Effects of linoleic acid on capping, lectin mediated mitogenesis, surface antigen expression, and fluorescent polarization in lymphocytes and BHK cells

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.

Docosahexaenoic acid-induced alteration of Thy-1 and CD8 expression on murine splenocytes

Here we test whether the incorporation of docosahexaenoic acid (DHA, 22:6), an (n-3) fatty acid, into lymphocyte membranes affects the expression of the surface proteins Thy-1.2 and CD8. DHA was incorporated into splenocytes by three methods: feeding mice diets containing menhaden (fish) oil, fusing splenocytes with DHA-containing phosphatidylcholine vesicles, and culturing splenocytes with DHA. Thy-1.2 and CD8 expression were measured by flow cytometry and complement-mediated lysis using a panel of monoclonal antibodies. As (n-3) fatty acid incorporation into the lymphocytes increased, the expression of one Thy-1.2 epitope and one CD8 epitope decreased; the expression of two CD8 epitopes increased. Although diet-induced changes in surface protein expression may result from selective migration of cell populations or the diet's effect on protein biosynthesis, fusion with lipid vesicles demonstrated that DHA-containing phospholipids can mediate a direct and immediate effect. The decrease in Thy-1.2 expression was sustained for more than a week after removal of (n-3) fatty acids from the diet, most likely due to retention of membrane-bound (n-3) fatty acids. Because Thy-1.2 and CD8 participate in T cell activation, modulation of their expression by DHA suggests that DHA, when serving as a membrane structural element, may alter immune function.

Interaction of free fatty acids with phospholipid bilayers

The partition of free fatty acids (FFA) to egg-phosphatidylcholine (egg-PC) and egg-phosphatidylethanolamine (egg-PE) vesicles was studied. Upon the addition of FFA to the suspension of vesicles, the pH of the aqueous phase changed depending on the length and saturation of the FFA hydrocarbon chain, as well as on the vesicle composition. The medium pH decreased faster if FFA was added to egg-PE as compared to egg-PC vesicles. The fluorescent free fatty acid indicator (ADIFAB) was used to measure the amount of FFA remaining in the aqueous phase. Most of the FFA added to the suspension of egg-PE vesicles remained in the aqueous phase, whereas in the presence of egg-PC vesicles the FFA partitioned preferentially into the lipid phase. The amount of FFA incorporated into the lipid bilayers was estimated by measuring the changes of pH at the lipid bilayer surface, using fluorescein-PE. At high surface concentrations of FFA, decreasing pH at the bilayer surface caused the protonation of FFA, and raised the pK of FFA at the bilayer surface from 5 to about 7. The partition of FFA in egg-PE vesicles was an order of magnitude lower than that in egg-PC vesicles. The incorporation amount was determined more by the molecular packing than by the nature of lipid headgroups, because steroylcaprioyl-PE, which preferred the bilayer structure, behaved more like egg-PC than egg-PE. Understanding FFA partition characteristics would help to interpret the hydrolysis measurements of phospholipids, and to explain many biological activities of FFA.

Omega-3 fatty acid modification of membrane structure and function. I. Dietary manipulation of tumor cell susceptibility to cell- and complement-mediated lysis

Omega-3 fatty acids, abundant in fish oil, are reported to alter membrane properties when incorporated into membrane phospholipids. We report that dietary omega-3 fatty acids, incorporated into tumor cell membranes, alter tumor recognition and cytolysis by the immune system. Mice were fed diets rich in corn oil, hydrogenated coconut oil, or menhaden (fish) oil. T27A leukemia cells were grown as an ascites tumor in these mice and harvested for biochemical and immunologic assays. The incorporation of the long-chain omega-3 fatty acid docosahexaenoic acid (22:6) into tumor plasma membranes correlated with an increased susceptibility to tumor cytolysis by alloreactive cytotoxic T lymphocytes and decreased expression of a class I major histocompatibility complex epitope, monitored by complement-mediated lysis and radioimmunoassay. Thus the immunologic phenotype of this ascites tumor reflected the source of oil present in the diet during tumor growth.

Supplementation of polyunsaturated fatty acids in multiple sclerosis

For several years polyunsaturated fatty acids (PUFAs) and in particular essential fatty acids (EFAs) have been proposed for the treatment of multiple sclerosis (MS). There are contrasting data in literature regarding the effects of the n-6 and the n-3 PUFA series on different aspects of the disease, in particular on the frequency and severity of relapses and platelet function. This can be ascribed to the different criteria of patient selection in relation to the form and severity of disease at the beginning of the various studies. Till now authors have tended to consider the effect of PUFA supplementation only on some clinical aspects of the disease. Modification in the more sensitive indices (immunological or biochemical) of the disease activity should be taken into account and also the influence of dietary lipid intake by patients in relation to n-3 or n-6 EFA supplementation.

The effect of free fatty acids on spectrin organization in lymphocytes

Previous studies have shown that cis unsaturated free fatty acids (uFFAs) are able to cause alterations in the normal distribution pattern of certain cytoskeletal proteins in lymphocytes, including tubulin, actin, alpha-actinin, and myosin. The cytoskeletal protein spectrin naturally possesses a marked heterogeneity of distribution among resting T and B lymphocytes isolated from all murine lymphoid organs. In some cells, spectrin is observed in a ring-like staining pattern at the periphery of the cell, reflecting a likely association with the cell membrane; in other cells, spectrin is found within the cytoplasm as a large single aggregate or in several smaller aggregates. Addition of uFFA to freshly isolated murine lymphocytes causes disruption in the latter pattern of spectrin organization. Following short-term incubation (15 min) of tissue-derived lymphocytes (from spleen, thymus, and lymph node) and 1 microgram/mL uFFA (oleic [18:1 cis], linoleic [18:2 cis, cis], arachidonic [20:4], or elaidic [18:1 trans] acid) there is a loss of cytoplasmic aggregates of spectrin and a concomitant increase in cells in which spectrin is diffusely distributed. This effect is not seen when two saturated FFAs (sFFAs) were used. When using DO11.10 cells, a T-cell hybridoma in which nearly all cells constitutively express a cytoplasmic aggregate of spectrin, a similar effect was observed, but greater concentrations (10-20 micrograms/mL) of FFA were needed to obtain the same effect. Addition of calcium to the incubation buffer substantially blocks spectrin reorganization. In several disease states, serum levels of FFA are observed to be excessively high; our data support the hypothesis that cytoskeletal reorganization in lymphocytes may be related to the altered immune function frequently observed in these conditions.

Plasma membrane enrichment with cis-unsaturated fatty acids enhances LDL metabolism in U937 monocytes

The mechanism by which dietary cis-unsaturated fatty acids lower low density lipoprotein (LDL) cholesterol is unknown. Because cis-unsaturated fatty acids incorporated into cell membranes increase membrane fluidity and, as a result, can alter membrane-dependent cell functions, we examined LDL binding, uptake, and degradation in upregulated U937 monocytes enriched in membrane oleate, a monounsaturated fatty acid, and membrane linoleate, a polyunsaturated fatty acid. The same parameters were also examined in upregulated U937 monocytes enriched in membrane stearate, a saturated fatty acid, and in upregulated, unmodified U937 monocytes. Monocytes enriched in cis-unsaturated fatty acids exhibited augmented LDL binding, internalization, and degradation compared with both stearate-enriched monocytes and unmodified monocytes. The molar potency of linoleate in augmenting LDL metabolism was 50% greater than that of oleate. Enrichment with oleate and linoleate resulted in a decrease in the fatty acyl mole-weighted melting point of the plasma membrane and an increase in plasma membrane fluidity, as indicated by a reduction in the steady-state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene incorporated into the membrane. Stearate-enriched monocytes exhibited a slight increase in the plasma membrane fatty acyl mole-weighted melting point and essentially no change in plasma membrane fluidity. Thus, one mechanism by which cis-unsaturated fatty acids lower LDL cholesterol may involve alteration in membrane lipid composition and physical properties, thereby leading to an increase in cellular clearance of this atherogenic lipoprotein.

Effect of dietary fat saturation and cholesterol on low density lipoprotein degradation by mononuclear cells of Cebus monkeys

The mechanism by which dietary unsaturated fatty acids lower low density lipoprotein (LDL) cholesterol is unknown. Unsaturated fatty acids incorporated into the cell membrane can increase membrane fluidity and, as a result, dramatically alter membrane-dependent cell functions. Therefore, we examined the effect of long-term dietary consumption of corn oil and coconut oil with and without cholesterol in amounts equivalent to those of a typical Western diet on the degradation of human LDL by peripheral blood mononuclear cells in Cebus albifrons monkeys. Cellular LDL degradation was dramatically enhanced in the mononuclear cells isolated from animals fed corn oil in comparison with those from animals fed coconut oil. The addition of cholesterol to the diets resulted in a slight attenuation of LDL degradation in the corn oil group while no effect was noted in the coconut oil group. Crossover LDL binding and degradation experiments with LDL isolated from animals fed corn oil diets and coconut oil diets demonstrated increased binding and degradation of LDL in mononuclear cells from animals fed corn oil diets. Enhanced mononuclear cell LDL degradation was accompanied by increased cellular cis-unsaturated fatty acyl content, increased membrane fluidity, and decreased plasma cholesterol. Increased cellular cis-unsaturated fatty acyl content with its concomitant increase in membrane fluidity mirrored the dietary lipid profile of the host animal. A linear relationship was observed between cellular LDL degradation and both cellular cis-unsaturated fatty acyl content and membrane fluidity. These observations parallel results noted in whole-animal LDL catabolic studies with these same animals described elsewhere. These data suggest a novel mechanism by which dietary unsaturated fatty acids exert their LDL-lowering effect.

Effects of dietary linoleic acid and gamma linolenic acid on platelets of patients with multiple sclerosis

The effects of dietary evening primrose oil (rich in linoleic acid and gamma-linolenic acid) were studied on platelets of multiple sclerosis (MS) patients and controls. It was found that platelet aggregation (ADP, thrombin and collagen), platelet fibrinogen binding and platelet glycoprotein (sialic acid and N-acetyl glucosamine) content were not significantly modified by evening primrose oil in MS patients and controls. Moreover, platelet fibrinogen binding and platelet glycoprotein (sialic acid and N-acetyl glucosamine) content were determined for the first time in MS patients and found similar to controls. Platelets of MS patients aggregated more to thrombin and collagen compared to controls, but the difference was only significant with thrombin aggregation after the oil treatment. This study does not show a significant effect of evening primrose oil on platelets of MS patients.

Unsaturated fatty acids enhance low density lipoprotein uptake and degradation by peripheral blood mononuclear cells

The precise mechanism by which unsaturated fatty acids lower low density lipoprotein cholesterol is not known. Because cis-unsaturated fatty acids incorporated in cell membranes increase membrane fluidity and can thereby dramatically alter membrane-dependent cellular functions, we examined the effect of linoleate and oleate incorporation in peripheral blood mononuclear cell membranes on the physical properties of the membrane and concomitantly on low density lipoprotein uptake and degradation. We found that membrane enrichment with linoleate increased the rate of low density lipoprotein degradation in both freshly isolated and derepressed mononuclear cells. Enrichment with oleate led to similar increases in degradation. "Specific" low density lipoprotein uptake by derepressed cells was also enhanced by linoleate and oleate incorporation. Enrichment with both of these fatty acids produced an increase in membrane fluidity, as indicated by a reduction in the steady-state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene incorporated in the membrane. In contrast, stearate enrichment had little effect on uptake or degradation of low density lipoprotein, nor did it affect membrane fluidity. These data point to a novel mechanism for the reduction in low density lipoprotein produced by unsaturated fatty acids that involves their physical effects on cell membranes as it relates to metabolism of the lipoprotein.

Temperature-mediated processes in teleost immunity: the effects of temperature on membrane immunoglobulin capping on channel catfish B lymphocytes

1. In order to better understand ligand-induced redistribution of membrane receptors and lymphocyte activation in ectothermic vertebrates, flow cytometry was used to monitor the effects of both in vivo acclimation temperature and in vitro assay temperatures on the kinetics of monoclonal antibody-induced membrane immunoglobulin (mIg) capping on channel catfish lymphocytes. 2. It was observed that the kinetics of mIg capping were dependent on in vitro assay temperatures, in vivo acclimation temperatures, and the length of time of in vivo acclimation. In the latter situation in vivo acclimation of fish to 27, 22 and 17 degrees C was considered complete after 3 weeks, while acclimation to 12 degrees C required a minimum of 5 weeks. 3. The energies of activation required for mIg capping ranged from 33 to 24 kcal/mol; lower energies of activation were observed with lower temperature acclimation. 4. It was also noted that the lower energies of activation were associated with concomitant decreases in cellular phospholipid saturated/unsaturated fatty acid ratios. 5. It appears that channel catfish B cell mIg capping, presumably a requisite for immune function, can be significantly affected by environmental temperatures; most likely such effects are attributable to changes in plasma membrane viscosities.

Increased adhesiveness of Down syndrome fetal fibroblasts in vitro

We compared the in vitro rate of divalent cation-independent aggregation of fibroblasts derived from abortuses with normal karyotypes and with trisomy 21 (Down syndrome). Fibroblasts from five lung and two of three cardiac cultures from subjects with Down syndrome aggregated more rapidly than matched fibroblasts from normal controls or lung fibroblasts from an abortus with trisomy 13. In contrast, skin fibroblasts derived from the trisomy 21 subjects had low rates of aggregation. The high rates of aggregation of trisomy 21 lung fibroblasts were not affected by hyaluronidase treatment. Lung fibroblasts from both normal and Down syndrome subjects had similar membrane polarization values in an assay using the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene. Thus, the increased aggregation rate we observed for trisomy 21 fibroblasts was restricted to specific fibroblast cultures, was not mediated by hyaluronic acid or gross membrane lipid alterations, and was specific for trisomy of chromosome 21. As illustrated in computer simulations presented elsewhere, increased intercellular adhesiveness during organogenesis could explain the frequent occurrence of malformations, including pulmonary hypoplasia and congenital heart defects, in Down syndrome.

Formation of diacylglycerol and degradation of phosphatidylinositol induced in rat lymphocytes by non-esterified oleic or linoleic acid

Rat spleen lymphocytes were incubated for 3 h with [14C]arachidonic acid in foetal calf serum. It was found that arachidonic acid distributed into phospholipids in the order phosphatidylcholine greater than phosphatidylethanolamine greater than phosphatidylinositol. After labelling with arachidonic acid the lymphocytes were washed, and incubated for up to 2 h with non-radioactive palmitic, oleic or linoleic acid dissolved in ethanol. The presence of ethanol or palmitic acid during a 2 h post-incubation had little effect on the amount of radioactivity found in different lipid fractions. Both oleic acid and linoleic acid, however, brought about an accumulation (up to 8-fold) of radioactivity in the diacylglycerol fraction. These fatty acids also brought about a change of radioactivity in several phospholipids, notably in phosphatidylinositol, which lost more than 50% of its counts during the 2 h incubation. Although maximum effects were seen at 2 h, diacylglycerol radioactivity was increased by 100% within 5 min after adding the fatty acids. The minimum concentration of fatty acids used (50 microM) gave an almost maximum response. The results indicate that unsaturated fatty acids may activate phosphatidylinositol phosphodiesterase in lymphocytes, as they do in brain. The possibility that a phospholipase A is activated is discussed. Possible implications for any experiments in which cells are incubated with fatty acids are pointed out.

Arachidonic acid deficiency in streptozotocin-induced diabetes

Fatty acid compositions of phospholipids of heart, liver, kidney, aorta, and serum from rats having streptozotocin-induced diabetes were determined and compared with those of nondiabetic controls. Linoleic and dihomo-gamma-linolenic acids were increased whereas arachidonic acid was decreased in most tissues, suggesting an impairment of delta 5-desaturase activity. Acids derived from linolenic acid were increased in some diabetic tissues from diabetic animals although the linolenic content was normal, indicating less impairment in the desaturation of the omega 3 series of fatty acids. Diabetes suppressed all polyunsaturated acids in the whole animal, but the competition between omega 3 and omega 6 acids favored the excessive suppression of long-chain omega 6 acids and an increase in the proportion of omega 3 acids in lipids of vital tissues. These changes in fatty acid composition of the phospholipids may have significant effects on cellular functions and vasoregulatory control mechanisms in diabetes.

Effects of free fatty acids on the organization of cytoskeletal elements in lymphocytes

Treatment of mouse lymphocytes with cis-unsaturated free fatty acids produced alterations in the immunofluorescence patterns of the cytoskeleton and contractile proteins. Saturated free fatty acids and trans-unsaturated free fatty acids had no effect. In untreated cells, the microtubular pattern exhibited radiation from an organizing center, resembling the spokes of an umbrella. The addition of linoleic acid produced a polarized submembranous aggregate. Under control conditions, staining for actin revealed a diffuse pattern over the entire cell, but the addition of linoleic acid caused the formation of a single large patch, or polarized submembranous aggregate. The pattern for alpha-actinin normally revealed intense perinuclear staining on a diffuse background. Linoleic acid caused the loss of this pattern and the formation of a polarized submembranous aggregate. Linoleic acid treatment also caused the pattern for myosin to change from diffuse to uniform submembranous patching around the periphery of the cell. For all of these proteins, calcium (8 mM), but not magnesium, partially reversed the effects of linoleic acid. Sodium azide had little effect on the normal distribution of actin, tubulin, and alpha-actinin; however, myosin staining revealed prominent patch formation. Colchicine treatment caused diffuse staining, some polarized submembranous aggregate formation of tubulin, and some patching of myosin, but not as extensively as did treatment with linoleic acid. Actin and alpha-actinin were unaffected. These results, in view of the previously shown facts that pretreatment of cells with linoleic acid followed by anti-immunoglobulin inhibits capping of surface immunoglobulin (Klausner, et al., Proc. Natl. Acad. Sci. U.S.A. 77:437-441, 1980) and that free fatty acids partition into the surface membrane (Klausner et al., J. Biol. Chem. 255:1286-1295, 1980), suggest that the perturbation of the plasma membrane with unsaturated free fatty acids alters the interaction of surface receptors with the cytoskeleton, which in turn affects cytoplasmic distribution of the proteins.

Culture of A-431 human epidermoid carcinoma cells in serum-free medium: effect of culture conditions on the binding of [125I]-epidermal growth factor

Serum-free culture conditions that permit the continuous growth of A-431 human epidermoid carcinoma cells were developed. In Dulbecco's modified Eagle's synthetic nutritional medium (DME) supplemented with fetuin, insulin, transferrin, biotin, and oleic acid-fatty acid-free bovine serum albumin complex A-431 cells grew at a rate comparable to that observed in the presence of calf or fetal calf serum. Of the factors tested, oleic acid had the most pronounced stimulatory effect on the growth and [3H]-thymidine incorporation of A-431 cells in serum-free medium. A-431 cells have a high number of receptors for epidermal growth factor (EGF); they bind and rapidly internalize EGF. Nevertheless, EGF did not stimulate either the growth or the [3H]-thymidine incorporation of these cells. Analyses of [125I]-EGF binding data indicated that A-431 cells grown in the presence of calf serum had about 3.2-3.9 X 10(6) specific, saturable EGF receptor sites on their surface. Linear Scatchard plots indicated a single class of noninteracting receptors with an apparent equilibrium dissociation constant of about 2.8 X 10(-9) M. The average number of receptors of A-431 cells maintained in DME supplemented with only fetuin, insulin, and transferrin for several months was significantly less, 1.54 X 10(6), than that of A-431 stock cells cultured in the same medium for 2 days only (2.68 X 10(6)). The apparent dissociation constants for the same cell populations were, however, similar, 4.5 X 10(-9) M and 4.1 X 10(-9) M, respectively. Stimulation of growth by oleic acid resulted in about 20% decrease in the average number of receptor sites, with an increase in the apparent equilibrium dissociation constant.

Effects of free fatty acids on the organization of cytoskeletal elements in lymphocytes

Treatment of mouse lymphocytes with cis-unsaturated free fatty acids produced alterations in the immunofluorescence patterns of the cytoskeleton and contractile proteins. Saturated free fatty acids and trans-unsaturated free fatty acids had no effect. In untreated cells, the microtubular pattern exhibited radiation from an organizing center, resembling the spokes of an umbrella. The addition of linoleic acid produced a polarized submembranous aggregate. Under control conditions, staining for actin revealed a diffuse pattern over the entire cell, but the addition of linoleic acid caused the formation of a single large patch, or polarized submembranous aggregate. The pattern for alpha-actinin normally revealed intense perinuclear staining on a diffuse background. Linoleic acid caused the loss of this pattern and the formation of a polarized submembranous aggregate. Linoleic acid treatment also caused the pattern for myosin to change from diffuse to uniform submembranous patching around the periphery of the cell. For all of these proteins, calcium (8 mM), but not magnesium, partially reversed the effects of linoleic acid. Sodium azide had little effect on the normal distribution of actin, tubulin, and alpha-actinin; however, myosin staining revealed prominent patch formation. Colchicine treatment caused diffuse staining, some polarized submembranous aggregate formation of tubulin, and some patching of myosin, but not as extensively as did treatment with linoleic acid. Actin and alpha-actinin were unaffected. These results, in view of the previously shown facts that pretreatment of cells with linoleic acid followed by anti-immunoglobulin inhibits capping of surface immunoglobulin (Klausner, et al., Proc. Natl. Acad. Sci. U.S.A. 77:437-441, 1980) and that free fatty acids partition into the surface membrane (Klausner et al., J. Biol. Chem. 255:1286-1295, 1980), suggest that the perturbation of the plasma membrane with unsaturated free fatty acids alters the interaction of surface receptors with the cytoskeleton, which in turn affects cytoplasmic distribution of the proteins.