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Biomedical subjects

A T Diplock

Publications and source records attributed to A T Diplock.

At least 55 records · Page 3Linked to original sources
PubMed1991

A fibroblast cell culture model to study vitamin K metabolism and the inhibition of vitamin K epoxide reductase by known and suspected antagonists.

The metabolism and antagonism of vitamin K has been studied in cultured fibroblasts. Monolayers of 3T3 mouse fibroblasts (grown in the absence or presence of warfarin or other putative antagonists) were incubated for 24 h with [1',2'-3H2]phylloquinone (K1) or [1',2'-3H2]phylloquinone epoxide (K1O), the cells harvested and lipid extracts fractionated by high performance liquid chromatography. [3H]K1 was converted to [3H]K1O (about 20% of [3H] lipids) and to unidentified polar metabolites (30%). [3H]K1O was converted to [3H]K1 (3%) and to polar metabolites (50%). Cells grown with warfarin showed a marked increase in the [3H]K1O:K1 ratio and in the proportion of polar metabolites. The metabolic interconversion of K1 and K1O and inhibitory response to warfarin provide evidence for a fibroblast pathway analogous to the vitamin K-epoxide cycle in the liver. From the K1O:K1 ratios it was possible to grade the antagonism of vitamin K epoxide reductase activity by known and suspected inhibitors. Inhibitory ratios were seen for racemic warfarin down to 10(-8) M. S-warfarin was a more potent antagonist than the R-enantiomer. Consistently low K1O:K1 ratios were observed for N-methyl-thiotetrazole and antibiotics with (moxalactam) or without (cefotaxime) this side chain suggesting that none of these compounds are direct inhibitors of vitamin K epoxide reductase. Fibroblasts grown in cell culture provide a useful model to study the extrahepatic role of vitamin K and the mode of action of vitamin K antagonists.

Animals↗
PubMed1991

Effect of selenium supplementation in hypothyroid subjects of an iodine and selenium deficient area: the possible danger of indiscriminate supplementation of iodine-deficient subjects with selenium.

Selenium and seleno dependent glutathione peroxidase (GPX) deficiency has been described in endemias of myxedematous cretinism. In northern Zaire, a selenium supplementation trial has been conducted. Beside correcting the GPX activity, two months of selenium supplementation was shown to modify the serum thyroid hormones parameters in clinically euthyroid subjects and to induce a dramatic fall of the already impaired thyroid function in clinically hypothyroid subjects. These results further support a role of selenium in thyroid hormone metabolism. In an iodine deficient area, this selenium deficiency could lead to opposite clinical consequences: protect the general population and the fetus against iodine deficiency and brain damage; and in turn, favour the degenerative process of the thyroid gland leading to myxoedematous cretinism.

Child↗
PubMed1990

Mineral insufficiency and cancer.

There are excellent theoretical reasons why the mineral nutrients selenium, manganese, copper and zinc, known as the antioxidant minerals, may be involved in the prevention of cancer aetiogenesis. The biochemistry is discussed of the part played by the antioxidant minerals, in the wider context of the other dietary antioxidants vitamins A, E and C, and beta carotene, in preventing tissue damage caused by activated metabolites of oxygen. The likely part played by these oxygen metabolites is described and a detailed review given of the evidence that suggests a role for antioxidant minerals, notably selenium, in preventing carcinogenesis in a range of animal models. There follows a summary of the emerging epidemiological evidence that suggests clearly that low selenium intake is a risk factor in the aetiology of human cancer.

Animals↗
PubMed1990

Iodine and selenium deficiency associated with cretinism in northern Zaire.

Selenium status was determined in an endemic-goiter area and in a control area of Zaire. Compared with the reference values of a noniodine-deficient area, serum selenium in subjects living in the core of the northern Zaire endemic-goiter belt (Karawa villages) was seven times lower in 52 school-children and similarly low in 23 cretins; erythrocyte glutathione peroxidase (RBC-GPX) was five times lower in schoolchildren and still two times lower in cretins (P = 0.004). In a less severely iodine-deficient city of the same endemia (Businga), selenium status was moderately altered. RBC-GPX activity was linearly associated with serum selenium concentration up to a value of 1140 nmol/L and leveled off at approximately 15 U/g Hb at greater selenium concentration. At Karawa villages, selenium supplementation normalized both the serum selenium and the RBC-GPX. This combined iodine and selenium deficiency could be associated with the elevated frequency of endemic myxedematous cretinism in Central Africa.

Adolescent↗
PubMed1989

Iron overload and the predisposition of cells to antioxidant consumption and peroxidative damage.

We have investigated the effects of iron overload in vivo on the tocopherol levels and the extent of lipid peroxidation in rat liver microsomes and their response to subsequent oxidative stress in vitro. The results demonstrate a direct correlation between consumption of antioxidant defences and the induction and extent of malondialdehyde production in microsomes prepared from iron-loaded rats. The data are consistent with the requirement for iron (II)/iron (III) ratios in lipid peroxidation in control microsomes.

Animals↗
PubMed1988

The alpha-tocopherol and phospholipid fatty acid content of rat liver subcellular membranes in vitamin E and selenium deficiency.

(1) Rats were given a diet deficient in vitamin E and selenium, or diets supplemented with either or both of these nutrients. The livers were subfractionated by standard procedures, and the purity of the fractions was assessed by marker enzyme techniques. alpha-Tocopherol was measured and profiles of phospholipid fatty acids were determined. (2) All the organelles studied were severely depleted of alpha-tocopherol in the rats deprived of vitamin E: no organelle was particularly severely depleted. There was a large rise in the alpha-tocopherol content in organelles of rats deprived of selenium but given adequate amounts of vitamin E, suggesting an increased uptake or mobilization of tocopherol to compensate for the detrimental effects of selenium deficiency. (3) The following general conclusions were reached from the results of the phospholipid fatty acid analyses. (i) vitamin E deficiency caused a consistent fall in the polyunsaturated fatty acid (PUFA) content (13-66% of the control level); (ii) selenium deficiency alone caused no consistent effect on phospholipid PUFA in the fractions studied; (iii) double deficiency of vitamin E and selenium caused a consistent rise in the proportion of PUFA in the fractions studied, ranging from 11 to 311%. (4) The result given in 3(i) is consistent with peroxidative destruction of membrane phospholipid PUFA during vitamin E deficiency. The result in 3(iii) is paradoxical: a possible explanation is that during severe disruption of antioxidant defences, there is an overshoot in the increased incorporation of unsaturated fatty acids into the membrane phospholipids, or in the chain-elongation and desaturation process required for the formation of PUFA, which may require vitamin E and/or selenium for its regulation.

Animals↗
PubMed1988

Purification and chemical characterisation of the inhibitor of lipid peroxidation from intestinal mucosa.

The antioxidant previously isolated from intestinal mucosa has been subjected to further purification and identification. Although this inhibitor moved as a single spot on thin-layer chromatography in a number of different solvent systems, it proved to be a mixture of free carboxylic acids whose relative composition was similar in different batches. Detailed studies involving the use of high-pressure liquid chromatography, combined gas chromatography-mass spectrometry, high-field 360 MHz proton nuclear magnetic resonance spectroscopy, fast atom bombardment mass spectrometry and other techniques established that the inhibitor was a mixture of carboxylic acids of the following identity and relative composition (the major components comprising 92% of the total fatty acids): palmitic acid, 14.8%; palmitoleic acid, 3.6%; stearic acid, 7.0%; oleic acid, 21.0%; linoleic acid, 27.6% arachidonic acid, 18.0%. Mixtures of authentic fatty acids of the same relative concentration showed inhibition of peroxidation, comparable with the purified inhibitor from intestinal mucosa. A study of the inhibitory activity of the components of the mixture using malonaldehyde estimation, diene conjugation and arachidonic acid estimation showed that the inhibitory activity was due to palmitoleic and oleic acids only, the latter being the major component.

Animals↗
PubMed1988

The relationship between alpha-tocopherol and phospholipid fatty acids in rat liver subcellular membrane fractions.

(1) A method was devised for the subfractionation of normal rat liver and for the subfractionation of the mitochondrial fraction into inner and outer membrane fractions. The purity of the fractions was assessed using marker enzyme measurements. (2) alpha-Tocopherol was measured in all the fractions by a sensitive HPLC technique. Profiles of phospholipid fatty acids were also determined by gas-liquid chromatography in all the fractions, and these values were calculated in terms of the percentage of each fatty acid in the total fatty acid of the fraction, as well as of the mass of each fatty acid per mumol of phospholipid phosphorus. Tocopherol values were expressed as the mass of tocopherol per g wet liver and per mumol of phospholipid phosphorus. (3) The results show that the mitochondrial and microsomal fractions were the major tocopherol-containing fractions, and both the inner and outer mitochondrial fractions contained substantial amounts of alpha-tocopherol. (4) The mitochondrial and microsomal fractions also had the highest levels of polyunsaturated fatty acids (PUFA) in their phospholipid fraction, especially 20:4 and 22:6, which were particularly localised in the inner mitochondrial membrane fraction. The high inner mitochondrial and microsomal PUFA levels were particularly apparent when the sum of all the unsaturated fatty acids with three or more double bonds was calculated. (5) Calculation of molar ratios of of some phospholipid fatty acids to alpha-tocopherol gave values of the order of several thousand to one. (6) It is concluded that the protective effect of each molecule of alpha-tocopherol must be exerted towards a large number of molecules of membrane unsaturated fatty acids simultaneously. This perhaps implies specific localisation of tocopherol in regions of membrane particularly liable to attack, such as might be expected to occur close to respiratory enzymes that can donate electrons to molecular oxygen.

Animals↗
PubMed1987

Dietary supplementation with antioxidants. Is there a case for exceeding the recommended dietary allowance?

The containment of damaging oxygen species by antioxidant nutrients has led to the speculation that the RDA for these specific nutrients may be overly low. Among these nutrients are vitamin E, vitamin C, and to a lesser extent beta-carotene and selenium. Evidence for the role of these nutrients in cancer and heart disease is evaluated. The case is presented for an increase of two-fold for the vitamin C RDA and between three and five-fold for vitamin E; for establishing 15 mg as the RDA for beta-carotene; for no change in the vitamin A RDA; and for further study on selenium.

Antioxidants↗
PubMed1985

The glutathione S-transferases in selenium and vitamin E deficiency.

Preliminary experiments confirmed the work of others showing that the total glutathione peroxidase (GSH-px) activity of rat liver supernatant fraction may be resolved into two peaks of activity (peaks I and II) by gel filtration, and that peak I is the selenium-containing enzyme and peak II is another peroxidase indistinguishable from glutathione S-transferase (GST). In selenium and vitamin E deficiency, the total activity of the GSH-px became very low, and the total activity of GST with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate was enhanced. Study of the time course of these changes as deficiency progressed indicated that the stimulus for the rise in GST (CDNB) activity was the fall in GSH-px activity which preceded it. The peroxidase activity of GST was found to reside only in the GST AA, B and B2 forms of the enzyme, which were shown to be respectively a homodimer of the Yc subunit, a homodimer of the Ya subunit and a heterodimer of the YaYc subunit. As vitamin E and selenium deficiency progressed, the B2 and AA forms of the enzyme showed enhanced activity, which was interpreted as implying that the Yc subunit of the enzyme becomes enriched as a consequence of the withdrawal of selenium from the animal's diet. Densitometric measurements of the Yc and Ya subunits confirmed that the amount of the Yc subunit was nearly doubled in selenium deficiency, relative to the Ya subunit.

Animals↗
PubMed1983

The role of vitamin E in biological membranes.

The view that vitamin E functions in living systems primarily as a lipid antioxidant and free-radical scavenger has gained widespread acceptance. As a result of a large recent increase in knowledge of the potentially damaging effects of certain oxygen metabolites, the role of vitamin E can now be placed in context as one factor in a complex protective system that includes superoxide dismutase, catalase, and peroxidases, including the seleno-enzyme glutathione peroxidase. alpha-Tocopherol is presumed to occur in association with intracellular membranes, but the techniques on which this presumption was based have been insufficiently sensitive to allow its confident acceptance. The hypothesis that the unique molecular structure of the phytyl side-chain of alpha-tocopherol enables specific physicochemical interactions with arachidonyl residues of membrane phospholipids can explain how molecules of alpha-tocopherol are bound within biological membranes. The interaction between alpha-tocopherol and unsaturated phospholipids has been studied using a tissue culture technique. The results suggest that alpha-tocopherol is capable of exerting a controlling influence upon the linoleyl and arachidonyl residues within membrane phospholipids which cannot be explained on the basis of the antioxidant function of the vitamin, and which may provide evidence for the above hypothesis.

Animals↗