsis. As such, an emerging application of n-3 FA is in surgical or critically ill patients where they may be added to parenteral or enteral formulas. Parenteral or enteral nutrition including n-3 FA appears to preserve immune function better than standard formulas and appears to partly prevent some aspects of the inflammatory response. Studies to date are suggestive of clinical benefits from these approaches, especially in postsurgical patients.

Fatty acids and the immune system: from basic science to clinical applications

Over the last 25 years, the effects of fatty acids on the immune system have been characterized using in vitro, animal and human studies. Advances in fatty acid biochemistry and molecular techniques have recently suggested new mechanisms by which fatty acids could potentially modify immune responses, including modification of the organization of cellular lipids and interaction with nuclear receptors. Possibilities for the clinical applications of n-3 PUFA are now developing. The present review focuses on the hypothesis that the anti-inflammatory properties of n-3 PUFA in the arterial wall may contribute to the protective effects of n-3 PUFA in CVD, as suggested by epidemiological and secondary prevention studies. Studies are just beginning to show that dietary n-3 PUFA can be incorporated into plaque lipid in human subjects, where they may influence the morphology and stability of the atherosclerotic lesion.

Effects of oils rich in eicosapentaenoic and docosahexaenoic acids on immune cell composition and function in healthy humans

BACKGROUND

Supplementation of the diet with fish oil, which is rich in the long-chain n-3 polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), is reported to decrease several markers of immune function. However, whether EPA, DHA, or a combination of the 2 exerts these immunomodulatory effects is unclear.

OBJECTIVE

The objective of the study was to determine the effects of supplementation with an EPA-rich or DHA-rich oil on a range of immune outcomes representing key functions of human neutrophils, monocytes, and lymphocytes in healthy humans.

DESIGN

In a placebo-controlled, double-blind, parallel study, 42 healthy subjects were randomly allocated to receive supplementation with either placebo (olive oil), EPA (4.7 g/d), or DHA (4.9 g/d) for 4 wk. Blood samples were taken before and after supplementation.

RESULTS

The fatty acid composition of plasma phospholipids and neutrophils was dramatically altered by supplementation with EPA or DHA, and the effects of EPA differed notably from those of DHA. DHA supplementation decreased T lymphocyte activation, as assessed by expression of CD69, whereas EPA supplementation had no significant effect. Neither the EPA-rich oil nor the DHA-rich oil had any significant effect on monocyte or neutrophil phagocytosis or on cytokine production or adhesion molecule expression by peripheral blood mononuclear cells.

CONCLUSIONS

Supplementation with DHA, but not with EPA, suppresses T lymphocyte activation, as assessed by expression of CD69. EPA alone does not, therefore, influence CD69 expression. No other marker of immune function assessed in this study was significantly affected by either EPA or DHA.

Lack of effect of foods enriched with plant- or marine-derived n-3 fatty acids on human immune function

BACKGROUND

Greatly increasing dietary flaxseed oil [rich in the n-3 polyunsaturated fatty acid (PUFA) alpha-linolenic acid (ALA)] or fish oil [rich in the long-chain n-3 PUFAs eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids] can reduce markers of immune cell function. The effects of more modest doses are unclear, and it is not known whether ALA has the same effects as its long-chain derivatives.

OBJECTIVE

The objective was to determine the effects of enriching the diet with ALA or EPA+DHA on immune outcomes representing key functions of human neutrophils, monocytes, and lymphocytes.

DESIGN

In a placebo-controlled, double-blind, parallel study, 150 healthy men and women aged 25-72 y were randomly assigned to 1 of 5 interventions: placebo (no additional n-3 PUFAs), 4.5 or 9.5 g ALA/d, and 0.77 or 1.7 g EPA+DHA/d for 6 mo. The n-3 PUFAs were provided in 25 g fat spread plus 3 oil capsules. Blood samples were taken at 0, 3, and 6 mo.

RESULTS

The fatty acid composition of peripheral blood mononuclear cell phospholipids was significantly different in the groups with higher intakes of ALA or EPA+DHA. The interventions did not alter the percentages of neutrophils or monocytes engaged in phagocytosis of Escherichia coli or in phagocytic activity, the percentages of neutrophils or monocytes undergoing oxidative burst in response to E. coli or phorbol ester, the proliferation of lymphocytes in response to a T cell mitogen, the production of numerous cytokines by monocytes and lymphocytes, or the in vivo delayed-type hypersensitivity response.

CONCLUSION

An intake of <or= 9.5 g ALA/d or <or= 1.7 g EPA+DHA/d does not alter the functional activity of neutrophils, monocytes, or lymphocytes, but it changes the fatty acid composition of mononuclear cells.

Influence of dietary supplementation with long-chain n-3 or n-6 polyunsaturated fatty acids on blood inflammatory cell populations and functions and on plasma soluble adhesion molecules in healthy adults

Greatly increasing the amounts of flaxseed oil [rich in alpha-linolenic acid (ALNA)] or fish oil (FO); [rich in eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)] in the diet can decrease inflammatory cell functions and so might impair host defense. The objective of this study was to determine the effect of dietary supplementation with moderate levels of ALNA, gamma-linolenic acid (GLA), arachidonic acid (ARA), DHA, or FO on inflammatory cell numbers and functions and on circulating levels of soluble adhesion molecules. Healthy subjects aged 55 to 75 yr consumed nine capsules per day for 12 wk. The capsules contained placebo oil (an 80:20 mix of palm and sunflowerseed oils) or blends of placebo oil with oils rich in ALNA, GLA, ARA, or DHA or FO. Subjects in these groups consumed 2 g ALNA; approximately 700 mg GLA, ARA, or DHA; or 1 g EPA plus DHA (720 mg EPA + 280 mg DHA) daily from the capsules. Total fat intake from the capsules was 4 g per day. None of the treatments affected inflammatory cell numbers in the bloodstream; neutrophil and monocyte phagocytosis or respiratory burst in response to E. coli; production of tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 in response to bacterial lipopolysaccharide; or plasma concentrations of soluble intercellular adhesion molecule-1. In contrast, the ALNA and FO treatments decreased the plasma concentrations of soluble vascular cell adhesion molecule-1 (16 and 28% decrease, respectively) and soluble E-selectin (23 and 17% decrease, respectively). It is concluded that, in contrast to previous reports using higher amounts of these fatty acids, a moderate increase in consumption of long-chain n-6 or n-3 polyunsaturated fatty acids does not significantly affect inflammatory cell numbers or neutrophil and monocyte responses in humans and so would not be expected to cause immune impairment. Furthermore, we conclude that moderate levels of ALNA and FO, which could be incorporated into the diet, can decrease some markers of endothelial activation and that this mechanism of action may contribute to the reported health benefits of n-3 fatty acids.

Polyunsaturated fatty acids, inflammation, and immunity

The fatty acid composition of inflammatory and immune cells is sensitive to change according to the fatty acid composition of the diet. In particular, the proportion of different types of polyunsaturated fatty acids (PUFA) in these cells is readily changed, and this provides a link between dietary PUFA intake, inflammation, and immunity. The n-6 PUFA arachidonic acid (AA) is the precursor of prostaglandins, leukotrienes, and related compounds, which have important roles in inflammation and in the regulation of immunity. Fish oil contains the n-3 PUFA eicosapentaenoic acid (EPA). Feeding fish oil results in partial replacement of AA in cell membranes by EPA. This leads to decreased production of AA-derived mediators. In addition, EPA is a substrate for cyclooxygenase and lipoxygenase and gives rise to mediators that often have different biological actions or potencies than those formed from AA. Animal studies have shown that dietary fish oil results in altered lymphocyte function and in suppressed production of proinflammatory cytokines by macrophages. Supplementation of the diet of healthy human volunteers with fish oil-derived n-3 PUFA results in decreased monocyte and neutrophil chemotaxis and decreased production of proinflammatory cytokines. Fish oil feeding has been shown to ameliorate the symptoms of some animal models of autoimmune disease. Clinical studies have reported that fish oil supplementation has beneficial effects in rheumatoid arthritis, inflammatory bowel disease, and among some asthmatics, supporting the idea that the n-3 PUFA in fish oil are anti-inflammatory and immunomodulatory.

Effect of a moderately energy-restricted diet on obese patients with fatty liver

The effects of a moderately energy-restricted (25 kcal/kg) diet on liver-function tests, anthropometric measurements, mononuclear-cell phospholipid fatty acid, lymphocyte blastogenesis, and plasma prostaglandin E2 and alpha-tocopherol levels were observed at weeks 0, 8, and 24 in 14 obese patients with fatty liver. Serum aminotransferase levels were improved significantly, with decreases in the body mass index and waist circumference. Decreases in energy intake from carbohydrate and increases in intake of vitamin A, vitamin C, and vegetables were observed at week 24. In mononuclear-cell phospholipids, linoleic acid (18:2omega 6), which was significantly lower in patients than in controls at week 0, was increased at week 24. In contrast, arachidonic acid was decreased. Plasma prostaglandin E2 levels were significantly lower in patients than in controls at week 0 and increased at week 24. The mononuclear-cell response for phytohemagglutinin correlated with 18:2omega 6 in mononuclear-cell phospholipids (r = 0.692, P < 0.01). Improvement of the serum alanine-aminotransferase level correlated with an increase in the plasma alpha-tocopherol level (r = -0.667, P < 0.01) and increases in consumption of vitamin A, omega 3 polyunsaturated fatty acids, and vegetables. These findings suggest that a hypoenergetic diet rich in omega 3 polyunsaturated fatty acids and antioxidants might be beneficial for obese patients with fatty liver.

Modulation of human immune and inflammatory responses by dietary fatty acids

I review the effects of the amount and composition of dietary fat on indices of human immune and inflammatory responses. A reduction in the amount of fat intake enhanced several indices of immune response, including lymphocyte proliferation, natural-killer-cell activity, cytokine production, and delayed-type hypersensitivity. When total fat intake was held constant, an increase in the intake of linoleic acid (18:2 omega-6) or arachidonic acid (20:4 omega-6) by healthy human volunteers did not inhibit many indices of immune response tested but did increase the production of inflammatory eicosanoids (prostaglandin E2 and leukotriene B4). Supplementation of human diets with omega-3 fatty acids reduced several aspects of neutrophil, monocyte, and lymphocyte functions, including the production of inflammatory mediators. Most of the studies have indicated reductions in these functions, with a minimum of 1.2 g/d of supplementation with eicosapentaenoic acid and docosahexaenoic acid for 6 wk. However, other studies concomitantly supplementing with 205 mg/d of vitamin E did not find inhibition of immune-cell functions, even with larger amounts and longer durations of supplementation with these fatty acids. One study reported that supplementation with docosahexaenoic acid selectively inhibits inflammatory responses without inhibiting T- and B-cell functions. Despite some discrepancies, fish oils have been used successfully in the management of several inflammatory and autoimmune diseases. The potential for the use of fish oils in the management of these diseases is tremendous, even though further studies are needed to establish safe and adequate intake levels of omega-3 fatty acids.

Health benefits of docosahexaenoic acid (DHA)

Docosahexaenoic acid (DHA) is essential for the growth and functional development of the brain in infants. DHA is also required for maintenance of normal brain function in adults. The inclusion of plentiful DHA in the diet improves learning ability, whereas deficiencies of DHA are associated with deficits in learning. DHA is taken up by the brain in preference to other fatty acids. The turnover of DHA in the brain is very fast, more so than is generally realized. The visual acuity of healthy, full-term, formula-fed infants is increased when their formula includes DHA. During the last 50 years, many infants have been fed formula diets lacking DHA and other omega-3 fatty acids. DHA deficiencies are associated with foetal alcohol syndrome, attention deficit hyperactivity disorder, cystic fibrosis, phenylketonuria, unipolar depression, aggressive hostility, and adrenoleukodystrophy. Decreases in DHA in the brain are associated with cognitive decline during aging and with onset of sporadic Alzheimer disease. The leading cause of death in western nations is cardiovascular disease. Epidemiological studies have shown a strong correlation between fish consumption and reduction in sudden death from myocardial infarction. The reduction is approximately 50% with 200 mg day(-1)of DHA from fish. DHA is the active component in fish. Not only does fish oil reduce triglycerides in the blood and decrease thrombosis, but it also prevents cardiac arrhythmias. The association of DHA deficiency with depression is the reason for the robust positive correlation between depression and myocardial infarction. Patients with cardiovascular disease or Type II diabetes are often advised to adopt a low-fat diet with a high proportion of carbohydrate. A study with women shows that this type of diet increases plasma triglycerides and the severity of Type II diabetes and coronary heart disease. DHA is present in fatty fish (salmon, tuna, mackerel) and mother's milk. DHA is present at low levels in meat and eggs, but is not usually present in infant formulas. EPA, another long-chain n-3 fatty acid, is also present in fatty fish. The shorter chain n-3 fatty acid, alpha-linolenic acid, is not converted very well to DHA in man. These longchain n-3 fatty acids (also known as omega-3 fatty acids) are now becoming available in some foods, especially infant formula and eggs in Europe and Japan. Fish oil decreases the proliferation of tumour cells, whereas arachidonic acid, a longchain n-6 fatty acid, increases their proliferation. These opposite effects are also seen with inflammation, particularly with rheumatoid arthritis, and with asthma. DHA has a positive effect on diseases such as hypertension, arthritis, atherosclerosis, depression, adult-onset diabetes mellitus, myocardial infarction, thrombosis, and some cancers.

The effect of supplementation with omega-3 fatty acids on soluble markers of endothelial function in patients with coronary heart disease

During progression of atherosclerosis the overlying endothelial cells alter their expression of some surface molecules. Circulating levels of such molecules may be quantified. We investigated the effect of omega-3 fatty acids (n-3 FA) on the levels of tissue plasminogen activator antigen, von Willebrand factor, and the soluble forms of thrombomodulin, P-selectin, E-selectin, and vascular cell adhesion molecule-1 in 54 patients with coronary heart disease. Twenty-three of the patients had taken 5.1 g/d n-3 FA for 6 months (group I) and 31 were given corn oil as placebo (group II). For another 4 weeks ("the study period") they all got 5.1 g/d of n-3 FA. Compliance was confirmed by demonstration of changes in relevant fatty acids in serum phospholipids. At baseline, significant differences between the groups were found with lower median values of von Willebrand factor (128% versus 147%) and soluble thrombomodulin (24.9 versus 32.5 ng/mL) and higher median values of soluble E-selectin (41.4 versus 35.5 ng/mL) and soluble vascular cell adhesion molecule-1 (573 versus 473 ng/mL) in group I. During the study period differences in changes between the groups were found; tissue plasminogen activator antigen and soluble thrombomodulin decreased (P for difference between the groups 0.001 and 0.015, respectively), whereas soluble E-selectin and soluble vascular cell adhesion molecule-1 increased (P for difference between the groups <0.01 for both) in group II relative to group I. Our results indicate that n-3 FA supplementation decreases hemostatic markers of atherosclerosis, whereas markers of inflammation may be increased. The latter may be the result of lipid peroxidation as a simultaneous decrease of vitamin E and increase in thiobarbituric acid-reactive substances were observed.

Clinical use of lipids to control inflammatory disease

Selective dietary supplementation with lipids has long been used to influence the course of chronic inflammatory diseases. This review describes new aspects of the molecular mechanism of lipids to modulate leukocyte activity and highlights some recent clinical studies on therapeutic lipid administration. New promising advances in parenteral application of lipids as well as the impact on acute inflammatory disorders are discussed.