Effects of long-term feeding of marine oils with different positional distribution of eicosapentaenoic and docosahexaenoic acids on lipid metabolism, eicosanoid production, and platelet aggregation in hypercholesterolemic rats

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were distributed mainly in the sn-1,3 positions of seal oil triglyceride and in the sn-2 position of squid oil triglyceride. Seal oil-rich or squid oil-rich fats having constant saturated/monounsaturated/polyunsaturated fatty acid (PUFA) and n−6/n−3 PUFA ratios were fed to exogenously hypercholesterolemic rats for 160 d. The control fat contained linoleic acid as the sole PUFA. Before starting the experimental diets, rats were orally treated with high doses of vitamin D for 4 d to accelerate atherogenesis. The percentage of arachidonic acid in phosphatidylcholine and phosphatidylethanolamine of liver, platelets, and aorta was lower in the marine oil groups than in the control group, seal oil being more effective than squid oil. Maximal platelet aggregation induced by collagen was significantly lower both marine oil groups. Platelet thromboxane (TX) A₂ production induced by collagen or thrombin was markedly reduced by feeding seal or squid oils, the reduction being more pronounced in the seal oil than in the squid oil group. Aortic prostacyclin (PGI₂) production was the same among the three groups. The ratio of the productions of aortic PGI₂ and platelet TXA₂ was significantly higher in the seal oil than in the control group. Although there was no difference in intimal thickness among the three groups, the aortic cholesterol content was significantly lower in the marine oil groups than in the control group. These results showed that the main effects in rats of the different intramolecular distributions of EPA and DHA in dietary fats were on arachidonic acid content in tissue phospholipids and on platelet TXA₂ production.     

Sterol synthesis in the liver intestine,and lung of the guinea pig

The relative rates of sterol synthesis in the liver, ileum, and lung of the guinea pig have been studied by measuring the incorporation by tissue slices of¹⁴C-labeled acetate into digitonin-precipitable sterols. The liver showed maximum incorporation of acetate at pH 6.5, the ileum at pH 7.5, and the lung at pH 6.0. The incorporation of acetate approached the maximum rate at a concentration of 10 mM with the liver and lung and 5 mM with the ileum. Using these conditions of assay, sterol synthesis was measured in the liver, ileum, and lung of four groups of guinea pigs killed at 6-hourly intervals. Depending on the time of day, the rate of sterol synthesis in the ileum was from 6 to 14 times that in the liver, while in the lung the rate was up to 3 times that shown by the liver. Additional studies showed that all regions of the small intestine synthesized sterol at a higher rate than the liver, with the highest rate of synthesis occurring in the ileum. The rates observed in the adrenal, testis, muscle, adipose tissue, and skin indicated that these tissues are not quantitatively important sites of sterol synthesis in the guinea pig.     

Effect of dietary vitamin E levels on fatty acid profiles and nonenzymatic lipid peroxidation in the guinea pig liver

Guinea pigs were fed for five weeks with three diets containing different levels of vitamin E: LOW (but nondeficient, 15 mg of vitamin E/kg diet), MEDIUM (150 mg/kg diet), and HIGH (1,500 mg/kg diet). Dietary vitamin E supplementation did not change oxidative stress indicators in the hydrophilic compartment but increased liver α-tocopherol in a dose-dependent way and strongly decreased sensitivity to nonenzymaticin vitro liver lipid peroxidation. This last effect was already observed in group MEDIUM, and no further decrease inin vitro lipid peroxidation occurred from group MEDIUM to group HIGH. The protective effect of vitamin E againstin vitro lipid peroxidation was observed even though an optimum dietary concentration of vitamin C for this animal model was present in the three different vitamin E diets. Both HIGH and LOW vitamin E decreased percentage fatty acid unsaturation in all phospholipid fractions from membrane origin in relation to group MEDIUM. The results, together with previous information, show that both vitamin E and vitamin C at intermediate concentrations are needed for optimal protection against lipid peroxidation and loss of fatty acid unsaturation even in normal nonstressful conditions. These protective concentrations are higher than those needed to avoid deficiency syndromes.     

Effect of cholesterol and cholestyramine feeding and of fasting on sterol synthesis in the liver,ileum, and lung of the guinea pig

The effects of feeding diets containing either cholesterol (0.24% w/w) or cholestyramine (2.5% w/w) and of fasting on sterol synthesis in the liver, ileum, and lung of both male and female guinea pigs have been studied by measuring the incorporation by tissue slices of¹⁴C-labeled acetate into total digitonin-precipitable sterols. Cholesterol feeding significantly decreased (P<0.05) sterol synthesis in the liver, ileum, and lung of the males and in the ileum of females. Cholestyramine feeding stimulated the rate of hepatic sterol synthesis 13-fold but did not significantly affect sterologenesis in the ileum. Sterol synthesis in the lung was significantly increased (P<0.05) but to a much lesser extent than in the liver. Fatty acid synthesis in the liver, ileum, and lung was not significantly affected by either cholesterol or cholestyramine feeding. In guinea pigs fasted for 24 hr, sterol synthesis was inhibited in all three tissues, the most pronounced effect occurring in the liver. Only in the lung was fatty acid synthesis significantly decreased (P<0.001) by fasting. Cholesterol feeding resulted in increased concentrations of cholesterol in the plasma and liver. Cholestyramine feeding reduced plasma cholesterol concentration by 81% in females and by 64% in males. However, it did not significantly change the tissue cholesterol concentrations. Fasting resulted in a significant increase (P<0.05) in plasma cholesterol concentration but did not affect the concentration of cholesterol in the tissues. It was concluded that in the normal guinea pig, the feedback inhibition produced by both cholesterol and also possibly by bile acids suppresses sterol synthesis in the liver to very low rates compared to those in the small intestine, where sterologenesis is not only less sensitive to the cholesterol negative feedback system than that in the liver, but also is not subject to regulation by the bile acid negative feedback system.     

Effects of dietary vitamin E,selenium, and polyunsaturated fats on in vivo lipid peroxidation in the rat as measured by pentane production

Starting at 21 days of age, groups of six rats each were fed a basal Torula yeast diet supplemented with 0,4% L-methionine and varying amounts of vitamin E as dl-alpha tocopherol acetate, selenium as sodium selenite, and with either 10% stripped corn oil, stripped lard, or coconut oil. By 7 wk, pentane production by rats fed a corn oil diet deficient in both vitamin E and selenium was twice that by rats fed 0.1 or 1 mg of selenium per kg of the same basal diet. Blood glutathione peroxidase activity after 7 wk was proportional to the logarithm of dietary selenium. Groups of rats fed the vitamin E- and selenium-deficient diets with lard or coconut oil had one-half the pentane production of rats fed the vitamin E- and selenium-deficient corn oil diets. The plasma level of linoleic plus arachidonic acid was 1.8 times greater on a wt % basis in rats fed corn oil than in rats fed lard or coconut oil as the fat source. Pentane production by rats fed 40 i.u. dl-alpha tocopherol acetate per kg of the selenium-deficient corn oil diet was one-sixth of that by rats fed the same diet without vitamin E; the plasma of the rats fed the vitamin E-supplemented corn oil diet had a level of vitamin E that was about six times greater than that of the rats fed the vitamin E-deficient corn oil diet.     

5c, 11c, 14c-Eicosatrienoic acid and 5c, 11c, 14c, 17c-eicosatetraenoic acid ofBiota orientalis seed oil affect lipid metabolism in the rat

The effects of 5c, 11c, 14c-eicosatrienoic acid (20∶3BSO) and 5c, 11c, 14c, 17c-eicosatetraenoic acid (20∶4BSO), polyunsaturated fatty acids (PUFA) contained inBiota orientalis seed oil (BSO), on lipid metabolism in rats were compared to the effects of fats rich in linoleic acid (LA) or α-linolenic acid (ALA) under similar conditions. The potential effect of ethyl 20∶4BSO as an essential fatty acid also was examined in comparison with the ethyl esters of LA. ALA and γ-linolenic acid (GLA). BSO- and ALA-rich fat decreased the concentration of plasma total cholesterol, high density lipoprotein cholesterol, triglyceride and phospholipid as compared to LA-rich fat. BSO was more effective in reducing plasma cholesterol concentrations than was the ALA-rich fat. Dietary BSO markedly decreased the hepatic triglyceride concentration as compared to the LA-rich or ALA-rich fats. Aortic production of prostaglandin I₂ tended to decrease in rats fed BSO or ALA-rich fat compared to those fed the LA-rich fat. Adenosine diphosphate-induced platelet aggregation was similar in the three groups. The proportion of arachidonic acid (AA) in liver phosphatidylcholine (PC) of rats fed BSO was lowest compared to that of rats fed ALA-rich or LA-rich fats. Administration of 20∶4BSO, ALA or GLA to essential fatty acid-deficient rats decreased the ratio of 20∶3n−9 to AA in liver PC to the same extent; administration of LA was more effective. The results indicate that the effects of specific PUFA contained in BSO on lipid metabolism are different from those of LA and ALA. It is also suggested that 20∶4BSO may exhibit some essential fatty acid effects.     

Biokinetics of dietaryRRR-α-tocopherol in the male guinea pig at three dietary levels of vitamin C and two levels of vitamin E. Evidence that vitamin C does not “spare” vitamin Ein vivo

The net rates of uptake of “new” and loss of “old”2R,4′ R,8′ R-α-tocopherol (RRR-α-TOH, which is natural vitamin E) have been measured in the blood and in nine tissues of male guinea pigs over an eight week period by feeding diets containing deuterium-labelled α-tocopheryl acetate (d ₆-RRR-α-TOAc). There was an initial two week “lead-in” period during which 24 animals [the “high” vitamin E (HE) group] received diets containing 36 mg of unlabelled (d ₀)RRR-α-TOAc and 250 mg of ascorbic acid per kg diet, while another 24 animals [the “low” vitamin E (LE) group] received diets containing 5 mgd ₀-RRR-α-TOAc and 250 mg ascorbic acid per kg diet. The HE group was then tivided into three equal subgroups, which were fed diets containing 36 mgd ₆-RRR-α-TOAc and 5000 mg [the “high” vitamin C (HEHC) subgroup], 250 mg [the “normal” vitamin C (HENC) subgroup] and 50 mg [the “low” vitamin C (HELC) subgroup] ascorbic acid per kg diet. One animal from each group was sacrificed each week and the blood and tissues were analyzed ford ₀- andd ₆-RRR-α-TOH by gas chromatography-mass spectrometry. The LE group was similarly divided into three equal subgroups with animals receiving diets containing 5 mgd ₆-RRR-α-TOAc and 5,000 mg (LEHC), 250 mg (LENC) and 50 mg (LELC) ascorbic acid per kg diet with a similar protocol being followed for sacrifice and analyses. In the HE group the totald ₀-+d ₆-)RRR-α-TOH concentrations in blood and tissues remained essentially constant over the eight week experiment, whereas in the LE group the totalRRR-α-TOH concentrations declined noticeably (except in the brain, an organ with a particularly slow turnover of vitamin E). There were no significant differences in the concentrations of “old”d ₀-RRR-α-TOH nor in the concentrations of “new”d ₆-RRR-α-TOH found in any tissue at a particular time between the HEHC, HENC and HELC subgroups, nor between the LEHC, LENC and LELC subgroups. We conclude that the long-postulated “spring” action of vitamin C on vitamin E, which is well documentedin vitro, is of negligible importancein vivo in guinea pigs that are not oxidatively stressed in comparison with the normal metabolic processes which consume vitamin E (e.g., by oxidizing it irreversibly) or elminate it from the body. This is true both for guinea pigs with an adequate, well-maintained vitamin E status and for guinea pigs which are receiving insufficient vitamin E to maintain their body stores. The biokinetics of vitamin E uptake and loss in the HE guinea pigs are compared with analogous data for rats reported previously (Lipids 22, 163–172, 1987). For most guinea pig tissues the uptake of vitamin E under “steadystate” conditions was faster than for the comparable rat tissues. However, the brain was an exception with the turnover of vitamin E occurring at only one-third of the rate for the rat. NRCC Publication No. 30775.