Increased resistance of GPx-1 transgenic mice to tumor promoter-induced loss of glutathione peroxidase activity in skin

Sex-specific perinatal expression of glutathione peroxidases during mouse lung development

Reports indicate that antioxidant enzymes like the glutathione peroxidases (GPx) can be regulated by sex steroids. The GPx, a major class of antioxidants involved in H(2)O(2) and lipid hydroperoxides neutralization, showed an age- and sex-specific expression in many adult organs including the lung. High levels of androgens in the male lung are known to delay the surge of surfactant synthesis during gestation in several species. However, the impact of male androgens on antioxidant GPx early in life remains to be determined. The objective was to study the lung sex-specific expression of GPx during BALB/c mouse perinatal development. The mRNA expression of four seleno-dependent Gpx (Gpx1 to 4) in the lung of both sexes was characterized by real-time PCR from gestational day 15 to postnatal day 30, covering the entire canalicular, saccular and alveolar stages. Immunohistochemistry of GPx-1, -3 and -4, and seleno-dependent GPx enzymatic assays were also performed in the lung. We found a transient lower Gpx1 mRNA level in male than in female lungs during the first 5 days after birth, corresponding to the saccular phase. This dimorphic expression was concomitant to a sex difference in GPx enzymatic activity corrected for blood. It is, to our knowledge, the first report of a sex dimorphism for murine lung enzymatic antioxidant defenses during the perinatal period.

Antioxidant defenses are modulated in the cow oviduct during the estrous cycle

The balanced presence of reactive oxygen species and antioxidants has a positive impact on sperm functions, oocyte maturation, fertilization, and embryo development in vitro. The mammalian oviduct is likely to provide an optimal environment for final gamete maturation, sperm-egg fusion, and early embryonic development. However, the expression and distribution of antioxidant enzymes in the bovine oviduct are poorly characterized. We analyzed the mRNA expression and enzymatic activities of major antioxidants glutathione peroxidase (GPx), superoxide dismutase (Cu,ZnSOD), and catalase in the bovine oviduct throughout the estrous cycle. The high levels of expression for GPx-3 in the isthmus were in contrast to expression of GPx-1 and GPx-2, which occurred mostly in the ampulla and infundibulum of the oviduct. The highest levels of mRNA expression for GPx-1 were observed toward the end of the estrous cycle before ovulation, whereas GPx-2 was mostly expressed at midcycle. Catalase and Cu,ZnSOD mRNA analyses revealed a homogenous expression along the oviduct. The highest levels of glutathione and enzymatic activities for GPx and catalase occurred at the middle (10-12 days) and end (18-20 days) of the estrous cycle, whereas total SOD activity remained constant throughout the estrous cycle in the oviductal fluids. These findings underscore the importance of hydrogen peroxide and hydroperoxide removal by GPx in the oviduct. The heterogeneous expression of antioxidants such as GPx along the oviduct is a possible indication of their physiological role in the events leading to successful fertilization and implantation in vivo.

Oxidative stress and its role in skin disease

Skin is a major target of oxidative stress due to reactive oxygen species (ROS) that originate in the environment and in the skin itself. ROS are generated during normal metabolism, are an integral part of normal cellular function, and are usually of little harm because of intracellular mechanisms that reduce their damaging effects. Antioxidants attenuate the damaging effects of ROS and can impair and/or reverse many of the events that contribute to epidermal toxicity and disease. However, increased or prolonged free radical action can overwhelm ROS defense mechanisms, contributing to the development of cutaneous diseases and disorders. Although ROS play a role in diseases such as skin cancer, their biological targets and pathogenic mode of action are still not fully understood. In addition, strategies useful in the therapeutic management of ROS action in human skin are still lacking. This review is intended to give investigators an introduction to ROS, antioxidants, two skin disorders influenced by ROS action (skin cancer and psoriasis), and relevant model systems used to study ROS action.

Hyperoxia induces S-phase cell-cycle arrest and p21(Cip1/Waf1)-independent Cdk2 inhibition in human carcinoma T47D-H3 cells

Little is known about cell-cycle checkpoint activation by oxidative stress in mammalian cells. The effects of hyperoxia on cell-cycle progression were investigated in asynchronous human T47D-H3 cells, which contain mutated p53 and fail to arrest at G1/S in response to DNA damage. Hyperoxic exposure (95% O(2), 40-64 h) induced an S-phase arrest associated with acute inhibition of Cdk2 activity and DNA synthesis. In contrast, exit from G2/M was not inhibited in these cells. After 40 h of hyperoxia, these effects were partially reversible during recovery under normoxic conditions. The inhibition of Cdk2 activity was not due to degradation of Cdk2, cyclin E or A, nor impairment of Cdk2 complex formation with cyclin A or E and p21(Cip1). The loss of Cdk2 activity occurred in the absence of induction and recruitment of cdk inhibitor p21(Cip1) or p27(Kip1) in cyclin A/Cdk2 or cyclin E/Cdk2 complexes. In contrast, Cdk2 inhibition was associated with increased Cdk2-Tyr15 phosphorylation, increased E2F-1 recruitment, and decreased PCNA contents in Cdk2 complexes. The latter results indicate a p21(Cip1)/p27(Kip1)-independent mechanism of S-phase checkpoint activation in the hyperoxic T47D cell model investigated.

Effect of selenium supplementation on the activities of glutathione metabolizing enzymes in human hepatoma Hep G2 cell line

Cell culture is an important tool for studying injury to cells exposed to oxidative stress. The human hepatoblastoma derived Hep G2 cells retain their morphology and most of their function in culture and are therefore widely used as an in vitro model of human hepatocytes. Conventional cell culture media are deficient in selenium, which is essential for activation of glutathione peroxidase (GPx), a key enzyme in the defense against oxidative stress. Supplementation of the culture media with 1 microM sodium selenite increased the activities of total GPx by threefold and the selenium-dependent GPx by fourfold as compared to cells cultured in control media. The non-selenium-dependent GPx activity was unchanged. The activities of the other glutathione (GSH)-related enzymes were practically unchanged despite a tendency toward elevation. The activities of oxidized glutathione (GSSG) reductase and catalase increased by 22.4 and 27.4%, respectively. These relatively small increases did not carry statistical significance. Supplementation of tissue culture media with selenium may prove important, particularly for cell protection against oxidative stress.