Developmental Changes in Murine Brain Antioxidant Enzymes

Abstract

Reactive oxygen species produced in cells during normal aerobic metabolism have the ability to induce lipid peroxidation and protein oxidation; therefore, their detoxification and elimination are necessary for physiologic cellular activity and survival. The changes in neuronal antioxidant enzymes from fetal life to adulthood have not been fully described. We investigated protein expression, using Western blot analysis, and enzymatic activity of the antioxidant system-copper-zinc superoxide dismutase (SOD), manganese SOD, catalase, and glutathione peroxidase, as well as reduced glutathione level as an indicator of the nonenzymatic system-in CD1 murine brain at embryonic d 18 (E18), and postnatal d 1 (P1), d 4, d 7, d 14, and d 21. Copper-zinc SOD and glutathione peroxidase protein levels were low, whereas manganese SOD and catalase protein levels were high at E18 and P1. Total SOD activity was high at E18 and P1 and paralleled elevated manganese SOD activity; however, copper-zinc SOD activity was relatively unchanged throughout development. Catalase activity doubled and glutathione peroxidase activity tripled between E18 and P1. Reduced glutathione increased between E18 and P1. Except for catalase and manganese SOD, peak protein levels do not occur until later developmental ages. We suggest that as the fetus moves from an in utero hypoxic to a relatively hyperoxic environment with an approximate 4-fold elevation in oxygen concentration, these developmental changes in antioxidant enzymes are compensatory mechanisms aimed at protecting the newborn from oxidative stress. These data will be important in our future understanding of the mechanisms by which hypoxia mediates injury in the immature and the mature brain. ROS are continuously produced in mammalian cells during normal aerobic metabolism, and represent a class of biologically generated species that threaten neuronal survival by their ability to induce lipid peroxidation, protein oxidation, and DNA damage (1-3). These free radicals are processed by a highly complex and integrated antioxidant defense system that is composed of the enzymes CuZnSOD, MnSOD, catalase, GPx, and glutathione reductase, as well as nonenzymatic substances such as vitamins A, C, and E and low molecular weight molecules including reduced GSH. The SODs constitute the first line of defense against the deleterious effects of ROS.CuZnSOD is a key cytosolic enzyme, whereas MnSOD is present in high concentration in the mitochondria. Under physiologic conditions, the mitochondria are the most important source of the superoxide radical (4). Mitochondrial MnSOD, therefore, plays a significant protective role in neurons at a major site of ROS production. SOD enzymatically scavenges superoxide, converting it to H 2 O 2 , which is subsequently catabolized to water by catalase, GPx, and GSH reductase. H 2 O 2 is constantly generated in cells, and the predominant biochemical source of H 2 O 2 in the brain appears to be through reactions catalyzed by SOD.The detoxification of ROS is especially important...

Dynamic expression of manganese superoxide dismutase during mouse embryonic organogenesis

“…development (Chen et al, 1999). As the fetus moves from a hypoxic to a relatively hyperoxic environment, accompanying changes in antioxidant enzymes constitute a compensatory mechanism aimed at protecting the newborn from oxidative stress (Khan and Black, 2003). In the present study, MnSOD mRNA was found in chorion, allantois, and amnion as well as extraembryonic tissues including placenta.…”

Relationship of antioxidant enzyme activities with myelomeningocele

“…Authors (14,18) studying the levels of various antioxidant enzymes and studies on rat embryos and in rabbit fetuses found a gradual increase in the activity of most enzymes. In addition, multiple studies have demonstrated that the genetic susceptibility plays a key role in MM (2,5,20,21).…”

Reduced tumorigenesis in p53 knockout mice exposed in utero to low‐dose vitamin E

“…11,32,33 The deleterious embryonic and fetal effects of ROS, in the absence of maternal toxicity, likely reflects, in part, the low levels of most embryonic antioxidative enzymes and antioxidants. 6,9 On GD 13, among control embryos exposed in utero to the unsupplemented diet, the increased level of DNA oxidation in p53 null embryos, compared with both their þ/À and þ/þ littermates, suggests that endogenous embryonic oxidative stress in the absence of repair of oxidative DNA damage, one role of p53, may contribute to the more rapid onset of postnatal tumorigenesis in this genotype. Loss of only one p53 allele had no measurable effect on embryonic DNA oxidation, suggesting that, at least in the absence of enhanced oxidative stress, DNA repair in the heterozygous littermates is adequate to contribute, in part, to their slower development of postnatal FIGURE 6.…”