The role of vitamin E in cellular energy metabolism in cultured adrenocortical cells

Abstract

ACT cells, a bovine adrenocortical cell clone, are rapidly arrested and killed by 2 mM aminooxyacetate, an inhibitor of transamination reactions. Toxicity of aminooxyacetate to cultured bovine adrenocortical cells was previously linked to a high ratio of capacity for oxidation of glutamine relative to pyruvate and was reversible by adding excess glutamine. The toxic effects of aminooxyacetate were shown in the present study to be completely prevented by the simultaneous addition of low concentrations ( < 100 nM) of d-a-tocopherol (vitamin E) or selenious acid or higher concentration of other tocopherols, antioxidants, and ubiquinones (coenzymes Q6 and Q,J. When antioxidant analogs were tested, it was found that structural features of the molecules that increase antioxidant potency increased potency for prevention of aminooxyacetate toxicity. a-Tocopherol-supplemented AC 1 cells were found to be significantly less sensitive than nonsupplemented cells to growth inhibition by rotenone but not by fluorocitrate or dinitrophenol. Dinitrophenol (100 pM) stimulated substrate oxidation fivefold but had relatively slight effects on growth, either with or without a-tocopherol, indicating that limitation of the maximal activity of the tricarboxyiic acid cycle and respiratory chain is probably not responsible for the sensitivity to aminooxyacetate and rotenone in cells not supplemented with a-tocopherol. Sensitivity to growth inhibition by rotenone and the prevention by ubiquinones of aminooxyacetate toxicity suggest a restriction of electron flow at the NADH-ubiquinone step. The resultant higher NADHINAD' ratio would result in a lowered capacity for metabolism of pyruvate with consequent dependence for tricarboxylic acid cycle function and energy production on 2-oxoglutarate from glutamine by the transamination pathway. Vitamin E and other antioxidants may restore efficient function of ubiquinone by preventing side reactions involving lipid peroxidation. Selenium may have a similar effect as cofactor for glutathione peroxidase. A high ratio of capacity for oxidation of glutamine relative to pyruvate and accompanying sensitivity to aminooxyacetate may reflect a deficiency of vitamin E and selenium in adrenocortical cells in culture.

Effects of glucose, glutamine, ethylenediaminetetraacetic acid and oxygen tension on the concentration of reactive oxygen species and on development of the mouse preimplantation embryo in vitro

“…Thus, an early indication of disturbed mitochondrial function in cells in culture is a shift from oxidative use of pyruvate to use of glutamine (Breen & Shreffler, 1979;Reitzer et al, 1979;Hornsby & Gill, 1981). This transition occurs more rapidly in atmospheric oxygen than in 2% oxygen and is slowed by efficient removal of oxidative species (Hornsby & Gill, 1981;Hornsby, 1982), thereby implicating oxidative damage in the causation of the metabolic transition. Hornsby (1982) suggested that the ubiquinone cycle of mitochondria in cells in culture is interrupted by lipid radicals formed by lipid peroxidation.…”

“…The ubiquinone cycle, with ubiquinone (Q), ubisemiquinone (QH*), and ubiquinol (QH2) is shown to be interrupted by lipid radical formation (L*). SDH: succinate dehydrogenase; NADH-dh: NADH dehydrogenase (after Hornsby, 1982). Embryos were cultured in aminooxyacetate from 28 to 70 h after injection of mice with human chorionic gonadotrophin and they were then transferred to T6 + bovine serum albumin.…”

Developmentally related changes in the uptake and metabolism of glucose, glutamine and pyruvate by cattle embryos produced in vitro

“…An alternative explanation may be a difference in the relative activity of the two halves of the Krebs cycle. The ratio of glutamine to pyruvate metabolism has been shown to increase with proliferation of bovine adrenocortical cells in culture (Hornsby and Gill 1981), possibly because the NAD+substrate-dehydrogenases in the oxaloacetate to 2-oxoglutarate segment of the Krebs cycle are more sensitive to inhibition by NADH than are those in the segment from 2-oxoglutarate to oxaloacetate (Hornsby 1982). Similar mechanisms during expansion and hatching of the cattle blastocyst, may be responsible for the apparent increased significance of the activity of the 2-oxoglutarate-to-oxaloacetate segment of the Krebs cycle, relative to the activity of the pathway from pyruvate to 2-oxoglutarate.…”

“…The production of 14c02 from [2-14c] pyruvate was used as a measure of the activity of the entire Krebs cycle, and the production of 3~2~ from L-[3,4-3~(~)]glutamine (via deamination to glutamate and 2-oxoglutarate) was used as a measure of the activity of the 2-oxoglutarate-to-oxaloacetate segment (Hornsby and Gill 1981;Hornsby 1982).…”

Inhibition of tumor cell glutamine uptake by isolated neutrophils.

“…Growth of most mammalian cells in vitro requires high levels of glutamine (21,22), although this requirement may be an artifact of the tissue-culture system (23). High rates of glutamine use may be characteristic oftumor cells both in vitro and in vivo (24)(25)(26), and experimental cancer therapies have been developed based on depriving tumor cells of glutamine (27)(28)(29)(30).…”