Studies on vitamin E. 4. The simultaneous determinations of tocopherols, ubiquinones and ubichromenols (substance SC) in animal tissues: a reconsideration of the Keilin-Hartree heart preparation

VITAMIN A AND ISOPRENOID SYNTHESIS IN THE RAT

1. Vitamin A-deficient rats were compared with similar animals given small amounts of vitamin A sufficient for adequate growth and with animals given large amounts of vitamin A. The effects of pair-feeding and feeding ad libitum were compared. 2. Ubiquinone and cholesterol concentrations in liver were measured at various stages of the deficiency, and the uptake of radioactive mevalonate and acetate into isoprenoid compounds was studied. 3. Ubiquinone concentrations in liver increased markedly in deficient rats compared with adequate controls, and heavy vitamin A supplementation had a further effect in depressing ubiquinone concentrations. These effects were unrelated to food intake or to the size of the organs. 4. Radioactive uptake into ubiquinone was often greater in deficient livers, especially during the early stages of the experiments, but the effect was not consistent. 5. Cholesterol concentrations were usually higher in deficient livers and these were more affected by the feeding regimen. 6. No consistent effect of vitamin A deficiency or of vitamin A dosage on the incorporation of mevalonate into cholesterol or squalene was found. 7. No evidence has been found for a specific effect of vitamin A on isoprenoid synthesis at the metabolic level.

Identification of vitamin K1 chromenol--a novel metabolite of vitamin K1 formed in vitro by a component in blood

A newly recognized metabolite of vitamin K1, vitamin K1 chromenol, is produced when the vitamin is added to the plasma or serum of a number of species. The metabolite was identified by comparison of its uv and mass spectra and high-performance liquid chromatographic retention times with those of the synthetic vitamin K1 chromenol. In aqueous solution vitamin K chromenol decomposed to a variety of products and reacted with nucleophilic substances. Optimal conditions for its formation and evidence that chromenol formation may be an enzyme catalyzed reaction are presented.

Protection of vitamin E from oxidation by increased ascorbic acid content within Plasmodium vinckei-infected erythrocytes

Erythrocytes isolated from mice at a late stage of infection with the malarial parasite Plasmodium vinckei contained increased levels of vitamin E, but neither control nor infected erythrocytes contained detectable levels of alpha-tocopherolquinone, an oxidation product of vitamin E. Total levels of the antioxidant, vitamin C, were more than doubled in the same populations of highly parasitized erythrocytes. These observations, and the lower ratio of oxidized to reduced forms of ascorbic acid in parasitized compared to nonparasitized erythrocytes, raise the possibility that increased redox-cycling between the two vitamins may account for the failure to detect alpha-tocopherolquinone. Thus, late in infection of mice with the lethal parasite P. vinckei, the content and redox state of erythrocytic ascorbic acid is altered so that it protects vitamin E, and presumably the parasitized red cell and its contents, from oxidative damage.

Sensitive fluorometric method for tissue tocopherol analysis

A sensitive, highly reproducible method for tissue tocopherol analysis that combines saponification in the presence of large nmount of ascorbic acid to remove interfering substances, extraction fo the nonsponifiable lipids with hexane, and fluorometric measurement of the tocopherol is presented. The nonsaponifiable lipids phase contained only one fluorochrome in the 290 am excitation and 330 nm emission range, and it was identified as tocopherol by thin layer and column chromatography. Column chromatography of the hexane extract of a saponified, 14C-tocopherolspiked microsomal fraction showed that no measurable oxidation to tocopherylquinone had occurred. The flurometric method for tocopherol analysis was applied to homogenates and subcellular fractions from rat liver, kidney, lung, and heart and red blood cells. The heavy mitochondrial and microsomal fractions had the highest subcellular concentrations of tocopherol.

On the existence of lipid peroxides in rat tissue

1. The colorimetric micro-adaption of the iodometric method and the colorimetric thiocyanate method for the determination of lipoperoxides were compared. Similar results were obtained when methyl linoleate hydroperoxide was tested, but when lipid from rat liver, muscle, kindney and testes was examined, substantial amounts were found by the iodometric, but almost nothing by the thiocyanate method.

2. The main reason for the discrepancy between the methods seems to be that the iodometric micromethod also estimates substances other than true lipoperoxides. The presence of ubiquinone and vitamin A in the organ extracts was shown to interfere in this way in the method.

3. The yellow colour which develops when retinol and its esters are tested by the iodometric micromethod is due not to liberated iodine but to conversion products of retinol.

4. It is concluded that the occurrence of substantial amounts of lipoperoxides in vivo has so far been demonstarted only in the adipose tissue, and not in the parenchymatous organs of the rat.

Vitamin E and hepatotoxic agents. 1. Carbon tetrachloride and lipid peroxidation in the rat

1. It has been suggested that carbon tetrachloride damages rat liver by accelerating processes of lipid peroxidation at subcellular sites and that the protective action of vitamin E is due to its functioning as an antioxidant in vivo. Direct evidence for these mechanisms in vivo has been sought and is critically examined.

2. The increased production of malondialdehyde by rat liver microsomal fractions during incubation with CCl4 was shown to be a function of the vitamin E status of the rat and of an in vitro reaction, which could not be correlated with the hepatotoxic action of CCI4.

3. Evidence for the production of lipid peroxides by CCl4 in the livers of vitamin E-deficient and vitamin E-supplemented rats was sought (I) by measurement of ultraviolet spectral changes ('diene' formation) and (2) by direct micro-iodimetric determination of the peroxide. No differences in peroxide content were found between CC14-treated and control rats, nor were the spectrophotometric changes in the ultraviolet region related to the presence of vitamin E.

4. The effect of CCI4 (2.0 ml/kg orally) on ATP levels in rat liver was studied at intervals from 3 to 68 h. The primary lesion leading to necrosis and fat accumulation after CCl4 treatment occurred many hours before the eventual slight decline in ATP. Although the levels of ATP were somewhat higher in vitamin E-deficient rats, vitamin E did not prevent the slight decline in ATP that took place. Since ATP is known to be highly sensitive to peroxidation, the results suggest that lipid peroxidation is not the primary event in CCl4 poisoning.

5. The effect of CC14on the metabolism of [14C]D-α-tocopherol in the rat was studied. A single intraperitoneal dose of CCl4 (2.0 m/kg) did not increase the destruction of α-tocopherol in the liver or carcass after 24 h. Three smaller daily doses of CC14 (0.25 ml/kg) also did not increase α-tocopherol catabolism; on the contrary, significantly more α-tocopherol was found in the livers of rats treated with CCI4. These results suggest that CCl4 does not increase lipid peroxidation in vivo.

Analysis and distribution of tocopherols and quinones in the pea plant

A procedure is described and evaluated for the analysis of ubiquinone, plastoquinone, tocopherols and vitamin K(1) in Pisum sativum L. Vitamin K(1) appears to be absent from the roots of this plant. While the pea seed contains only gamma-tocopherol, the root and shoot contain only alpha-tocopherol. During the greening of etiolated tissue, plastoquinone and vitamin K(1) levels increase markedly while ubiquinone and alpha-tocopherol levels are unaffected. On homogenization or damage to tissue, considerable losses of alpha-tocopherol occur in the pea plant.

Vitamin E and stress. I. Dietary unsaturated fatty acid stress and the metabolism of alpha-tocopherol in the rat

1. A critical analysis of the biological antioxidant theory of vitamin E function has been made and the implications of the theory have been tested.

2. When small amounts of [5-Me-14C]α-tocopherol were present in lipid systems subject to autoxidation in vitro, it was found that, whether the tocopherol was the sole antioxidant or was in synergistic combination with a secondary antioxidant (ascorbic acid), peroxidation did not occur without concomitant destruction of the tocopherol. This was so, whether a simple fat substrate or a liver homogenate (subject to catalysis) was used. The decomposition of tocopherol took place even when the secondary antioxidant was in large excess, as would occur under physiological conditions in the vitamin E-deficient animal, and accelerated as the induction period neared its end.

3. When [5-Me-14C,3H]α-tocopherol and ascorbic acid were used as a synergistic antioxidant couple in vitro, tocopherol recovered from the peroxidizing system always had the same isotopic ratio as the starting material. This means that regeneration of tocopherol by the secondary antioxidant cannot involve, as an intermediate, a tocopherol carbon radical formed by loss of hydrogen from the 5-methyl group. Such radicals probably dimerize before they can be regenerated. The same result was found when doubly labelled α-tocopherol was given to the rat and recovered later from its tissues.

4. In a series of experiments, rats were rigorously depleted of vitamin E for periods up to 7 months and then given as little as 50 μg [14C]D-α-tocopherol. They were then given, either by stomach tube daily or by dietary addition, large amounts of methyl linoleate or vitamin E-free polyunsaturated fatty acid methyl esters prepared from cod-liver oil and compared with controls given methyl oleate for up to 31 days. When the possibility of interaction between the lipid and tocopherol in the gut was eliminated, analyses of liver, kidney, testis, adrenal, adipose tissue, whole carcass and faeces showed that there was no effect of the polyunsaturated fatty acids on either the metabolism or recovery of [14C]α-tocopherol in any of the animals.

5. When interaction between the administered fatty acid esters and tocopherol in the gut was allowed to take place, a marked destruction of [14C]α-tocopherol in the tissues was observed in animals given the polyunsaturated esters. The importance of oxidative destruction of tocopherol in the gut before absorption was demonstrated in a nutritional trial, in which cod-liver oil and lard were compared and the degrees of resistance of rats' erythrocytes to dialuric acid-induced haemolysis was used as an index of vitamin E depletion.

6. Similar experiments with [14Cα-tocopherol in weanling rats given large amounts of cod-liver oil methyl esters also showed little effect. Although there was a suggestion that prolonged feeding of partly peroxidized polyunsaturated esters could lead to a slight depression of tissue tocopherol concentrations, no significant differences were usually obtained.

7. Fourteen-day-old rats were given a vitamin E-deficient diet and received three weekly doses of 0.5 mg α-tocophcryl acetate. The dosage was stopped, the rats were then given a deficient diet containing 4% of either vitamin E-free linseed oil fatty acids or oleic acid, and the rate of their tocopherol depletion was measured by the erythrocyte haemolysis test. No effect of the polyunsaturated fatty acids was found. Nor was there any effect on the concentrations of ‘secondary antioxidants’ (glutathione and ascorbic acid) in liver, kidney, testis, muscle or adipose tissue.

8. The results of the experiments in vivo contrast strongly with those in vitro. They lead to the conclusion that lipid peroxidation, if it occurs in the living animal, is irrelevant to the problem of vitamin E function. This conclusion has been substantiated by a critical review of the literature on the quantitative aspects of the vitamin E-dietary fat relationship.

9. The effects of dietary fat stress in vitamin E-deficient animals are, we believe, due to two causes: (1) destruction of tocopherol in the diet or in the gastro-intestinal tract of the animal, and (2) the existence of an increased requirement for vitamin E for the metabolism of certain long-chain fatty acids. The specific effects of certain of these substances in producing or accelerating some vitamin E deficiency diseases may be related to the toxic states known to be induced in vitamin E-deficient animals by other stress factors.

The analysis of alpha-tocopherol and ubiquinone in rat liver

1. A comparative study has been made of five methods of saponifying normal and vitamin E-deficient rat liver and subsequently measuring ubiquinone and α-tocopherol. 2. Losses of ubiquinone and α-tocopherol occur under certain conditions, and three of the methods were judged to be unsatisfactory. Recoveries of α-tocopherol are nearly quantitative under the conditions of ToŠić & Moore (1945), but methods that use large reaction times or weaker alkali destroy tocopherol, and over 50 % loss can be encountered. Ubiquinone does not seem as sensitive to the time of reaction, but is sensitive to the concentration of alkali and amount of water present during saponification.