Effects of linoleic acid and mitogenic stimulation on the fatty acid composition of human lymphocytes

Exogenous tetracosahexaenoic acid modifies the fatty acid composition of human primary T lymphocytes and Jurkat T cell leukemia cells contingent on cell type

Tetracosahexaenoic acid (24:6ω-3) is an intermediate in the conversion of 18:3ω-3 to 22:6ω-3 in mammals. There is limited information about whether cells can assimilate and metabolize exogenous 24:6ω-3. This study compared the effect of incubation with 24:6ω-3 on the fatty acid composition of two related cell types, primary CD3+ T lymphocytes and Jurkat T cell leukemia, which differ in the integrity of the polyunsaturated fatty acid (PUFA) biosynthesis pathway. 24:6ω-3 was only detected in either cell type when cells were incubated with 24:6ω-3. Incubation with 24:6ω-3 induced similar increments in the amount of 22:6ω-3 in both cell types and modified the homeoviscous adaptations fatty acid composition induced by activation of T lymphocytes. The effect of incubation with 18:3ω-3 compared to 24:6ω-3 on the increment in 22:6ω-3 was tested in Jurkat cells because primary T cells cannot convert 18:3ω-3 to 22:6ω-3. The increment in the 22:6ω-3 content of Jurkat cells incubated with 24:6ω-3 was 19.5-fold greater than that of cells incubated with 18:3ω-3. Acyl-coA oxidase siRNA knockdown decreased the amount of 22:6ω-3 and increased the amount of 24:6ω-3 in Jurkat cells. These findings show exogenous 24:6ω-3 can be incorporated into primary human T lymphocytes and Jurkat cells and induces changes in fatty acid composition consistent with its conversion to 22:6ω-3 via a mechanism involving peroxisomal β-oxidation that is regulated independently from the integrity of the upstream PUFA synthesis pathway. One further implication is that consuming 24:6ω-3 may be an effective alternative means of achieving health benefits attributed to 20:5ω-3 and 22:6ω-3.

α-linolenic acid interconversion is sufficient as a source of longer chain ω-3 polyunsaturated fatty acids in humans: An opinion

α-linolenic acid (αLNA) conversion into the functionally important ω-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), has been regarded as inadequate for meeting nutritional requirements for these PUFA. This view is based on findings of small αLNA supplementation trials and stable isotope tracer studies that have been interpreted as indicating human capacity for EPA and, in particular, DHA synthesis is limited. The purpose of this review is to re-evaluate this interpretation. Markedly differing study designs, inconsistent findings and lack of trial replication preclude robust consensus regarding the nutritional adequacy of αLNA as a source of EPC and DHA. The conclusion that αLNA conversion in humans is constrained is inaccurate because it presupposes the existence of an unspecified, higher level of metabolic activity. Since capacity for EPA and DHA synthesis is the product of evolution it may be argued that the levels of EPA and DHA it maintains are nutritionally appropriate. Dietary and supra-dietary EPA plus DHA intakes confer health benefits. Paradoxically, such health benefits are also found amongst vegetarians who do not consume EPA and DHA, and for whom αLNA conversion is the primary source of ω-3 PUFA. Since there are no reported adverse effects on health or cognitive development of diets that exclude EPA and DHA, their synthesis from αLNA appears to be nutritionally adequate. This is consistent with the dietary essentiality of αLNA and has implications for developing sustainable nutritional recommendations for ω-3 PUFA.

The Partitioning of Newly Assimilated Linoleic and α-Linolenic Acids Between Synthesis of Longer-Chain Polyunsaturated Fatty Acids and Hydroxyoctadecaenoic Acids Is a Putative Branch Point in T-Cell Essential Fatty Acid Metabolism

Longer-chain polyunsaturated fatty acids (LCPUFAs) ≥20 carbons long are required for leukocyte function. These can be obtained from the diet, but there is some evidence that leukocytes can convert essential fatty acids (EFAs) into LCPUFAs. We used stable isotope tracers to investigate LCPUFA biosynthesis and the effect of different EFA substrate ratios in human T lymphocytes. CD3⁺ T cells were incubated for up to 48 h with or without concanavalin A in media containing a 18:2n-6:18:3n-3 (EFA) ratio of either 5:1 or 8:1 and [¹³C]18:3n-3 plus [d₅]18:2n-6. Mitogen stimulation increased the amounts of 16:1n-7, 18:1n-9, 18:2n-6, 20:3n-6, 20:4n-6, 18:3n-3, and 20:5n-3 in T cells. Expression of the activation marker CD69 preceded increased FADS2 and FADS1 mRNA expression and increased amounts of [d₅]20:2n-6 and [¹³C]20:3n-3 at 48 h. In addition, 22-carbon n-6 or n-3 LCPUFA synthesis was not detected, consistent with the absence of ELOVL2 expression. An EFA ratio of 8:1 reduced 18:3n-3 conversion and enhanced 20:2n-6 synthesis compared to a 5:1 ratio. Here, [d₅]9- and [d₅]-13-hydroxyoctadecadienoic (HODE) and [¹³C]9- and [¹³C]13-hydroxyoctadecatrienoic acids (HOTrE) were the major labelled oxylipins in culture supernatants; labelled oxylipins ≥20 carbons were not detected. An EFA ratio of 8:1 suppressed 9- and 13-HOTrE synthesis, but there was no significant effect on 9- and 13-HODE synthesis. These findings suggest that partitioning of newly assimilated EFA between LCPUFA synthesis and hydroxyoctadecaenoic acid may be a metabolic branch point in T-cell EFA metabolism that has implications for understanding the effects of dietary fats on T lymphocyte function.

Dietary Supplementation with Transgenic Camelina sativa Oil Containing 20:5n-3 and 22:6n-3 or Fish Oil Induces Differential Changes in the Transcriptome of CD3+ T Lymphocytes

Eicosapentaenoic acid (20:5n-3) and docosahexaenoic acid (22:6n-3) are important for leukocyte function. This study investigated whether consuming transgenic Camelina sativa (tCSO) seed oil containing both 20:5n-3 and 22:6n-3 is as effective as fish oil (FO) for increasing the 20:5n-3 and 22:6n-3 content of leukocytes and altering mitogen-induced changes to the T cell transcriptome. Healthy adults (n = 31) consumed 450 mg/day of 20:5n-3 plus 22:6n-3 from either FO or tCSO for 8 weeks. Blood was collected before and after the intervention. 20:5n-3 and 22:6n-3 incorporation from tCSO into immune cell total lipids was comparable to FO. The relative expression of the transcriptomes of mitogen-stimulated versus unstimulated T lymphocytes in a subgroup of 16 women/test oil showed 4390 transcripts were differentially expressed at Baseline (59% up-regulated), 4769 (57% up-regulated) after FO and 3443 (38% up-regulated) after tCSO supplementation. The 20 most altered transcripts after supplementation differed between test oils. The most altered pathways were associated with cell proliferation and immune function. In conclusion, 20:5n-3 and 22:6n-3 incorporation into immune cells from tCSO was comparable to FO and can modify mitogen-induced changes in the T cell transcriptome, contingent on the lipid matrix of the oil.

The effects of dietary fatty acids on the proliferation of normal human urothelial cells in vitro

Little is known of the mechanisms by which dietary fatty acids (FAs) may affect normal epithelial cell physiology and thereby directly or indirectly influence tumour incidence and progression. In this study, we have used normal human urothelial cell cultures to investigate whether FAs may modify proliferation of normal human epithelial cells in vitro. FAs were presented as albumin complexes in serum-free medium and the effects on proliferation over a concentration range of 1-100 microM were assayed by thymidine incorporation. Saturated FAs had no effect. At lower concentrations (1-10 microM), mono-unsaturated FAs (MUFAs) and n-3 polyunsaturated FAs (PUFAs) were slightly stimulatory. Concentrations of unsaturated FAs above 10 microM were growth inhibitory in a dose-dependent manner. Oleic acid showed least cytostatic effect, whereas gamma-linolenic acid induced irreversible growth arrest. Although marked morphological effects were observed in irreversibly growth-inhibited cells, the cells remained attached to the substratum and showed no evidence of nuclear pyknosis or apoptosis. The inhibitory effects of single PUFAs could be reduced, but not abolished, by the addition of saturated FAs or MUFAs. Mixtures of different PUFAs were inhibitory in an additive manner. These data suggest that PUFAs have a cytostatic effect on rapidly proliferating epithelial cells which appears unrelated to malignant transformation.

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.

Fatty acid content in lymphocytes from children with syndromic paucity of interlobular bile ducts, Alagille syndrome

Fatty acid (FA) concentrations were studied in lymphocytes isolated from children with syndromic paucity of interlobular bile ducts (PILBD), Alagille syndrome. The aim of this study was to assess whether the specific FA changes previously observed in fibroblast cultures from such patients were also present in other tissues. Lymphocyte FA, obtained both from controls and patients were studied under two experimental conditions, either after separation of the mononuclear cells or after 48 hours of culture. Freshly isolated lymphocytes from patients presented few FA changes compared to the controls. However, when patient lymphocytes were placed in culture medium for 48 hours, FA changes were amplified compared to those observed in controls; the decrease in the sum of saturated and n-6 polyunsaturated FA of total lipids was significant only in patients, and the n-3 FA of phospholipids was strikingly increased in patients (p < or = 0.001), compared to controls. These results are related to those previously observed in fibroblast cultures and suggest that placing cells in culture could reveal a pre-existing cellular abnormality in patients with PILBD.

Cytokine production and DNA synthesis by human peripheral lymphocytes in response to palmitic, stearic, oleic, and linoleic acid

Effects of palmitic, stearic, oleic, and linoleic acid on mitogen-induced DNA synthesis, on production of IL-1 beta, IL-2, IFN-gamma, and TNF-alpha, and on IL-2R expression were determined in human peripheral lymphocytes. Free fatty acids (FFA) were added over a wide range of concentrations to cells cultured under serum free conditions with fatty acid free albumin. DNA synthesis was stimulated by low and inhibited by high FFA concentrations. Physiological concentrations were stimulatory, except for linoleic acid. Cytokine production became affected by all FFA tested. Palmitic acid enhanced the release of IFN-gamma at concentrations that diminished TNF-alpha production. Saturated fatty acids were significantly more potent than unsaturated fatty acids in affecting cytokine production. IFN-gamma secretion was significantly more stimulated or inhibited by the various FFA compared with the other cytokines. IL-2R expression correlated with the production of IL-2. When tested in combination, stimulatory as well as inhibitory effects of the individual FFA became attenuated. It is suggested that palmitic, stearic, oleic, and linoleic acid are physiological regulators of DNA synthesis and cytokine release in human peripheral lymphocytes. Modulation of FFA ratios may be an effective means for the fine tuning of the immune system. As secretory mechanisms of cytokines appear to exhibit substrate specificity for FFA, the release of individual cytokines may be selectively influenced by FFA.

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.

Fatty acid metabolism in human lymphocytes. II. Activation of fatty acid desaturase-elongase systems during blastic transformation

The fatty acid desaturation-elongation ability of human T-lymphocytes during blastic transformation was determined both by gas-liquid chromatography and incubation with radiolabeled precursors. Human peripheral blood mononuclear cells (PBMC) were activated with phytohemagglutinin (PHA) and cultured in media supplemented with different fatty acids (18:0, 18:1(n - 9), 18:2(n - 6), 18:3(n - 3) and 20:4(n - 6)) at a final concentration of 30 microM. All the fatty acids added were elongated by activated PBMC and the maximal activity was observed on 20:4(n - 6) (a 25% of conversion to 22:4(n - 6)). Supplementation with stearic acid increased the proportion of oleic (from 21.4% to 23.7%) and eicosaenoic (from 3.1% to 5.7%) acids in cellular lipids, indicating the existence of a delta 9-desaturase activity. Supplementation with linoleic and linoleic acids increased slightly the cell content in their more unsaturated derivatives. Direct measurement of desaturase activities was performed by incubating quiescent and activated PBMC with [1-14C]stearic, [1-14C]linoleic and [1-14C]linolenic acids. Quiescent cells exhibited a very low delta 9-desaturase and no sign of delta 6-desaturase activity. A moderate and progressive activation of delta 9-, delta 6- and delta 5-desaturases was observed during blastic transformation of human PBMC. Up to 8% of 18:0 was converted to monoenes, 4% and 1.5% of 18:2(n - 6) was converted to trienes and tetraenes, respectively, and 14.5% of 18:3(n - 3) was converted to pentaenes. The maximal relative activities were found after 48 h of PHA-stimulation for delta 9-desaturase (around 90 pmol of 18:0 converted per 10(6) cells in the last 24 h) and at 72 h for delta 6- and delta 5-desaturases (around 75 and 140 pmol of 18:2 and 18:3, respectively, converted per 10(7) cells in the last 24 h). Although these activities are not enough to explain all the changes in fatty acid composition of human PBMC during blastic transformation, they may contribute to a more controlled cell phospholipid composition.

Fatty acid metabolism in human lymphocytes. I. Time-course changes in fatty acid composition and membrane fluidity during blastic transformation of peripheral blood lymphocytes

The time-course changes in fatty acid composition of human T-lymphocytes during blastic transformation were analysed, as well as the variations in membrane fluidity determined by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH), using a fluorescence-activated cell sorter. The more important changes observed, in activated relative to quiescent cells, started after 24 h and consisted in an increase in the proportion of oleic (18:1(n - 9)), docosapentaenoic (22:5(n - 3)) and docosahexaenoic (22:6(n - 3)) acids and a decrease in that of linoleic (18:2(n - 6)) and arachidonic (20:4(n - 6)) acids. This represented a relative increase of 26% for 18:1, 56% for 22:5 and 84% for 22:6 in peripheral blood mononuclear cells (PBMC) and 35%, 182% and 94%, respectively, in purified T-lymphocytes, both activated for 72 h. The decrease in n - 6 fatty acids was of 42% for 18:2 and 14% for 20:4 in PBMC and 30% and 19%, respectively, for 72 h. The decrease in n - 6 fatty acids was of 42% for 18:2 and 14% for 20:4 in PBMC and 30% and phosphatidylethanolamine) rather than neutral lipids. The 18:1/18:0 ratio increased greatly in major cell phospholipids. The proportion of 20:4, 22:5 and 22:6 in phosphatidylinositol was not significantly altered after 72 h of activation. The molar ratio cholesterol/phospholipids was reduced in 72-h-activated lymphocytes (0.29) compared to quiescent cells (0.5). On the other hand, the stimulation of human T-lymphocytes caused a significant decrease in the order parameter (S) of DPH, according to the observed changes in lipid composition. After 72 h in culture, the S value for quiescent and stimulated T-lymphocytes was 0.530 and 0.326, respectively. In conclusion, the blastic transformation of human T-lymphocytes is associated with changes in lipid composition which modify the physical properties of their membranes. These modifications could modulate, in turn, the activity of membrane proteins implicated in the process of blastic transformation.