Uptake and incorporation of saturated and unsaturated fatty acids into macrophage lipids and their effect upon macrophage adhesion and phagocytosis

Modulatory effects of dietary lipids on immune system functions

Dietary lipid manipulation may affect a great number of immune parameters, such as lymphocyte proliferation, cytokine synthesis, natural killer (NK) cell activity, phagocytosis and so on. The immunomodulation induced by dietary fatty acids may be applied in the amelioration of inflammatory disorders, such as autoimmune diseases. However, the mechanisms that participate in these processes are still poorly understood. It is probable that modulation of immune system by fatty acids of the diet may occur by alteration of membrane fluidity, lipid peroxide formation, eicosanoid production or regulation of gene expression. However, recent studies have reported the effects of several free fatty acids on apoptosis induction of in vitro cultures. In fact, a possible explanation of the effects that fatty acids promote on the immune system cells could be associated with an apoptotic process performed in an irreversible way. In vivo studies have demonstrated the ability of fatty acids to alter the survival of animals fed diets containing oils and infected with a pathogenic bacterium. Experimental infection in animals fed dietary lipids produces a modification of resistance to micro-organisms. The present review analyses all of these parameters that dietary fatty acids are capable of altering in order to modify the immune response. Further studies will be needed to establish the mechanisms involved in immune system regulation, reduction of symptoms derived from autoimmune pathologies and so on.

Determination of natural resistance of mice fed dietary lipids to experimental infection induced by Listeria monocytogenes

Current understanding based on the effect of dietary lipid manipulation upon immune system function indicates that fatty acids are involved in the modulation of the immune response through different and complex pathways. Reduction of several immune parameters by fatty acid action may be applied in the treatment of diseases characterised by an overactivation of the immune system. As a consequence, a reduction of host resistance against infectious agents has been reported in animals fed dietary lipids. The present study confirms the action of dietary lipids on the survival of mice infected with the pathogenic bacterium Listeria monocytogenes. A significant increase in peritoneal cells from mice fed a hydrogenated coconut oil diet was found, while a significant reduction of bacterial recovery from spleens of these mice was observed in this group. In addition, both eicosanoid and phospholipase inhibitors did not promote any modification of lymphocyte proliferation from mice fed olive oil or fish oil.

Giardia lamblia: incorporation of free and conjugated fatty acids into glycerol-based phospholipids

Giardia lamblia trophozoites are flagellated protozoa that inhabit the human small intestine, where they are exposed to various dietary lipids and fatty acids. It is believed that G. lamblia, which colonizes a lipid-rich environment of the human small intestine, is unable to synthesize phospholipids, long-chain fatty acids, and sterols de novo. Therefore, it is possible that this protozoan has developed a special process for acquiring lipids from its host. We have previously shown that G. lamblia can take up saturated fatty acids and incorporate them into phosphatidylglycerol (PG) and other glycerol-based phospholipids (Stevens et al., Experimental Parasitology, 86, 133-143, 1997). In the present study, an attempt has been made to investigate the underlying mechanisms of transesterification and interesterification reactions of giardial phospholipids by free and conjugated fatty acids. Results show that exogenously supplied, unsaturated, fatty acids were taken up by Giardia and incorporated into various phosphoglycerides, including PG. To test whether this intestinal pathogen can utilize conjugated fatty acids, live trophozoites were exposed to either [3]H;cbphosphatidylcholine (PC), where the fatty acid was 3H-labeled at its sn2 position, or to [14C]lyso-PC (fatty acid was 14C-labeled at the sn1 position) for 90 min, followed by phospholipid analysis using thin-layer chromatography. The results suggest that conjugated fatty acids, like free fatty acids, were incorporated into PG. It was also observed that aristolochic acid, an inhibitor of Ca2+-ionophore-stimulated phospholipase A2, decreased the transfer of fatty acids from [3H]PC to PG, indicating that giardial phospholipases were involved in these esterification reactions. Additional experiments, which include culturing trophozoites in serum-supplemented and serum-deprived medium, along with numerous biochemical analyses suggest that (i) PG is a major transesterified and interesterified product, (ii) it is likely that giardial phospholipases are involved in esterification reactions, (iii) in G. lamblia, PG is localized in perinuclear membranes, as well as intracellularly, but not in the plasma membrane, and (iv) various synthetic analogs of PG inhibit the growth of the parasite in vitro. These studies suggest that PG is an important phospholipid of Giardia and a potential target for lipid-based chemotherapy against giardiasis.

The effect of dietary lipid manipulation on murine splenic lymphocytes apoptosis and heat shock protein over expression

In this study, we kept BALB/c mice on a hyperlipidic diet for 120 days and then assessed the predisposition to apoptosis and the appearance of heat shock protein (Hsp) on splenic lymphocytes. By immunoblot analysis, bands corresponding to Hsp 60 and Hsp 70 in cells from mice kept on a saturated fatty acid diet showed a greater expression already after 1 month while two other bands, which correspond to Hsp 25 and Hsp 27, were slightly present after 1 month of treatment. In cells from mice kept on a diet rich in unsaturated fatty acid, there was a marked expression of Hsp 25 and Hsp 27 after only 30 days of treatment, which was maintained constant for up to 4 months; while for bands corresponding to Hsp 60 and Hsp 70, a significant minor signal was only detectable after 2-4 months from the beginning of the treatment. Splenic lymphocytes from animals kept on a lipidic diet containing saturated fatty acids were more susceptible to death by apoptosis, while cells of animals treated with unsaturated fatty acid were shown to be more resistant.

Effect of tetracosahexaenoic acid on the content and release of histamine, and eicosanoid production in MC/9 mouse mast cell

6,9,12,15,18,21-Tetracosahexaenoic acid (24:6n-3) was isolated from a brittle star, Ophiura sarsi Lütken, at >95% purity to evaluate its physiological functions. The effects of 24:6n-3 on the production of leukotriene (LT)-related compounds such as LTB4, LTC4 and 5-hydroxyeicosatetraenoic acid, and the accumulation and release of histamine in an MC/9 mouse mast cell line were studied. We found that 24:6n-3 could inhibit the antigen-stimulated production of LT-related compounds as well as other n-3 polyunsaturated fatty acids (PUFA) such as eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3), which are major n-3 PUFA in fish oils; 24:6n-3 was also shown to reduce the histamine content in MC/9 cells at 25 microM (27% reduction from the control), and the effect was diminished with increase of the fatty acid concentration (up to 100 microM). These two n-3 PUFA, 20:5n-3 and 22:6n-3, also reduced the histamine content (16 and 20% reduction at 25 microM, respectively), whereas arachidonic acid (20:4n-6) increased it (18% increase at 25 microM). Spontaneous- and antigen-induced release of histamine was not influenced with these PUFA (at 25 microM). Ionophore-stimulated release of histamine was suppressed by the PUFA (13, 9, 15, and 11% reduction with 20:4n-6, 20:5n-3, 22:6n-3, and 24:6n-3, respectively). The patterns of the effects of 24:6n-3 on the synthesis of eicosanoids and histamine content were more similar to those of 22:6n-3 than 20:5n-3. From these results, 24:6n-3 can be expected to have anti-inflammatory activity and antiallergic activities similar to those of 22:6n-3.

Macrophage populations of different origins have distinct susceptibilities to lipid peroxidation induced by beta-haematin (malaria pigment)

We investigated the susceptibility of peritoneal mouse macrophages and macrophage and microglia cell lines to the peroxidative activity of beta-haematin, the synthetic polymer identical to native malaria pigment. The extent of lipid peroxidation, measured as production of thiobarbituric acid reactive substances (TBARS), was greater for peritoneal macrophages than for cell lines and microglia cells. TBARS production apparently was not attributable to the release of free iron from the protoporphyrin moiety, but related to lower glutathione content and different lipid composition of the cell membrane. These findings offer a new interpretation for the contentious immunomodulatory effects of beta-haematin reported for phagocytes of different origins.

Effect of dietary energy level and oil source on broiler performance and response to an inflammatory challenge

Broiler chicks were fed one of five diets from 3 d of age: a low energy diet containing 7% cellulose (ME 2,714 kcal/kg), or high energy diets containing approximately 7% of either tallow, corn oil, safflower oil, or fish oil (each 3,302 kcal/kg). Half of the chicks were injected intra-abdominally with Salmonella typhimurium lipopolysaccharide (LPS) on Day 11, sephadex on Day 13, and Freund's complete adjuvant on Day 15; samples were collected on Day 16. The uninjected chicks served as controls. In a second experiment, 3-d-old chicks were fed one of eight isocaloric diets containing tallow as the sole supplemental fat source, or tallow plus either 2% corn oil, 1, 1.5, or 2% fish oil, or fish meal at an amount to provide 1, 1.5 or 2% supplemental oil. Half of the chicks were injected intra-abdominally with S. typhimurium LPS on Days 10, 12 and 14; the uninjected chicks served as controls. Samples were taken on Day 15. In Experiment 1, the cellulose diet decreased performance to 10 d of age relative to the other diets, whereas immunogen injection decreased weight gain and feed efficiency and increased indices of inflammation among all dietary groups. Fish oil at approximately 7% of the diet did not improve weight gain. Fish oil diets improved weight gain and feed efficiency in Experiment 2 relative to the other diets, in spite of minimal effects on indices of inflammation. Injection of LPS decreased performance and increased inflammation across dietary treatment, although the second LPS injection was less potent in altering performance responses and inflammation compared to the first injection, indicating that repeated injections of LPS amy cause the chicks to become refractory to that stimulus. The fish meal diets resulted in poorer performance than similar levels of lipid provided as fish oil. Lower levels of dietary fish oil were more efficacious in improving broiler performance than higher levels, and fish oil provided from fish meal was not as efficacious as oil per se, possibly due to nonlipid components of the meal.

Dietary fish oil diminishes lymphocyte adhesion to macrophage and endothelial cell monolayers

To further investigate the immunomodulatory effects of dietary lipids, rats were fed on a low-fat diet or on high-fat diets that contained hydrogenated coconut, olive, safflower, evening primrose or fish oil as the principal fat source. The fish oil diet decreased the level of expression of CD2, CD11a, CD18 and CD44 on the surface of freshly prepared lymphocytes and of CD2, CD11a, CD18, CD54 (intercellular adhesion molecule-1; ICAM-1) and CD62L (L-selectin) on the surface of concanavalin A (Con A)-stimulated lymphocytes. The olive oil diet also resulted in decreased expression of some adhesion molecules. The fish or olive oil diets, and to a lesser extent the safflower or evening primrose oil diets, decreased the adhesion of both freshly prepared and Con A-stimulated lymphocytes to macrophage monolayers. The fish oil diet, and to a lesser extent the olive or evening primrose oil diets, reduced the ability of Con A-stimulated lymphocytes to adhere to untreated endothelial cells. Furthermore, the fish oil diet resulted in a 50% reduction in Con A-stimulated lymphocyte adhesion to tumour necrosis factor-alpha (TNF-alpha)-stimulated endothelial cells. This study demonstrates that dietary lipids affect the expression of functionally important adhesion molecules on the surface of lymphocytes. Furthermore, this study suggests that such diet-induced effects on adhesion molecule expression might alter the ability of lymphocytes to bind to macrophages and to endothelial cells. Of the diets studied fish oil causes the most significant effects. The results of this study suggest that a reduction in cellular infiltration may partly explain the protective effect of a fish-oil-rich diet against the development of inflammatory and cardiovascular diseases.

Dietary fatty acids influence the activity and metabolic control of mitochondrial carnitine palmitoyltransferase I in rat heart and skeletal muscle

The fatty acid composition of the diet has been found to influence the activity and sensitivity of mitochondrial carnitine palmitoyltransferase I (CPT I; EC 2.3.1.21) to inhibition by malonyl CoA in rat heart and skeletal muscle. The nutritional state of rats has been shown to have less influence on the activity and metabolic control of mitochondrial CPT I in heart and skeletal muscle tissue than in the liver, a tissue in which CPT I activity and sensitivity to inhibition by malonyl CoA can be shown to be regulated acutely under different nutritional conditions. However, because manipulation of the nutritional state in these previous studies was restricted mainly to examining the effect of starvation, this study was undertaken to determine whether, as in liver, the fatty acid content and composition of the diet can regulate the activity and metabolic control of CPT I in heart and skeletal muscle. Rats were fed for up to 10 wk either a nonpurified low fat diet (30 g fat/kg) or a high fat diet (200 g fat/kg) containing one of the following five oil types: hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO), evening primrose oil (EPO) or menhaden (fish) oil (MO). Feeding a diet enriched in MO had the most pronounced effect. Rats fed MO had a significantly greater skeletal muscle CPT I specific activity and tissue capacity, and a lower sensitivity of CPT I to malonyl CoA inhibition compared with rats fed a low fat diet, but the duration of feeding required to modulate this sensitivity was longer than that observed previously for the liver enzyme. Progressively greater sensitivity of heart CPT I to malonyl CoA occurred with feeding duration in all groups. These studies indicate that the fatty acid composition of the diet is involved in the regulation of mitochondrial CPT I activity in heart and skeletal muscle.

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.

Enhancement of neutrophil-mediated killing of Plasmodium falciparum asexual blood forms by fatty acids: importance of fatty acid structure

Effects of fatty acids on human neutrophil-mediated killing of Plasmodium falciparum asexual blood forms were investigated by using a quantitative radiometric assay. The results showed that the antiparasitic activity of neutrophils can be greatly increased (>threefold) by short-term treatment with fatty acids with 20 to 24 carbon atoms and at least three double bonds. In particular, the n-3 polyenoic fatty acids, eicosapentaenoic and docosahexaenoic acids, and the n-6 fatty acid, arachidonic acid, significantly enhanced neutrophil antiparasitic activity. This effect was >1.5-fold higher than that induced by an optical concentration of the known agonist cytokine tumor necrosis factor alpha (TNF-alpha). At suboptimal concentrations, the combination of arachidonic acid and TNF-alpha caused a synergistic increase in neutrophil-mediated parasite killing. The fatty acid-induced effect was independent of the availability of serum opsonins but dependent on the structure of the fatty acids. The length of the carbon chain, degree of unsaturation, and availability of a free carboxyl group were important determinants of fatty acid activity. The fatty acids which increased neutrophil-mediated killing primed the enhanced superoxide radical generation of neutrophils in response to P. falciparum as detected by chemiluminescence. Scavengers of oxygen radicals significantly reduced the fatty acid-enhanced parasite killing, but cyclooxygenase and lipoxygenase inhibitors had no effect. These findings have identified a new class of immunoenhancers that could be exploited to increase resistance against Plasmodium species.

Lead disrupts eicosanoid metabolism, macrophage function, and disease resistance in birds

Lead (Pb) affects elements of humoral and cell-mediated immunity, and diminishes host resistance to infectious disease. Evidence is presented supporting a hypothesis of Pb-induced immunosuppression stemming from altered fatty acid metabolism, and mediated by eicosanoids and macrophages (MO). Chronic Pb exposure increases the proportion of arachidonate (ArA) among fatty acids in lipid from avian tissues, and this change provides precursors for eicosanoids, the oxygenated derivatives of ArA that mediate MO acute inflammatory response. In the current study, we showed that the concentration of ArA in phospholipids of MO elicited from turkey poults fed 100 ppm dietary Pb acetate was twice that of controls. In vitro production of eicosanoids by these MO was substantially increased, and this effect was most pronounced following lipopolysaccharide stimulation: prostaglandin F2 alpha was increased 11-fold, thromboxane B2 increased threefold, and prostaglandin E2 increased by 1.5 times. In vitro phagocytic potential of these MO was suppressed, such that the percentage of MO engulfing sheep red blood cell (RBC) targets was reduced to half that of control MO. In vivo susceptibility of Pb-treated and control birds to Gram-negative bacteria challenge was also evaluated. The morbidity of chicks inoculated with Salmonella gallinarum and fed either control or 200 ppm Pb acetate-supplemented diets was similar, except early in the course of the disease when mortality among Pb-treated birds was marginally greater. In these studies, effects of Pb that could influence immunological homeostasis were demonstrated for MO metabolism of ArA, for production of eicosanoids, and for phagocytosis. There was also the suggestion that these in vitro indices of immune function are related to in vivo disease resistance.

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

The n-3 fatty acids (FA) from marine sources are known to exert antiinflammatory effects on monocyte function. There is still controversy whether n-3 FA may increase the susceptibility to infections. The present study was designed to assess the effect of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on monocyte phagocytosis and respiratory burst activity. Fifty-eight healthy men were randomized to take a daily supplement of 3.8 g highly purified EPA (n = 20), 3.6 g DHA (n = 19), or corn oil (n = 19) for 7 wk. Mononuclear leukocytes were collected, isolated, and cryopreserved prior to and after dietary supplementation. Paired samples were analyzed in the presence of autologous serum in a crossover design. Monocyte phagocytosis and respiratory burst activity were measured by flow cytometry after ingestion of Escherichia coli. Monocytes retained their phagocytic ability and respiratory burst activity after supplementation. No reduction in internalization of bacteria was registered. Dietary n-3 FA and particularly EPA improved bacterial adherence to the monocyte surface. In the crossover experiments, there was an adverse effect of serum enriched with n-3 FA on bacterial adherence. We conclude that monocytes retain their phagocytic potential after supplementation with purified EPA and DHA.

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.

Effect of conjugated linoleic acid on body composition in mice

The effects of conjugated linoleic acid (CLA) on body composition were investigated. ICR mice were fed a control diet containing 5.5% corn oil or a CLA-supplemented diet (5.0% corn oil plus 0.5% CLA). Mice fed CLA-supplemented diet exhibited 57% and 60% lower body fat and 5% and 14% increased lean body mass relative to controls (P < 0.05). Total carnitine palmitoyltransferase activity was increased by dietary CLA supplementation in both fat pad and skeletal muscle; the differences were significant for fat pad of fed mice and skeletal muscle of fasted mice. In cultured 3T3-L1 adipocytes CLA treatment (1 x 10(-4)M) significantly reduced heparin-releasable lipoprotein lipase activity (-66%) and the intracellular concentrations of triacylglyceride (-8%) and glycerol (-15%), but significantly increased free glycerol in the culture medium (+22%) compared to control (P < 0.05). The effects of CLA on body composition appear to be due in part to reduced fat deposition and increased lipolysis in adipocytes, possibly coupled with enhanced fatty acid oxidation in both muscle cells and adipocytes.

Fatty acid composition of lymphocytes and macrophages from rats fed fiber-rich diets: a comparison between oat bran- and wheat bran-enriched diets

The effect of oat bran- (OBD) and wheat bran-enriched diets (WBD) on fatty acid composition of neutral lipids and phospholipids of rat lymphocytes and macrophages was investigated. In neutral lipids of lymphocytes, OBD reduced the proportion of palmitoleic acid (48%), whereas WBD reduced by 43% palmitoleic acid and raised oleic (18%), linoleic (52%), and arachidonic (2.5-fold) acids. In neutral lipids of macrophages, OBD increased palmitic (16%) and linoleic (29%) acids and slightly decreased oleic acid (15%). The effect of WBD, however, was more pronounced: It reduced myristic (60%), stearic (24%) and arachidonic (63%) acids, and it raised palmitic (30%) and linoleic (2.3-fold) acids. Neither OBD nor WBD modified the composition of fatty acids in phospholipids of lymphocytes. In contrast, both diets had a marked effect on composition of fatty acids in macrophage phospholipids. OBD raised the proportion of myristic (42%) and linoleic (2.4-fold) acids and decreased that of lauric (31%), palmitoleic (43%), and arachidonic (29%) acids. WBD increased palmitic (18%) and stearic (23%) acids and lowered palmitoleic (35%) and arachidonic (78%) acids. Of both cells, macrophages were more responsive to the effect of the fiber-rich diets on fatty acid composition of phospholipids. The high turnover of fatty acids in macrophage membranes may explain the differences between both cells. The modifications observed due to the effects of both diets were similar in few cases: an increase in palmitic and linoleic acids of total neutral lipids occurred and a decrease in palmitoleic and arachidonic acids of phospholipid. Therefore, the mechanism involved in the effect of both diets might be different.

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.

Fatty acid unsaturation increases expression and capping of murine lymphocyte CD44 and CD45

We studied the effect of incubating murine lymphocytes with cis-unsaturated fatty acids on expression and capping of CD44 and CD45. Lymphocytes were incubated with stearic (18:0) or oleic (18:1 omega-9) acid bound to bovine serum albumin (BSA). After incubation with rat anti-CD44 or anti-CD45 monoclonal antibodies and then with fluorescent-labeled anti-rat antibody, mean fluorescence intensity (FI) was measured by using flow cytometry. Capping was measured after warning and fixation in paraformaldehyde. Steady-state fluorescence anisotropy (rs) was measured after the cells had been incubated with trimethylammoniumdiphenylhexatriene. Incubation with oleic acid, but not stearic acid or BSA alone, was associated with an increase in FI of CD44. Expression of CD45, however, was increased by both stearic and oleic acids to the same degree over BSA controls. CD44 and CD45 capping were both increased by incubation with oleic acid. Rs was decreased in cells incubated with oleic acid, suggesting an increase in membrane fluidity. We conclude that incubation with oleic acid increases expression of CD44 and increases capping of both CD44 and CD45. These findings were confirmed in feeding experiments, in which rs was reduced and CD44 capping increased by polyunsaturated fatty acid diets.

Omega-3 lipid infusion in a heart allotransplant model. Shift in fatty acid and lipid mediator profiles and prolongation of transplant survival

BACKGROUND

omega-3 Fatty acids may have a major impact on immune responses involved in heart transplant rejection. We compared the effects of posttransplant intravenous supplementation with omega-3-rich versus omega-6-rich lipid emulsions on graft survival, plasma fatty acid profiles, and levels of arachidonic acid versus eicosapentaenoic acid-derived lipid mediators.

METHODS AND RESULTS

Inbred PVG and Wistar-Kyoto rats were used as donors and recipients, respectively, in a model of heterotopic heart transplantation. Animals received 9 g/kg body wt per day of either fish oil-derived (n = 8) or soybean oil-derived fat (n = 7) in the form of a continuously infused lipid emulsion; controls were sham-infused with saline (n = 8). Graft rejection was assessed by loss of activity of the transplant. The fish oil-derived preparation but not that originating from soybean oil caused an increase in total and free plasma fatty acids. Substantial quantities of eicosapentaenoic acid and docosahexaenoic acid appeared in the free fatty acid fraction, surpassing those of arachidonic acid. Ex vivo stimulation of neutrophils with the Ca2+ ionophore A23187 demonstrated an increase in 5-series leukotriene (LT) generation in animals undergoing omega-3 lipid infusion (LTB5, omega-oxidation products of LTB5, LTA5 secretion), with 5-series/4-series LT ratios ranging between 0.08 and 0.36. Ratios of TX B3/B2 liberated from ex vivo stimulated platelets even approached 1:1 in omega-3 supplemented rats. Graft survival was 7.6 +/- 0.3 (mean +/- SEM) days in saline-infused, 10.4 +/- 0.7 in omega-6 lipid-infused, and 12.9 +/- 0.4 in omega-3 lipid-infused animals.

CONCLUSIONS

Posttransplant intravenous alimentation with fish oil-derived lipid emulsions prolongs heart transplant survival in excess to omega-6 lipids. Profound changes in fatty acid profiles and lipid mediator generation may underlie this finding.

Polyunsaturated fatty acid enrichment increases ultraviolet A-induced lipid peroxidation in NCTC 2544 human keratinocytes

The influence of cell enrichment with fatty acids with increasing degree of unsaturation on the ultraviolet A-induced formation of lipid-peroxidation products (thiobarbituric acid reactive substances [TBARS]) has been investigated in NCTC 2544 human keratinocytes. A 48-h preculture of cells in controlled medium supplemented with unsaturated fatty acids resulted in a marked increase in TBARS appearance under ultraviolet A exposure. This effect was dependent upon the degree of unsaturation of the fatty acids, with the following order of efficiency: arachidonic > linolenic > linoleic > oleic acid. For arachidonic acid (AA), the potentiating effect on ultraviolet A-induced lipid peroxidation was dependent upon the fatty acid concentration, with about a 2.5-fold increase in TBARS formation in cells pre-cultured with 5 x 10(-5) M AA, then exposed to a UVA dose of 13 J/cm2. The increase in TBARS formation by AA was almost totally prevented by supplementation of cells with 5 x 10(-5) M vitamin E, whereas buthionine sulfoximine, a chemical which depletes cell glutathione, potentiated lipid peroxidation. These results suggest that the nature of the fatty acids of cellular lipids could influence the response of keratinocytes to ultraviolet A, and especially the ultraviolet A-induced lipid peroxidation.

Immunoactivating potential of multilamellar liposome vesicles (MLV) in murine popliteal lymph node (PLN) test

Immunoactivating properties of subcutaneously injected small unilamellar vesicles (SUV) and multilamellar liposome vesicles (MLV) were studied in relation to different transition temperatures (Tc) of phospholipids. Liposome-induced proliferative reaction in the popliteal lymph node (PLN) was quantified by subsequent cytometric assay. Early cell activation during the onset of PLN reaction was monitored by immunophenotyping of lymphocyte subsets stained with a panel of monoclonal antibodies (mAbs) and gating the subset-specific large/activated cells. Injection of MLV liposomes containing distearoyl phosphatidylcholine (DSPC) and dipalmityl phosphatidylcholine (DPPC), characterized by relatively high Tc, resulted in a marked PLN reaction, increased numbers of CD4+, CD8+, Ig+ subsets and increased proportions of large/activated EAM+ (CD69+) and CD25+ (IL-2 receptor+) cells. The reaction was dose and time dependent. In contrast, injection of MLV liposomes containing lipids of low Tc, such as egg phosphatidylcholine (egg PC) and dimyristoyl phosphatidylcholine (DMPC), did not show any immunoactivation. In addition, there was a highly reduced immunoactivating potential of small-size SUV liposomes over large-sized MLV of identical phospholipid composition. Generally, both lipid composition and vesicle size appeared to be essential for the immunoactivating potential of liposomes. The data suggest a possible correlation between the Tc of the phospholipid and the immunoactivating potential of the large-sized MLV liposomes.

Influence of cell culture conditions on diet-induced changes in lymphocyte fatty acid composition

The effect of a range of dietary lipids on the fatty acid composition and membrane fluidity of lymphocytes was investigated. The effects of subsequent culture of these lymphocytes in medium containing autologous serum, foetal calf serum or a serum-free supplement were assessed; this was considered important, since many studies investigating the effects of dietary lipid manipulation on immune function have used protocols involving a variety of cell culture conditions when performing tests of immune function. Weanling Lewis rats were fed for 10 weeks on a low-fat (LF; 20 g/kg) diet or on high fat diets containing 200 g/kg of either hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO), evening primrose oil (EPO) or menhaden oil (MO). The fatty acid composition of the phospholipid fractions of lymphocytes from the spleen was altered by dietary lipid manipulation, whereas the fatty acid composition of thymic lymphocytes was not modified significantly. In general, the changes in the fatty acid composition of spleen lymphocytes reflected the fatty acid composition of the diets themselves. Despite the considerable changes in the fatty acid composition of lymphocytes from spleen, dietary lipid manipulation had no effect on the plasma membrane fluidity of these cells. Culturing lymphocytes in autologous serum allowed some, but not all, of the diet-induced changes in fatty acid composition to be maintained. The effects of dietary lipid manipulation were totally reversed when lymphocytes were cultured in FCS. Culturing lymphocytes in serum-free medium not only reversed any effects of dietary manipulation, but also markedly increased the appearance of palmitoleic and oleic acids, at the expense of palmitic and stearic acids, suggesting activation of the delta 9 desaturase when these cells were cultured in the absence of exogenous lipid. This study suggests that cell culture conditions have significant influence on the changes in lymphocyte fatty acid composition brought about by dietary lipid manipulation and may therefore influence the outcome of functional tests.

Comparison of the effects of a range of dietary lipids upon serum and tissue lipid composition in the rat

Since the type of fat consumed in the diet may play a role in the development of several disorders, it is important to ascertain the effects of different dietary fats upon parameters such as serum lipid levels and adipose deposition. The aim of this study was to determine the effects of feeding rats a range of fats with differing fatty acid compositions. Weanling male rats were fed for 10 weeks on a low fat (LF) diet or on one of five high fat diets, which contained 20% by weight of either hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO), evening primrose oil (EPO) or menhaden (fish) oil (MO). Food intake, animal growth, tissue weights at sacrifice, serum and liver lipid concentrations and serum, heart, brain and adipose tissue fatty acid compositions were studied. The food intake of the LF-fed animals was greater than that of animals fed on the high fat diets; there were no differences in food intake between animals fed the high fat diets. The total energy intake was lower for animals fed on the HCO diet than for those fed on the LF, OO, EPO or MO diets; there were no other differences in energy intake between the groups. Animals fed the different diets had almost identical rates of weight gain up to 5 weeks; after this period of rapid growth, the increase in weight was slower in all groups but especially in the LF-fed animals. The LF-fed rats had a lower total weight gain and smaller final weights than rats fed on the high fat diets. Animals fed on the MO diet had a greater weight gain than those fed on the OO or EPO diets and their final weights were greater. The MO diet resulted in greatly increased liver weight compared with each of the other diets. The HCO, OO and EPO diets also increased liver weight compared with the LF diet. The total lipid content of the livers from rats fed the high fat diets was greater than that of those from rats fed the LF diet; the livers from animals fed the MO diet contained more lipid than those from animals fed each of the other diets. MO feeding increased the free cholesterol, cholesterol ester and triacylglycerol contents of the liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Propionate modifies lipid biosynthesis in rat peritoneal macrophages

1. This study examines the effect of propionate, normally produced in the gut, on lipid metabolism of resident macrophage. This cell is very abundant in the epithelial lining of the gut. 2. The activity of propionyl-CoA synthetase in macrophages was shown to be 0.39 nmol/min per mg protein, so this cell presents the ability to use propionate. Propionate at concentrations varying from 0.5 to 5 mM did not affect the activities of carnitine acetyltransferase, ATP-citrate lyase, acetoacetyl-CoA thiolase and 3-oxoacid-CoA transferase. 3. Thus this short chain fatty acid did not alter the capacity for transferring acetyl-CoA from mitochondria to cytosol and for ketone bodies formation and oxidation. However, propionate (40 mM) inhibited the incorporation of [1-14C]-palmitate into phospholipids, cholesterol, cholesterol ester and triacylglycerol and the incorporation of [3-14C]-pyruvate into phospholipids. 4. These findings suggest that fibre-rich diet by generating propionate may regulate macrophage lipid metabolism.

Susceptibility of phospholipids of oxidizing LDL to enzymatic hydrolysis modulates uptake by P388D1 macrophage-like cells

Addition of the phospholipids 1-O-hexadecyl-2-arachidonoyl-sn-glycero-3-phosphocholine (PLE) and 1-O-hexa-decyl-2-desoxy-2-amino-arachidonyl-sn-glycero-3- phosphocholine (PLA) to [125I]LDL and subsequent Cu(2+)-induced oxidation result in significant differences in protein modification and uptake by P388D1 macrophage-like cells. PLE-treated LDL is ingested at a 1.27-fold rate compared to PLE-treated LDL and displays enhanced electrophilic mobility. Similar results (1.43-fold enhanced uptake of LDL preloaded with PLE) are obtained when the uptake of phospholipid-enriched oxLDL particles are examined. The preference for ingestion as well as protein modification of both preparations is, however, reversed under experimental conditions allowing diffusion and inactivation of a fraction of the peroxidation products. These findings suggest that LDL-associated PAF-acetylhydrolase can exert a dual role and, to be protective to LDL, require an appropriate microenvironment, capable of binding certain species of oxidatively fragmented lipids.

In vitro effects of oxidized low density lipoprotein on CD11b/CD18 and L-selectin presentation on neutrophils and monocytes with relevance for the in vivo situation

Oxidized LDL (oxLDL) has been identified as a potent stimulus of leukocyte adhesion to endothelium, a hallmark of early atherogenesis. A cytofluorometric study was performed to further characterize the mechanisms by which oxLDL stimulates the rapid adhesion of leukocytes to endothelium in vitro and in vivo. Incubation (30 minutes at 37 C) of whole blood (diluted with buffered saline to 1 x 10(6) leukocytes/ml) with oxLDL (0.85 mg LDL cholesterol/ml; oxidized by 7.5 mumol/L Cu2+ for 18 hours) but not native LDL stimulated the upregulation of CD11b/CD18 adhesion receptors on neutrophils (anti-leu-15 binding: 178 +/- 16% of baseline, P < 0.01, means +/- SD of n = 10 experiments) and on monocytes (169 +/- 34% of baseline, P < 0.01). This phenomenon was almost entirely inhibited by n-butanol or the vasoactive drug pentoxifylline (PTX), which also significantly reduced oxLDL-induced leukocyte adhesion to venular and arteriolar endothelium, as assessed by intravital microscopy on the dorsal skinfold chamber in hamsters (venules: 49 +/- 19 versus 120 +/- 34 cells/mm2, P < 0.05; arterioles: 9 +/- 4 versus 52 +/- 7 cells/mm2, P < 0.01) 30 minutes after intravenous injection of oxLDL (4 mg/kg body weight; means +/- SD of n = 7 hamsters per group). Butanol and PTX also significantly reduced the upregulation of CD11b/CD18 by f-methionyl-leucyl-phenylalanine (fMLP) and platelet-activating factor (PAF) but not by phorbol myristate acetate (PMA). Whereas fMLP and PAF stimulate leukocytes via binding to specific cell surface receptors and triggering complex signal transduction pathways, PMA bypasses these pathways and directly activates intracellular protein kinase C. By analogy, we propose that oxLDL upregulates CD11b/CD18 through its previously documented ability to stimulate the generation of second messengers. The effect of n-butanol and PTX on receptor presentation cannot be explained by changes in plasma membrane fluidity, as both agents failed to reverse the decrease in plasma membrane fluidity of neutrophils after stimulation with oxLDL, as assessed by fluorescence anisotropy measurement of the membrane marker diphenylhexatriene. Incubation of isolated neutrophils but not of whole blood with oxLDL resulted in a significant loss of L-selectin from the neutrophil surface (anti-TQ-1 binding: 40 +/- 13% of baseline, P < 0.01). A significant loss of this adhesion receptor on neutrophils and monocytes was also observed after stimulation of isolated neutrophils and whole blood with fMLP, PAF, and PMA.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of continuous tube feeding of dietary fat emulsions on eicosanoid production and on fatty acid composition during an acute septic shock in rats

The effects of a short-term (5 days) continuous intragastric tube feeding of diets containing n - 6 polyunsaturated fatty acids (PUFA) from safflower oil (SO) or n - 3 PUFA from menhaden oil (MO) on the production of proinflammatory mediators, and on the number of animals surviving after an intravenous injection of lipopolysaccharide (LPS) were investigated in rats. The phospholipid fatty acid composition of cell membranes from several organs and of plasma were also analyzed. No marked differences in the number of animals surviving or in the production of tumor necrosis factor-alpha were observed between the 2 groups of animals. However, 90 min after LPS exposure the plasma levels of prostaglandin (PG) E2 and 6-keto-PGF1 alpha decreased significantly (40% and 60%, respectively) for the group of rats fed MO diet compared to those fed SO diet (P < 0.05). Following continuous infusion of liquid MO diet, the amount of arachidonic acid (AA) detected was significantly lower in plasma (23%), spleen (43%), lungs (41%), and liver (38%), but was unchanged in the heart tissues. The percent of eicosapentaenoic acid (EPA) incorporated into phospholipids of plasma, spleen, lungs, liver, and heart were 7.6, 4.4, 2.1, 7.2, and 1.1%, respectively. These data indicate that after continuous MO feeding, a significant decrease in the production of proinflammatory eicosanoids was associated with a marked reduction in AA content. Further, these data suggest that nutritional intervention may have a therapeutic potential to ameliorate clinical symptoms due to excessive productions of eicosanoids during acute septic complications.

Modulation of exercise-induced immunosuppression by dietary polyunsaturated fatty acids in mice

The possible interaction between intense exercise, known to suppress the immune response, and nutritive factors, such as polyunsaturated fatty acids (PUFA), was examined in inbred female C57Bl/6 mice. The animals received for 8 wk either a natural ingredient diet or a diet supplemented with 10 g/100 g linseed oil containing over 50% of 18:3 (n-3) alpha-linoleic acid. Other groups received PUFA containing only traces of 18:3 (n-3) fatty acid; beef tallow, containing mostly 18:1 (n-9) saturated fat, safflower oil, an 18:2 (n-6) PUFA, and fish oil, containing longer chain (n-3) PUFA. Each dietary group was divided into two subgroups: sedentary diet controls and exercised animals. Exercise consisted of continuous swimming at high intensity until exhaustion. It was shown in three separate experiments that (1) the primary humoral response to sheep red blood cells, determined by the plaque-forming cell (PFC) assay, was affected by PUFA diet in sedentary animals in the order beef tallow > control diet > safflower oil > fish oil > linseed oil, and (2) the PFC response was suppressed by the exhaustive exercise, as compared to sedentary controls, except for animals fed 18:3 (n-3) linseed oil, where the normal response was noted. Phagocytosis of fluorescent microspheres by peritoneal macrophages, determined by flow cytometry, was significantly lower in exercised animals receiving the linseed oil diet, whereas other diets either increased or did not significantly change the macrophage phagocytic activity, compared to the sedentary diet controls. Spleen lymphocyte subsets were unchanged in exercised animals except for a marked shift from the lymphoid peak toward the erythroid peak. Generally, our data showed a marked immunomodulatory effect of 18-3 (n-3) alpha-linoleic acid on the exhaustive exercise-related immunosuppression, as compared to the effects of other selected PUFA.

The effect of dietary lipid manipulation on rat lymphocyte subsets and proliferation

Polyunsaturated fatty acids (PUFA) have been shown to suppress immune cell functions in vitro. Dietary studies investigating the effects of PUFA-containing oils on lymphocyte functions have yielded contradictory findings: such studies are difficult to compare as there are many variations in protocols. The present study investigated the effects of diets containing oils rich in saturated fatty acids, monounsaturated fatty acids, n-6 PUFA or n-3 PUFA on rat lymphocyte proliferation and on receptor and surface marker expression. Rats were fed for 10 weeks on a low-fat (LF) diet (approximately 2% fat by weight) or on one of five high-fat diets, which contained 20% (by weight) hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO), evening primrose oil (EPO) or menhaden (fish) oil (MO). Compared with feeding the LF diet, all of the high-fat diets suppressed the proliferation of lymphocytes from the spleen: although there was no significant effect of diet on the proliferation of lymphocytes from the thymus, there was a trend towards decreased proliferation with high-fat feeding. Feeding the OO, EPO or MO diets significantly suppressed proliferation of mesenteric lymph node lymphocytes compared with feeding the LF, HCO or SO diets. Dietary lipid manipulation had no effect on the proportion of T cells, B cells or monocytes/macrophages in the spleen, thymus or lymph nodes. Dietary lipid manipulation also had no significant effect on the proportions of CD4+ or CD8+ lymphocytes in spleen, thymus or lymph nodes, either in freshly prepared cells or in cells cultured in the presence of mitogen. There were no significant effects of dietary lipid manipulation on the expression of IL-2 receptors or transferrin receptors by concanavalin A (Con A)-stimulated lymphocytes. However, there was a trend towards a decrease in transferrin receptor expression by Con A-stimulated lymphocytes from the thymus and lymph nodes of the MO-fed rats and towards a decrease in the expression of IL-2 receptors by lymphocytes from the spleens and thymi of the MO-fed rats. These observations provide evidence that some dietary oils, particularly OO, EPO and MO, possess immunosuppressive properties and so may be useful in the therapy of diseases involving inappropriate lymphocyte activation.

Lipid mediated modification of rat heart allograft survival

The effect on allograft survival of intravenous fat emulsions that differed in the ratio of functionally important n-3 and n-6 fatty acids was studied in a heterotopic cardiac transplant model in rats. Twenty percent fat emulsions were administered by continuous infusion at a dosage of 9 g fat/kg body weight per day, starting immediately after transplantation and continuing until complete rejection. The n-6 and n-3 fatty acids represent 75%, 43%, 60%, and 59% of all fatty acids in safflower oil, fish oil, soybean oil, and a 1:1 mixture of safflower and fish oil, respectively. The n-6 fatty acids predominate in safflower oil (370/1) and soybean oil (6.5/1), while the n-3 fatty acids dominate in the fish oil (7.6/1). The 1:1 mixture of safflower and fish oil has the balanced composition (n-6/n-3 = 2.1/1) recommended by Kinsella and served as oil-treated controls. Continuous infusion of safflower oil, fish oil, and soybean oil prolonged graft survival time to 13.3, 12.3, and 10.4 days, respectively, compared to 6.8 days in the oil-treated controls (P < 0.01 for all comparisons). Another control group infused with saline rejected the allografts after 7.8 days (P = NS compared to oil-treated controls; P < 0.01 for all other comparisons). The data suggest that intravenous administration of polyunsaturated fat emulsions results in an immunosuppressive effect that seems to be dependent on the n-3/n-6 fatty acid ratio of the fat emulsion.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of natural killer cell activity by dietary lipids

Natural killer (NK) cells are a subset of cytotoxic lymphocytes found mainly in blood and the spleen. NK cells play a role in natural immunity to microbes, viruses and tumor cells and are involved in the rejection of grafts. The present study investigated the effects of diets containing oils rich in saturated fatty acids, mono-unsaturated fatty acids, n-6-poly-unsaturated fatty acids (PUFA) or n-3-PUFA on the NK cell activity and on the lymphokine-activated killer (LAK) cell activity of rat spleen lymphocytes. Weanling rats were fed for 10 weeks on a low-fat (LF) diet (approximately 2% fat by weight) or on 1 of 5 high-fat (HF) diets, which contained 20% (by weight) hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO), evening primrose oil (EPO) or menhaden (fish) oil (MO). Each of the HF diets suppressed the NK activity of freshly prepared spleen lymphocytes compared with the LF diet; cells from the MO-fed rats exhibited the lowest NK activity. Culture with IFN alpha for 3 h increased the NK activity of spleen lymphocytes from all animals, except those fed the OO diet; the increase in NK activity varied from 20% (LF) to 50% (MO). Although feeding the OO, EPO or MO diets resulted in lower IFN alpha-stimulated NK activity than that obtained by feeding the LF diet, the only consistent significant difference was the lower activity of the cells from the OO-fed rats compared with those from the LF-fed rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Incorporation of fatty acids by concanavalin A-stimulated lymphocytes and the effect on fatty acid composition and membrane fluidity

The fatty acid compositions of the neutral lipid and phospholipid fractions of rat lymph node lymphocytes were characterized. Stimulation of rat lymphocytes with the T-cell mitogen concanavalin A resulted in significant changes in the fatty acid composition of both neutral lipids and phospholipids (a decrease in the proportions of stearic, linoleic and arachidonic acids and an increase in the proportion of oleic acid). Membrane fluidity was measured using nitroxide spin-label e.s.r., and increased during culture with concanavalin A. Culturing the lymphocytes in the absence of mitogen did not affect fatty acid composition or membrane fluidity. The uptake and fate of palmitic, oleic, linoleic and arachidonic acids were studied in detail; there was a time-dependent incorporation of each fatty acid into all lipid classes but each fatty acid had a characteristic fate. Palmitic and arachidonic acids were incorporated principally into phospholipids whereas oleic and linoleic acids were incorporated in similar proportions into phospholipids and triacylglycerols. Oleic acid was incorporated mainly into phosphatidylcholine, palmitic and linoleic acids were incorporated equally into phosphatidylcholine and phosphatidylethanolamine, and arachidonic acid was incorporated mainly into phosphatidylethanolamine. Supplementation of the culture medium with particular fatty acids (myristic, palmitic, stearic, oleic, linoleic, alpha-linolenic, arachidonic, eicosapentaenoic or docosahexaenoic acid) led to enrichment of that fatty acid in both neutral lipids and phospholipids. This generated lymphocytes with phospholipids differing in saturated/unsaturated fatty acid ratio, degree of polyunsaturation, index of unsaturation and n - 6/n - 3 ratio. This method allowed the introduction into lymphocyte phospholipids of fatty acids not normally present (e.g. alpha-linolenic) or usually present in low proportions (eicosapentaenoic and docosahexaenoic). These three n - 3 polyunsaturated fatty acids replaced arachidonic acid in lymphocyte phospholipids. Fatty acid incorporation led to an alteration in lymphocyte membrane fluidity: palmitic and stearic acids decreased fluidity whereas the unsaturated fatty acids increased fluidity. It is proposed that the changes in lymphocyte phospholipid fatty acid composition and membrane fluidity brought about by culture in the presence of polyunsaturated fatty acids are responsible for the inhibition of lymphocyte functions caused by these fatty acids.

Metabolic changes in lymphoid organs as induced by fatty acids-rich diets during ageing

Previous reports of our laboratory have shown that w-6 PUFA-rich diets (UC) given to rats during 6 weeks causes important changes of the metabolism of the lymphoid organs. In this study, the effect of saturated fatty acids-rich diet (SC) and also the persistence of the changes caused by (UC) were investigated during ageing (14 months). The major changes previously reported for UC fed rats, during 6 weeks, fully persisted when this feeding condition was maintained for 14 months. Moreover, the SC group also showed modifications of the activities of key enzymes of glucose and glutamine metabolism of the lymphoid organs with ageing. Both groups fed fatty acids-rich diets markedly reduced the rate of lipogenesis in the liver, spleen, and thymus in contrast to slight changes reported for 6 weeks. These results suggest that fatty acids-rich diets, by causing important metabolic alterations, may pronounce the impairment of the immune function observed during ageing.

Inhibition of lymphocyte proliferation in vitro by two lipid emulsions with different fatty acid compositions

The effects of two lipid emulsions upon the proliferation of rat and human lymphocytes in vitro were investigated. The emulsions used were Intralipid, a soya bean oilbased emulsion in widespread clinical use, and Omegavenous, a newly-developed emulsion in which n-3 polyunsaturated fatty acids comprise approximately 40% of the total fatty acids. Both emulsions inhibited lymphocyte proliferation in a concentration- and time-dependent manner. Omegavenous was a much more potent inhibitor than Intralipid.

Triacylglycerol metabolism by lymphocytes and the effect of triacylglycerols on lymphocyte proliferation

This study investigates the ability of lymphocytes to utilize fatty acids originating from triacylglycerols and the effect of triacylglycerols upon mitogen-stimulated lymphocyte proliferation. Lymphocytes isolated from rat lymph nodes, spleen, thymus and lymphatic duct had a lipoprotein lipase activity of approx. 10 units/mg of protein, indicating that the fatty acids of circulating triacylglycerols are accessible to these cells. In culture lymph node lymphocytes hydrolysed triacylglycerols added to the medium as emulsions. Both non-esterified fatty acids and free glycerol appeared in the cell culture medium, but their concentrations indicated that a high proportion of each (65-90% of fatty acids and 60-80% of glycerol) was taken up by the cells. The incorporation and fate of triacylglycerol-fatty acids was studied by culturing the cells in the presence of tri[3H]oleoylglycerol or tri[14C]inoleoylglycerol. Both fatty acids were incorporated into lymphocyte lipids in a time-dependent manner; linoleic acid was incorporated at a significantly greater rate than oleic acid. The majority of oleic acid (greater than 70%) was incorporated into cellular triacylglycerol, while less than 10% was incorporated into phospholipids. In contrast, linoleic acid incorporation into cellular triacylglycerol never exceeded 25%, while up to 45% was incorporated into phospholipids. Triacylglycerols containing polyunsaturated fatty acids inhibited concanavalin A-stimulated lymphocyte proliferation in a concentration- and time-dependent manner; triacylglycerols containing saturated fatty acids or oleic acid were not inhibitory. Such direct effects of certain triacylglycerols on lymphocyte function may explain why some clinical trials of polyunsaturated fatty acid-rich diets have been successful in improving the condition of patients suffering from inflammatory diseases.