Effects of dietary antioxidants on in vivo lipid peroxidation in the rat as measured by pentane production

The hypothesis that pentane is an in vivo product of lipid peroxidation was confirmed by a study of the effects of a nonbiological antioxidant on pentane production in rats fed a diet deficient in vitamin E and supplemented with 0.01% N,N′-diphenyl-p-phenylenediamine (DPPD). Seven rats were fed a vitamin E-deficient diet starting at 3 wk of age. After 5 wk, 0.01% DPPD was added to the diets of three rats (group DPPD) while the diet of the other four rats remained unchanged (group OE). Within 2 wk of the diet change, rats in group DPPD exhaled 65% less pentane than rats of the same age in group OE. After 5 wk of being fed the DPPD-supplemented diet, rats in group DPPD were again fed the basal vitamin E-deficient diet; within 3 wk, these rats produced pentane levels similar to those of rats in group OE. The effects of vitamin E depletion and repletion on in vivo lipid peroxidation in rats were also studied. Three groups of three rats each were initially fed a vitamin E-deficient diet starting at 3 wk of age. After 8, 8, and 5 wk of being fed this diet, the three groups were fed diets supplemented with 3.3 (group 0→3.3E), 11 (group 0→11 E), and 200 (group 200E) i.u. vitamin E acetate/kg diet, respectively. Another group of three rats (group 11 E) was fed a diet supplemented with 11 i.u. vitamin E/kg starting at 3 wk of age for the duration of the study. There were significant decreases in pentane production by rat groups 0→3.3E, 0→11E, and 200E within 2 wk of the change to the vitamin E-supplemented diets. After about 5 wk of being fed their respective vitamin E-supplemented diets, pentane breath levels had stabilized. Breath pentane levels were inversely proportional to the log of dietary vitamin E concentration.     

Effect of age and dietary fat (fish,corn and coconut oils) on tocopherol status of C57BL/6Nia mice

The effect of age and dietary fat type on tocopherol status was investigated using young and old C57BL/6Nia mice fed semipurified diets containing 5% (by weight) fish, corn or coconut oils and supplemented with 30, 100 or 500 ppm dl-α-tocopheryl acetate for 6 wk. Tocopherol levels in the diets, plasma, liver, kidney and lung were measured by high performance liquid chromatography following appropriate extractions. The results indicate that mice fed fish oil maintain lower plasma and tissue tocopherol concentrations than those fed corn and cononut oils (fish<corn oil<coconut oil). The difference was not due to a loss of tocopherol prior to consumption, but rather appeared to occur during the absorption process. Old mice had lower plasma and liver tocopherol concentrations than young mice. Old mice fed fish oil, however, maintained plasma tocopherol levels better than young mice fed fish oil, presumably due to their larger tocopherol pool. No age effect was detected on kidney and lung tocopherol levels. It is concluded that tocopherol status is affected by age and dietary fat type, especially fish oil.     

Effect of vitamin E on pentane exhaled by rats treated with methyl ethyl ketone peroxide

One useful method to monitor in vivo lipid peroxidation is the measurement of volatile hydrocarbons, mainly pentane and ethane, that derive from unsaturated fatty acid hydroperoxides. Vitamin E, the biological antioxidant, inhibits lipid peroxidation and the production of pentane and ethane. The rates of pentane production by male Sprague-Dawley rats fed a diet that contained 10% vitamin E-stripped corn oil and 0, 1, 3, 5 or 10 IU dl-α-tocopherol acetate/kg were monitored over a 12-wk period. During the eleventh and twelfth weeks, the rats were injected intraperitoneally with 3.3 and 13 mg of methyl ethyl ketone peroxide (MEKP)/kg body wt, respectively. Pentane production was then measured at intervals over a 50-min period, and the total amount of pentane produced over this time interval was estimated. An asymptotic function was found to describe the relationship between exhaled pentane and the low levels of dietary vitamin E that were fed to the rats. As measured by pentane production, rats had a higher minimal vitamin E requirement after they were treated with the potent peroxidation initiator MEKP than they did prior to treatment. The level of pentane exhaled by rats injected with 13 mg MEKP/kg body wt was significantly correlated with kidney and spleen tocopherol levels.     

Effect of dietary fat upon aflatoxicosis in rats fed torula yeast containing diet

This study was designed to study the possible interrelationships between Torula yeast, vitamin E, and the dietary fat source on aflatoxin-induced tumors. Rats were fed Torula yeast-containing basal diets which included 1.7 ppm aflatoxin B₁ with either lard, corn oil or no fat, and with or without vitamin E supplements for 3 months. Thereafter, the respective diets without aflatoxin were fed for ca. 9 months. Animals receiving the vitamin E-deficient diets had a high mortality. Although the vitamin E-deficient, aflatoxin-treated rats had lower wt gains than did the vitamin E-deficient controls, they lived twice as long. In addition, regardless of the dietary fat source, the kidneys and adrenals of these vitamin E-deficient, aflatoxin-supplemented rats were found to be significantly heavier than the controls, and plasma cholesterol levels were elevated. Increased amounts of liver lipid were observed in response to aflatoxin in both corn oil-fed and fat-deficient rats. No such differences were observed in the responses of the vitamin E-supplemented groups to aflatoxin. On the corn oil diet, aflatoxin administration resulted in an increased deposition of polyunsaturated fatty acids in cholesteryl ester and phospholipid fractions in livers of vitamin E-deficient rats and the phospholipid fraction of vitamin E-sufficient rats. The vitamin E-deficient rats exhibited necrosis of the liver, which was alleviated when aflatoxin was included in the diet, and calcification of the kidneys, which was potentiated by the dietary aflatoxin. No tumors were observed in these animals. In animals maintained on vitamin E-sufficient diets for 1 year, growth was depressed as a result of aflatoxin administration with the greatest depression occurring in the group fed corn oil. Spleen wt were decreased in all groups given aflatoxin. However, there were no changes in either plasma or liver cholesterol or total liver lipids which could be attributed to aflatoxin administration. When aflatoxin was fed with lard, the cholesteryl ester, triglyceride, and free fatty acid fractions of plasma had decreased amounts of the C20:4 acid. In the cholesteryl ester fraction only, this change was accompanied by increased levels of C16:0, C18:0, and C18:1 acids. In the liver phospholipids, there were increased levels of mono- and polyunsaturated fatty acids and decreases in the saturated fatty acids. All of the animals receiving aflatoxin exhibited severe necrosis and tumor formation in the kidneys; the animals fed lard had the highest level of involvement and those in the fat-free group the least. Liver pathology was the least marked among the rats fed the fat-free diet. Since aflatoxin-induced tumors are rich in lipids, the fat-free diet may be protective to the animal.     

Lipid peroxidation: A mechanism involved in acute ethanol toxicity as demonstrated by in vivo pentane production in the rat

The effect of a single dose of ethanol on lipid peroxidation in three groups of rats fed different amounts of vitamin E was determined by the measurement of pentane in the breath. All rats had increased pentane production above basal levels by 15 min following oral administration of 6 g ethanol/kg body wt. The increase in total pentane production during a 13-hr test period after intragastric administration of ethanol was greater in the rats fed the vitamin E-deficient diet than in the rats, fed vitamin E-supplemented diets (α=2P=0.02). The results support the hypothesis that acute ethanol toxicity involves lipid peroxidation and further demonstrate the usefulness in toxicological studies of monitoring pentane as an index of lipid peroxidation in vivo.     

The role of lipid peroxidation during chronic and acute exposure to ethanol as determined by pentane expiration in the rat

Weanling rats were fed one of 3 diets containing 0, 11 or 200 international units (IU) dl-α-tocopherol acetate/kg diet for 4 weeks. Following this period, the drinking water was replaced with an 18% solution of ethanol (v/v). An isocaloric D-glucose solution was substituted for the drinking water of a control group of rats fed the vitamin-E-deficient diet for 4 weeks. The 4 treatment groups were maintained on the diet and drinking regimen for 20 weeks. Basal levels of expired pentane were determined at weeks 0, 1, 3, 5, 7 and 9. Chronic ethanol consumption did not influence basal pentane production during the 9-week treatment. Basal levels of expired pentane were affected by dietary vitamin E. Rats supplemented with vitamin E had basal pentane levels less than one-half of the level of rats fed a vitamin-E-deficient diet (p<0.001). After 14 weeks of treatment, the 2 groups of rats fed a vitamin-E-deficient diet were administered p.o. an acute dose of 6 g of ethanol/kg body wt. Pentane expired above basal levels during the following 4-hr period correlated with the amount of hepatic triglycerides determined at the conclusion of the experiment. The etiology of ethanol toxicity is a complex and multifactorial system made up to many biological variables that influence lipid peroxidation. The appropriate choices of experimental designs and methods are important in examining the role of lipid peroxidation.     

Atherogenesis in swine fed several types of lipid-cholesterol diets

Eighteen-month-old Nebraska strain minipigs were fed diets containing 2% cholesterol and 20% corn oil, lard, or coconut oil for 12 to 18 months. Concentrations of serum total lipid, total cholesterol, and total phospholipid increased 200 to 300% with each diet. Changes in serum concentrations of S_f 20+ and S_f 0–20 lipoproteins varied with diets fed. Serum concentration of high density lipoprotein was increased in all cases. Intima concentration of S_f 0–20 lipoprotein fraction was elevated by feeding the corn oil diet. There was no development of atherosclerosis as a result of feeding the corn oil-cholesterol diet, but there was an increase in atherosclerosis as a result of feeding the lard or coconut oil diet. There were no correlations between fatty acid patterns of several lipid fractions from serum and corresponding lipid fractions from aortic intima of corn oil fed animals. Deceased.     

Dietary fat composition and tocopherol requirement: I. Lack of correlation between nutritional indices and results of in vitro peroxide hemolysis tests

In general, the native tocopherols in polyunsaturated vegetable oils such as cottonseed oil, corn oil and their lightly hydrogenated products include sufficient vitamin E for growth, reproduction, lactation and normal lipid metabolism in the rat. The administration of vitamin E to animals fed diets deficient in essential fatty acids (e.g., a hydrogenated coconut oil or a fat-free diet) does not stimulate growth or reproductive performance per se, although testes development in the male rats is improved and some improvement in lipid metabolism is also noted. Hemolysis of the erythrocytes in vitro by hydrogen peroxide is increased in animals on diets rich (30%) in polyunsaturated vegetable oils or on diets providing no essential fatty acids at all. However, the conditions of the in vitro hemolysis test are not related to those in vivo and the in vitro test is not a measure of erythrocyte fragility. In addition, the in vitro hemolysis test does not necessarily reflect plasma tocopherol levels nor an abnormal nutritional state as a result of subsistence on high linoleate, low tocopherol intake, but rather measures the susceptibility to oxidation of a labile biological substrate and indicates the effective balance between potentially oxidizable lipids (polyunsaturates) in the stroma of the red blood cell and the antioxidant present (tocopherol or vitamin E). The labile lipid substrate may be either of exogenous origin (diet) or may be formed endogenously through tissue synthesis (as a result of an essential fatty acid deficiency). It is concluded that the in vitro hemolysis test may not be a valid indicator of vitamin E nutriture unless it is used in conjunction with other nutritional tests.     

Effect of dietary vitamin E on expiration of pentane and ethane by the rat

An analytical method for the measurement of hydrocarbon gases in the breath of rats is described. The method was used to follow the expiration in rat breath of in vivo formed scission products of hydroperoxides. The major products are pentane from the linoleic acid family and ethane from the linolenic acid family. Rats were fed 0, 11 or 40 i.u. vitamin E acetate/kg diet for 7 wk starting at age 21 days. Data obtained by gas chromatographic analysis of breath samples were analyzed by the Mann-Whitney nonparametricU-test. This statistical analysis showed that pentane evolved by the group of rats not supplemented with vitamin E was significantly higher during the period 1–7 wk than that evolved by either of the two supplemented groups of rats. Ethane from the nonsupplemented group was significantly higher than that from the group supplemented with 40 i.u. vitamin E/kg of diet by 5 wk, and significantly higher than both supplemented groups by 6 wk. By 7 wk, pentane production was tenfold greater in the nonsupplemented group than in either supplemented group, and ethane was about twofold greater. There was no significant difference between the groups supplemented with 11 and 40 i.u. vitamin E/kg diet for either ethane or pentane. This new technique, which measures scission products from in vivo lipid peroxidation, promises to be useful for application to many experimental areas where lipid peroxidation is expected or known to occur.     

Effect of antioxidants on lipid peroxidation in iron-loaded rats

Indirect evidence has suggested that lipid peroxidation is associated with iron overload in vivo. As a measure of lipid peroxidation, pentane expired in the breath of rats loaded with an accumulated dose of either 100 mg or 186–200 mg of iron injected intraperitoneally as iron dextran was measured over a 7 to 8 week period, and the effect on pentane production of feeding antioxidant-supplemented diets was determined. By the seventh week of feeding the diets, rats fed 0.3% L-ascorbic acid produced 17% less (P=0.03) pentane than did rats fed the basal antioxidant-deficient diet, whereas rats fed 0.004% dl-α-tocopherol acetate produced 92% less (P<0.001). After being fed the basal diet for 7 weeks, iron-loaded rats produced 76±9 pmol pentane/100 g body wt/min. When synthetic antioxidants were added to the diet at a concentration of 0.25%, the order of effectiveness in decreasing pentane production after 1 week was: N,N′-diphenyl-p-phenylenediamine > ethoxyquin > butylated hydroxyanisole > butylated hydroxytoluene > propyl gallate ∼ no antioxidant. After removal of either ethoxyquin or N,N′-diphenyl-p-phenylenediamine from the diets for 1 week, pentane production increased to a high level. The total amount of lipid soluble fluorophores in individual spleens of rats fed N,N′-diphenyl-p-phenylenediamine, ethoxyquin, dl-α-tocopherol acetate, ascorbic acid and no antioxidant were correlated significantly with the corresponding total integrated amount of pentane produced by the individual rats over the 7 to 8 week period. This study has provided some of the most direct evidence to date that lipid peroxidation is associated with iron overload in vivo.     

The effect of dietary vitamin E supply and a moderately oxidized oil on activities of hepatic lipogenic enzymes in rats

Diets rich in polyunsaturated fatty acids (PUFA) are well known to suppress hepatic lipogenic enzymes compared to fat-free diets or diets rich in saturated fatty acids. However, the mechanism underlying suppression of lipogenic enzymes is not quite clear. The present study was undertaken to investigate whether lipid peroxidation products are involved in suppression of lipogenic enzymes. Therefore, an experiment with growing male rats assigned to six groups over a period of 40 d was carried out. Rats received semisynthetic diets containing 9.5% coconut oil and 0.5% fresh soybean oil (coconut oil diet, peroxide value 5.1 meq O₂/kg oil), 10% fresh soybean oil (fresh soybean oil diet, peroxide value 0.5 meq O₂/kg oil), or 10% thermally treated soybean oil (oxidized soybean oil diet, peroxide value 74 meq O₂/kg oil). To modify the antioxidant state of the rats, we varied the vitamin E supply (11 and 511 mg α-tocopherol equivalents per kg of diet) according to a bi-factorial design. Food intake and body weight gain were not influenced by dietary fat and vitamin E supply. Activities of hepatic lipogenic enzymes were markedly influenced by the dietary fat. Feeding either fresh or oxidized soybean oil diets markedly reduced activities of fatty acid synthase, (FAS), acetyl CoA-carboxylase, (AcCX), glucose-6-phosphate dehydrogenase, (G6PDH), 6-phosphogluconate dehydrogenase, and ATP citrate lyase (ACL) relative to feeding the coconut oil diet. Moreover, feeding oxidized soybean oil slightly, but significantly, lowered activities of FAS, AcCX, and ACL compared to feeding fresh soybean oil. Activities of hepatic lipogenic enzymes were reflected by concentrations of triglycerides in liver and plasma. Rats fed the coconut oil diet had markedly higher triglyceride concentrations in liver and plasma than rats consuming fresh or oxidized soybean oil diets, and rats fed oxidized soybean oil had lower concentrations than rats fed fresh soybean oil. The vitamin E supply of the rats markedly influenced concentrations of thiobarbituric acid-reactive substances in liver, but it did not influence activities of hepatic lipogenic enzymes. Because the vitamin E supply had no effect, and ingestion of an oxidized oil had only a minor effect, on activities of hepatic lipogenic enzymes, it is strongly suggested that neither exogenous nor endogenous lipid peroxidation products play a significant role in the suppression of hepatic lipogenic enzymes by diets rich in PUFA. Therefore, we assumed that dietary PUFA themselves are involved in regulatio of hepatic lipogenic enzymes. Nevertheless, the study shows that ingestion of oxidized oils, regardless of the vitamin E supply, also affects hepatic lipogenesis, and hence influences triglyceride levels in liver and plasma.     

Oral contraceptive-α-tocopherol interrelationships

After observing that some of the side effects of the administration of oral contraceptive drugs to rats resemble those resulting from vitamin E deficiency, a possibility of an increased requirement for vitamin E during oral contraceptive therapy was considered. Female rats were kept on the following diets all of which contained 15% stripped corn oil: (A) basal (no tocopherol), (B) basal + α-tocopherol to provide 1 mg/rat/day, (C) basal+butylated hydroxytoluene, and (D) basal with the α-tocopherol given only during drug administration. At 13 weeks of age, Enovid E was administered orally at a level corresponding to 0.002 mg mestranol and 0.05 mg norethynodrel/day for either 4 or 28 days, at which time the rats were sacrificed. In addition to previously shown changes, lowering of plasma tocopherol levels was observed in rats receiving the drug. On the other hand, the effects of an oral contraceptive were not as drastic in vitamin E deficient rats. Possible implications of these findings are discussed. One of six papers presented in the symposium “Effect of Drugs on Lipid Metabolism,” AOCS Spring Meeting, New Orleans, April 1973.     

Effects of fish oil,corn oil and lard diets on lipid peroxidation status and glutathione peroxidase activities in rat heart

In this study, we investigated the effect of various types of fats on heart lipid peroxidation status and on blood lipid parameters. Rats were fed either a low-fat diet (2.2% lard plus 2.2% corn oil), a corn oil diet (17%), a salmon oil diet (12.5%) supplemented with 4.5% corn oil, or a lard diet (15%) supplemented with 2% corn oil. All diets were supplemented with 1% cholesterol. Rats were fed for eight weeks. When compared with the low-fat diet, the salmon oil-diet intake resulted in a lower blood cholesterol, triglyceride and phospholipid concentrations (−50, −56 and −30%, respectively). Corn oil only tended to lower blood lipids; this decrease was significant for triglycerides only (−40%). The hypocholesterolemic effect of salmon oil diet is even more pronounced, if blood cholesterol values are compared with those of rats fed the lard diet. Heart lipid composition was not affected by dietary manipulations. Fatty acid composition of cardiac phosphatidylcholines and phosphatidylethanolamines, however, were altered by high-fat diets. In phosphatidylcholine, salmon oil induced a twelvefold decrease in the n−6/n−3 ratio and a 26% increase in the unsaturation index. For phosphatidylethanolamine, the n−6/n−3 ratio decreased 7.7-fold and the unsaturation index increased by 13%. A 50% decrease of the n−6/n−3 ratio was observed in animals fed the lard diet. Ultramicroscopic examination of ventricles revealed that those of the salmon oil group significantly accumulated lipofuscin-like or ceroid material, whereas this accumulation was barely detectable in hearts of the other groups. Seleniumdependent glutathione peroxidase activity tended to be the highest in hearts of rats fed the salmon oil diet; this increase is significant (+36% and +54% for total and specific activities, respectively), if values are compared with those of the rats fed the lard diet. Liver glutathione peroxidase and heart glutathione S-transferases activities remained unchanged. These results indicate that fish oil did not lower the selenium involved in glutathione peroxidase activity. This rules out that a deficiency in this enzyme was at the origin of heart lipofuscinosis. Also, it is concluded that the n−6/n−3 ratio of the diet is likely more determinant in the alteration of heart lipid peroxidation status than is the polyunsaturated/saturated ratio. Part of this work was presented at the International Congress: “Selenium in Medicine and Biology,” Avoriaz, France, March, 15–18, 1988.     

Nutritional properties of the triglycerides of saturated fatty acids of medium chain-length

Summary The influence of a purified rat diet containing 20 or 33% of the saturated medium chain-length triglycerides (MCT) with and without linoleic acid supplements on growth, caloric requirements for weight maintenance and weight increase, fertility, lactation performance, and serum cholesterol levels was compared with that of similar diets containing lard, coconut oil, or no fat. Among male rats maintained on diets containing 20% lard or 20% MCT and .09% linoleic acid for 18 months no differences were observed between the groups other than the depressed body weight and lowered serum cholesterol levels of the group fed MCT. When groups of male rats were kept at constant weight by the daily restricted feeding of diets containing lard, MCT, or coconut oil or no fat plus 2% linoleic acid, the weight-maintenance requirements of the group fed MCT were higher than of those on lard and coconut oil and even somewhat higher than the requirements of the animals fed the fat-free diet. The requirements for weight increase over those for maintenance were 0.9 g. per gram increase for all diets. Additional linoleic acid in the MCT diet decreased the weight and maintenance differences between groups fed MCT and lard. The lactation performance of mothers on MCT plus .09% linoleic acid was poor. The second generation animals initially showed signs of more severe linoleic acid deficiency which however disaappeared without linoleic acid supplements. Some cholesterol levels of animals on MCT were significantly below those of groups on lard. Addition of linoleic acid to the MCT diet did not change the results. Presented at the 48th Annual Meeting, American Oil Chemists’ Society, April 28 to May 1, 1957, New Orleans, La.     

Effect of oxidized oil on lipogenic enzymes

Male Wistar rats were fed for 4 wk on diets containing 2% oxidized corn oil. Liver tissue was then studied to determine the effect of feeding peroxidized oil on lipogenic enzymes. Although substances which reacted with thiobarbituric acid increased in liver microsomes and mitochondria with increasing peroxide values of the dietary corn oil fed, the activities of glucose-6-phosphate dehydrogenase, malic enzyme and acetyl-CoA carboxylase in liver were unchanged. However, when rats were fed for 2 wk on diets containing 10% fat, of which 0.5, 5 or 10% was unoxidized corn oil and the remainder was hydrogenated beef tallow filler, the lipogenic enzyme activities and also the liver triglyceride levels were observed to decrease with increasing amounts of dietary corn oil. Therefore, although a synthetic diet containing corn oil was easy to oxidize spontaneously, the reductions of lipogenic enzymes in rats fed the diet would not have been caused by lipid peroxides but by unsaturated fatty acids themselves.     

Short term essential fatty acid deficiency in rats. Influence of dietary carbohydrates

The effects of long term (8–14 wk) essential fatty acid (EFA)-deprived diets in rats are well documented. In the present study, we compared, in weanling rats, the effect of a short term (two wk) hydrogenated coconut oil, EFA-deprived, diet (D) with that of a corn oil, EFA-adequate, diet (A), using either sucrose (SU) or starch (ST) as carbohydrate. After two wk, rats fed the sucrose/hydrogenated coconut oil diet developed some characteristic features of EFA deprivation: slower growth rate, decreases in linoleic and arachidonic acid of plasma phospholipids and an increase in n−9 eicosatrienoic acid of plasma phospholipids. When rats ate the starch/hydrogenated coconut oil diet, there was a similar decrease in linoleic acid of plasma phospholipids, but only a small effect on growth rate and no change in the arachidonic acid content of plasma phospholipids. EFA deprivation and sucrose had opposite effects on plasma triglyceride (TG) levels: deprivation induced a decrease, whereas the sucrose induced an increase in very low density lipoprotein (VLDL) triglycerides. The observed decrease in plasma triglyceride during EFA deporivation might result from an activation of lipoprotein lipase during the early stages of deprivation.     

Reduction of atherogenicity of natural fats by small additions of ethyl linoleate in the diet of the rat

Ethyl linoleate was substituted in part for the 20% of butterfat, hydrogenated coconut oil, lard, or tallow in an atherogenic diet fed to rats throughout a 40-week experimental period. Aortic degeneration, evidenced by lipid infiltration of the intima, was observed in the control groups but not in the linoleate-fed groups. Groups that received butterfat or hydrogenated coconut oil showed reduced plasma and hepatic cholesterol levels when fed 2% of ethyl linoleate; groups that received lard or tallow showed no significant change in plasma and hepatic cholesterol levels when fed 2% of ethyl linoleate; and groups that received a fat-free diet with 2% of ethyl linoleate showed lower plasma and hepatic cholesterol levels and more complete aortic protection than groups that were fed 20% of corn oil or cottonseed oil. The data suggest that, in the cholesterol-fed rat, the kind and amount of dietary fatty esters may influence aortic condition via some route(s) other than control of plasma and hepatic cholesterol levels. Presented at the AOCS Meeting, Los Angeles, April 1966. Journal Paper No. 2952 of the Agricultural Experiment Station, Purdue University, Lafayette, Ind.     

Autoxidation of tissue lipids. I. Incorporation of dietary fatty acids and formation of monocarbonyl compounds in adipose tissue lipids of the vitamin E-deficient rat

Male weanling rats were fed vitamin E-deficient and vitamin E-supplemented diets containing 5% corn oil or cod-liver oil for 16 weeks, after which their adipose tissue lipids were extracted and analyzed in a nitrogen atmosphere for carbonyl compounds and fatty acids. The vitamin E-deficient cod-liver oil-fed rats, exhibiting incisor depigmentation and darkened adipose tissue, yielded lipids which had a lower iodine value, contained less polyunsaturated fatty acids, and contained more carbonyl compounds, particularly alkanals and alk-2-enals, than the lipids from the animals fed the vitamin E-supplemented cod-liver oil diet. The tissues of the vitamin E-deficient corn oil-fed rats contained less linoleate and more monocarbonyl compounds than those of the vitamin E-supplemented corn oil-fed animals. The results indicate that vitamin E protection is necessary for the incorporation of C₂₀ and C₂₂ fatty acids into the tissues from the diet and that in the deficiency of vitamin E, a low level of autoxidation occurs in the tissues.     

Effects of dietary thermoxidized fats on expression and activities of hepatic lipogenic enzymes in rats

This study was undertaken to investigate the effect of dietary oxidized fats on the relative mRNA concentrations and the activities of fatty acid synthase (FAS) and glucose-6-phosphate dehydrogenase (G6PDH) in the liver of rats treated with vitamin E or selenium. Two experiments with male Sprague-Dawley rats were carried out. The first experiment included eight groups of rats fed diets with either fresh fat or three different types of oxidized fat, preparated by heating at temperatures of 50, 105, or 190°C, over a period of 6 wk. The diets contained either 25 or 250 mg α-tocopherol equivalents per kg. The second experiment included four groups of rats fed diets with fresh fat or oxidized fat, heated at a temperature of 55°C, containing either 70 or 570 μg selenium per kg, over a period of 8 wk. Feeding the diets with oxidized fats led to a significant overall reduction of the relative mRNA concentrations and the activities of FAS and G6PDH in both experiments. The effects of the oxidized fats on mRNA concentrations and activities of these enzymes were independent of the dietary concentrations of vitamin E or selenium. Moreover, in both experiments the rats whose diet contained the oxidized fats had significantly lower concentrations of TG in liver, plasma, and VLDL than the rats whose diet contained fresh fat. The study suggests that oxidized fats contain substances that suppress gene expression of lipogenic enzymes in the liver.     

Dietary antioxidants in young swine

Young swine obtained by hysterectomy were fed purified diets low in vitamin E and supplemented with d-α-tocopheryl acetate and ethoxyquin (Santoquin^R). It was demonstrated that with very low levels of polyunsaturated fatty acids (PUFA) in the diet, both tocopherol and Santoquin protected the tissues of the pig from increased thiobarbituric acid (TBA) values and from increased hemolysis usually associated with low vitamin E status. When the dietary PUFA were increased to levels over 5%, the supplements of tocopherol and Santoquin protected against increased TBA values of tissue homogenates, but not against increased hemolysis of erythrocytes, even when blood serum showed substantial amounts of tocopherol. Some of the interrelationships of dietary PUFA and α-tocopherol were demonstrated. It was shown that for each 1% of peroxidized corn oil added to the diet above 4%, roughly 100 mg of d-α-tocopheryl acetate was necessary to protect the pigs from erythrocyte hemolysis. The failure to reach a “zero” TBA value in vitamin E-deficient swine tissue homogenates substantiated the theory ofin vivo lipid autoxidation, and the increased TBA values of incubated tissue homogenates demonstratedin vitro lipid autoxidation in tissues not protected by a biological antioxidant. Presented at the AOCS meeting in Toronto, Canada, 1962. Supported by grants from the Monsanto Chemical Co., St. Louis, Mo., and The Hormel Foundation.