Docosahexaenoic acid and other dietary polyunsaturated fatty acids suppress leukotriene synthesis by mouse peritoneal macrophages

Prospects on the Use of Schizochytrium sp. to Develop Oral Vaccines

Although oral subunit vaccines are highly relevant in the fight against widespread diseases, their high cost, safety and proper immunogenicity are attributes that have yet to be addressed in many cases and thus these limitations should be considered in the development of new oral vaccines. Prominent examples of new platforms proposed to address these limitations are plant cells and microalgae. Schizochytrium sp. constitutes an attractive expression host for vaccine production because of its high biosynthetic capacity, fast growth in low cost culture media, and the availability of processes for industrial scale production. In addition, whole Schizochytrium sp. cells may serve as delivery vectors; especially for oral vaccines since Schizochytrium sp. is safe for oral consumption, produces immunomodulatory compounds, and may provide bioencapsulation to the antigen, thus increasing its bioavailability. Remarkably, Schizochytrium sp. was recently used for the production of a highly immunoprotective influenza vaccine. Moreover, an efficient method for transient expression of antigens based on viral vectors and Schizochytrium sp. as host has been recently developed. In this review, the potential of Schizochytrium sp. in vaccinology is placed in perspective, with emphasis on its use as an attractive oral vaccination vehicle.

Dietary n-3 Fatty Acids Inhibit Fever Induced by Inflammation in the Rat

Modification of endogenous eicosanoid synthesis by dietary n-3 fatty acid supplementation reduces febrile responses, but the mechanisms underlying these effects in vivo have not been determined. In the present study, local inflammation was induced by intramuscular injection ofturpentine in rats fed control or n-3 supplemented diets for 8-9 weeks. In animals fed the control diet, turpentine induced fever, hypermetabolism, marked local inflammation (oedema), increased plasma IL-6 concentrations and raised cerebrospinal fluid (CSF) concentrations of PGE2. N-3 fatty acid supplementation significantly inhibited the rise in CSF PGE2, fever and hypermetaboHsm induced by turpentine. Local inflammation and increased plasma IL-6 concentrations were not affected by n-3 supplementation. These findings suggest that modification of dietary fat intake inhibits fever via reduced release of prostaglandins, probably within the brain, but does not affect the local or afferent signals involved in fever generation.

Comparative effects of DHA and EPA on cell function

Fish oil supplementation has been reported to be generally beneficial in autoimmune, inflammatory and cardiovascular disorders. Most researchers have attributed these beneficial effects to the high content of omega-3 fatty acids in fish oil (FO). The effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are not differentiated in most studies. In fact, up to 1990, purified DHA was not available for human use and there was no study regarding its effects on human immune response. In this review, the differences in the effects of these two fatty acids on cell function are discussed. Studies have shown that EPA and DHA have also different effects on leukocyte functions such as phagocytosis, chemotactic response and cytokine production. DHA and EPA modulate differently expression of genes in lymphocytes. Activation of intracellular signaling pathways involved with lymphocyte proliferation is also differently affected by these two fatty acids. In relation to insulin producing cell line RINm5F, DHA and EPA are cytotoxic at different concentrations and the proteins involved with cell death are differently modulated by these two fatty acids. Substantial improvement in the therapeutic usage of omega-3 fatty acid-rich FO will be possible with the discovery of the different mechanisms of actions of DHA and EPA.

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.

Important differences exist in the dose-response relationship between diet and immune cell fatty acids in humans and rodents

Omega-3 polyunsaturated fatty acids (n-3 PUFA) are noted for their ability to diminish inflammatory and immune responses in vitro and in a variety of animal-based models of autoimmunity and inflammation. Yet, recent systematic reviews suggest that the evidence for these fatty acids having beneficial effects on inflammation or autoimmunity in humans is equivocal. A possible explanation for these disappointing and somewhat paradoxical findings emerged from the analyses described in this review. The available data on the changes in immune cell fatty acid profiles in mice, rats and humans, fed various forms and amounts of n-3 PUFA are summarized and displayed graphically. The dose-response curves generated provide new insights into the relationship between dietary n-3 PUFA and immune cell fatty acid profiles. The author suggests that the poor predictive value of most in vitro as well as many animal trials may, in part, be a consequence of the frequent adoption of experimental conditions that create differences in immune cell fatty acid profiles that far exceed what is possible in free-living humans through dietary intervention. Recommendations for improving the preclinical value of future in vitro and animal-based studies with n-3 PUFA are provided.

1-Tetradecanol complex reduces progression of Porphyromonas gingivalis-induced experimental periodontitis in rabbits

BACKGROUND

It has been recently shown that monounsaturated fatty acids inhibit endothelial activation and reduce tissue responsiveness to cytokines. The present study has been planned to investigate topical application of a novel monounsaturated fatty acid complex (1-tetradecanol complex) for prevention of Porphyromonas gingivalis-induced periodontitis in rabbits.

METHODS

Experimental periodontitis was induced in New Zealand white rabbits with silk sutures tied around the mandibular second premolars bilaterally, followed by the topical application of 10(9) colony forming units (CFU) of P. gingivalis. 1-Tetradecanol complex (1-TDC) was topically applied at 1- and 10-mg/ml concentrations in five animals in each group, whereas control animals received olive oil vehicle (five animals) three times per week for 6 weeks. Negative controls included ligature alone (14 animals) or ligature + P. gingivalis (non-treatment; 15 animals). Rabbits were sacrificed after 6 weeks, and mandibular block sections were obtained; tissues were decalcified and embedded in paraffin. Thin sections (5 microm) were stained with hematoxylin and eosin or tartrate-resistant acid phosphatase. Macroscopic and histologic evaluation of samples was followed by the characterization of cellular inflammatory infiltrate and quantitative histomorphometric measurements.

RESULTS

Treatment with both concentrations of 1-TDC and vehicle resulted in significant prevention of macroscopic periodontal inflammation and bone loss (75%; P <0.05) compared to the non-treatment (ligature + P. gingivalis) group, where significant periodontal tissue destruction characterized by attachment and bone loss was detected. However, there was no statistically significant difference between the vehicle and both 1-TDC groups. Histologically, 1-TDC inhibited inflammatory cell infiltration and prevented osteoclastogenesis, whereas treatment with vehicle did not show the same effect as in the 1-TDC groups; the difference between vehicle and the higher concentration of 1-TDC (10 mg/ml) was statistically significant.

CONCLUSION

Topical application of an esterified monounsaturated fatty acid complex (1-TDC) was found promising in preventing bone loss, inflammatory cell infiltration, and connective tissue destruction in the rabbit periodontitis model.

Oxygenation of omega-3 fatty acids by human cytochrome P450 4F3B: effect on 20-hydroxyeicosatetraenoic acid production

Cytochrome P450 (CYP) omega-oxidases convert arachidonic acid (AA) to 20-hydroxyeicosatetraenoic acid (20-HETE), a lipid mediator that modulates vascular tone. We observed that a microsomal preparation containing recombinant human CYP4F3B, which converts AA to 20-HETE, converted eicosapentaenoic acid (EPA) to 20-OH-EPA. Likewise, docosahexaenoic acid (DHA) was converted to 22-OH-DHA, indicating that human CYP4F3B also can oxidize 22-carbon omega-3 fatty acids. Consistent with these findings, addition of 0.5-5 microM EPA, DHA or omega-3 docosapentaenoic acid (DPA) to incubations containing 0.5 microM [3H]AA inhibited [3H]20-HETE production by 15-65%. [3H]20-OH-EPA was rapidly taken up by COS-7 cells, and almost all of the incorporated radioactivity remained as unmodified 20-OH-EPA. The 20-OH-EPA stimulated luciferase activity in COS-7 cells that express peroxisome proliferator-activated receptor alpha, indicating that this EPA metabolite may function as a lipid mediator. These findings suggest that some functional effects of omega-3 fatty acid supplementation may be due to inhibition of 20-HETE formation or the conversion of EPA to the corresponding omega-oxidized product.

Different ratios of eicosapentaenoic and docosahexaenoic omega-3 fatty acids in commercial fish oils differentially alter pro-inflammatory cytokines in peritoneal macrophages from C57BL/6 female mice

The use of fish oil (FO) as a dietary supplement to prevent or reduce the severity of cardiovascular diseases and autoimmune disorders such as rheumatoid arthritis is receiving much attention. Several recent reports indicate that eating fish often or the use of small doses of FO capsules appears to have benefits against cardiovascular diseases. We have reported in the past that diets enriched with FO protect against renal diseases and prolong the life span of autoimmune-prone mice compared to corn oil (CO) diets. However, the optimum ratio of eicosapentaenoic acid (EPA) to docosahexaenoic acid (DHA) in commercially available FOs to reduce the production of various pro-inflammatory cytokines has not been well established. We, therefore, obtained deodorized FO from three sources containing different EPA/DHA contents, fed them to C57BL/6 mice for 8 weeks in a 10% (vol/wt) diet (oil A, 11/10; oil B, 14/9; oil C, 23/14) and compared them with (10%) CO-fed mice as control. TNF-alpha, IL-6 and IL-1beta were measured by enzyme-linked immunosorbent assay in thioglycollate-induced macrophages, 8 and 24 h after lipopolysaccharide treatment. The results showed a significant decrease in TNF-alpha after only 8 h in oil C. After 24 h, TNF-alpha, IL-6 and IL-1beta levels decreased only in mice fed oil C, although nonsignificant decreases were seen in mice fed oil A compared to mice fed CO. The antioxidant enzymes, catalase and glutathione transferase, were higher in kidneys of mice fed oil C compared to mice fed CO. The study suggests that anti-inflammatory activity may vary among different sources of FO due to variations in EPA/DHA content.

Fatty acids, the immune response, and autoimmunity: a question of n-6 essentiality and the balance between n-6 and n-3

The essentiality of n-6 polyunsaturated fatty acids (PUFA) is described in relation to a thymus/thymocyte accretion of arachidonic acid (20:4n-6, AA) in early development, and the high requirement of lymphoid and other cells of the immune system for AA and linoleic acid (1 8:2n-6, LA) for membrane phospholipids. Low n-6 PUFA intakes enhance whereas high intakes decrease certain immune functions. Evidence from in vitro and in vivo studies for a role of AA metabolites in immune cell development and functions shows that they can limit or regulate cellular immune reactions and can induce deviation toward a T helper (Th)2-like immune response. In contrast to the effects of the oxidative metabolites of AA, the longer-chain n-6 PUFA produced by gamma-linolenic acid (18:3n-6, GLA) feeding decreases the Th2 cytokine and immunoglobulin (Ig)G1 antibody response. The n-6 PUFA, GLA, dihomo-gamma-linolenic acid (20:3n-6, DHLA) and AA, and certain oxidative metabolites of AA can also induce T-regulatory cell activity, e.g., transforming growth factor (TGF)-beta-producing T cells; GLA feeding studies also demonstrate reduced proinflammatory interleukin (IL)-1 and tumor necrosis factor (TNF)-alpha production. Low intakes of long-chain n-3 fatty acids (fish oils) enhance certain immune functions, whereas high intakes are inhibitory on a wide range of functions, e.g., antigen presentation, adhesion molecule expression, Th1 and Th2 responses, proinflammatory cytokine and eicosanoid production, and they induce lymphocyte apoptosis. Vitamin E has a demonstrable critical role in long-chain n-3 PUFA interactions with immune functions, often reversing the effects of fish oil. The effect of dietary fatty acids on animal autoimmune disease models depends on both the autoimmune model and the amount and type of fatty acids fed. Diets low in fat, essential fatty acid deficient (EFAD), or high in long-chain n-3 PUFA from fish oils increase survival and reduce disease severity in spontaneous autoantibody-mediated disease, whereas high-fat LA-rich diets increase disease severity. In experimentally induced T cell-mediated autoimmune disease, EFAD diets or diets supplemented with long-chain n-3 PUFA augment disease, whereas n-6 PUFA prevent or reduce the severity. In contrast, in both T cell- and antibody-mediated autoimmune disease, the desaturated/elongated metabolites of LA are protective. PUFA of both the n-6 and n-3 families are clinically useful in human autoimmune-inflammatory disorders, but the precise mechanisms by which these fatty acids exert their clinical effects are not well understood. Finally, the view that all n-6 PUFA are proinflammatory requires revision, in part, and their essential regulatory and developmental role in the immune system warrants appreciation.

Local application of n-3 or n-6 polyunsaturated fatty acids in the treatment of human experimental gingivitis

BACKGROUND

Polyunsaturated fatty acids have the potential to attenuate inflammation by the synthesis of mediators of the 15-lipoxygenase pathways, which show opposite effects to the pro-inflammatory arachidonic acid metabolites such as leukotriene B4 (LTB4).

AIMS

The aim of this clinical study was to evaluate the effects of topical application of n-6 or n-6 polyunsaturated fatty acids in patients with experimental gingivitis.

METHODS

In each subject, similar teeth served as experimental and control over a 21-day non-hygiene phase and a 9-day resolving phase. Efficacy assessment was based on the bleeding on probing frequency (BOP) and the gingivocrevicular fluid volume (GCF). GCF was determined by inserting a filter paper strip for 30 s and measurements were performed on a Periotron 8000. The LTB4 concentration was analyzed by reversed-phase high-pressure liquid chromatography.

RESULTS

After 21 days of plaque growth, the BOP, GCF and LTB4 levels were significantly increased in all groups, with no differences between the control and experimental side. Rinsing of an area with established gingivitis for a 9-day period significantly reduced the GCF in the n-6 group (71.9 (18.7) versus 47.4 (11.4) Periotron Units, median (inter quartile range)).

CONCLUSION

The topical application of n-6 or n-6 fatty acids failed to inhibit the development of experimental gingivitis. Rinsing with n-6 fatty acids could reduce the level of GCF in established experimental gingivitis.

Total fat and (n-3):(n-6) fat ratios influence eicosanoid production in mice

Previous studies have not addressed the effect of differing fat intake on the effectiveness of varying (n-3) polyunsaturated fatty acid (PUFA) ingestion in altering tissue composition and eicosanoid production. This study examined (n-3):(n-6) PUFA ratios of 0, 0.1:1, 0.2:1, 0.4:1, and 1:1 with total fat at 5, 10, 15, and 20 g/100 g of diet and (n-6) PUFA fixed at 1.5 g/100 g of diet on tissue composition and peritoneal cell eicosanoid response to an in vivo inflammatory stimulus in 240 mice. Both (n-3) PUFA and total fat intake influenced tissue composition and eicosanoid biosynthesis. Increased (n-3) PUFA intake was associated with an increase in tissue (n-3) PUFA and a decrease in long-chain (n-6) PUFA. Although hepatic tissue linoleic acid (LA) was not altered by (n-3) PUFA intake or changes in total fat, peritoneal cell LA increased in response to increasing total fat but was unaffected by changes in dietary (n-3) PUFA. Four-series leukotrienes (LT) decreased progressively with increased (n-3) PUFA at all fat intake levels. In addition, four-series LT decreased with increased total fat at low (n-3):(n-6) ratios (0 and 0.1). At high (n-3):(n-6) ratios (0.4 and 1.0) increasing dietary fat between the 5 and 15 g/100 g diets increased four-series LT synthesis, which reached a plateau between 15 and 20 g fat/100 g diets. Five-series LT production generally rose with increased (n-3) PUFA intake; this effect was most evident in mice fed the 5 g fat/100 g diet. Increasing total dietary fat at the three highest (n-3):(n-6) ratios (0.2, 0.4, 1.0) decreased five-series LT production. Elevated (n-3) PUFA and total fat intake exerted an additive effect with respect to prostacyclin (PGI(2)) production because it was reduced with increasing intakes of both. Compared with the mice consuming the no (n-3) 5 g/100 g diets, PGI(2) levels were reduced by 88% in mice consuming the highest total fat and (n-3) PUFA diets. At low fat intake (5 and 10 g/100 g diet), increasing the (n-3) PUFA intake was associated with a decrease in PGE(2) synthesis. However, unlike PGI(2), high fat intake reduced PGE(2) to basal levels with no further reduction induced by increased (n-3) PUFA intake.

N-3 polyunsaturated fatty acids and immune cell function

The amount and type of eicosanoids made can be affected by the type of fat consumed in the diet. It is now apparent that both eicosanoids and n-3 PUFAs are potent modulators of lymphocyte and M phi functions in vitro. Inclusion in the diet of high levels of certain lipids containing n-3 PUFAs markedly affects the functions of cells of the immune system subsequently tested in vitro. Cellular components of both natural and acquired immunity are affected. In vivo tests are perhaps the most appropriate approach for determining the effect of different dietary n-3 PUFAs upon immune function. Several studies indicate that diets rich in n-3 PUFAs are anti-inflammatory and immunosuppressive in vivo, although there have been relatively few studies in man. Although some of the effects of n-3 PUFAs may be brought about by modulation of the amount and types of eicosanoids made, it is clear that these fatty acids can also elicit their effects by eicosanoid-independent mechanisms (Fig. 12). Such n-3 PUFA-induced effects may be of use as a therapy for acute and chronic inflammation, for disorders which involve an inappropriately-activated immune response and for the enhancement of graft survival.

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.

The metabolic distinctiveness of emulsified lipid particles in the bloodstream and its clinical implications

The advantages of administering intravenous fat emulsions are well known. Primarily, they are important sources of essential fatty acids; they allow the administration of many calories within a small volume; and they are isotonic compared to body fluid. In this review, the metabolic distinctiveness of parenterally infused fat particles in the bloodstream is evaluated under four main headings: (1) the structure and metabolism of fat emulsion particles; (2) the metabolism of phospholipid-rich fat emulsion; (3) the interactions between fat emulsion particles and plasma lipoproteins; and (4) the acquisition of protein moieties (apolipoproteins) by fat emulsion particles and its clinical implications.

Role of capsaicin, curcumin and dietary n-3 fatty acids in lowering the generation of reactive oxygen species in rat peritoneal macrophages

Reactive oxygen species (ROS) generated by activated macrophages play an important role in the initiation of inflammation. Ten different spice principles, some of which with known anti-inflammatory properties, were tested for their effect on generation of superoxide anions, hydrogen peroxide and nitrite radical generation by activated rat peritoneal macrophages. Preincubation of macrophages with 10 microM capsaicin (from red pepper) or 10 microM curcumin (from turmeric) completely inhibited the superoxide anions, hydrogen peroxide and nitrite radical production in vitro by macrophages. Higher concentrations (500 microM) of eugenol (from clove) and piperine (from pepper) were required to completely inhibit superoxide anion and hydrogen peroxide release by macrophages. Capsaicin and curcumin were then fed to rats which were on a diet containing 8 wt% of coconut oil or olive oil or peanut oil or cod liver oil for 8 weeks, by gavage for 2 weeks. The peritoneal macrophages isolated from these animals produced lower levels of ROS compared to the macrophages from the control groups fed with the oil alone. Macrophages from cod liver oil fed animals generated lower levels of superoxide anions (76%), hydrogen peroxide (70%) and nitrite radicals (88%) compared to those isolated from coconut oil fed animals. Peanut oil and olive oil feeding also lowered the extent of ROS generation in macrophages compared to those from coconut oil fed animals. Capsaicin and curcumin feeding further lowered the generation and release of ROS. It is concluded that capsaicin or curcumin in combination with dietary fatty acids differentially lowers the production of ROS in macrophages.

Effect of dietary linseed oil on tumoricidal activity and eicosanoid production in murine macrophages

Diets that contain high levels of n-3 fatty acids from fish oil have been shown to significantly effect macrophage cytolytic capacity, tumor necrosis factor alpha production and eicosanoid production. The present study was undertaken to determine whether n-3 fatty acids from vegetable origin [linseed oil (LIN)] would have the same effects on murine macrophage tumoricidal capacity and eicosanoid production as would fish oil. Mice were fed for three weeks diets that contained 10% (wt/wt) of either LIN, which is high in linolenic acid (18:3n-3), menhaden fish oil (MFO), which is high in eicosapentaenoic (20:5n-3) and docosahexaenoic (22:6n-3) acids, or safflower oil (SAF), which is high in linoleic acid (18:2n-6). In vivo- or in vitro-activated macrophages were assessed for select functions. As expected, macrophages from mice fed LIN and MFO produced significantly lower levels of both prostaglandins and leukotriene C4 when compared with macrophages from mice fed SAF. In addition, LIN and MFO macrophages were able to synthesize leuko-triene C5, which could not be produced by macrophages from mice fed SAF. The effects of LIN, however, were not as pronounced as those of MFO. With respect to specific functions, macrophages from mice fed LIN did not have altered cytolytic capacity when compared with macrophages from mice fed SAF and activated in vitro with either lipopolysaccharide (LPS) alone for 24 h or with LPS plus interferon gamma (IFN gamma) for 5 h. Diet did not significantly alter tumoricidal capacity of macrophages activated completely in vivo either.(ABSTRACT TRUNCATED AT 250 WORDS)

Acyl-chain selectivity of the 85 kDa phospholipase A2 and of the release process in intact macrophages

The selectivity of the intracellular 85 kDa phospholipase A2 (PLA2-85) towards fatty acids closely related to arachidonic acid has been investigated, using purified PLA2-85 from J774 cells and mixed phospholipids, dually acyl-chain-labelled in the sn-2 position. In parallel experiments, we assessed the acyl-chain selectivity of the release process in intact, dually labelled, peritoneal mouse macrophages responding to either calcium ionophore or zymosan beads in the presence of indomethacin and BSA. The results obtained in the two systems were very similar, which supports previous evidence that PLA2-85 is responsible for stimulus-induced release of eicosanoid precursor in mouse macrophages. In the in vitro system, PLA2-85 was found to exhibit a moderate selectivity towards C20 acyl chains differing in double-bond structure, while the sensitivity to acyl-chain length was more pronounced. Together with previous data, these results demonstrate a striking preference for C20 over either C18 or C22 unsaturated acyl chains.

Influence of dietary (n-3)-polyunsaturated fatty acids on leukotriene B4 and prostaglandin E2 synthesis and course of experimental tuberculosis in guinea pigs

In the present study eicosanoid synthesis was studied in macrophages of guinea pigs fed different amounts of (n-6)- and (n-3)-polyunsaturated fatty acids (PUFA). Three groups of weanling guinea pigs were fed by isocaloric diets differing only in their contents of PUFA: controls with 2.8 Cal% of linoleic acid (LA; 18:2(n-6)); (n-6)-rich fed animals with 15.4 Cal% of LA; and (n-3)-rich fed animals with 10.1 Cal% of LA, 1.4 Cal% of eicosapentaenoic acid (20:5(n-3)) and docosahexaenoic acid (22:6(n-3)). After 13 weeks half the number of animals from each group was infected i.m. by 180 colony forming units of Mycobacterium tuberculosis strain H37Rv. Seven weeks after infection the release of leukotriene (LT)B4 and prostaglandin (PG)E2 was quantified in calcium ionophore stimulated whole blood, peritoneal macrophage cultures and alveolar macrophages by immunoassays after high performance liquid chromatography. Synthesis of LTB4 and PGE2 was found to be reduced in (n-3)-rich fed guinea pigs (p < 0.05), and equivalent between controls and (n-6)-rich fed animals. Controls and (n-6)-rich fed animals showed the same mycobacterial counts in the spleen whereas (n-3)-rich fed guinea pigs demonstrated an increased number of mycobacteria (p < 0.05). Our results demonstrate that an increased dietary intake of (n-3)-PUFA suppress LTB4 and PGE2 synthesis. The increased number of M. tuberculosis found in the spleens of (n-3)-rich fed animals could represent persistence of the experimental infection. It may be speculated that a functional relationship exists between the two findings.

A possible mechanism by which dietary fat can alter tumorigenesis: lipid modulation of macrophages function

It has been known for at least 20 years that fatty acids can alter immune functions in vitro. More recently we have begun to understand the role that dietary fats play in immunity [formula: see text] and specifically how they may alter macrophage function. In the future it will be important not simply to redefine that fatty acids can alter select macrophage functions but to understand the mechanisms by which that occurs. Whether the same or different mechanisms are operational for those functions that are altered by dietary fat remains to be determined. Nevertheless, tumoricidal responses can be modified depending on the fatty acids in the diet. Hopefully, these recent observations will expand our understanding of how lipids regulate macrophage tumoricidal function and thus, might lead to new insights of how dietary fat may be manipulated to affect breast tumor regression.

Intravenous infusion of tridocosahexaenoyl-glycerol emulsion into rabbits. Effects on leukotriene B4/5 production and fatty acid composition of plasma and leukocytes

Leukotriene (LT) B4 is a major chemical activator of PMN. Inhibitory effects of oral administration of docosahexaenoic acid (DHA) on LTB4 synthesis by PMN are known. We intravenously infused tridocosahexaenoyl-glycerol (DHA-TG) emulsion into rabbits in three different doses, namely 0.8, 0.4, or 0.2 g DHA/kg, and investigated the changes in LTB4/5 production by ionophore-activated PMN. The averaged LTB4 production by PMN was significantly reduced to 57 and 59% of baseline at 6 h after the infusion of 0.8 and 0.4 g DHA/kg, respectively (P < 0.05), but not after the infusion of 0.2 g DHA/kg or 0.8 g soybean oil/kg. The combined concentrations of both DHA and eicosapentaenoic acid in the PMN phospholipid fraction were significantly increased at 6 h after the infusion of 0.8 or 0.4 g DHA/kg but not after the infusion of 0.2 g DHA/kg or 0.8 g soybean oil/kg. Oral administration of 0.8 g DHA/kg did not increase DHA or eicosapentaenoic acid in the PMN phospholipid fraction and did not decrease LTB4 production by PMN at 6 h after administration. We suggest that the infusion of 0.4-0.8 g DHA/kg might be beneficial to patients who suffer from diseases that are related to the acute elevation of LTB4 production.

Inhibition of the thermogenic and pyrogenic responses to interleukin-1 beta in the rat by dietary N-3 fatty acid supplementation

The thermogenic (increase in oxygen consumption, VO2) and pyrogenic (Tc) responses to the cytokine interleukin-1 beta (IL-1 beta) were studied in rats fed a n-3 fatty acid supplemented diet (8.75% n-3 fatty acids/kg diet). 4-6 weeks after commencing the diets, the n-3 supplemented rats exhibited reduced pyrogenic (0.5 +/- 0.1 degrees C versus 1.1 +/- 0.2 degrees C in control animals) and thermogenic (9 +/- 3% versus 22 +/- 6% in control animals) responses to intraperitoneal (i.p.) injection of IL-1 beta (1 micrograms/rat). However, responses to centrally administered IL-1 beta (5ng intracerebroventricular (i.c.v.)) were similar in both groups at this time. After 8-9 weeks of supplementation, n-3 supplemented animals exhibited attenuated responses to both ip IL-1 beta (VO2 responses reduced by 68% and Tc by 0.8 degrees C) and also i.c.v. IL-1 beta (VO2 responses reduced by 56% and Tc by 0.7 degrees C). N-3 supplementation did not, however, influence the thermogenic capacity of these animals since responses to noradrenaline were similar in control and n-3 fed animals (50% increase in VO2). These findings demonstrate that n-3 supplementation modifies the pyrogenic and thermogenic responses to IL-1 beta, probably via changes in eicosanoid metabolism. Modification of central responses to IL-1 are delayed compared to the effects of peripheral administration indicating separate mechanisms of IL-1 on fever and thermogenesis in the brain and the periphery.

Stearidonic acid, an inhibitor of the 5-lipoxygenase pathway. A comparison with timnodonic and dihomogammalinolenic acid

Leukotrienes have been shown to play an important role as mediators in various disease processes, including asthma and inflammation; thus, their synthesis is tightly regulated. The major precursor of leukotrienes is arachidonic acid (20:4n-6). Fatty acids which are structurally similar to 20:4n-6, such as eicosatrienoic acid (20:3n-6; dihomogammalinolenic acid) and eicosapentaenoic acid (20:5n-3; timnodonic acid) have been found to inhibit leukotriene biosynthesis. Because of the structural similarity of octadecatetraenoic acid (18:4n-3; stearidonic acid) with 20:4n-6, the present study was undertaken to determine whether stearidonic acid also exerts an inhibitory effect on the 5-lipoxygenase pathway. Human leukocytes were incubated with 18:4n-3 (20 microM or 10 microM), 20:5n-3 (20 microM) or 20:3n-6 (20 microM) and subsequently stimulated with 1 microM ionophore A23187 and 20:4n-6 (20 microM or 10 microM). The 5-lipoxygenase products were then measured by high-performance liquid chromatography. Leukotriene synthesis was reduced by 50% with 20 microM 18:4n-3 and by 35% with 10 microM 18:4n-3. Formation of 5S,12S-di-hydroxy-eicosatetraenoic acid and of 5-hydroxy-eicosatetraenoic acid was decreased by 25% with 20 microM 18:4n-3 and by 3% with 10 microM 18:4n-3. The inhibition observed with 20 microM 18:4n-3 appeared to be of the same order as that observed with 20 microM 20:5n-3; the inhibition observed with 18:4n-3 was shown to be dose-dependent. The inhibition produced by 20 microM 20:3n-6 was greater than that observed with either 20 microM 18:4n-3 or with 20 microM 20:5n-3.(ABSTRACT TRUNCATED AT 250 WORDS)

Dietary N-3 fatty acids inhibit ischaemic and excitotoxic brain damage in the rat

Arachidonic acid [20:4(N-6)] has been implicated in neurological damage induced by cerebral ischaemia. Membrane arachidonate concentrations can be reduced by changes in dietary fat intake. Therefore, in the present study, we have investigated the effects of N-3 fatty acid supplementation on neuronal damage induced by permanent focal cerebral ischaemia or pharmacological activation of striatal NMDA receptors. Weanling rats were fed either a control diet or an N-3 supplemented diet (1.75% by weight as N-3 fatty acids) for 6 weeks. N-3-supplemented animals reduced ischaemic damage following middle cerebral artery occlusion (36%, p < 0.05), and excitotoxic damage induced by infusion of the selective NMDA agonist (1-aminocyclobutane-cis-1,3-dicarboxylic acid, 43%, p < 0.001) compared to the control-fed group. These data are consistent with the proposed role of arachidonic acid in ischaemic and excitotoxic brain damage, and suggest that modest dietary supplementation with N-3 fatty acids may offer benefit to populations at high risk of stroke.

Tumor necrosis factor production by murine resident peritoneal macrophages is enhanced by dietary n-3 polyunsaturated fatty acids

Tumor necrosis factor (TNF) is a macrophage derived peptide that has an antitumor action and modulates immune and inflammatory reactions. Dietary fatty acids may modulate TNF production as dietary n-3 polyunsaturated fatty acids suppress human monocyte TNF production, but enhance its secretion by murine peritoneal macrophages. Mice were maintained for 5 weeks on diets containing different amounts of n-3 and n-6 fatty acids. TNF, PGE2 and 6-keto PGF1 alpha production was monitored following in vitro stimulation of resident peritoneal macrophages with lipopolysaccharide. Macrophages from mice fed the high n-3 diet produced 8-fold more TNF and half the PGE2 produced by macrophages from mice on the other diets. Indomethacin caused an increase in the TNF production by macrophages from mice on all diets but macrophages from mice on the high n-3 diet produced more TNF than macrophages from mice on the other diets. Exogenous PGE2 (100 nM) greatly decreased TNF production by macrophages from mice on all diets, but macrophages from mice on the high n-3 diet secreted 70% more TNF than macrophages from mice fed the other diets, indicating that PGE2 is only partly responsible for the effects observed. The results show that feeding n-3 polyunsaturated fatty acids may cause enhanced TNF production by resident peritoneal macrophages and that PGE2 is partly responsible for the effect.

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.

In vivo formation of leukotriene E5 by murine peritoneal cells

Resident mouse peritoneal cells, stimulated in vivo with opsonized zymosan, produced leukotriene C4 and E4, with LTE4 being the major (80-90%) product. When mice were placed on diets containing increasing amounts of fish oil, four additional sulfidopeptide leukotrienes (SP-LT), LTC5, LTE5, 11-trans LTC5 and 11-trans LTE5, were identified. The identity of LTE5 was confirmed by spectrophotometric, chromatographic and enzymatic methods. When equivalent amounts of n-6 and n-3 polyunsaturated fatty acids (PUFA) were included in the diet, the stimulated peritoneal cells (in vivo) produced higher quantities of LTE5 (30.2 +/- 5.4 ng/10(6) cells) than LTE4 (22.8 +/- 7.3 ng/10(6) cells). In addition, in vitro studies demonstrated a 60% reduction in LTC4 (42.0 +/- 10.8 ng/10(6) cells to 16.7 +/- 6.2 ng/10(6) cells) and the appearance of LTC5 (2.1 +/- 0.9 ng/10(6) cells) in resident macrophages (stimulated with A23187) from mice maintained on a fish oil diet compared to mice fed the control diet. This study demonstrated that formation of the pentaenyl SP-LT in vivo, in particular LTE5, by peritoneal cells can significantly contribute to the endogenous SP-LT pool in response to an inflammatory stimulus following a dietary regimen containing fish oil.

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.

5-series peptido-leukotriene synthesis in mouse peritoneal macrophages: modulation by dietary n-3 fatty acids

This study was undertaken to elucidate the metabolic fate of dietary eicosapentaenoic acid (20:5n-3), a major n-3 polyunsaturated fatty acid constituent of fish oil, in the mouse peritoneal macrophage. Mice were fed diets containing menhaden fish oil (FO) or safflower oil (SO). After 3 weeks, resident or responsive peritoneal macrophages were isolated and stimulated with zymosan and A23187, respectively. We demonstrate the novel synthesis of leukotriene C5 (LTC5), derived from 20:5n-3, in addition to LTC4 in both resident and responsive macrophages from FO fed mice. The structures of these peptido-leukotrienes were characterized by their retention times on reverse phase high pressure liquid chromatography, by their u.v. absorbance spectra, and by cross-reactivity with peptido-leukotriene antibody. These results demonstrate for the first time that macrophages are capable of metabolizing dietary 20:5n-3 to LTC5, a pentaene peptido-leukotriene.

Lipids, membrane receptors, and enzymes: effects of dietary fatty acids

Dietary polyunsaturated fatty acids can significantly affect many biochemical and physiologic functions that are related to inflammatory, immune, and protective reactions. The different types of fatty acids can impact on energy metabolism, determine the lipid composition of membranes, and influence eicosanoid synthesis, all of which are relevant to prevention of and recovery from illness. In this paper, the effects of dietary polyunsaturated fatty acids on membrane composition, membrane-associated enzyme and receptor functions, signal transduction, second messenger, and eicosanoid generation are summarized. The differential effects of the polyunsaturated fatty acids of the n-6 and n-3 families are reviewed in the context of optimizing levels in diets.

The suppression of eicosanoid synthesis by peritoneal macrophages is influenced by the ratio of dietary docosahexaenoic acid to linoleic acid

The efficacy of docosahexaenoic acid (DHA) in suppressing eicosanoid synthesis by peritoneal macrophages in vivo was influenced by the relative amount of dietary DHA when linoleic acid (LA) was held constant. Increasing DHA from 0 to 37% of the fatty acids in diets containing 10 weight % fat (of which LA was 40%) caused an eleven-fold increase in the DHA content of macrophages. Limited retroconversion of DHA to eicosapentaenoic acid was observed. Macrophages in animals consuming DHA synthesized significantly lower amounts of leukotriene E4, prostaglandin E2 and 6-keto prostaglandin F1 alpha in vivo upon stimulation with zymosan. The maximum inhibition of eicosanoid synthesis was observed when the dietary DHA/LA ratio was 0.16 and no further inhibition occurred when the ratio was increased up to 0.81.

Studies on the accumulation of serum proteins in zymosan-induced inflammation in mouse peritoneum

Inflammatory responses were induced in mice by intraperitoneal (i.p.) injection of zymosan. This resulted in a rapid accumulation of protein in the peritoneum that was dependent on the time of the injection and concentration of zymosan used. Though other stimuli, e.g., phorbol myristate acetate, lipopolysaccharide, carrageenan and latex beads, caused the accumulation of proteins, the maximum response was obtained only with zymosan. Injection of free fatty acids were unable to induce protein accumulation in peritoneum. Factors which decreased leukotriene production in mouse peritoneum, i.e., dietary n-3 fatty acids essential fatty acid deficient diets, did not affect protein accumulation. Direct injection of leukotrienes also failed to induce protein accumulation. Analyses revealed that the proteins were similar to serum proteins, indicating that zymosan causes the leakage of serum proteins into peritoneum.