Renee C. Peters

Effects of omega-3 fatty acid and vitamin E supplementation on erythrocyte membrane fluidity, tocopherols, insulin binding, and lipid composition in adult men

Abstract Dietary supplementation with an omega-3 fatty acid preparation (fish oil) together with pharmacologic doses of vitamin E increased both insulin binding and membrane fluidity in erythrocytes from human adult males. Supplementation with fish oil alone induced significant increases in the α- and γ-tocopherol contents of the red blood cell membranes. Forty healthy men were given controlled diets and supplements, which together provided 40% of energy from fat (polyunsaturated:monosaturated:saturated ratio of 0.8:1:1), 360 mg cholesterol/day, and a minimum of 22 mg α-tocopherol (αT)/day for three successive experimental periods of 10, 10, and 8 weeks, during which they were given capsules containing 15 g of a placebo oil/day, 15 g fish oil concentrate (FOC)/day, and 15 g fish oil + 200 IU αT (FOC + αT)/day, respectively. Erythrocyte ghost insulin binding (IB) and 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescence-determined fluidity were significantly increased following the FOC + αT period, however FOC alone had no effect. At the end of each experimental period, IB values, as percentage bound/100 μg ghost protein at 4° C, were 0.96, 0.91, and 1.35, and DPH steady state fluorescence anisotropies were 0.311, 0.303, and 0.296, at 4° C, respectively. Small but statistically significant decreases in fluorescence lifetimes further indicated increased fluidity. FOC supplementation resulted in significantly lower membrane cholesterol:phospholipid ratios and increased membrane tocopherols despite daily vitamin E consumption of only 22 mg as in the placebo period. Membrane incorporation of n-3 fatty acids was, however, limited. Thus, dietary polyunsaturated fatty acids exerted substantial effects on erythrocyte membranes by affecting membrane contents of lipid molecules other than the fatty acids.

Heart and liver fatty acid composition and vitamin E content in miniature swie fed diets containing corn and menhaden oils

Female miniature swine, 4-11 yr, were fed 15% fat diets containing n-3 and/or n-6 polyunsaturated fat for 6 months, at 1.95 g fat/kg body weight. Liver lipids from menhaden oil-fed minipigs were elevated in the n-3 fatty acids: 20:5, 22:5 and 22:6, but heart lipids only in 20:5 and 22:6. Liver cell plasma membrane was elevated in 20:5, 22:5 and 22:6 and lowered in the n-6 acids 18:2 and 20:4 in menhaden oil-fed animals, to a greater extent than in the total tissue lipids. Liver alpha-tocopherol tended to decrease upon feeding menhaden oil, but heart alpha-tocopherol concentrations were not affected.

Fatty acid modification of membrane fluidity in Chinese hamster ovary (TR715-19) cells.

Dietary saturated fatty acids, especially lauric (12:0), myristic (14:0) and palmitic (16:0) acids, which are hypercholesterolemic, influence cell membrane fatty acid composition and affect LDL receptor function. When membrane phospholipid fatty acids in Chinese hamster ovary cells, containing the human LDL receptor, were modified (Hannah J. S. et al., 1995 Metabolism 44, 1428-1434), LDL receptor function was affected, but correlations with DPH-determined membrane fluidity were weak. The role of fluidity in various membrane domains with respect to the LDL receptor is examined here. Membrane fluidity was assessed by measuring steady-state fluorescence polarization of diphenylhexatriene (DPH) and its polar propionic acid (DPH-PA) and trimethylammonium (TMA-DPH) derivatives from 38 to 4 degrees C in fatty acid modified Chinese hamster ovary cells. Fatty acid changes modulated mid-bilayer fluidity as determined with DPH, but fluidity in phospholipid headgroup domains, assessed with DPH-PA and TMA-DPH, was independent of fatty acyl composition. The DPH fluidity was related to membrane unsaturation (P < 0.02), oleate contents (P < 0.009) in particular, but inversely related (P < 0.0002) to the longer chain (> or = 20 C atoms) unsaturated fatty acids with from four to six double bonds. The LDL binding was independent of fluidity, but there were weak relations between LDL internalization and DPH-PA anisotropy and between LDL degradation and TMA-DPH anisotropy. It was concluded that LDL binding was not related to mid-bilayer fluidity, but the results with the polar probes suggest a role of fluidity in modulating vertical displacement of the LDL/LDL receptor complex across the plasma membrane.

Effect of dietary corn, coconut, and menhaden oils on lipoprotein, liver, and heart membrane composition in the hypercholesterolemic rabbit

Abstract The relative capacities of n-3 and n-6 polyunsaturated fatty acid-containing diets (PUFA) to modify chemical composition in plasma lipoproteins, liver membrane, and heart phospholipids and to thereby modulate lipoprotein and membrane fluidity were studied in the rabbit. Stock diet-fed New Zealand rabbits were made hypercholesterolemic by feeding a casein-based, semi-purified diet containing coconut oil. Subsequent replacement of the coconut oil with corn or menhaden oil caused reduction or elevation, respectively, of blood cholesterol levels. Very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL) became progressively less fluid following transfer from the PUFA containing low fat stock diet to the coconut oil diet. Subsequent corn oil feeding induced significant increases in VLDL and LDL, but not HDL, fluidities. Menhaden oil feeding did not affect lipoprotein fluidity. Liver membranes were less fluid in corn oil-fed and menhaden oil-fed than in coconut oil-fed rabbits. Despite these differences in lipoprotein and membrane fluidity the amount of rabbit 125I-LDL capable of binding to liver membranes from the animals was not affected by the dietary fat modifications. Fatty acyl compositions were affected by the diets. Heart and liver phospholipids showed extensive incorporation of n-3 fatty acids and deletion of linoleate in the menhaden oil-fed animals. Dietary effects on lipoprotein phospholipid fatty acids were statistically significant but not as pronounced as in these tissues.

Human erythrocyte membrane fluidity and insulin binding are independent of dietary trans fatty acids

Abstract Substitution of selected saturated fatty acids of the diet of 29 men and 29 women with cis or trans monounsaturated fatty acids did not affect erythrocyte membrane fluidity, insulin binding, and the membrane cholesterol and phospholipid concentrations. Subjects were fed four different controlled diets with a total fatty acid content of 39 to 40 energy percent for four 6-week periods in a Latin square design. The diets were: (1) high oleic acid (16.7 energy percent oleic); (2) moderate trans (3.8 energy percent trans fatty acids); (3) high trans (6.6 energy percent trans fatty acids); and saturated (16.2 energy percent lauric + myristic + palmitic acids). There were no significant diet effects on red cell ghost fluidity determined by fluorescence polarization of the hydrocarbon probe 1,6-diphenyl-1,3,5-hexatriene (DPH) and the polar analog trimethylammonium-DPH (TMA-DPH). There were limited diet effects on fluidity of membranes as determined with DPH-propionic acid (DPH-PA) for the men. Insulin binding was more closely associated with anisotropy of fluorescence of the surface probe, DPH-PA, than with that of the other probes, which is compatible with the localization of the insulin receptor in a domain at the cell membrane surface.

Effect of dietary cholesterol on the lipoprotein profile and binding of radioiodinated lipoproteins to hepatic membranes in the cockerel (gallus domesticus)

1. Cockerels fed a cholesterol-supplemented diet experienced a marked elevation of lipoprotein particles of density less than or equal to 1.006 g/ml (VLDL) and a diminution of lipoprotein particles of density 1.02-1.05 g/ml (LDL). 2. Unlike VLDL of some cholesterol-fed animals, cholesterol-fed cockerel VLDL did not display beta-mobility on agarose gel electrophoresis. 3. [125I]LDL and [125I]HDL binding to cockerel liver membranes was not affected by cholesterol feeding. 4. Different lipoprotein types appear to bind to a common site on cockerel liver membranes. 5. The results suggest that liver cells of cockerels may not possess LDL binding sites that are analogous to those of mammalian species.

Aging and Miniature Swine Heart and Liver Plasma Membranes

Age related changes in heart and liver plasma membranes were assessed over a wide age range, prepubertal, < 0.5 yr; young, 0.5 to 2.5 yr; middle aged, 5.9 to 10 yr; and old, 11.5 to 13.9 yr, in male and female Hormel-Hanford miniature swine fed the same energy restricted, low fat, cholesterol free, stock diet continuously post weaning. Mid bilayer heart plasma membrane fluidity, by diphenylhexatriene (DPH) polarization, was increased in old pigs, but fluidity in polar membrane domains was not increased in the old pigs. Age had no effect on fluidity by DPH in liver cell membranes, but surface domains were influenced by age. Liver cell membrane fluidity, by polar probes, followed a U shaped pattern with age and reached a maximum in the middle aged minipig group. In heart, middle aged pigs were reduced in total n-6 polyunsaturates, especially 18:2, and increased in saturates. Conversely, liver plasma membranes in middle aged pigs were elevated in unsaturated and reduced in saturated fatty acids. Heart membrane lipid peroxidation tended to be increased in middle aged and elderly pigs, perhaps due to increased membrane vitamin E in middle aged and old pigs. Thus, lipid peroxidation tended to increase over the lifespan of miniature swine, even when they were food restricted.

Blood Risk Factor Metabolites Associated with Heart Disease and Myocardial Fatty Acids in Copper-Deficient Male and Female Rats

Abstract Intact and castrated males and intact and ovariectomized female rats were fed a copper-deficient diet in order to establish whether the protection provided in females against cardiovascular pathology and mortality is due to endogenous sex hormones, and different levels of blood lipids and/or myocardial fatty acids. Seventy-three male and female rats were assigned to a copper-deficient diet (0.6 μg of copper/g diet) containing 62% fructose for 8 weeks. Twelve of the male rats underwent castration and 12 of the females were ovariectomized. All animals exhibited high levels of plasma cholesterol, triglycerides, and uric acid, which were neither affected by the sex of the rat nor by the surgical treatment. The composition of fatty acids of the myocardium was similar in males and females. Except for those animals that were sacrificed by us, all other male rats died of heart pathology. In contrast, none of the female rats exhibited heart pathology and none died of the deficiency. It is suggested that heart pathology and mortality in copper deficiency are sex related and not due to high levels of plasma cholesterol, triglycerides, and uric acid or to differences in myocardial fatty acid composition.

Brain and heart membrane fatty acid composition in miniature swine fed diets containing corn and menhaden oils

Abstract Thirty-six female minipigs, from 4.7–10.6 years old, were fed corn oil (CO) and/or menhaden oil (MO) in diets containing 0, 0.75, or 15% MO and sufficient CO to provide 15% total oil for 6 months. Half the animals were made hypercholesterolemic by feeding them a 13% lard, 2% cholesterol diet for 2 months prior to the experimental feeding period. Samples were taken from the same location in each animal from forebrain, caudate nucleus, cerebellum, and heart to isolate brain synaptosomes and heart plasma membranes. Pretreatment of the minipigs with cholesterol had no effect on the fatty acid composition of the fractions isolated and their membrane fluidity. Despite MO feeding, the long chain n-3 fatty acids were low in the heart plasma membranes compared to heart tissue homogenates from the same animals. Minipigs fed 15% MO showed significant increases in synaptosomal eicosapentaenoate (EPA) and docosapentaenoate (DPA). Docosahexaenoate (DHA) was incorporated into synaptosomes in animals fed 0.75% MO, at concentrations significantly higher than in the CO-fed pigs. Pigs fed 15% MO showed significantly lower brain DHA than those fed CO. The synaptosomal data for the pigs fed the various diets suggest that metabolic synthesis from linolenate, 18:3(n-3), may be a more important source of brain DHA than diet, but that dietary n-6n-3 ratios and levels of 18:3(n-3), EPA, DPA and DHA may require careful attention. The fatty acid changes did not affect fluidity determined by fluorescence anisotropy of diphenylhexatriene or its polar derivatives.