The effects of vitamin E deficiency on the total fatty acids and the phospholipid fatty acids of rat tissues

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 alpha-tocopherol in a dose-dependent way and strongly decreased sensitivity to nonenzymatic in vitro liver lipid peroxidation. This last effect was already observed in group MEDIUM, and no further decrease in in vitro lipid peroxidation occurred from group MEDIUM to group HIGH. The protective effect of vitamin E against in 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.

Alteration of brain and liver microsomal polyunsaturated fatty acids following dietary vitamin E deficiency

The effects of dietary vitamin E deficiency on fatty acid composition of brain and liver microsomes were studied in rats fed a vitamin E-deficient diet for 9 weeks. In brain microsomes, vitamin E deficiency resulted in a significant decrease in palmitic acid and total saturated fatty acids. Cervonic acid was increased. In contrast, no marked changes were observed in the levels of (n-6) polyunsaturated fatty acid (PUFA). In liver microsomes, vitamin E deficiency resulted in significant alterations in fatty acid composition: higher amounts of stearic acid and total saturated fatty acids, lower amounts of mono-unsaturated fatty acids, linoleic and dihomo gamma linoleic acids. In contrast, arachidonic acid was not altered. The overall decrease in the amounts of (n-6) PUFA was compensated by an increase in the level of (n-3) PUFA. It is concluded that vitamin E may alter the enzymatic activities of chain elongation-desaturation and the relationship between vitamin E and PUFA in brain and liver microsomes.

Alteration of delta-6 desaturase by vitamin E in rat brain and liver

delta-6 Desaturase, measured at substrate saturation using linoleic acid, was found to be increased by more than two-fold when the content of vitamin E in brain microsomal membrane suspension was increased (up to 7.5 micrograms/mg membrane protein, i.e. 100 micrograms/g tissue from which microsomes were prepared). In contrast, this activity was reduced by 25% in the liver. This raises the question of the multiple role of vitamin E in membranes, the control of membrane polyunsaturated fatty acids through synthesis, and their protection against peroxidation.

Postischemic cerebral lipid peroxidation in vitro: modification by dietary vitamin E

Using an in vitro system, we studied the effect of postischemic reoxygenation on cerebral lipid peroxidation in relation to the dietary intake of vitamin E (VE) in rats. Homogenates prepared from VE-deficient, -normal, and -supplemented brains, which were previously rendered ischemic for 30 min by decapitation, were incubated under air or nitrogen gas for 60 min. The extent of peroxidation in brain tissue was estimated by a thiobarbituric acid (TBA) test and by diene conjugation in total lipid extracts. The brain levels of alpha-tocopherol and of total and free fatty acids (FAs) were also determined. Aerobic incubation increased TBA reactants in all dietary groups; the effect was largest in the VE-deficient group, intermediate in the VE-normal group, and smallest in the VE-supplemented group. In contrast, nitrogen incubation did not alter the basal levels of TBA reactants except for a small rise associated with VE deficiency. Conjugated dienes changed in parallel with TBA reactants. alpha-Tocopherol decreased after aerobic incubation and also, to a lesser degree, after nitrogen incubation in each dietary group. Only in the reoxygenated samples of the VE-deficient group was there a significant fall in total polyunsaturated FAs. The levels of free FAs continuously increased throughout ischemia and subsequent incubation. However, the level of free polyunsaturated FAs was similar after aerobic and nitrogen incubation in each dietary group, and was not affected by VE. Thus, cerebral reoxygenation after ischemia propagates peroxidative reactions within esterified polyunsaturated FAs. The modification by VE of reoxygenation-induced lipid peroxidation suggests free radical mediation.

Release of ethane and pentane from rat tissue slices: effect of vitamin E, halogenated hydrocarbons, and iron overload

The effects of in vitro addition of halogenated hydrocarbons on the susceptibility of various rat tissues to lipid peroxidation, and of iron overload and dietary vitamin E in the intact rat on subsequent lipid peroxidation in rat tissue slices were examined. The ease and speed of tissue slice preparation allowed testing of multiple tissues from the same animals. Total ethane and pentane (TEP) released from the slices was as reliable as and more sensitive than thiobarbituric acid-reactive substances as an index of lipid peroxidation. TEP was released by tissues from vitamin E-deficient rats in the following order of magnitude:intestine = brain = kidney greater than liver = lung greater than heart greater than testes = diaphragm greater than skeletal muscle. The potency of halogenated hydrocarbons for causing increased TEP release from vitamin E-deficient rat liver slices was CBrCl3 greater than CCl4 = 1,1,2,2-tetrabromoethane = 1,1,2,2-tetrachloroethane greater than perchloroethylene. CBrCl3 also stimulated TEP release from kidney, intestine, and heart slices, thus identifying these as potential target organs for CBrCl3 toxicity. Dietary vitamin E decreased TEP release from liver and, to a lesser extent, from kidney. Iron overload in the rat increased TEP release by slices from all tissues tested except the brain.

Effects of vitamin E and selenium deficiency on the fatty acid composition of rat retinal tissues

The fatty acid composition of retinal tissues was measured in rats maintained for 26--32 weeks on each of the following diets: a purified basal diet deficient in alpha-tocopherol and selenium, an identical control diet supplemented with alpha-tocopherol and selenium, and a commerical laboratory rat chow. Dietary deficiencies of antioxidant nutrients were found to cause a large decrease in total polyunsaturated fatty acids in the retinal pigment epithelium, a small decrease in the retinal rod outer segments, but no change in the whole retina or liver when compared to tissues from animals fed the vitamin E- and selenium-supplemented control diet. The polyunsaturated fatty acid content which we have observed for the retinal pigment epithelium from rats fed commerical lab chow is similar to that which we observed for bovine retinal pigment epithelium. Our results indicate that changes in fatty acid composition are not generalized to all tissues in severely antioxidant-deficient animals, but that changes do occur in some tissues, such as the retinal pigment epithelium, which appears to be particularly sensitive to in vivo lipid peroxidation.

The urinary excretion of aromatic acids by starved sheep

1. Four wether sheep were maintained on a diet of hay for 2 weeks and then starved for a period of 4 days.

2. Immediately before and during starvation the urinary excretion in the following fractions was determined: hippuric acid, creatinine, total diethyl ether-soluble acids of hydrolysed and unhydrolysed urine, total aromatic acids in hydrolysed and unhydrolysed urine and the proportion of the former present as benzoic and phenylacetic acids.

3. A method for determining the benzoic acid content of light petroleum extracts of urine has been developed and is described.

4. Starvation had little effect on the urinary excretion of phenylacetic acid or creatinine, but during the first 2 days of starvation there were large decreases in the excretion of all the other urinary fractions studied.

5. Of the fractions examined, 43% of the diethyl ether-soluble acids of hydrolysed urine and 42% of those of unhydrolysed urine were of exogenous origin; 76% of the total urinary aromatic acids were of exogenous origin. Partition of the aromatic acids in the urine of two of the four sheep indicated that the reduction in aromatic acid excretion on starvation was completely accounted for by the decline in benzoic acid output. Almost all the hippuric acid (97%) was of exogenous origin.

6. These results have been compared with the urinary output of aromatic acids by nonruminants when fasted, and possible reasons for the relatively large amounts of phenylacetic acid found in the urine of starved sheep have been discussed.