Effect of short-term enteral feeding with eicosapentaenoic and gamma-linolenic acids on alveolar macrophage eicosanoid synthesis and bactericidal function in rats

Polyunsaturated fatty acids and rheumatoid arthritis

Rheumatoid arthritis is characterized by infiltration of T lymphocytes, macrophages and plasma cells into the synovium, and the initiation of a chronic inflammatory state that involves overproduction of proinflammatory cytokines and a dysregulated T-helper-1-type response. Eicosanoids synthesized from arachidonic acid and cytokines cause progressive destruction of cartilage and bone. The n-6 polyunsaturated fatty acid gamma-linolenic acid is the precursor of di-homo-gamma-linolenic acid. The latter and the n-3 polyunsaturated fatty acid eicosapentaenoic acid, which is found in fish oil, are able to decrease the production of arachidonic acid-derived eicosanoids and to decrease the production of proinflammatory cytokines and reactive oxygen species, and the reactivity of lymphocytes. A number of double-blind, placebo-controlled trials of gamma-linolenic acid and fish oil in rheumatoid arthritis have shown significant improvements in a variety of clinical outcomes. These fatty acids should be included as part of the normal therapeutic approach to rheumatoid arthritis. However, it is unclear what the optimal dosage of the fatty acids is, or whether there would be extra benefit from using them in combination.

Activity of the leukocyte NADPH oxidase in whole neutrophils and cell-free neutrophil preparations stimulated with long-chain polyunsaturated fatty acids

Fish oils are known for their anti-inflammatory effects. In this paper we investigated the influence of eicosapentaenoic acid and docosahexaenoic acid (omega-3 fatty acids), as well as docosapentaenoic acid, a metabolic product of omega-3 fatty acid metabolism, on O2(-)-production catalyzed by the NADPH oxidase in whole neutrophils and in a cell-free system consisting of neutrophil membranes and cytosol. As a standard we used arachidonic acid (an omega-6 fatty acid) found in a high proportion in the Western diet, and known as an effective activator of the oxidase in both systems. Our data show that with omega-3 fatty acids, the O2(-)-production in both systems is reduced as compared to the effect of arachidonic acid. The effects are more pronounced with increasing carbon chain length and increasing numbers of double bonds. Our results suggest another mechanism besides the inhibition of eicosanoid and cytokine production to explain the beneficial effects of fish oils in reducing inflammation.

Lipid modulation and systemic inflammation

N-6 and n-3 PUFAs from the diet are absorbed and reach the cell where they interact with fatty acid binding proteins within cell membranes and cytoplasm. They are processed in the endoplasmic reticulum (desaturation-elongation reactions, lipid synthesis, eicosanoid and epoxide production) and in peroxisomes (beta-oxidation, synthesis, oxidation products). They interact with receptors, ion channels, and nuclear elements; the result is modulation of gene expression. PUFA-induced alterations result in modulation of local and systemic inflammation and inflammatory disease activity.

Immune cell functions, lipids and host natural resistance

Nutritional status may exert a profound effect on immune system functions. Hence, several parameters of immune system are modified by dietary lipid administration, as lymphocyte proliferation, cytokine production, natural killer activity, antigen presentation, etc. Thus, numerous studies have indicated the key role of lipids as immune response modulators. These properties have been applied in the treatment of autoimmune and inflammatory diseases. As a result, the reduction or suppression of immune status due to lipid incorporation promotes an impairment in the ability of host natural response to eliminate infectious microorganisms as bacteria or parasites. In the present review, we analyze the current status about the relationship among dietary lipids, reduction of immune parameters and reduction of host natural response against infectious diseases. Many discrepancies are discussed, although several studies indicate a close association between dietary lipid manipulation and impairment in the elimination of bacteria, viruses or parasites. On the other hand, other studies point out a beneficial effect of dietary lipid manipulation on the host natural response. Future investigations will determine the events involved in the regulation of immune response by fatty acids and their role in the elimination of pathogenic agents.

Comparison of growth and fatty acid metabolism in rats fed diets containing equal levels of gamma-linolenic acid from high gamma-linolenic acid canola oil or borage oil

We have utilized transgenic technology to develop a new source of gamma-linolenic acid (GLA) using the canola plant as a host. The aim of the present study was to compare the growth and fatty acid metabolism in rats fed equal amounts of GLA obtained from the transgenic canola plant relative to GLA from the borage plant. Young male Sprague-Dawley rats (n = 10/group) were randomized and fed a purified AIN93G diet (10% lipid by weight) containing either a mixture of high GLA canola oil (HGCO) and corn oil or a control diet containing borage oil (BO) for 6 wk. GLA accounted for 23%, of the triglyceride fatty acids in both diets. Growth and diet consumption were monitored every 2-3 d throughout the study. At study termination, the fatty acid composition of the liver and plasma phospholipids was analyzed by gas chromatography. The growth and diet consumption of the HGCO group were similar to the BO group. There were no adverse effects of either diet on the general health or appearance of the rats, or on the morphology of the major organs. There was no significant difference between the diet groups for total percentage of n-6 polyunsaturated fatty acids present in either the total or individual phospholipid fractions of liver or plasma. The relative percentage of GLA and its main metabolite, arachidonic acid, in each phospholipid fraction of liver or plasma were also similar between groups. The percentage of 18:2n-6 in liver phosphatidylethanolamine and phosphatidylinositol/serine was higher (P < 0.05) and 22:5n-6 was lower in the HGCO group than the BO group. This finding could be attributed to the higher 18:3n-3 content in the HGCO diet than the BO diet. Results from this long-term feeding study of rats show for the first time that a diet containing transgenically modified canola oil was well-tolerated, and had similar biological effects, i.e., growth characteristics and hepatic metabolism of n-6 fatty acids, as a diet containing borage oil.

Nutritional support in sepsis: still skeptical?

The immediate metabolic response to a septic challenge is probably adaptive, meaning that nutritional interference, mainly via the parenteral route, during this early phase of instability can do more harm than good. During the later phases, a gradual increase in enteral nutrition, at the expense of parenteral nutrition, combined with the administration of nutraceuticals such as glutamine and omega-3 fatty acids, can counteract wasting and modulate the complex inflammatory response and immunosuppression associated with sepsis. In these times of scarce resources, there is an urgent need to clearly document the efficacy of immuno/pharmaconutrients, individually and in combination, enterally or parenterally, before proposing them for routine management of septic patients in the intensive care unit.

Metabolism of dietary alpha-linolenic acid vs. eicosapentaenoic acid in rat immune cell phospholipids during endotoxemia

Short-term (i.e., 3 d) continuous enteral feeding of diets containing eicosapentaenoic (EPA) and gamma-linolenic (GLA) polyunsaturated fatty acids (PUFA) to endotoxemic rats reduces the levels of arachidonic acid (AA) and linoleic acid (LA) in alveolar macrophage (AM) and liver Kupffer and endothelial (K&E) cell phospholipids with attendant decreases in prostaglandin formation by these cells in vitro. Diets that contain alpha-linolenic acid (LNA) as a substrate for endogenous formation of EPA may not be as effective in facilitating these immune cell modifications given the limited activity of delta6 desaturase. In the present study we compared the effectiveness of an LNA-enriched diet vs. an (EPA + GLA)-enriched diet to displace phospholipid AA from AM and liver K&E cells in vivo in endotoxemic rats fed enterally for 3 or 6 d. We determined the fatty acid composition of AM and K&E cell phospholipids by gas chromatography. We found that AM and K&E cells from rats that had received the EPA + GLA diet for 3 d had significantly (P < 0.001) higher mole percentage of EPA and the GLA metabolite, dihomoGLA, than corresponding cells from rats given the LNA diet or a control diet enriched with LA. Rats given the LNA diet had relatively low levels of stearidonic acid, EPA and other n-3 PUFA, while rats given the LA diet had low levels of GLA and dihomoGLA. We conclude that diets enriched with LNA or LA may not be as effective as those enriched with EPA + GLA for purposes of fostering incorporation of EPA or dihomoGLA into and displacement of AA from macrophage phospholipids under pathophysiologic conditions commonly found in acutely septic patients.