Comparison of the effects of linseed oil and different doses of fish oil on mononuclear cell function in healthy human subjects

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.

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.

Fish oils--adjuvant therapy in chronic heart failure?

Despite advances in medical management and device therapy, chronic heart failure (CHF) remains a condition of high mortality and poor quality of life. Patients with CHF endure frequent admissions to hospital, with exacerbations of breathlessness or recurrent acute myocardial infarction and have a high incidence of sudden death. A high intake of marine polyunsaturated fatty acids (PUFAs) is associated with lower cardiovascular mortality in the general population, and diabetics, and can reduce cardiovascular deaths post-infarction. Many of the effects of PUFAs could be of benefit in CHF patients. They can improve endothelial function, reduce vascular tone, reduce platelet aggregability, improve myocardial relaxation, stabilize myocardial cells by prolonging the refractory period, and lead to increased appetite and weight gain. They also have potentially important immune-modulating effects, reducing cytokine production and release and altering prostaglandin metabolism. In this review article we discuss the potential benefits of PUFA supplementation in CHF patients using data from clinical trials and in vitro experiments.

Effect of docosahexaenoic acid administration on plasma lipid profile and metabolic parameters of children with methylmalonic acidaemia

AIM

To evaluate the effect of administration of docosahexaenoic acid (DHA) on dyslipidaemia, plasma fatty acid composition and metabolic parameters of children with isolated methylmalonic acidaemia (MMA) (McKusick 25100).

METHODS

Four children (3 male, 1 female) with MMA (mut(0)), participated in a crossover, randomized study of DHA administration (25 mg/kg per day, divided into three daily doses). The control group comprised 56 healthy children, aged 10+/- 2.7 years, (51 male, 5 female), who were followed in our clinic owing to possible familial risk of cardiovascular disease.

RESULTS

The comparison of plasma fatty acid composition of children with MMA versus control children demonstrated that the patients had significantly higher values for oleic acid (p = 0.004) and linolenic acid (p = 0.008). No differences were observed in the levels of DHA and arachidonic acid. Plasma concentrations of insulin, glycine, ammonia, total cholesterol and cholesterol fractions did not change with DHA administration. No significant changes were observed in urinary excretion of methylmalonic acid. As expected, the percentage of DHA and n-3 fatty acids in plasma increased significantly after therapy (p = 0.005 and 0.014, respectively). The most remarkable result was a decrease of plasma levels of triglycerides after DHA therapy (p = 0.014).

CONCLUSION

As previously found in normal children, dietary supplementation with DHA decreases the triglyceride levels, normalizing the hypertriglyceridaemia of these children without any evidence of short-term adverse effects.

Dose-related effects of eicosapentaenoic acid on innate immune function in healthy humans: a comparison of young and older men

BACKGROUND

Increasing intakes of long-chain n-3 polyunsaturated fatty acids (PUFAs) can decrease markers of immunity. However, dose- and age-related responses have not been identified.

OBJECTIVE

The objective was to determine the effects of different amounts of eicosapentaenoic acid (EPA) on innate immune outcomes in young and older males.

DESIGN

In a controlled, double-blind study, healthy young and older men consumed 1 of 4 supplements provided as capsules: placebo (corn oil) or different amounts of an oil providing 1.35, 2.7, or 4.05 g EPA/d for 12 wk. Blood samples were collected at baseline and after 12 wk.

RESULTS

EPA was incorporated in a linear dose-response fashion into plasma and mononuclear cell (MNC) phospholipids; incorporation was greater in the older men. EPA treatment did not alter neutrophil or monocyte phagocytosis, monocyte respiratory burst, or the production of inflammatory cytokines by MNCs in the young or older men. EPA treatment caused a dose-dependent decrease in neutrophil respiratory burst only in the older men. Increased incorporation of EPA into plasma or MNC phospholipids was associated with decreased production of prostaglandin E2 by MNCs from both young and older men.

CONCLUSIONS

Older subjects incorporate EPA into plasma and MNC phospholipids more readily than do younger subjects. Other than prostaglandin E2 production, innate immune responses in young subjects are not affected by an EPA intake of < or =4.05 g/d. Older subjects are more sensitive to the immunologic effects of EPA, and the neutrophil respiratory burst is lower at higher EPA intakes.

Polyunsaturated fatty acids and inflammation

The n-6 polyunsaturated fatty acid, arachidonic acid, is a precursor of prostaglandins, leukotrienes and related compounds that have important roles as mediators and regulators of inflammation. Consuming increased amounts of long chain n-3 polyunsaturated fatty acids (found in oily fish and fish oils) results in a partial replacement of the arachidonic acid in cell membranes by eicosapentaenoic and docosahexaenoic acids. This leads to decreased production of arachidonic acid-derived mediators. This alone is a potentially beneficial anti-inflammatory effect of n-3 fatty acids. However, n-3 fatty acids have a number of other effects that might occur downstream of altered eicosanoid production or are independent of this. For example, they result in suppressed production of pro-inflammatory cytokines and can modulate adhesion molecule expression. These effects occur at the level of altered gene expression.

Essential fatty acids and their derivatives

PURPOSE OF REVIEW

This review will address recent research in metabolism of essential fatty acids and their long chain derivatives. Our main focus will be the association between essential fatty acid status and various disease states, as well as the effects of supplementation with essential fatty acids or their derivatives on a number of clinical outcomes.

RECENT FINDINGS

There have been several papers over the last few years that show links between supplementation with fish oil (n-3 polyunsaturated fatty acids) and cardiovascular disease. Recent data suggest that the use of fish oil (containing n-3 fatty acids) in a variety of disorders such as cystic fibrosis, coronary disease and in the prevention of sudden death is beneficial. Several papers show reductions in systemic markers of inflammation. More widespread use of essential fatty acid derivatives in infant formula can certainly be questioned on the basis of the recent data. Fewer benefits are seen with ingestion of the essential fatty acids themselves, likely related to limited conversion to their long chain derivatives in humans.

SUMMARY

Derivatives of essential fatty acids have the potential to modify a number of disease states, either ingested in greater quantities in the diet, or taken as supplements in the form of fish oil.

Is there a case for n-3 fatty acid supplementation in cystic fibrosis?

PURPOSE OF REVIEW

This review evaluates our current knowledge on the association of fatty acid abnormalities in cystic fibrosis with the disease process, and makes a case for a well-designed clinical trial to evaluate the clinical efficacy of long chain n-3 fatty acids.

RECENT FINDINGS

It has long been known that cystic fibrosis patients exhibit fatty acid abnormalities, but these have not been well investigated in tissues affected by the disease. Recent studies have demonstrated that such tissues do indeed show abnormalities in the proportions of linoleic, arachidonic and docosahexaenoic acids, and have demonstrated alterations in fatty acid and phospholipid metabolism in cystic fibrosis. Work in other areas has identified novel anti-inflammatory actions of long chain n-3 fatty acids that might be relevant to cystic fibrosis. A recent systematic review of fish oil supplementation in cystic fibrosis did not allow firm conclusions to be drawn, but suggested that there may be some benefits.

SUMMARY

The restoration of abnormal fatty acid profiles may be beneficial in cystic fibrosis, but this approach has not been evaluated in studies with a suitable design to permit firm conclusions to be drawn. There is a need for a long-term randomized controlled study to evaluate the therapeutic benefit of fish oil supplementation in cystic fibrosis.

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.

Dietary polyunsaturated fatty acids modulate in vivo, antigen-driven CD4+ T-cell proliferation in mice

Our objective was to determine whether dietary lipids affect in vivo, antigen-driven, proliferation of naïve CD4(+) T lymphocytes. To accomplish this, we adoptively transferred lymphocytes from T-cell receptor (TCR) transgenic DO11.10 (i.e., donor) mice into syngeneic, nontransgenic BALB/c (i.e., recipient) mice. Before adoptive transfer, recipient mice were fed for 4 wk AIN93G-type diets that differed only in fat source: lard, low in PUFA, fish oil, rich in (n-3) PUFA, and soybean oil, rich in (n-6) PUFA. One week after transfer, recipient mice were immunized with antigen (i.e., ovalbumin), and expansion of CD4(+) T(DO11.10) cells in the spleen and draining lymph nodes (LN) was measured by flow cytometry. Five days postimmunization (p.i.), at the peak of expansion, CD4(+) T(DO11.10) cells in the draining LN and spleen were 5- to 10-fold higher than in unimmunized mice, then quickly declined during the contraction phase (i.e., 7 and 10 d p.i.). Recipients fed the (n-6) PUFA rich diet had approximately 25% greater in vivo expansion of CD4(+) T(DO11.10) cells than lard- and fish oil-fed recipient mice at 5 d p.i. (P < 0.05). However, at 7 and 10 d p.i., CD4(+) T(DO11.10) cells in the draining lymph nodes did not differ between groups, nor in the spleen at 5, 7, and 10 d p.i. In summary, we are the first to demonstrate that dietary PUFAs affect antigen-driven expansion of naïve CD4(+) T cells in vivo. Surprisingly, (n-3) PUFA consumption did not reduce CD4(+) T-cell expansion.

The influence of different combinations of gamma-linolenic acid, stearidonic acid and EPA on immune function in healthy young male subjects

To determine the effects of EPA, stearidonic acid (STA) or gamma-linolenic acid (GLA) on immune outcomes, healthy male subjects consumed one of seven oil blends for 12 weeks. EPA consumption increased the EPA content of peripheral blood mononuclear cells (PBMC). Consumption of GLA (2.0 g/d) in the absence of STA or EPA increased di-homo-GLA content in PBMC. Neither STA nor its derivative 20 : 4n-3 appeared in PBMC when STA (<1.0 g/d) was consumed. However, STA (1.0 g/d), in combination with GLA (0.9 g/d), increased the proportion of EPA in PBMC. None of the treatments altered neutrophil or monocyte phagocytosis or respiratory burst, production of inflammatory cytokines by monocytes, T lymphocyte proliferation or the delayed-type hypersensitivity response. Production of cytokines by T lymphocytes increased in all groups, with no differences among them. The proportion of lymphocytes that were natural killer cells decreased significantly in subjects receiving 2.0 g EPA or GLA/d. There were no other effects on lymphocyte sub-populations. Plasma IgE concentration decreased in most groups, but not in the control group. Plasma IgG2 concentration increased in the EPA group. Thus, EPA or GLA at a dose of 2.0 g/d have little effect on key functions of neutrophils, monocytes and T lymphocytes, although at this dose these fatty acids decrease the number of natural killer cells. At this dose EPA increases IgG2 concentrations. STA can increase immune cell EPA status, but at 1.0 g/d does not affect human immune function.

The influence of different combinations of gamma-linolenic, stearidonic and eicosapentaenoic acids on the fatty acid composition of blood lipids and mononuclear cells in human volunteers

This study set out to identify whether stearidonic acid (18:4n-3; STA) can be used to increase the eicosapentaenoic acid (20:5n-3; EPA) content of plasma lipids and cells in humans and to understand more about the effects of increased consumption of gamma-linolenic acid (18:3n-3; GLA), STA and EPA in humans. Healthy young males were randomised to consume one of seven oil blends for a period of 12 weeks (9g oil/day) (n = 8-12 subjects/group). Palm oil, sunflower oil, an EPA-rich oil, borage oil (rich in GLA), and Echium oil (rich in STA) were blended in various combinations to generate a placebo oil and oils providing approximately 2g GLA + STA + EPA per day, but in different combinations. Blood was collected at 0, 4, 8 and 12 weeks and the fatty acid compositions of plasma triacylglycerols, cholesteryl esters and phospholipids and of peripheral blood mononuclear cells (PBMCs) determined. Significant effects were observed with each lipid fraction. Neither STA nor its derivative 20:4n-3 appeared in any of the lipid fractions studied when STA (up to 1g/day) was consumed. However, STA (1g/day), in combination with GLA (0.9 g/day), increased the proportion of EPA in some lipid fractions, suggesting that STA-rich plant oils may offer a novel means of increasing EPA status. Furthermore, this combination tended to increase the dihomo-gamma-linolenic acid (20:3n-6; DGLA) content of PBMCs, without an increase in arachidonic acid (AA) (20:4n-6) content. EPA consumption increased the EPA content of all lipid fractions studied. Consumption of GLA (2g/day), in the absence of STA or EPA, increased DGLA content with a tendency to increase AA content in some fractions. This effect was prevented by inclusion of EPA in combination with GLA. Thus, this study indicates that STA may be used as a precursor to increase the EPA content of human lipids and that combinations of GLA, STA and EPA can be used to manipulate the fatty acid compositions of lipid pools in subtle ways. Such effects may offer new strategies for manipulation of cell composition in order to influence cellular responses and functions in desirable ways.

Flaxseed and cardiovascular risk

Flaxseed has recently gained attention in the area of cardiovascular disease primarily because it is the richest known source of both alpha-linolenic acid (ALA) and the phytoestrogen, lignans, as well as being a good source of soluble fiber. Human studies have shown that flaxseed can modestly reduce serum total and low-density lipoprotein cholesterol concentrations, reduce postprandial glucose absorption, decrease some markers of inflammation, and raise serum levels of the omega-3 fatty acids, ALA and eicosapentaenoic acid. Data on the antiplatelet, antioxidant, and hypotensive effects of flaxseed, however, are inconclusive. More research is needed to define the role of this functional food in reducing cardiovascular risk.

Modulation of immune and inflammatory responses by dietary lipids

PURPOSE OF REVIEW

There continues to be considerable interest in the modulating effect of dietary lipids on immune and inflammatory responses. Although controversy still exists in research in this area, new concepts and approaches have emerged providing useful suggestions. Analysis of the recent findings will help in understanding certain paradoxical findings as well as introducing new strategies to guide future studies.

RECENT FINDINGS

The tissue polyunsaturated fatty acid composition was found to be correlated with changes in certain indices of immune function in individuals consuming habitual diets. It seems that individuals or animals with disordered immune systems are more reactive to polyunsaturated fatty acid supplementation, and genetic variation is also a determinant. N-3 polyunsaturated fatty acids were shown to reduce both resistance to bacterial infection and host survival. The studies on other non-classic fatty acids also demonstrated interesting findings. A proposed immuno-enhancing effect of conjugated linoleic acid has not been confirmed by studies and even an adverse effect has been implied. Trans fatty acids have been shown to increase the production of inflammatory cytokines, which may contribute to their pro-atherogenic property.

SUMMARY

Current data suggest that the intake of polyunsaturated fatty acids, particularly n-3 polyunsaturated fatty acids, can modulate immune and inflammatory responses, although a discrepancy is still present. Some recent studies have provided useful information explaining possible underlying reasons. Factors such as genetic variation, health status, disease, immune response stage, stimulation type, and possibly age, all contribute to the responsiveness to polyunsaturated fatty acid supplementation in terms of immune function.

The Effect of Eicosapentaenoic Acid on Rat Lymphocyte Proliferation Depends Upon Its Position in Dietary Triacylglycerols

Animal and human studies have shown that greatly increasing the amount of fish oil [rich in long-chain (n-3) PUFA] in the diet can decrease lymphocyte functions. The effects of a more modest provision of long-chain (n-3) PUFA and whether eicosapentaenoic acid (20:5) and docosahexaenoic acid (22:6) have the same effects as one another are unclear. Whether the position of 20:5 or 22:6 in dietary triacylglycerols (TAG) influences their incorporation into immune cells and their subsequent functional effects is not known. In this study, male weanling rats were fed for 6 wk one of 9 diets that contained 178 g lipid/kg and that differed in the type of (n-3) PUFA and in the position of these in dietary TAG. The control diet contained 4.4 g alpha-linolenic acid (18:3)/100 g total fatty acids. In the other diets, 20:5 or 22:6 replaced a portion (50 or 100%) of 18:3, and were in the sn-2 or the sn-1(3) position of dietary TAG. There were significant dose-dependent increases in the proportion of 20:5 or 22:6 in spleen mononuclear cell phospholipids when 20:5 or 22:6 was fed. These increases were at the expense of arachidonic acid and were largely independent of the position of 20:5 or 22:6 in dietary TAG. Spleen lymphocyte proliferation increased dose dependently when 20:5 was fed in the sn-1(3) position of dietary TAG. There were no significant differences in interleukin-2, interferon-gamma or interleukin-10 production among spleen cells from rats fed the different diets. Prostaglandin E(2) production by spleen mononuclear cells was decreased by inclusion of either 20:5 or 22:6 in the diet in the sn-1(3) position. Thus, incorporation of 20:5 or 22:6 into spleen mononuclear cell phospholipids is not influenced by the position in dietary TAG. However, the pattern of incorporation may be influenced, and there are some differential functional effects of the position of long-chain (n-3) PUFA in dietary TAG. A moderate increase in the intake of 20:5 at the sn-1(3) position of dietary TAG increases lymphocyte proliferation.