Effect of glutathione peroxidase activity on lipid peroxidation in biological membranes

Rat hepatic cytosolic glutathione-dependent enzyme protection against lipid peroxidation in the NADPH-microsomal lipid peroxidation system

Dialyzed rat liver cytosol (105 000 X g supernatant), when added along with 2.5 mM glutathione, blocked malonaldehyde formation in the NADPH-microsomal lipid peroxidation system, thus protecting against lipid peroxidation. Preheating the cytosol for 10 min at 60 degrees C destroyed its protective ability. Ammonium sulfate fractionation and Sephadex G-100 gel filtration of cytosol indicated that more than one glutathione-dependent protective enzyme was present. Fractions from the G-100 column containing the selenoenzyme glutathione peroxidase failed to protect, but fractions containing the glutathione S-transferases, which have non selenium-dependent glutathione peroxidase activity, did protect. The glutathione S-transferases were purified further with ion exchange chromatography and shown to have protective activity. Thus the rat hepatic cytosolic glutathione-dependent enzyme protection against lipid peroxidation in the NADPH-microsomal lipid peroxidation system is in part due to some of the glutathione S-transferases. The selenium-dependent glutathione peroxidase appears to have no protective effect in this system.

Responses of mitochondrial superoxide dismutase, catalase and glutathione peroxidase activities to aging

The previous observation (Eur. J. Biochem., 82 (1978) 563--567) that age-dependent accumulation of lipid peroxides follows as a consequence of increased radical formation in mitochondria has prompted an examination of the response of a set of protective enzymes to the above situation. Levels of mitochondrial catalase activity as well as selenium-dependent glutathione peroxidase activity were found to be increased with age, while superoxide dismutase activity remained unchanged. No selenium-independent glutathione peroxidase activity could be detected either in preparations from young 3-month-old controls or in preparations from 2-year-old rats. Both the relatively high and unchanged levels of reduced glutathione and kinetic considerations suggest that glutathione peroxidase is preferentially involved in lipid peroxide metabolism, while catalase predominantly metabolizes mitochondrial H2O2.

Brain lipofuscin concentration and oxidant defense enzymes in lead-poisoned neonatal rats

Neonatal rats were given aqueous lead acetate intragastrically from d 2-20 of life at doses of 0, 10, 50, and 225 mg Pb/kg.d. Blood Pb concentrations on d 21 were (mean +/- SE) 23 +/- 3 (control), 63 +/- 19, 246 +/- 55, and 994 +/- 223 microgram/100 ml, and brain Pb concentrations were 14 +/- 2, 60 +/- 5, 114 +/- 15, and 275 +/- 26 microgram/100 g, respectively. Growth was significantly depressed only in rats given the highest dose of Pb (225 mg/kg.d). Solvent-extractable lipofuscin pigment concentration of brain tissue progressively decreased over the 21-d duration of the experiment but was not significantly altered at any dose of Pb. Brain glutathione peroxidase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase activities were stimulated on d 20 at the maximal dose of Pb, but the activities of brain superoxide dismutases and catalase were not altered by Pb exposure. Locomotor activity was significantly increased in the male animals on d 20, but only at the highest dose of Pb. These results indicate that Pb toxicity in neonatal rats is not associated with accelerated in vivo lipid peroxidation in the brain, but that certain oxidant defense mechanisms in the brain are stimulated by Pb.

Glutathione depletion in isolated hepatocytes: its relation to lipid peroxidation and cell damage

The effects of glutathione depletion in isolated hepatocytes have been studied. A list of compounds which depleted glutathione and induced lipid peroxidation and cell lysis is given. The effects of halogenated acetamides were studied in more detail and results of studies on the interaction of iodoacetamide with cellular constituents are presented. A single metabolite of iodoacetamide, tentatively identified as the glutathione conjugate, was excreted from the cells while less than one percent of the "parent compound" was retained, tightly bound to macromolecules. This bound component could not be associated with the cellular damage. Methionine, cysteine and alpha-tocopherol, as wellas paracetamol and ethylmorphine, were found to prevent lipid peroxidation and lysis. It is concluded that GSH deficiency per se can lead to lipid peroxidation and that this reaction caused the observed hepatocellular lysis.

The lipoxygenase of reticulocytes. Purification, characterization and biological dynamics of the lipoxygenase; its identity with the respiratory inhibitors of the reticulocyte

A lipoxygenase has been purified from rabbit reticulocyte-rich anaemic blood cells. It possesses a molecular weight of 78 000 and an isoelectric point of 5.5 and contains 5% neutral sugars and two iron atoms per enzyme molecule. The lipoxygenase has proved to be identical with the inhibitors of respiratory proteins described formerly. The actions of the lipoxygenase on linoleic acid, phospholipids, mitochondrial and erythrocyte membranes and electron transfer particles were studied. A special feature of the reticulocyte lipoxygenase is the suicidal character of its action on lipids. With electron transfer particles the reticulocyte lipoxygenase causes a loss of acid-labile sulfur which accompanies respiratory inhibition; the strong respiratory inhibition is not exerted by soybean lipoxygenase. The reticulocyte lipoxygenase acts preferably on mitochondrial membranes as compared with cell membranes of the erythrocyte; erythrocyte cytosol moderates the action on mitochondrial membranes. Furthermore, the lipoxygenase reaction can concomitantly and irreversibly inactivate sulfhydryl enzymes as demonstrated with muscle glyceraldehyde-3-phosphate dehydrogenase. The occurrence of the lipoxygenase here described is restricted to reticulocytes; very low amounts were observed in bone marrow and no lipoxygenase was detectable in normal blood. During the course of an experimental anaemia the lipoxygenase is produced owing to superinduction in large amounts, which may persist for a long time since they escape inactivation. Preliminary evidence was obtained for the occurrence of other lipoxygenases in tissues of lung, spleen, kidney and also epithelial tumours.

Long-term NO2 exposure of mice in the presence and absence of vitamin E. II. Effect of glutathione peroxidase

One hundred and twenty female mice fed diets containing various levels of vitamin E were continuously exposed to 0.5 ppm, 1.0 ppm nitrogen dioxide (NO2), and filtered air for 17 months. Blood, lung, and liver tissues were assayed for glutathione peroxidase (GSH-peroxidase) activity. Exposure to 0.5 ppm NO2 did not affect blood and lung GSH-peroxidase activity; 1.0 ppm NO2 exposure, however, caused suppression of the enzyme. A combination of vitamin E deficiency and 1.0 ppm NO2 exposure resulted in the lowest GSH-peroxidase activities in the blood and lung. High levels of vitamin E in the diet resulted in elevated GSH-peroxidase in the blood and lung. Liver GSH-peroxidase activity was unaffected by either dietary vitamin E or NO2 exposure. No inverse relationship was found between GSH-peroxidase levels and concentrations of organic solvent soluble lipofuscin pigments present in tissues.

The pulmonary and extrapulmonary effects of ozone

The toxicity of ozone is solely due to its action as an oxidant. It is an extremely reactive gas which rapidly forms intermediate oxidizing derivatives after inhalation. High concentrations cause death from pulmonary oedema. Both pulmonary and extrapulmonary toxicity have been observed at lower concentrations of ozone, including those currently present in urban air. Pulmonary cellular and subcellular membranes appear to be particularly susceptible. A primary mechanism of this effect is the oxidative decomposition of polyunsaturated fatty acids, which has been demonstrated in rodent lungs after inhalation of ozone. Supporting evidence includes the potentiation of ozone toxicity by vitamin E deficiency and an increased use of this antioxidant vitamin during repetitive exposure to ozone. Other membrane effects include oxidation of thiol groups and, perhaps, of tryptophan. Microsomal alterations include a loss of lung cytochrome P450 which may also be related to lipid peroxidation. Extrapulmonary toxicity is not directly due to ozone but may represent in effect due to lipid peroxide decomposition products, particularly malonaldehyde. This three-carbon dialdehyde has been shown to alter cell membrane fluidity and to have mutagenic properties; the latter perhaps due to cross-linkage of DNA to histone.

Effects of dietary vitamin E, selenium, and polyunsaturated fats on in vivo lipid peroxidation in the rat as measured by pentane production

Starting at 21 days of age, groups of six rats each were fed a basal Torula yeast diet supplemented with 0.4% L-methionine and varying amounts of vitamin E as dl-alpha tocopherol acetate, selenium as sodium selenite, and with either 10% stripped corn oil, stripped lard, or coconut oil. By 7 wk, pentane production by rats fed a corn oil diet deficient in both vitamin E and selenium was twice that by rats fed 0.1 or 1 mg of selenium per kg of the same basal diet. Blood glutathione peroxidase activity after 7 wk was proportional to the logarithm of dietary selenium. Groups of rats fed the vitamin E- and selenium-deficient diets with lard or coconut oil had one-half the pentane production of rats fed the vitamin E- and selenium-deficient corn oil diets. The plasma level of linoleic plus arachidonic acid was 1.8 time greater on a wt % basis in rats fed corn oil than in rats fed lard or coconut oil as the fat source. Pentane production by rats fed 40 i.u. dl-alpha tocopherol acetate per kg of the selenium-deficient corn oil diet was one-sixth of that by rats fed the same diet without vitamin E; the plasma of the rats fed the vitamin E-supplemented corn oil diet had a level of vitamin E that was about six times greater than that of the rats fed the vitamin E-deficient corn oil diet.