Effect of fish oils on rat plasma lipoproteins

Linoleate supplementation in steers modifies lipid composition of plasma lipoproteins but does not alter their fluidity

The health value for man of lipids in bovine muscles can be improved by the addition of PUFA to the animals' diets, but such treatments can modify fluidity of plasma lipoproteins and therefore their metabolic functions. The aim of the present study was to analyse whether changes in chemical composition of lipoproteins in steers fed sunflower oil-rich diets altered lipoprotein fluidity, measured by fluorescence polarization and electron spin resonance. LDL, light HDL and heavy HDL fractions were isolated by ultracentrifugation from plasma of eighteen crossbred Charolais×Salers steers. For a period of 70d, animals were given a control diet (C,n6) consisting of hay (540g/kg) and concentrate mixture (460g/kg) or the same basal diet supplemented with sunflower oil rich inn-6 PUFA (40g/kg diet DM), given either as crushed seeds (S,n6) or as a free oil infused directly into the duodenum (O,n6), thus avoiding ruminal hydrogenation of PUFA. We have shown that in bovine animals: (1) fluidity measurements by fluorescence polarization must be made at the bovine physiological temperature (38·5°C); (2) heavy HDL always appear as the less fluid lipoparticles; (3) electron spin resonance, which does not depend on lipoparticle size, is more appropriate to compare the fluidity of LDL with that of light HDL. The values for lipoprotein fluidity measured by both methods indicated that linoleate-rich diets did not have any effect when compared with diet C; however, chemical variables support a fluidification of lipoparticles, since in steers given the diet O,n-6 PUFA concentrations increased in polar (×1·8) and neutral (×1·6) lipids in lipoparticles (P=0·0001). The phospholipid:protein ratio increased in light (+20%,P=0·019) and heavy (+23%,P=0·06) HDL and especially in LDL (+46%,P=0·0001); the total cholesterol:phospholipid ratio decreased in the three lipoprotein classes (−15 to −30%, NS). Diet S led to similar but less pronounced effects. We concluded that linoleate-rich diets modified the chemical composition of plasma lipoproteins in steers, but did not alter their fluidity; this probably occurred as a result of ‘homeoviscous adaptation’, which ensured their functional capacity.

Probucol, but not MaxEPA fish oil, inhibits mononuclear cell adhesion to the aortic intima in the rat model of atherosclerosis

We have examined the influence of both dietary fish oil and probucol on monocyte adhesion to the aortic endothelium rats fed an atherogenic diet for 2 weeks. All rats were fed a low-fat diet supplemented with 4% cholesterol, 1% cholic acid, and 0.5% 2-thiouracil. In addition to the atherogenic diet, group 1 (FO; n = 20) received a dietary supplement of the fish oil concentrate MaxEPA (5% w/w); group 2 (CO; n = 20) received a supplement of a control oil with same polyunsaturated-monounsaturated-saturated fatty acid ratio as Max-EPA; and group 3 (PR; n = 20) received both the control oil supplement (5% w/w) and a 1% (w/w) supplement of probucol. Analysis of blood samples taken at 2 weeks revealed that both fish oil and probucol lowered total plasma cholesterol by 30% compared with the CO group. In addition, fish oil supplementation caused a significant decrease in cholesterol contained in the VLDL fraction while probucol supplementation caused a significant lowered cholesterol in the HDL fraction. Analysis of mononuclear cell adhesion to the aortic endothelium in vivo revealed that, fish oil had no significant effect probucol reduced adhesion by 40%. The results of this study suggest that probucol, but not fish oil, may inhibit the initiation of lesion formation in the rat model of atherosclerosis.

Effect of dietary alpha-linolenic acid on functional characteristic of Na+/K(+)-ATPase isoenzymes in whole brain membranes of weaned rats

The influence of dietary fatty acids on Na+ sensitivity and ouabain affinity of Na+/K(+)-ATPase isoenzymes of whole brain membranes were studied in weaned rats fed for two generations with diets either devoid of alpha-linolenic acid (sunflower oil diet) or rich in alpha-linolenic acid (soya oil diet). The (n--3) deficiency induced by the sunflower oil diet led to an increase in the (n--6)/(n--3) molar ratio in whole brain membranes. Na+/K(+)-ATPase isoenzymes were discriminated on the basis of their differential affinities for ouabain. In rats fed sunflower oil diet, the ouabain titration displayed three inhibitory processes with markedly different affinities: low affinity (alpha 1); high affinity (alpha 2); and very high affinity (alpha 3). Membranes of rats fed soya oil diet exhibited only two inhibitory processes, i.e., low affinity (likely alpha 1+ alpha 2) and high affinity (likely alpha 2+ alpha 3) with the low affinity form intermediate between the sunflower alpha 1 and alpha 2 forms, and the high affinity form intermediate between the sunflower alpha 2 and alpha 3 forms. In fact, the Na+ response shows that the three isoenzymes have different Na+ sensitivities. Regardless of the diet, alpha 1 has a similar Na+ sensitivity (less than 1 mM), whilst alpha 2 and alpha 3 are more sensitive in soya oil membranes compared to sunflower oil membranes (5.1 vs. 7.2 mM and about 11 vs. 22.5 mM, respectively). Thus, sodium appears to be a better criterion of heterogeneity than ouabain.

Interactive effects of dietary (n-3) polyunsaturated fatty acids and chronic ethanol intoxication on synaptic membrane lipid composition and fluidity in rats

The influence of dietary polyunsaturated fatty acids on fatty acid composition, cholesterol and phospholipid content as well as 'fluidity' (assessed by fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) probes) of brain synaptic plasma membranes (SPM) and their interactions with chronic ethanol effects were studied in rats fed for two generations with diets either devoid of (n-3) fatty acids (sunflower oil diet), rich in alpha-linolenic acid (soya oil diet) or in long chain (n-3) fatty acids (sunflower + cod liver oil diet). Results were compared with rats fed standard lab chow. Sunflower oil led to an increase in the (n-6)/(n-3) ratio in the membranes with an increase of the 'fluidity' at membrane apolar level; sunflower + cod liver oil decreased the (n-6)/(n-3) ratio without affecting membrane 'fluidity' while no difference was seen between the SPM of rats fed soya oil and standard diet. After 3 weeks alcohol intoxication in rat fed the standard diet: oleic alpha-linoleic acids and cholesterol levels were increased, arachidonic acid and the double bond index/saturated fatty acids were decreased and there was a decrease of 'fluidity' in the lipid core of the SPM. Soya oil almost totally abolished these usually observed changes in the SPM fatty acids composition but increased oleic acid and cholesterol without any change in fluidity. Sunflower oil led to the same general alterations of fatty acid as seen with standard diet but to a greater extent, with decrease of the 'fluidity" at the apolar level and in the region probed by TMA-DPH. When sunflower oil was supplemented with cod liver oil, oleic and alpha-linoleic acids were increased while the 'fluidity' of the apolar core of SPM was decreased. So, the small changes in fatty acid pattern seem able to modulate neural properties i.e. the responses to a neurotoxic like ethanol. A structurally specific role of PUFA is demonstrated by the pernicious effects of the alpha-linolenic acid deficient diet which are not totally prevented by the supply of long chain (n-3) PUFA.