Nicola M. Jeffery

Eicosapentaenoic and docosahexaenoic acids alter rat spleen leukocyte fatty acid composition and prostaglandin E2 production but have different effects on lymphocyte functions and cell-mediated immunity

Weanling rats were fed on high-fat (178 g/kg) diets which contained 4.4 g α-linolenic (ALA), γ-linolenic, arachidonic (ARA), eicosapentaenoic (EPA), or docosahexaenoic acid (DHA)/100 g total fatty acids. The proportions of all other fatty acids, apart from linoleic acid, and the proportion of total polyunsaturated fatty acids (PUFA) (approximately 35 g/100 g total fatty acids) were constant, and the n−6 to n−3 PUFA ratio was maintained as close to 7 as possible. The fatty acid compositions of the serum and of spleen leukocytes were markedly influenced by that of the diet. Prostaglandin E2 production was enhanced from leukocytes from rats fed the ARA-rich diet and was decreased from leukocytes from the EPA- or DHA-fed rats. Replacing dietary ALA with EPA resulted in diminished ex vivo lymphocyte proliferation and natural killer (NK) cell activity and a reduced cell-mediated immune response in vivo. In contrast, replacing ALA with DHA reduced ex vivo lymphocyte proliferation but did not affect ex vivo NK cell activity or the cell-mediated immune response in vivo. Replacement of a proportion of linoleic acid with either γ-linolenic acid or ARA did not affect lymphocyte proliferation, NK cell activity, or the cell-mediated immune response. Thus, this study shows that different n−3 PUFA exert different immunomodulatory actions, that EPA exerts more widespread and/or stronger immunomodulatory effects than DHA, that a low level of EPA is sufficient to influence the immune response, and that the immunomodulatory effects of fish oil may be mainly due to EPA.

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)

The ratio of n-6 to n-3 polyunsaturated fatty acids in the rat diet alters serum lipid levels and lymphocyte functions.

Previous studies have reported that feeding rats diets rich in fish oils, which contain high proportions of the n-3 polyunsaturated fatty acids (PUFA) eicosapentaenoic and docosahexaenoic acids, results in lowering of blood lipid levels and suppression of lymphocyte functions testedex vivo andin vivo. The effects of other n-3 PUFA, such as α-linolenic acid, which is found in high proportions in linseed oil, are not as well documented. Therefore, in the present study, weanling male rats were fed for six weeks on one of five high-fat (20% by weight) diets made by mixing together sunflower and linseed oils; the resulting blends had n-6/n-3 PUFA ratios of 112.5:1 (pure sunflower oil), 14.8:1, 6.5:1, 0.8:1, and 0.33:1 (pure linseed oil); the levels of all other components in the diet were identical. The final body weight and total dissectable fat were lowest in rats fed the pure linseed oil diet. Serum cholesterol, triacylglycerol and nonesterified fatty acid concentrations decreased as the n-6/n-3 PUFA ratio of the diet decreased. The fatty acid composition of the serum and of spleen lymphocytes was influenced by the diet fed-there was a progressive decrease in the proportions of linoleic and arachidonic acids and a progressive increase in the proportion of α-linolenic acid as the n-6/n-3 PUFA ratio of the diet decreased. Eicosapentaenoic and docosahexaenoic acids were detected in the serum but not in spleen lymphocytes. Inclusion of α-linolenic acid in the diet resulted in significant suppression of spleen lymphocyte proliferation in response to the T-cell mitogen concanavalin A and in spleen lymphocyte natural killer cell activity, both measuredex vivo. The localized graft vs. host response, a measure of cellmediated immunityin vivo, progressively decreased as the n-6/n-3 PUFA ratio of the diet decreased. Thus, this study shows that dietary α-linolenic acid results in lowered blood lipid levels and suppressed lymphocyte functionsex vivo andin vivo. With respect to these effects, α-linolenic acid is as potent as dietary fish oil.

The Effects of Olive Oil upon Rat Serum Lipid Levels and Lymphocyte Functions Appear to Be Due to Oleic Acid

In order to investigate whether previously reported effects of feeding olive oil (OO) upon rat serum lipid concentrations and immune cell functions are due to oleic acid, weanling rats were fed for 6 weeks on diets containing 20% by weight of OO, safflower oil (SO), or high oleic acid sunflower oil (HOSO); a low-fat (LF) diet containing 2.5% by weight of lipid was used as a control. Feeding the OO or HOSO diets resulted in an elevated serum triacylglycerol concentration as compared with feeding the LF or SO diets. The serum total cholesterol concentrations were raised in the animals fed the high-fat diets and were highest in animals fed the OO or the HOSO diet. The fatty acid composition of the serum and of spleen lymphocytes reflected that of the diet fed. The mitogen-stimulated spleen lymphocyte proliferation ex vivo was significantly lower following OO or HOSO feeding as compared with LF or SO feeding. Similarly, feeding the OO or the HOSO diet resulted in lower spleen natural killer cell activity as compared with LF or SO feeding. These observations indicate that the effects of OO feeding are most likely due to oleic acid rather than to other components of OO.

Level of polyunsaturated fatty acids and the n-6 to n-3 polyunsaturated fatty acid ratio in the rat diet alter serum lipid levels and lymphocyte functions

In order to further examine the effects of dietary polyunsaturated fatty acids (PUFA) upon blood lipid levels and lymphocyte functions, weanling rats were fed for 6 weeks on high fat (178 g/kg) diets which differed in the ratio of n-6:n-3 PUFA (100, 20, 10, 5, 1) and in the absolute level of PUFA (17.5 or 35 g/100 g fatty acids). The n-6:n-3 PUFA ratio of the diets was decreased by replacing linoleic acid with alpha-linolenic acid while the PUFA content of the diets was decreased by replacing PUFA with palmitic acid. Serum cholesterol concentrations decreased as the n-6:n-3 PUFA ratio of the low PUFA diet decreased. The ex vivo proliferation of spleen lymphocytes from rats fed the low PUFA diets decreased as the n-6:n-3 PUFA ratio of the diet decreased; the proliferation of spleen lymphocytes from high PUFA-fed rats was less affected by the n-6:n-3 PUFA ratio of the diet. Natural killer cell activity was lower for spleen lymphocytes from rats fed high PUFA diets with n-6:n-3 PUFA ratios of 100 or 20 than for those from rats fed low PUFA diets with these ratios. The natural killer cell activity of spleen lymphocytes decreased as the n-6:n-3 PUFA ratio of the low PUFA diet decreased. These findings indicate that dietary alpha-linolenic acid has significant blood lipid-lowering and immunomodulatory effects in rats, but that the effect is dependent upon the total PUFA content of the diet. The ratios of linoleic and alpha-linolenic acids to other fatty acids (e.g. palmitic, oleic) are important in determining the precise effect of manipulations of the fatty acid composition of the diet.

Effects of variations in the proportions of saturated, monounsaturated and polyunsaturated fatty acids in the rat diet on spleen lymphocyte functions.

To obtain further information about the immunomodulatory effects of specific dietary fatty acids, weanling male rats were fed for 6 weeks on high-fat (178 g/kg) diets which differed according to the principal fatty acids present. The nine diets used differed in their contents of palmitic, oleic, linoleic and alpha-linolenic acids; as a result the total polyunsaturated fatty acid (PUFA) content and the PUFA:saturated fatty acid ratio varied (from 17.8 to 58.5 g/100 g fatty acids and from 0.28 to 5.56 respectively). The n-6 PUFA:n-3 PUFA ratio was kept constant in all diets at approximately 7.0. The fatty acid composition of the serum and of spleen lymphocytes were significantly influenced by that of the diet fed. The ex vivo proliferation of spleen lymphocytes decreased as the level of oleic acid in the diet increased. Spleen natural killer cell activity decreased as the oleic acid content of the diet increased and increased as the palmitic acid content of the diet increased. The extent of the effects of these fatty acids on lymphocyte functions was modified by the nature of the background fatty acid composition of the diet.

Effects of varying the type of saturated fatty acid in the rat diet upon serum lipid levels and spleen lymphocyte functions

To obtain further information about the effects of specific dietary saturated fatty acids, weanling male rats were fed for 6 weeks on low fat (7.7% by weight) or high fat (17.8% by weight) diets which differed according to the principal fatty acids present. The diets were rich in caprylic and capric acids (medium chain triacylglycerols; MCT), lauric acid, palmitic acid at the sn-1(3) position, palmitic acid at the sn-2 position or stearic acid. The total proportions of saturated (42-46%), monounsaturated (36%), n-6 polyunsaturated (15%) and n-3 polyunsaturated (2.2%) fatty acids were the same in all diets. Serum cholesterol concentrations were not different among rats fed the different diets, except that the concentration in the serum of rats fed the high fat diet with palmitic acid in the sn-2 position was high. This was reflected in higher HDL and LDL cholesterol concentrations in the serum of animals fed this diet. Triacylglycerol (TAG) concentrations tended to be higher in the serum of rats fed the low fat diets compared with those fed the high fat diets. They were lowest in the serum of MCT-fed rats irrespective of the level of fat in the diet and were highest in the serum of rats fed the low fat diet rich in stearic acid. These differences were due to lower chylomicron and VLDL TAG concentrations in the serum of MCT-fed rats and higher chylomicron and VLDL TAG concentrations in the serum of low fat, stearic acid-fed animals. The fatty acid compositions of the serum and of spleen lymphocytes were influenced by that of the diet fed. The ex vivo proliferation of lymphocytes from the spleens of rats fed the high fat diet rich in palmitic acid at the sn-2 position was greater than that of lymphocytes from animals fed the other diets. Natural killer (NK) cell activity tended to be lower for spleen lymphocytes from rats fed high fat diets than for those fed low fat diets irrespective of the principal saturated fatty acid present. NK cell activity was highest for spleen lymphocytes from animals fed the diets rich in palmitic acid and was lowest for those from animals fed the high fat diet rich in stearic acid. Spleen lymphocytes from the latter animals had the lowest proportion of CD16+ cells, a marker for NK cells. Thus, this study shows that the type of saturated fatty acid present in the diet not only has subtle effects upon blood lipid and lipoprotein levels but can significantly affect lymphocyte functions. Spleen lymphocyte NK cell activity is decreased as the fat content of the diet increases. NK cell number and activity are reduced by a high fat diet rich in stearic acid. Spleen lymphocyte proliferation is enhanced by palmitic acid-rich diets, particularly if palmitic acid is in the sn-2 position of dietary TAG.

Characterization of lipoprotein composition in rats fed different dietary lipids and of the effects of lipoproteins upon lymphocyte proliferation

Abstract Weanling Lewis rats were fed for 10 weeks on a low fat (2.5% by weight; LF) diet or on diets containing 20% by weight of hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO), evening primrose oil (EPO), or menhaden (fish) oil (MO); all other components of the diets were identical. The chylomicron (CM), very low density lipoprotein (VLDL), low density lipoprotein (LDL), and high density lipoprotein (HDL) fractions were isolated from the serum. The serum from MO-fed animals had lower LDL and HDL cholesterol concentrations than the serum from animals fed each of the other diets. The apolipoprotein A-1 concentration in the HDL fraction from animals fed the MO diet was also low. The serum from HCO-fed animals had a higher CM triacylglycerol concentration than serum from animals fed each of the other diets. The serum from OO-fed animals had a higher VLDL triacylglycerol concentration than serum from animals fed each of the other diets. The concentration of apolipoprotein B was also high in the VLDL fraction from OO-fed animals. The fatty acid composition of each lipoprotein fraction was affected by the nature of the lipid in the diet; the greatest effects were observed in the CM and VLDL fractions. Each lipoprotein fraction isolated from LF-fed rats inhibited mitogen-stimulated rat spleen lymphocyte proliferation in a concentration-dependent manner; LDL and HDL caused greater inhibition than CM and VLDL. Dietary lipid manipulation did not alter the inhibitory effects of any of the lipoprotein fractions upon lymphocyte proliferation, except that CM and HDL from MO-fed animals and HDL from OO-fed animals resulted in enhanced proliferation compared with either CM or HDL from animals fed the other diets. We conclude that the inhibition of lymphocyte proliferation caused by feeding rats certain dietary lipids (OO, EPO, MO) may be mediated by non-lipoprotein serum components.

Characteristics of lipid and lymphocytes collected from the lymph of rats fed a low fat diet or high fat diets rich in N-6 or N-3 polyunsaturated fatty acids

Abstract Lymphatic fluid and lymphocytes were isolated from lymph collected by cannulation of the thoracic duct of rats which had been fed for six weeks on a low fat (LF) diet or on high fat diets with safflower oil (SO) or fish oil (FO) as the sources of fat. The fatty acid composition of lymphatic fluid was markedly influenced by that of the diet. There were significant linear correlations between the proportions of lauric, myristic, palmitic, palmitoleic, stearic, oleic and linoleic acids in the diet and in the lymphatic fluid. Eicosapentaenoic and docosahexaenoic acids appeared in the lymphatic fluid of rats fed the FO diet. The fatty acid composition of lymph lymphocytes was influenced by that of the diet fed, but the effects of diet were weaker than those upon lymphatic fluid. The principal effect was seen in cells from the FO-fed rats; these had a significantly lower proportion of arachidonic acid than cells from rats fed either of the other diets and they contained measurable proportionss of eicosapentaenoic and docosahexaenoic acids. The amount and type of fat fed did not affect the proportions of CD4-positive, CD8-positive, CD11b/c-positive or κ-light chain-positive lymph lymphocytes. Lymph lymphocytes from rats fed either the SO or FO diets proliferated less well than those from rats fed the LF diet.