Distribution of glutathione peroxidases and glutathione reductase in rat brain mitochondria

Dietary restriction affects antioxidant levels in rat liver mitochondria during ageing

Six experimental groups of young (7-month-old) and aged (24-32-month-old) rats, underwent different dietary manipulations (i.e. dietary restriction and/or a vitamin E-depleted diet), and their liver mitochondria were assayed for several antioxidants and peroxidation markers. Glutathione levels were affected both by age and dietary treatment. Coenzyme Q9 and C0Q10 showed the highest levels in the oldest rats where ageing, as well as other oxidative stresses, could induce ubiquinone biosynthesis.

Noxious effects of oxygen reactive species on energy-coupling processes in Ehrlich ascites tumor mitochondria and the protection by pantothenic acid

Irradiation of Ehrlich ascites tumor cells with ultraviolet light or exposure to the Fenton reaction results in lesions in the mitochondrial energy-coupling system. Formation of the membrane potential and its utilization for ATP synthesis are more affected than the respiratory chain. Preincubation of the cells with pantothenic acid or its derivatives which can serve as precursors of CoA largely protects against the damage of mitochondrial energetics by oxygen reactive species formed by UV light or the Fenton reaction. Incubation of Ehrlich ascites tumor cells with pantothenic acid increases their content of glutathione (most of which is present in the reduced form) by 40%. It is concluded that the protective effect of precursors of CoA against lesions of the mitochondrial energy-coupling system by oxygen reactive species is mainly due to removal of free radicals and peroxides by glutathione peroxidase and phospholipid hydroperoxide glutathione peroxidase.

PHGPx and phospholipase A2/GPx: comparative importance on the reduction of hydroperoxides in rat liver mitochondria

The comparative importance of phospholipid hydroperoxide glutathione peroxidase (PHGPx) and of "classic" glutathione peroxidase (GPx) in the reduction of phospholipid hydroperoxides is unclear. Although GPx activity is 500-fold higher than that of PHGPx in rat liver, the reduction of phospholipid hydroperoxides by glutathione (GSH) through GPx may be strongly limited by a low PLA2 activity. We address this issue using a moderately detailed kinetic model of mitochondrial lipid peroxidation in rat liver. The model was based on published data and was subjected to validation as reported in the references. It is analysed by computer simulation and sensitivity analysis. Results suggest that in rat liver mitochondria PHGPx is responsible for almost all phospholipid hydroperoxide reduction. Under physiological conditions, the estimated flux of phospholipid hydroperoxides reduction through PHGPx is about four orders of magnitude higher than the estimated hydrolysis flux through PLA2. On the other hand, virtually all hydrogen peroxide is reduced through GPx. Therefore, a functional complementarity between PHGPx and GPx is suggested. Because the results are qualitatively robust to changes of several orders of magnitude in PLA2 and PHGPx levels, the conclusions may not be limited to mitochondria.

Age- and peroxidative stress-related modifications of the cerebral enzymatic activities linked to mitochondria and the glutathione system

The aging brain undergoes a process of enhanced peroxidative stress, as shown by reports of altered membrane lipids, oxidized proteins, and damaged DNA. The aims of this review are to examine: (1) the possible contribution of mitochondrial processes to the formation and release of reactive oxygen species (ROS) in the aging brain; and (2) the age-related changes of antioxidant defenses, both enzymatic and nonenzymatic. It will focus on studies investigating the role of the electron transfer chain as the site of ROS formation in brain aging and the alterations of the glutathione system, also in relation to the effects of exogenous pro-oxidant agents. The possible role of peroxidative stress in age-related neurodegenerative diseases will also be discussed.

Distribution of glutathione and glutathione-related enzyme systems in mitochondria and cytosol of cultured cerebellar astrocytes and granule cells

The cellular and regional distribution of glutathione (GSH) and GSH-related enzyme systems involved in cellular defense against reactive oxygen species and electrophilic xenobiotics in the nervous system has been extensively studied. However, little is known about the subcellular distribution of GSH systems in brain tissue and cultured neural cells. The present study investigates the distribution of mitochondrial and cytosolic GSH and GSH-related enzymes in cultured cerebellar astrocytes and granule cells, and compares them with levels in the adult rat cerebellum. Cytosolic GSH levels and cytosolic activities of glutathione reductase (GR), glutathione peroxidase (GPX) and glutathione-S-transferase (GST) in astrocytes were 57, 153, 245, and 92% higher than those found in granule cells, respectively. In contrast, granule cells contained significantly higher mitochondrial GSH levels than astrocytes. Granule cells also demonstrated comparable mitochondria/cytosolic concentrations of GSH and GR, GPX and GST activities to those observed in the cerebellar tissue, whereas ratios in astrocytes were markedly lower. Although in vitro treatments with 100 microM ethacrynic acid depleted both cytosolic and mitochondrial GSH in cultured astrocytes and granule cells in a time-dependent fashion, cellular GSH in granule cells was more resistant to the GSH-depleting agent than astrocytes. These results suggest that although GSH and GSH-related enzymes are abundant in cytosolic compartments of astrocytes, mitochondrial pools are relatively small. Since brain mitochondria are sites of significant hydrogen peroxide generation, the mitochondrial localization of GSH and its associated enzymes in neural cells provide important defenses against toxic oxygen species in the nervous system. Differences in subcellular distribution of GSH systems in individual neural cell types may provide a basis for selective cellular and/or subcellular expression of neurotoxicity.

A comparison of the effects of dietary selenium on selenoprotein expression in rat brain and liver

In studies with rodents, when dietary supplies of the essential nutrient Se are restricted, in most tissues there are parallel substantial losses of the element and the important antioxidant selenoenzyme glutathione peroxidase (GPx) for which it is a cofactor. In brain, however, there appears to be both a sequestration of Se and a conservation of GPx activity when dietary Se is limited. To further explore the relation between these phenomena, we have undertaken a comparison of the effects of diets low, normal and high in Se on GPx activity, and labeling of selenoproteins following short-term (72 h) in vivo exposure to 75Se, in subcellular fractions from rat brain and liver, the latter serving as a representative tissue which does not retain Se and is depleted of most GPx activity following dietary restriction. Brains and livers from animals on the three diets showed different patterns of response with respect to both GPx activity and retention of the 75Se dose. The low-Se diet (0.006 ppm) substantially reduced GPx activity in liver but not brain, while high levels (1 ppm) did not increase GPx in either tissue relative to a normal (0.1 ppm) intake. The 75Se was retained in brain homogenates and subcellular fractions to the greatest extent by rats on the restricted diet, while in liver, retention was greater in rats fed the normal supplement than in animals on either the low- or high-Se diets. Levels of non-protein-bound 75Se were higher in brain than liver and increased with dietary Se in both tissues. When proteins in brain and liver homogenates and subcellular fractions where separated by one-dimensional SDS-PAGE and exposed to X-ray film, the resulting autoradiograms revealed the existence of seven distinct selenoprotein bands in brain and eight in liver. Different patterns of selenoprotein expression were observed in subcellular fractions isolated from both tissues. Dependence of levels of individual selenoproteins on diet paralleled the effects on 75Se retention. Dietary influences on expression of protein bands tentatively identified as GPx were more pronounced in liver than brain. All of these observations provide further evidence of the unique nature of Se metabolism in brain.