Cu/Zn superoxide dismutase mRNA and enzyme activity, and susceptibility to lipid peroxidation, increases with aging in murine brains

Abstract

To protect against reactive oxygen species, prokaryotic and eukaryotic cells have developed an antioxidant defence mechanism where O 2 − is converted to H 2O 2 by superoxide dismutase ( Sod), and in a second step, H 2O 2 is converted to H 2O by catalase ( Cat) and/or glutathione peroxidase ( Gpx). If Sod levels are increased without a concomitant Gpx increase, then the intermediate H 2O 2 accumulates. This intermediate could undergo the Fenton's reaction, generating hydroxyl radicals which may lead to lipid peroxidation in cells. In this study, we investigate the expression of Sod1, Gpx1 and susceptibility to lipid peroxidation during the aging process in mouse brains. We demonstrate that the mRNA levels and enzyme activity of Sod1 are higher in brains from adult mice compared to neonatal mice. Furthermore, we show that a linear increase in Sod1 mRNA and enzyme activity occurs with aging (1–100 weeks). On the contrary, we find that the mRNA and enzyme activity for Gpx1 does not increase with aging in mouse brains. In addition, our results demonstrate that the susceptibility of murine brains to lipid peroxidation increases with aging. The data in this study are consistent with the notion that reactive oxygen species may contribute to the aging process in mammalian brains. These results are discussed in relation to the normal aging process in mammals, and to the premature aging and mental retardation in Down syndrome.