Modulation of prostaglandin synthesis in rat peritoneal macrophages with omega-3 fatty acids

Effects of Omega-3 Fatty Acids on Immune Cells

Alterations on the immune system caused by omega-3 fatty acids have been described for 30 years. This family of polyunsaturated fatty acids exerts major alterations on the activation of cells from both the innate and the adaptive immune system, although the mechanisms for such regulation are diverse. First, as a constitutive part of the cellular membrane, omega-3 fatty acids can regulate cellular membrane properties, such as membrane fluidity or complex assembly in lipid rafts. In recent years, however, a new role for omega-3 fatty acids and their derivatives as signaling molecules has emerged. In this review, we describe the latest findings describing the effects of omega-3 fatty acids on different cells from the immune system and their possible molecular mechanisms.

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.

NF-kappa B inhibition by omega -3 fatty acids modulates LPS-stimulated macrophage TNF-alpha transcription

Omega-3 fatty acid (FA) emulsions reduce LPS-stimulated murine macrophage TNF-alpha production, but the exact mechanism has yet to be defined. The purpose of this study was to determine the mechanism for omega-3 FA inhibition of macrophage TNF-alpha production following LPS stimulation. RAW 264.7 cells were pretreated with isocaloric emulsions of omega-3 FA (Omegaven), omega-6 FA (Lipovenos), or DMEM and subsequently exposed to LPS. IkappaB-alpha and phospho-IkappaB-alpha were determined by Western blotting. NF-kappaB binding was assessed using the electromobility shift assay, and activity was measured using a luciferase reporter vector. RT-PCR and ELISA quantified TNF-alpha mRNA and protein levels, respectively. Pretreatment with omega-3 FA inhibited IkappaB phosphorylation and significantly decreased NF-kappaB activity. Moreover, omega-3-treated cells demonstrated significant decreases in both TNF-alpha mRNA and protein expression by 47 and 46%, respectively. These experiments demonstrate that a mechanism for proinflammatory cytokine inhibition in murine macrophages by omega-3 FA is mediated, in part, through inactivation of the NF-kappaB signal transduction pathway secondary to inhibition of IkappaB phosphorylation.

Parenteral lipid emulsions and phagocytic systems

Lipid emulsions (LE) for parenteral use are complex emulsions containing fatty acids, glycerol, phospholipids and tocopherol in variable amounts and concentrations. In clinical practice, LE have been employed for more than 30 years. Fatty acids may have different impacts on phagocytic cells according to their structure. Experimental and clinical studies have consistently shown that LE modify monocyte/macrophage and polymorphonuclear phagocytosis. The inhibitory effect of LE on the functional activity of the phagocytic system, although still clinically controversial, may have a harmful impact because total parenteral nutrition with lipids may be recommended in hypercatabolic conditions where inflammation and infection are present. LE based on triglycerides containing long chain fatty acids (termed long chain triglycerides or LCT) are the main parenteral fat source and are typically rich in n-6 polyunsaturated fatty acids. They may have adverse effects on the immune system, especially when given in high doses over a short period of time. However when administered properly they can be used safely. LE containing medium chain triglycerides (MCT) may have some advantages because of their positive effects on polymorphonuclear cells, macrophages, and cytokine production, particularly in critically ill or immunocompromised patients. New parenteral LE containing n-3 polyunsaturated fatty acids or monounsaturated olive oil are already available in Europe. Judicious use of these new LE is mandatory especially relating on their potential impact on the immune system. New experimental and clinical studies are required to further establish the role of LE in clinical nutrition.

Effect of long-chain fatty acids in the culture medium on fatty acid composition of WEHI-3 and J774A.1 cells

As a first step in determining the mechanism of action of specific fatty acids on immunological function of macrophages, a comparative study of the effect of long-chain polyunsaturated fatty acids (PUFA) in the medium was conducted in two macrophage cell lines, J774A.1 and WEHI-3. The baseline fatty-acid profiles of the two cell lines differed in the % distribution of saturated (SFA) and unsaturated fatty acids (UFA). J774A.1 cells had a higher % of SFA (primarily palmitic acid) than WEHI-3 cells. Conversely, WEHI-3 cells had a higher % of UFA (primarily oleic acid) than J774A.1 cells. Neither cell line had detectable amounts of alpha-linolenic acid (ALA) or eicosapentaenoic acid (EPA). The most abundant polyunsaturated fatty acid in both cells lines was arachidonic acid (AA). The efficiency of transport of fatty acids from the medium to the macrophages by two delivery vehicles (BSA complexes and ethanolic suspensions) was compared. Overall, fatty acids were transported satisfactorily by both delivery systems. Alpha-linolenic acid and doscosahexenoic acid (DHA) were transported more efficiently by the ethanolic suspension system. Linoleic acid (LA) was taken up more completely than ALA, and DHA was taken up more completely than EPA by both cell cultures and delivery systems. A dose-response effect was demonstrated for LA, ALA, EPA and DHA in both J774A.1 and WEHI-3 cells. Addition of polyunsaturated fatty acids (PUFA) to the cell cultures modified the total lipid fatty acid composition of the cells. The presence of ALA in the culture medium resulted in a significant decrease in AA in both cell lines. The omega-3/omega-6 fatty acid ratio (omega-3/omega-6), polyunsaturated/saturated fatty acid ratio (P/S), and unsaturation index (UI) increased directly with the amount of PUFA and omega-3 fatty acid provided in the medium. The results indicate that the macrophage cell lines have similar, but not identical, fatty acid profiles that may be the result of differences in fatty acid metabolism. These distinctions could in turn produce differences in immunological function. The ethanol fatty-acid delivery system, when compared with the fatty acid-BSA complex system, is preferable for measurement of dose-response effects, because the cellular fatty acid content increased in proportion to the amount of fatty acid provided in the medium. Similar dose-response results were observed in a previous in vivo study using flaxseed, rich in ALA, as a source of PUFA.

Activation state alters the effect of dietary fatty acids on pro-inflammatory mediator production by murine macrophages

Studies investigating the effect of dietary fats on pro-inflammatory cytokine production by macrophages (M phis) have yielded conflicting results. We hypothesised that this may be due to the different capacities of the M phis studied commonly (resident, thioglycollate-elicited) to produce prostaglandin E(2)(PGE(2)) and leukotriene B(4)(LTB(4)) which inhibit and stimulate, respectively, tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) production. To investigate this, male C57Bl6 mice were fed for 6 weeks on a low fat (LF) diet or on high fat diets which contained coconut oil (CO), olive oil (OO), safflower oil (SO) or fish oil (FO) as the main fat source. Production of TNF-alpha, IL-1 beta, PGE(2)and LTB(4)by lipopolysaccharide-stimulated resident and thioglycollate-elicited (i.e. inflammatory) peritoneal M phis was measured. PGE(2)production by both inflammatory and resident M phis was significantly decreased by FO feeding. FO also decreased LTB(4)production by resident M phis compared with LF feeding. Production of both cytokines by inflammatory M phis decreased with increasing unsaturation of the high fat diets, such that cells from FO-fed mice showed significantly decreased production of TNF-alpha and IL-1 beta compared to those from mice fed on each of the other diets. In contrast, resident M phis from mice fed FO showed increased TNF-alpha production compared to those from CO-fed mice. Thus, FO feeding decreases production of TNF-alpha and IL-1 beta by inflammatory M phis and increases production of TNF-alpha by resident M phis, at least in comparison to some other dietary fats. These results indicate the mechanisms by which dietary fats exert their effects upon pro-inflammatory cytokine production are most likely different for resident and inflammatory M phis.

Dietary fats affect macrophage-mediated cytotoxicity towards tumour cells

In the present study, the effects of feeding mice diets of different fatty acid compositions on the production of TNF-alpha and nitric oxide by lipopolysaccharide-stimulated peritoneal macrophages and on macrophage-mediated cytotoxicity towards L929 and P815 cells were investigated. C57Bl6 mice were fed on a low-fat (LF) diet or on high-fat diets (21% fat by weight), which included coconut oil (CO), olive oil (OO), safflower oil (SO) or fish oil (FO) as the principal fat source. The fatty acid composition of the macrophages was markedly influenced by that of the diet fed. Lipopolysaccharide (LPS)-stimulated macrophages from FO-fed mice showed significantly lower production (up to 80%) of PGE2 than those from mice fed on each of the other diets. There was a significant positive linear correlation between the proportion of arachidonic acid in macrophage lipids and the ability of macrophages, to produce PGE2. Lipopolysaccharide-stimulated TNF-alpha production by macrophages decreased with increasing unsaturated fatty acid content of the diet (i.e. FO < SO < OO < CO < LF). Macrophages from FO-fed mice showed significantly lower production of TNF-alpha than those from mice fed on each of the other diets. Nitrite production was highest for LPS-stimulated macrophages from mice fed on the LF diet. Macrophages from FO-fed mice showed significantly higher production of nitrite than those from mice fed on the OO and SO diets. Compared with feeding the LF diet, feeding the CO, OO or SO diets significantly decreased macrophage- mediated killing of P815 cells (killed by nitric oxide). Fish oil feeding did not alter killing of P815 cells by macrophages, compared with feeding the LF diet; killing of P815 cells was greater after FO feeding than after feeding the other high fat diets. Compared with feeding the LF diet, feeding the OO or SO diets significantly decreased macrophage-mediated killing of L929 cells (killed by TNF). Coconut oil or FO feeding did not alter killing of L929 cells by macrophages, compared with feeding the LF diet. It is concluded that the type of fat in the diet affects macrophage composition and alters the ability of macrophages to produce cytotoxic and immunoregulatory mediators and to kill target tumour cells.

Fish oil augments macrophage cyclooxygenase II (COX-2) gene expression induced by endotoxin

BACKGROUND

Fish oil-supplemented diets have anti-inflammatory and immunomodulating effects. Although fish oil is readily incorporated into the cell membrane and influences the production of eicosanoids, the exact mechanism is not clear. This study was designed to investigate the effects of eicosapentaenoic acid (EPA), a major component of fish oil, on macrophage (Mphi) cyclooxygenase (COX) gene expression induced by LPS.

METHODS

RAW 264.7 cells, a mouse Mphi cell line, were grown in EPA-rich media for 24 h. Mphi were washed and exposed to Escherichia coli LPS (10 microg/ml). Membrane lipid profile was determined by gas chromatographic analysis. COX-1 and COX-2 mRNA expressions were determined by Northern blot assays with mouse-specific cDNA probes. PGE(2) production of Mphi was measured by ELISA. Mphi production of COX-2 protein was determined by Western blot assays with an anti-COX-2 antibody.

RESULTS

Incubation in EPA-rich media increased membrane EPA and decreased arachidonic acid (AA) composition. COX-2 mRNA expression was induced by EPA and further augmented by LPS stimulation. EPA also augmented Mphi production of COX-2 protein. In comparison, COX-1 mRNA expression was not affected by either LPS stimulation or EPA incubation. EPA reduced PGE(2) production by LPS-stimulated Mphi. To further support that COX-2 mRNA was regulated by COX product, exogenous PGE(2) was added to Mphi prior to LPS stimulation. PGE(2) reduced COX-2 mRNA of LPS-stimulated Mphi.

CONCLUSION

EPA displaces AA and reduces PGE(2) production by LPS-stimulated Mphi. Fish oil inhibition of Mphi PGE(2) production induces COX-2 mRNA expression through a COX-2 product-mediated feedback mechanism.

Fish oil decreases macrophage tumor necrosis factor gene transcription by altering the NF kappa B activity

BACKGROUND

Fish oil-supplemented diets have anti-inflammatory and immunomodulating effects, though the exact mechanism(s) are unknown. This study investigated the effects of eicosapentanenoic acid (EPA), a major component of fish oil, on transcriptional regulation of tumor necrosis factor (TNF) gene in lipopolysaccharide (LPS)-stimulated macrophages (MO).

METHODS

RAW 264.7 cells, a mouse MO cell line, were grown in EPA-rich media for 24-48 h. MO were washed and exposed to Escherichia coli LPS (1 microg/ml) for 2 h. TNF mRNA expression was measured by Northern blot assays. Total nuclear extracts were harvested for the measurement of NF kappa B with electrophoretic mobility shift assays. Supershift assays were performed with anti-P50 or anti-P65 antibodies to show components of NF kappa B dimers. TNF production was determined by L929 bioassays.

RESULTS

LPS stimulated RAW cell TNF mRNA expression and NF kappa B activity. In contrast, RAW cells grown in EPA-rich media had less TNF mRNA expression and an altered composition of the NF kappa B subunits (P65/P50 dimers) in the presence of LPS. TNF production by LPS-stimulated MO was reduced by EPA.

CONCLUSIONS

The inhibitory effect of EPA on LPS-stimulated MO TNF gene transcription and protein elaboration is, in part, mediated through altering NF kappa B activation by reducing the P65/P50 dimers.

Nutritional modification of inflammatory diseases

Regulation of the immune system is extremely complex. We are only starting to understand how the immune system coordinates the body's response to a disease or invading pathogen. Immunomodulation, as the term implies, can be used to designate either a suppression or an augmentation of an immune response. Suppressing the function of the immune system may be important in cases of inflammation and augmenting the immune response when increased resistance to disease is required. Nutrition does and can play an important role in modulation of the animal's immune system. The majority of scientific literature published on the interaction of nutrition and the immune system correlates the effects of nutrient deficiency and modulation of an immune response. These studies have evaluated deficiencies of protein; energy; the fat soluble vitamins A, D, and E; the B-complex vitamins; vitamin C; and the minerals selenium, iron, zinc, and copper and their relationship to immune dysfunction. Most recently, researchers have concentrated efforts on evaluating the impact specific fatty acids have on modulation of the immune system. Undoubtedly, the nutritional status of the animal plays an important role in resistance mechanisms against disease causing organisms and may influence the outcome of disease in infected animals. The focus of this chapter is to concentrate on the role specific polyunsaturated fatty acids have on the immune response of animals and to consider the potential for nutritional modification of diseases related to inflammation.

A prospective, randomized trial of intravenous fat emulsion administration in trauma victims requiring total parenteral nutrition

OBJECTIVE

Intravenous fat infusions are a standard component of total parenteral nutrition (TPN). We studied the effects of withholding fat infusions in trauma patients requiring TPN.

DESIGN

Polytrauma patients receiving TPN were randomized to receive a standard fat emulsion dose (L) or to have fat infusions withheld (NL) for the first 10 days of TPN. The two groups received the same amino acid and carbohydrate dose (isonitrogenous, nonisocaloric).

MATERIALS AND METHODS

Clinical outcome parameters were measured. T-cell function was assessed by measuring lymphokine activated killer and natural killer cell activity.

MEASUREMENTS AND MAIN RESULTS

Demographics including Injury Severity Score (27 +/- 8; 30 +/- 9) and APACHE II scores (23 +/- 6; 22 +/- 5) were similar for the L (n = 30) and NL (n = 27) groups, respectively. Differences (p < 0.05) were found in length of hospitalization (L = 39 +/- 24; NL = 27 +/- 16), intensive care unit length of stay (L = 29 +/- 22; NL = 18 +/- 12), and days on mechanical ventilation (L = 27 +/- 21; NL = 15 +/- 12). The L group had a higher number of infections (72 in 30) than the NL group (39 in 27) and T-cell function was depressed in this group.

CONCLUSIONS

Intravenous fat emulsion infusions during the early postinjury period increased susceptibility to infection, prolonged pulmonary failure, and delayed recovery in critically injured patients. It is not clear whether the improved outcome in the NL group was directly related to withholding the fat infusions or due to the hypocaloric nutritional regimen (underfeeding) these patients received.

Effect of dietary flaxseed on fatty acid composition, superoxide, nitric oxide generation and antilisterial activity of peritoneal macrophages from female Sprague-Dawley rats

The impact of ground flaxseed (FS) or flaxseed meal (FSM) diets on the fatty acid composition and functions of rat peritoneal exudate cells (PEC) was determined. Female weanling Sprague-Dawley rats (10/group) were fed isocaloric AIN-76 diets supplemented with 0.0, 10.0% (w/w) FS or 6.2% (w/w) FSM. At the end of 56-days, rat serum and thioglycollate-elicited PEC were analyzed for total lipid fatty acids. Production of nitric oxide (NO) and superoxide (O2-), Listeria monocytogenes (LM) phagocytic index and antilisterial activity of resident PEC were also assessed. A significant increase in alpha-linolenic (C18:3), eicosapentanoic (C20:5) and docosahexanoic (C22:6) acids, as well as a significant reduction in arachidonic acid (C20:4) was observed in the serum of rats fed 10% FS. Dietary FS caused a significant reduction in palmitic acid (C16:0) and an increase in stearic acid (C18:0) of PEC. Defatted FSM produced a significant increase in long chain fatty acids, which included eicosadienoic acid (C20:2) in PEC and C22:6 in serum. PEC from rats fed 10.0% FS produced significantly less (about 50%) O2- in response to phorbol myristate acetate (PMA), than did PEC from control animals; dietary treatment had no effect on O2- in response to LM. FSM had no impact on the O2- production by PEC in response to PMA or LM. Antilisterial activity of PEC was determined by comparing bacterial uptake after 1 hr with recovery 24 hrs later. Despite comparably equivalent bacterial uptake, few viable intracellular LM were recovered at T = 24 for all test samples, indicating that, regardless of the dietary treatment, PEC were able to handle the in vitro LM infection. This bacterial clearance was accompanied by equivalent NO generation by PEC from each dietary group in response to LM. Summarily, dietary FS produced significant changes in fatty acid composition of serum and PEC, inhibited O2- generation by PEC, and was ineffectual to both NO production by and antilisterial activity of PEC.

Effect of fish oil on glucose metabolism in the interleukin-1 alpha-treated rat

Fish oil has been demonstrated to ameliorate many of the responses to infection. This study was conducted to determine whether fish oil feeding could modify the alterations of glucose metabolism induced by interleukin-1 alpha (IL-1 alpha) infusion in the rat. Male Sprague-Dawley rats were pair-fed for 5 weeks on two experimental diets in which the source of fat was either fish oil or soybean oil and provided 20% of calories; the diets were isonitrogenous and isocaloric. After 5 weeks of feeding, rats from both diet regimens were further divided into two subgroups to receive a 3-hour infusion of either 0.1% albumin in saline or 0.1% albumin in saline containing IL-1 alpha. A total of 20 micrograms/kg IL-1 alpha was administered, and half the dose of IL-1 alpha was given as a bolus and the remaining portion (10 micrograms/kg) was continuously infused into the jugular vein. During the last 2 hours of IL-1 alpha infusion, a primed constant infusion of D-(6-3H)glucose and D-(U-14C)glucose was combined to determine the effects of IL-1 alpha and diet on glucose kinetics. Plasma levels of glucose and insulin, energy expenditure, and respiratory quotient were also measured. IL-1 alpha significantly increased concentrations of plasma insulin and the percentage of glucose carbon recycling, confirming previous findings. Concentrations of glucose and insulin with IL-1 alpha treatment were significantly higher in soybean oil- fed animals compared with fish oil-fed animals.(ABSTRACT TRUNCATED AT 250 WORDS)

The comparative effects of dietary alpha-linolenic acid and fish oil on 4- and 5-series leukotriene formation in vivo

The comparative effects of dietary alpha-linolenic acid and fish oil on eicosanoid metabolism was studied in vivo. Resident murine peritoneal cells were stimulated in vivo with opsonized zymosan in animals maintained on diets containing increasing amounts of alpha-linolenic acid or fish oil concentrate with projected n-3/n-6 ratios of 0.2, 0.4 and 1.0. While fish oil feeding resulted in significant changes in eicosapentaenoate tissue levels, alpha-linolenic acid was preferentially metabolized to docosahexaenoate. High performance liquid chromatographic analysis revealed the formation of leukotriene E5 (LTE5) in all the fish oil groups (19.8 +/- 3.5 ng/mouse to 83.3 +/- 13 ng/mouse), but only in the highest linolenic acid group (6.0 +/- 3.2 ng/mouse). Concomitantly, the 4-series sulfidopeptide leukotrienes and PGI2 were significantly reduced in the two highest fish oil containing dietary groups. Similar reductions were observed in the highest linolenic acid group, but the changes were not statistically different from the control values. In summary, this paper reports the de novo synthesis of 5-series sulfidopeptide leukotrienes in animals consuming alpha-linolenic acid. It also reveals that dietary fish oil is 2.5 to 5 times more effective than alpha-linolenic acid in modulating eicosanoid metabolism and altering tissue phospholipid fatty acid composition.

Effects of moderate dietary supplementations with n-3 fatty acids on macrophage and lymphocyte phospholipids and macrophage eicosanoid synthesis in the rat

The effects of a moderate dietary intake of n-3 polyunsaturated fatty acids were determined on the eicosanoid synthesis by rat peritoneal macrophages: the availability of arachidonic acid (20:4 (n-6)) and eicosapentaenoic acid (20:5 (n-3] in the membrane phospholipids of peritoneal macrophages and splenic lymphocytes and the synthesis of the main eicosanoids were evaluated in parallel. The n-6/n-3 ratio was decreased from 13.5 in the control diet rich in 18:2(n-6) to about 2 by an addition of either linseed oil providing 18:3(n-3) (linseed oil diet) or fish oil providing 20:5(n-3) and 22:6(n-3) (fish oil diet). The dietary linoleic acid content was at least 3.5% of energy in each diet. In peritoneal macrophage and splenic lymphocyte membrane phospholipids, arachidonic acid content was significantly decreased with the linseed oil and fish oil diets. 20:5(n-3) content was significantly raised up in the linseed oil group (3-fold in macrophage phospholipids) and more strikely in the fish oil group (7-fold). In response to a stimulation by the calcium ionophore A23187, peritoneal macrophages released 6-ketoPGF1 alpha, TXB2, PGE2 and LTB4 and/or 5, but no or few peptidoleukotrienes. The linseed oil did not affect significantly the synthesis of these eicosanoids, except for LTB5, which was increased 2-fold. In contrast, the fish oil diet led to significant decreases in the productions of 6-ketoPGF1 alpha and PGE2 (-50%) and LTB4 (-40%) and to a 10-fold increase in the release of LTB5. TXB2 was also decreased (-35%), but not significantly. These results and the parallel evolutions of the two ratios 20:4(n-6)/20:5(n-3) and LTB4/LTB5 showed that eicosanoid synthesis is greatly dependent on the relative availability of the two substrates in competition.

Incorporation and effects of dietary eicosapentaenoate (20:5(n-3)) on plasma and erythrocyte lipids of the marmoset following dietary supplementation with differing levels of linoleic acid

The effect of dietary eicosapentaenoic acid (EPA, 20:5(n-3), as the ethyl ester) on plasma lipid levels and the incorporation of EPA into erythrocyte and plasma lipids were investigated in the marmoset monkey. Marmosets were fed high mixed-fat diets (14.5% total fat) supplemented with or without 0.8% EPA for 30 weeks. Markedly elevated plasma cholesterol (16.4 mmol/l) was induced by an atherogenic-type diet but with EPA supplementation, plasma cholesterol increased to only 6.6 mmol/l. Plasma triacylglycerol levels were not elevated with an atherogenic type diet. Substantial EPA incorporation was evident for plasma phospholipid, triacylglycerol and cholesterol ester fractions. The proportion of docosapentaenoic acid (22:5(n-3)) but not docosahexaenoic acid (22:6(n-3)) was also elevated in these plasma lipid fractions. Greatest incorporation of EPA occurred when it was administered with an atherogenic type diet having a P:M:S (polyunsaturated:monounsaturated:saturated) fatty acid ratio of about 0.2:0.6:1.0 in comparison to the control diet of 1.0:1.0:1.0. Incorporation of EPA and 22:5(n-3)) into erythrocyte phospholipids was also apparent and this was at the expense of linoleic acid (18:2(n-6)). These results in the marmoset highlight both the cholesterol-lowering properties of EPA and the extent of its incorporation into plasma lipids and erythrocyte membrane phospholipids with far greater incorporation occurring when the level of dietary linoleic acid was reduced.

Comparison of the inhibitory effect of polyunsaturated fatty acids on prostaglandin synthesis. II. Fibroblasts

In a previous publication we reported that PUFAs of the n-6 and n-3 series caused significant inhibition of synthesis of both PGE2 (28.4-92.8%) and PGF2 alpha (24.4-84.0%) in the oral squamous carcinoma cell line SCC-25. In this report we describe the inhibitory effect of the same acids on PG synthesis in normal human gingival fibroblasts under the same experimental conditions. It was found that a combination of EPA + DCHA (6:4), DCHA and ALA caused significant reduction in synthesis of PGE2 (10.1-87.8%) and PGF2 alpha (14.0-54.6%) at the four dose levels studied. The rank order of potency of acids in reduction of PG synthesis was: EPA + DCHA greater than DCHA greater than EPA greater than ALA greater than LA greater than DGLA greater than GLA. The data suggest that although PUFAs are effective inhibitors of PG synthesis by gingival fibroblasts and SCC-25, the fibroblast is less susceptible to the inhibitory effect of fatty acids.

Alteration of in vitro murine peritoneal macrophage function by dietary enrichment with eicosapentaenoic and docosahexaenoic acids in menhaden fish oil

The effects of diets containing menhaden fish oil (MFO), compared with those of diets containing safflower oil (SAF) or an essential fatty acid deficient hydrogenated coconut oil (HCO), on in vitro activation of tumoricidal capacity by murine macrophages were assessed. Mice fed the experimental diets for 4 weeks were injected intraperitoneally with sterile thioglycollate broth 3 days before use. There was no difference between any of the groups with respect to total peritoneal exudate cells or the percentage of macrophages, although the fatty acid profile of purified adherent macrophages closely paralleled that of the diets. Macrophages from mice fed MFO killed fewer P815 mastocytoma cells upon activation with recombinant interferon gamma (IFN gamma) and lipopolysaccharide. Macrophages from all diets were equally competent for tumoricidal capacity when activated pharmacologically with calcium ionophore, phorbol 12-myristate 13-acetate, and lipopolysaccharide (LPS), suggesting that MFO diet macrophages were hyporesponsive to IFN gamma. Priming with higher concentrations of IFN gamma restored the partial defect in activation of MFO macrophages. When activated for 24 hr with high levels of LPS, macrophages from mice fed SAF displayed little cytolytic capacity; addition of indomethacin. (1 microM) resulted in enhanced levels of P815 kill. In contrast, MFO and HCO diet macrophages were highly cytolytic with similar LPS treatment with or without indomethacin. Macrophages from mice fed SAF produced threefold more prostaglandin E in response to LPS than did MFO and HCO diet macrophages. These results suggest that dietary manipulation of fatty acids can alter activation of tumoricidal capacity of macrophages, possibly both dependent and independent of changes in eicosanoid synthesis.

Nutrition, immune function, and inflammation: an overview

The collective evidence suggests that nutritional insult to both cell-mediated and humoral immunity in the presence of protein-energy malnutrition contributes to abnormalities of inflammation. The primary goal of nutritional support in inflammatory disease is to provide adequate energy and protein to meet endogenous requirements for tissue repair, IL-1 production, and restored cellular function, thus preventing secondary infection. Substrate provision should aim at improving the acute phase of injury while avoiding immune dysfunction. This goal may be achieved by altering the eicosanoid pathway toward a more regulated inflammatory state. In the context of allograft response, macrophages are central to the initiation of allosensitization by virtue of their ability to present antigen to T-cells. Activated T-cells may further modulate macrophage function by the secretion of lymphokines. Manipulation of macrophage eicosanoid production by dietary omega-3 PUFA may reduce cellular immune response. (table; see text) Nutritional support should also focus on providing essential micronutrients, with their potentially immunomodulating role, as adjunctive therapy in order to protect the host from toxic effects of free-radicals and chemicals released during inflammatory events. (Feeding regimens currently under investigation and development are presented in Table 4.) By integrating dietary immunotherapy with the use of recombinant hormones, monoclonal antibodies, and various available monokines, an optimal outcome for each patient may be achieved. However, effective application of immunotherapy to nutritional supplementation will require accurate monitoring of immune function in individual patients in order to avoid inappropriate treatment.

Stimulation of anaphylaxis in the mouse footpad by dietary fish oil fatty acids

The effect of fish oil-derived omega-3 (omega-3) fatty acids on anaphylaxis, Arthus and delayed type hypersensitivity reactions in mice has been investigated. Mice on a normal chow diet were fed eicosapentaenoic acid and docosahexaenoic acid at a dose of 500 and 333 mg/kg/day, respectively, by a gastric tube over a period of 61 days. Control groups were given water, safflower oil or oleic acid. Anaphylactic and Arthus type reactions were induced in the mouse footpad using bovine serum albumin as an antigen. Carrageenin was utilized to produce a delayed type hypersensitivity reaction. The animals fed omega-3 fatty acids induced a more anaphylactic foodpad reaction. There was no significant effect of the diet on Arthus and delayed type hypersensitivity responses. There was no effect of the fish oil-supplemented diet on production of antibodies to bovine serum albumin. Synthesis of prostaglandin E2 by peritoneal macrophages was significantly inhibited in the animals fed omega-3 fatty acid-enriched fish oil, while leukotriene B4 production was not affected. These results suggest that a diet enriched in omega-3 fatty acids modulates production of arachidonic acid metabolites and this may influence anaphylaxis, but not Arthus and cellular mediated hypersensitivity responses.

Modulation of Kupffer cell membrane phospholipid function by n-3 polyunsaturated fatty acids

Dietary n-3 polyunsaturated fatty acids (PUFAs) have been reported to improve clinical outcome in a number of inflammatory diseases including burns and sepsis. One mechanism contributing to the anti-inflammatory effect is the incorporation of n-3 PUFAs into membrane phospholipids which decreases macrophage eicosanoid production. We hypothesize that an additional mechanism for their effects is an alteration of membrane signal transduction that decreases macrophage responsiveness to inflammatory stimuli. Kupffer cells, the fixed macrophages of the liver, were obtained from rats pair fed diets for 6 weeks with 15% of calories supplied as menhaden (high n-3), corn (control), or safflower (high n-6) oils. The effects of the dietary oils on Kupffer cell membrane signal transduction and eicosanoid production were assessed by measuring inositol phospholipid (PI) metabolism, intracellular calcium responses, and prostaglandin E2 (PGE2) production to the inflammatory signals endotoxin (LPS) and platelet activating factor (PAF). The menhaden oil diet resulted in significant incorporation of n-3 PUFAs into total cellular PUFAs compared to corn and safflower oil. (total n-3 PUFAs, 28.1% menhaden vs 2.1% corn vs 1.2% safflower, P less than 0.03). This incorporation altered signal transduction of PAF as both PI turnover (65% +/- 10% of corn oil) and calcium response (0.6-fold vs 5.0-fold for corn oil) were significantly reduced in the menhaden oil group. (P less than 0.05) The menhaden oil diet also reduced significantly PGE2 production in response to PAF and LPS (corn, 348 +/- 23 pg/ml; menhaden, 48 +/- 6 pg/ml, P less than 0.01). We conclude that, in addition to modulating eicosanoid production, n-3 PUFAs can also alter macrophage membrane signal transduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation of eicosanoid production and cell-mediated cytotoxicity by dietary alpha-linolenic acid in BALB/c mice

The effects of dietary alpha-linolenic acid (18:3n-3) on fatty acid composition, eicosanoid production, and cell-mediated cytotoxic activity of immune cells before and after challenge with virus or poly I-C from BALB/c mice were studied. Weanling BALB/c mice were fed purified diets containing either 10%-by-weight corn oil or linseed oil providing a ratio of 18:3n-3 to 18:2n-6 of 1/32 or 2/1, respectively, for 6-10 weeks. Fatty acid analysis of splenocyte phospholipids showed an appreciable increase in the percentage of n-3, and a decrease in n-6, fatty acids in splenocytes from mice fed the linseed oil diet. Splenocyte prostaglandin E and peritoneal exudate cell leukotriene C production was significantly lower in the linseed oil-fed mice. In general, cell-mediated cytotoxic activity was similar for immune cells from linseed oil and corn oil-fed mice. However, 6 days after the viral challenge, splenocyte cell-mediated cytotoxic activity was significantly higher in linseed oil mice. This higher activity was associated with nonspecific cytotoxicity rather than that of viral-specific cytotoxic T-lymphocytes. Cell yields from the spleen and peritoneum were frequently significantly higher in linseed oil mice. Interactions between dietary 18:3n-3, eicosanoid production, and immune cell proliferation and/or migration are discussed. In summary, feeding mice a diet rich in 18:3n-3 elevates immune cell n-3 fatty acid content, reduces eicosanoid synthesis and, to a limited extent, enhances the cell-mediated cytotoxic response to a viral challenge.

Inverse relationship between superoxide anion production of guinea pig alveolar macrophages and tracheal beta-adrenergic receptor function; influence of dietary polyunsaturated fatty acids

It was shown recently that dietary linoleic acid could modulate beta-adrenergic receptor function in guinea pig tracheal spirals (Loesberg, Folkerts & Nijkamp. Prostagland. Leukotr. essen. Fatty Acids, in press). In the present study the relationship between beta-adrenergic receptor function and oxygen radical production was examined by analyzing the effect of dietary linoleic acid (3, 6 and 12 energy%) on superoxide anion production of guinea pig alveolar macrophages and on relaxation of tracheal spirals upon beta-adrenergic receptor stimulation. An additional dietary group receiving fish oil (3 energy%) in addition to 3 energy% linoleic acid was also included in this study. The zymosan-stimulated (but not the basal) superoxide anion production of the alveolar macrophages differed between the dietary groups. Highest superoxide production was found in those diets that showed the greatest deterioration of beta-adrenergic receptor function. Moreover, a highly significant positive correlation was demonstrated between the amount of generated superoxide and the severity of the attenuation of the beta-adrenergic receptor function in the individual animals. These data suggest that optimal dietary conditions could lead to an improved lung function possibly via modulation of alveolar macrophage radical production.

Invited comment: lipids and the development of immune dysfunction and infection

Excessive W-6 PUFA metabolism due to high levels of dietary fat intake can encourage infection via prolonged inflammation, enhanced Gram negative survival, reticuloendothelial blockage, immunosuppression, and monokine depression. Lipids can influence host immunity by altering eicosanoid metabolism and membrane structure and function. Further investigations are essential to answer questions regarding the levels and properties of various essential fatty acids in TPN lipid emulsions. Combining the features of LCT in the form of W-3 PUFA (fish oil) and MCT in the form of medium-chain triglyceride in a "structured lipid" may decrease infection and may improve survival rates by producing fewer inflammatory eicosanoids of the two- and four-series, and serving as a more "efficient fuel." The introduction of W-3 polyunsaturated fatty acids into the TPN emulsions as well as into normal diets may provide an important therapeutic advance in the pathogenesis of disease. Such unique antiinflammatory properties of W-3 PUFA require intensive research.

Dietary manipulation of macrophage phospholipid classes: selective increase of dihomogammalinolenic acid

Because alterations in the dietary content of fatty acids are an important method for modulating macrophage eicosanoid production, we have quantitated the levels of n-6 and n-3 polyunsaturated fatty acids in peritoneal macrophage individual phospholipids from mice fed diets (3 wk) with either safflower oil (SAF), predominantly containing 18:2n-6, borage (BOR) containing 18:2n-6 and 18:3n-6, fish (MFO) containing 20:5n-3 and 22:6n-3, and borage/fish mixture (MIX) containing 18:2n-6, 18:3n-6, 20:5n-3 and 22:6n-3. Dietary n-3 fatty acids were readily incorporated into macrophage phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI). The increase in n-3 fatty acid levels was accompanied by a decrease in the absolute levels of 18:2n-6, 20:4n-6 and 22:4n-6 in PC, PE and PS. Interestingly, PI 20:4n-6 levels were not significantly lowered (P greater than 0.05) in MIX and MFO macrophages relative to SAF and BOR. These data demonstrate the unique ability of this phospholipid to selectively maintain its 20:4n-6 levels. In BOR and MIX animals, 20:3n-6 levels were significantly increased (P less than 0.05) in all phospholipids relative to SAF and MFO. The combination of borage and fish oils (MIX diet) produced the highest 20:3n-6/20:4n-6 ratio in all phospholipids. These data show that the macrophage eicosanoid precursor levels of 20:3n-6, 20:4n-6 and n-3 acids can be selectively manipulated through the use of specific dietary regimens. This is noteworthy because an increase in phospholipid levels of 20:3n-6 and 20:5n-3, while concomitantly reducing 20:4n-6, may have therapeutic potential in treating inflammatory disorders.

Effect of polyunsaturated fatty acids of the n-3 and n-6 series on lipid composition and eicosanoid synthesis of platelets and aorta and on immunological induction of atherosclerosis in rabbits

The effect of dietary fish oil (rich in n-3 polyunsaturated fatty acids (PUFA], corn oil (rich in n-6 PUFA) and coconut oil (low in n-3 and n-6 PUFA) on the induction of atherosclerosis by serum sickness in rabbits was investigated over a 12-month period. Dietary fish oil led to a significant increase in the level of eicosapentaenoic acid (EPA) in all platelet phospholipid fractions and to a significant reduction in the level of platelet phosphatidylethanolamine arachidonic acid (AA). In aortic total phospholipids, rabbits given fish oil showed a significant reduction in AA and a significant increase in EPA. Rabbits given fish oil showed significantly lower collagen-induced platelet thromboxane A2 release and aortic production of 6-keto-PGF1 alpha. Serum total immune complex levels and anti-horse serum IgG levels were not influenced by diet. There was a significant reduction in total aortic atherosclerosis in fish oil-fed animals compared with coconut oil fed animals.

Fatty acid composition of macrophage phospholipids in mice fed fish or borage oil

The polyunsaturated fatty acid (PUFA) composition of murine peritoneal macrophage phospholipids was dramatically altered in vivo following the four-wk feeding of specific dietary oils. Fish oil (containing 20:5n-3 and 22:6n-3) feeding significantly increased macrophage 20:5n-3, 22:5n-3, and 22:6n-3 (P less than 0.05), while borage oil (containing 18:2n-6 and 18:3n-6) increased (P less than 0.05) the macrophage 20:3n-6/20:4n-6 ratio, relative to safflower oil (containing 18:2n-6) and hydrogenated coconut oil (containing 12:0)-fed animals. The macrophage phospholipid PUFA profiles were compared with those of the liver, lung and spleen. The significance of the PUFA alterations is discussed.

Modulation of prostaglandin synthesis in mouse peritoneal macrophages by enrichment of lipids with either eicosapentaenoic or docosahexaenoic acids in vitro

The n-3 polyunsaturated fatty acids (PUFA) of fish oils alter arachidonic acid (AA) metabolism in macrophages. The present investigation studied the efficacy of eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA), two n-3 PUFA of fish, to alter lipid composition and specific functions of mouse peritoneal macrophages. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were readily incorporated by macrophages in vitro and replaced 25-50% of AA in cellular lipids. The EPA- or DHA-enriched cells synthesized significantly less (50-65%) prostaglandin E2 (PGE2), thromboxane B2 (TXB2) and 6 keto prostaglandin F1(1) alpha (6 keto PGF1 alpha) when stimulated with opsonized zymosan. The enrichment with EPA or DHA did not affect phagocytosis nor superoxide anion formation in macrophages. These studies demonstrated that EPA or DHA can be used to decrease prostaglandin synthesis selectively without affecting the other physiological functions of macrophages.

The effect of bovine serum albumin on the synthesis of prostaglandin and incorporation of [3H]acetate into platelet-activating factor

The binding of fatty acids by bovine serum albumin (BSA) is well documented. However, the interaction between the synthesis of prostaglandins (PGs) and the trapping of arachidonate released from cellular lipid stores is not as well understood. In this communication, we relate the trapping of fatty acids to the synthesis of PGs and the incorporation of [3H]acetate into platelet-activating factor (PAF). Our results show that, as determined by radioimmunoassay, BSA inhibits bradykinin (BK) (5 ng/ml) and ionophore A23187 (10 microM)-stimulated synthesis of PGs in human embryo lung fibroblasts (IMR-90) in a concentration-dependent manner. Experiments using prelabel with [3H]arachidonate followed by extraction and thin-layer chromatography show that, in the presence of 2 mg/ml BSA, IMR-90 release essentially only fatty acid following stimulation with bradykinin. Little if any prostaglandin and no endoperoxide are detected. In the same experiment, in absence of BSA, about 70% of the released label is detected as prostaglandin. alpha-Cyclodextrin, another trapper of fatty acid, inhibits PG synthesis in much the same way. BSA and alpha-cyclodextrin also inhibit prostacyclin synthesis in endothelial cells derived from the calf pulmonary artery. However, the inhibition of PG synthesis in these cells is not as complete as that in the IMR-90. In contrast to the effect of the trappers on PG synthesis, BSA and alpha-cyclodextrin are observed to potentiate BK- and ionophore-stimulated incorporation of [3H]acetate into PAF in the endothelial cells. The labeled PAF is not released from the cells in either the presence or absence of the trappers, leading us to conclude that BSA causes an increase in acetate-labeled cellular PAF by trapping released fatty acid.

Homologous physiological effects of nutritional antioxidants and eicosapentaenoic acid

Dietary fish oils rich in eicosapentaenoic acid (EPA) possess immunostimulant, anti-inflammatory, cancer-retardant, antithrombotic and ischemia-protective properties that are remarkably parallel to the effects of high-dose nutritional antioxidants. EPA and nutritional antioxidants may show complementary activities in a wide range of preventive and therapeutic applications.

Lipid composition and prostaglandin synthesis in mouse lung microsomes: alterations following the ingestion of menhaden oil

Three groups of male mice were fed a normal diet or a semisynthetic diet containing either 10% hydrogenated coconut oil (CO group) or 10% menhaden oil (MO group) for two wk. The synthetic diet altered the fatty acid composition of lung microsomal lipids. Mice ingesting menhaden oil contained greater amounts of eicosapentaenoic acid (20:5 n-3), docosapentaenoic acid (22:5 n-3) and docosahexaenoic acids (22:6 n-3) and decreased amounts of n-6 fatty acids such as arachidonic and adrenic. Synthesis of prostaglandin E2 and prostaglandin F2 alpha from exogenous arachidonic acid was significantly depressed in n-3 fatty acid-enriched lung microsomes. These studies indicated that dietary fish oil not only alters the fatty acid composition of lung microsomes but also lowers the capacity of lungs to synthesize prostaglandins from arachidonic acid.

Effect of culture in vitro with eicosatetraenoic (20:4(n-6) ) and eicosapentaenoic (20:5(n-3) ) acids on fatty acid composition, prostaglandin synthesis and chemiluminescence of rat peritoneal macrophages

Rat peritoneal macrophages were cultured in either eicosatetraenoic acid (20:4(n-6) ) or eicosapentaenoic acid (20:5(n-3) ) and the effects on phospholipid fatty acids, prostaglandin synthesizing capacity and the ability of the macrophages to show chemiluminescence were examined. Chemiluminescence is an activity resulting from the synthesis of reactive oxygen species. It has been reported that prostaglandins inhibit this activity. The fatty acid profile of the four major phospholipids reflected the fatty acid component of the medium. Macrophages cultured in 20:4(n-6) synthesized twice the prostaglandin produced by controls and those cultured in 20:5(n-3) synthesized 10% that of controls and 5% that of 20:4(n-6)-cultured cells. Macrophages cultured with 20:4(n-6) for 12 h showed half the chemiluminescence of those cultured with 20:5(n-3), while those cultured with 20:4(n-6) for 24 h showed 10% the chemiluminescence of 20:5(n-3)-cultured cells. Addition of the prostaglandin synthase inhibitor, indomethacin, had no effect on chemiluminescence.

Alterations in cerebral and microvascular prostaglandin synthesis by manipulation of dietary essential fatty acids

Sprague-Dawley rats were fed one of three purified diets--10% corn oil, 10% hydrogenated coconut oil, or 10% linseed oil--through two generations. At 60-80 days of age the animals were sacrificed. The fatty acyl composition of phosphatidylcholine, phosphatidylethanolamine, plasmalogen phosphatidylethanolamine, and combined phosphatidylinositol/phosphatidylserine from cerebral cortex and isolated cerebral microvessels was determined. Brain slice prostaglandin F2 alpha or microvascular prostacyclin synthesis was also measured. Major changes were noted in the fatty acid profiles, most dramatically in the phosphatidylethanolamine and ethanolamine plasmalogen fractions, with an active rise in docosahexaenoic acid resulting from linseed oil feeding. A depression in prostaglandin F2 alpha synthesis was seen in brain slices of hydrogenated coconut oil- and linseed oil-fed rats. Such a depression was also observed in microvascular prostaglandin synthesis at basal and stimulated levels but not in control incubations. The potential importance of these findings to cerebral microcirculation and hemostasis is discussed.

Reduction in thromboxane formation by n-3 fatty acids enriched lung microsomes from rat and guinea pig following the ingestion of dietary menhaden oil

Feeding rats and guinea pigs on a diet containing 5% menhaden oil altered the fatty acid composition of lung microsomes. The lung microsomal phospholipids contained increased amounts of n-3 fatty acids, eicosapentaenoic (20:5) and docosahexaenoic acid (20:6), following the ingestion of menhaden oil. There was a concomitant decrease in arachidonic acid (20:4) levels in rat lung microsomes, but no significant change of this fatty acid was observed in the microsomes from guinea pigs. The ability of lung microsomes to convert 14C-arachidonic acid into thromboxane (TXB) was reduced by the enrichment of n-3 fatty acids in the microsomal lipids.