Mice lacking glutathione peroxidase-1 activity show increased TUNEL staining and an accelerated inflammatory response in brain following a cold-induced injury

The role of selenoproteins in neurodevelopment and neurological function: Implications in autism spectrum disorder

Selenium and selenoproteins play a role in many biological functions, particularly in brain development and function. This review outlines the role of each class of selenoprotein in human brain function. Most selenoproteins play a large antioxidant role within the brain. Autism spectrum disorder (ASD) has been shown to correlate with increased oxidative stress, and the presumption of selenoproteins as key players in ASD etiology are discussed. Further, current literature surrounding selenium in ASD and selenium supplementation studies are reviewed. Finally, perspectives are given for future directions of selenoprotein research in ASD.

The role of glutathione peroxidase-1 in health and disease

Glutathione peroxidase 1 (GPx1) is an important cellular antioxidant enzyme that is found in the cytoplasm and mitochondria of mammalian cells. Like most selenoenzymes, it has a single redox-sensitive selenocysteine amino acid that is important for the enzymatic reduction of hydrogen peroxide and soluble lipid hydroperoxides. Glutathione provides the source of reducing equivalents for its function. As an antioxidant enzyme, GPx1 modulates the balance between necessary and harmful levels of reactive oxygen species. In this review, we discuss how selenium availability and modifiers of selenocysteine incorporation alter GPx1 expression to promote disease states. We review the role of GPx1 in cardiovascular and metabolic health, provide examples of how GPx1 modulates stroke and provides neuroprotection, and consider how GPx1 may contribute to cancer risk. Overall, GPx1 is protective against the development and progression of many chronic diseases; however, there are some situations in which increased expression of GPx1 may promote cellular dysfunction and disease owing to its removal of essential reactive oxygen species.

Physiological Functions of Thiol Peroxidases (Gpx1 and Prdx2) during Xenopus laevis Embryonic Development

Glutathione peroxidase 1 (Gpx1) and peroxiredoxin 2 (Prdx2) belong to the thiol peroxidase family of antioxidants, and have been studied for their antioxidant functions and roles in cancers. However, the physiological significance of Gpx1 and Prdx2 during vertebrate embryogenesis are lacking. Currently, we investigated the functional roles of Gpx1 and Prdx2 during vertebrate embryogenesis using Xenopus laevis as a vertebrate model. Our investigations revealed the zygotic nature of gpx1 having its localization in the eye region of developing embryos, whereas prdx2 exhibited a maternal nature and were localized in embryonic ventral blood islands. Furthermore, the gpx1-morphants exhibited malformed eyes with incompletely detached lenses. However, the depletion of prdx2 has not established its involvement with embryogenesis. A molecular analysis of gpx1-depleted embryos revealed the perturbed expression of a cryba1-lens-specific marker and also exhibited reactive oxygen species (ROS) accumulation in the eye regions of gpx1-morphants. Additionally, transcriptomics analysis of gpx1-knockout embryos demonstrated the involvement of Wnt, cadherin, and integrin signaling pathways in the development of malformed eyes. Conclusively, our findings indicate the association of gpx1 with a complex network of embryonic developmental pathways and ROS responses, but detailed investigation is a prerequisite in order to pinpoint the mechanistic details of these interactions.

Low oxygen tension activates glucose metabolism, improves antioxidant capacity and augment developmental potential of ovine embryos in vitro

Context Oxygen (O2) is one of the most powerful regulators of embryo function. Nevertheless, most in vitro embryo production studies do not consider O2 as a determining factor. Aim The present study was designed to assess the effect of different O2 (5 and 20%) concentrations on the developmental ability and expression of genes related to cellular antioxidant functions and glucose metabolism in the in vitro produced ovine embryos. Methods In vitro sheep embryos were produced at different O2 (5 and 20%) concentrations as per the laboratory protocol. Developmental stages of embryos at different O2 concentrations were compared. Messenger RNA abundance of antioxidant and glucose metabolism genes in embryos produced at different O2 concentrations were compared. Key results No significant (P < 0.05) effect of different O2 concentrations on oocyte maturation and cleavage rate was observed. In contrast, significantly (P < 0.05) more number of morula and blastocysts were observed at 5 compared with 20%O2. The expression level of the genes related to antioxidant functions (GPX, SOD1, SOD2 and CAT) and glucose metabolism (G6PD and HPRT) were found significantly (P < 0.05) greater in the embryos generated with 5 compared with 20% O2. In contrast, the expression of GAPDH did not differ significantly (P < 0.05) between the groups. Conclusions Ovine embryos at 5%O2 generated low ROS and synthesised more GSH due to the activation of G6PD and GPX that in turn increased the antioxidant capability and developmental potential of the embryos. Implications Embryos at higher O2 concentration (20%) generated more reactive oxygen species (ROS) that caused oxidative damage to the embryos and in turn reduced their developmental ability and alter gene expression.

l-Ergothioneine improves the developmental potential of in vitro sheep embryos without influencing OCTN1-mediated cross-membrane transcript expression

The objective of the study was to investigate the effect of l-ergothioneine (l-erg) (5 mM or 10 mM) supplementation in maturation medium on the developmental potential and OCTN1-dependant l-erg-mediated (10 mM) change in mRNA abundance of apoptotic (Bcl2, Bax, Casp3 and PCNA) and antioxidant (GPx, SOD1, SOD2 and CAT) genes in sheep oocytes and developmental stages of embryos produced in vitro. Oocytes matured with l-erg (10 mM) reduced their embryo toxicity by decreasing intracellular ROS and increasing intracellular GSH in matured oocytes that in turn improved developmental potential, resulting in significantly (P < 0.05) higher percentages of cleavage (53.72% vs 38.86, 46.56%), morulae (34.36% vs 20.62, 25.84%) and blastocysts (14.83% vs 6.98, 9.26%) compared with other lower concentrations (0 mM and 5 mM) of l-erg without change in maturation rate. l-Erg (10 mM) treatment did not influence the mRNA abundance of the majority of apoptotic and antioxidant genes studied in the matured oocytes and developmental stages of embryo. A gene expression study found that the SLC22A4 gene that encodes OCTN1, an integral membrane protein and specific transporter of l-erg was not expressed in oocytes and developmental stages of embryos. Therefore it was concluded from the study that although there was improvement in the developmental potential of sheep embryos by l-erg supplementation in maturation medium, there was no change in the expression of the majority of the genes studied due to the absence of the SLC22A4 gene in oocytes and embryos that encode OCTN1, which is responsible for transportation of l-erg across the membrane to alter gene expression.

Selenium-Dependent Glutathione Peroxidases During Tumor Development

Five out of eight human glutathione peroxidases (GPxes) are selenoproteins and thus their expression depends on the selenium (Se) supply. Most Se-dependent GPxes are downregulated in tumor cells, while only GPx2 is considerably upregulated. Whether expression profiles of GPxes predict tumor development and patient survival is controversially discussed. Also, results from in vitro and in vivo studies modulating the expression of GPx isoforms provide evidence for both anti- and procarcinogenic mechanisms. GPxes are able to reduce hydroperoxides, which otherwise would damage DNA, possibly resulting in DNA mutations, modulate redox-sensitive signaling pathways affecting proliferation, differentiation, and cellular metabolism or initiate cell death. Considering these different processes, the role and functions of individual Se-dependent GPx isoforms will be discussed herein in the context of tumorigenesis.

Analyses of antioxidant status and nucleotide alterations in genes encoding antioxidant enzymes in patients with benign and malignant thyroid disorders

Background

Synthesis of thyroid hormones and regulation of their metabolism involve free radicals that may affect redox balance in the body. Thyroid disorders causing variations in the levels of thyroid hormones may alter cellular oxidative stress. The aim of this study was to measure the antioxidant activities and biomarkers of oxidative stress in serum and red blood cells (RBC) of patients with benign and malignant thyroid disorders and to investigate if changes in the antioxidant activities in these patients were linked to alterations in genes encoding the antioxidant enzymes.

Methods

Forty-one patients with thyroid disorders from University of Malaya Medical Centre were recruited. They were categorised into four groups: multinodular goitre (MNG) (n = 18), follicular thyroid adenoma (FTA) (n = 7), papillary thyroid cancer (PTC) (n = 10), and follicular thyroid cancer (FTC) (n = 6). Serum and RBC of patients were analysed for antioxidant activities, antioxidant enzymes, and biomarkers of oxidative stress. Alterations in genes encoding the antioxidant enzymes were analysed using whole exome sequencing and PCR–DNA sequencing.

Results

Patients with thyroid disorders had significantly higher serum superoxide dismutase (SOD) and catalase (CAT) activities compared to control, but had lower activities in RBC. There were no significant changes in serum glutathione peroxidase (GPx) activity. Meanwhile, GPx activity in RBC was reduced in PTC and FTC, compared to control and the respective benign groups. Antioxidant activities in serum were decreased in the thyroid disorder groups when compared to the control group. The levels of malondialdehyde (MDA) were elevated in the serum of FTA group when compared to controls, while in the RBC, only the MNG and PTC groups showed higher MDA equivalents than control. Serum reactive oxygen species (ROS) levels in PTC group of both serum and RBC were significantly higher than control group. Whole exome sequencing has resulted in identification of 49 single nucleotide polymorphisms (SNPs) in MNG and PTC patients and their genotypic and allelic frequencies were calculated. Analyses of the relationship between serum enzyme activities and the total SNPs identified in both groups revealed no correlation.

Discussion

Different forms of thyroid disorders influence the levels of antioxidant status in the serum and RBC of these patients, implying varying capability of preventing oxidative stress. A more comprehensive study with a larger target population should be done in order to further evaluate the relationships between antioxidant enzymes gene polymorphisms and thyroid disorders, as well as strengthening the minor evidences provided in literatures.

Nanoporous Metal-Phenolic Particles as Ultrasound Imaging Probes for Hydrogen Peroxide

Nanoporous metal-phenolic particles are fabricated through the nanostructural replication of dense Fe^III -TA complexes in nanoporous CaCO₃ template particles. The particles have potential for the diagnostic detection of endogenous levels of H₂ O₂ ex vivo and in vivo by ultrasound imaging, which is based on the catalytic activity of the coordinated Fe³⁺ in the particles to break down H₂ O₂ to O₂ microbubbles.

Selenoproteins in nervous system development and function

Selenoproteins are a distinct class of proteins that are characterized by the co-translational incorporation of selenium (Se) in the form of the 21st amino acid selenocysteine. Selenoproteins provide a key defense against oxidative stress, as many of these proteins participate in oxidation-reduction reactions neutralizing reactive oxygen species, where selenocysteine residues act as catalytic sites. Many selenoproteins are highly expressed in the brain, and mouse knockout studies have determined that several are required for normal brain development. In parallel with these laboratory studies, recent reports of rare human cases with mutations in genes involved in selenoprotein biosynthesis have described individuals with an assortment of neurological problems that mirror those detailed in knockout mice. These deficits include impairments in cognition and motor function, seizures, hearing loss, and altered thyroid metabolism. Additionally, due to the fact that oxidative stress is a key feature of neurodegenerative disease, there is considerable interest in the therapeutic potential of selenium supplementation for human neurological disorders. Studies performed in cell culture and rodent models have demonstrated that selenium administration attenuates oxidative stress, prevents neurodegeneration, and counters cell signaling mechanisms known to be dysregulated in certain disease states. However, there is currently no definitive evidence in support of selenium supplementation to prevent and/or treat common neurological conditions in the general population. It appears likely that, in humans, supplementation with selenium may only benefit certain subpopulations, such as those that are either selenium-deficient or possess genetic variants that affect selenium metabolism.

Differential cellular localization of antioxidant enzymes in the trigeminal ganglion

Because of its high oxygen demands, neural tissue is predisposed to oxidative stress. Here, our aim was to clarify the cellular localization of antioxidant enzymes in the trigeminal ganglion. We found that the transcriptional factor Sox10 is localized exclusively in satellite glial cells (SGCs) in the adult trigeminal ganglion. The use of transgenic mice that express the fluorescent protein Venus under the Sox10 promoter enabled us to distinguish between neurons and SGCs. Although both superoxide dismutases 1 and 2 were present in the neurons, only superoxide dismutase 1 was identified in SGCs. The enzymes relevant to hydrogen peroxide degradation displayed differential cellular localization, such that neurons were endowed with glutathione peroxidase 1 and thioredoxin 2, and catalase and thioredoxin 2 were present in SGCs. Our immunohistochemical finding showed that only SGCs were labeled by the oxidative damage marker 8-hydroxy-2'-deoxyguanosine, which indicates that the antioxidant systems of SGCs were less potent. The transient receptor potential vanilloid subfamily member 1 (TRPV1), the capsaicin receptor, is implicated in inflammatory hyperalgesia, and we demonstrated that topical capsaicin application causes short-lasting mechanical hyperalgesia in the face. Our cell-based assay revealed that TRPV1 agonist stimulation in the presence of TRPV1 overexpression caused reactive oxygen species-mediated caspase-3 activation. Moreover, capsaicin induced the cellular demise of primary TRPV1-positive trigeminal ganglion neurons in a dose-dependent manner, and this effect was inhibited by a free radical scavenger and a pancaspase inhibitor. This study delineates the localization of antioxidative stress-related enzymes in the trigeminal ganglion and reveals the importance of the pivotal role of reactive oxygen species in the TRPV1-mediated caspase-dependent cell death of trigeminal ganglion neurons. Therapeutic measures for antioxidative stress should be taken to prevent damage to trigeminal primary sensory neurons in inflammatory pain disorders.

MyD88 is a critical regulator of hematopoietic cell-mediated neuroprotection seen after stroke

Neuroinflammation is critical in the neural cell death seen in stroke. It has been shown that CNS and peripheral responses drive this neuroinflammatory response in the brain. The Toll-like receptors (TLRs) are important regulators of inflammation in response to both exogenous and endogenous stressors. Taking advantage of a downstream adapter molecule that controls the majority of TLR signalling, this study investigated the role of the TLR adaptor protein myeloid differentiation factor 88 (MyD88) in the control of CNS and peripheral inflammation. Reversible middle-cerebral artery occlusion was used as the model of stroke in vivo; in vitro primary cultured neurons and glia were subject to four hours of oxygen and glucose deprivation (OGD). Both in vitro and in vivo Myd88^−/− animals or cells were compared with wild type (WT). We found that after stroke Myd88^−/− animals have a larger infarct volume compared to WT animals. Interestingly, in vitro there was no difference between the survival of Myd88^−/− and WT cells following OGD, suggesting that peripheral responses were influencing stroke outcome. We therefore generated bone marrow chimeras and found that Myd88^−/− animals have a smaller stroke infarct than their radiation naive counterparts if their hematopoietic cells are WT. Furthermore, WT animals have a larger stroke than their radiation naive counterparts if the hematopoietic cells are Myd88^−/−. We have demonstrated that MyD88-dependent signalling in the hematopoietic cell lineage reduces infarct size following stroke and that infiltrating cells to the site of neuroinflammation are neuroprotective following stroke.

Glutathione peroxidase-1 in health and disease: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species, such as superoxide and hydrogen peroxide, are generated in all cells by mitochondrial and enzymatic sources. Left unchecked, these reactive species can cause oxidative damage to DNA, proteins, and membrane lipids. Glutathione peroxidase-1 (GPx-1) is an intracellular antioxidant enzyme that enzymatically reduces hydrogen peroxide to water to limit its harmful effects. Certain reactive oxygen species, such as hydrogen peroxide, are also essential for growth factor-mediated signal transduction, mitochondrial function, and maintenance of normal thiol redox-balance. Thus, by limiting hydrogen peroxide accumulation, GPx-1 also modulates these processes. This review explores the molecular mechanisms involved in regulating the expression and function of GPx-1, with an emphasis on the role of GPx-1 in modulating cellular oxidant stress and redox-mediated responses. As a selenocysteine-containing enzyme, GPx-1 expression is subject to unique forms of regulation involving the trace mineral selenium and selenocysteine incorporation during translation. In addition, GPx-1 has been implicated in the development and prevention of many common and complex diseases, including cancer and cardiovascular disease. This review discusses the role of GPx-1 in these diseases and speculates on potential future therapies to harness the beneficial effects of this ubiquitous antioxidant enzyme.

The Roles of Glutathione Peroxidases during Embryo Development

Embryo development relies on the complex interplay of the basic cellular processes including proliferation, differentiation, and apoptotic cell death. Precise regulation of these events is the basis for the establishment of embryonic structures and the organ development. Beginning with fertilization of the oocyte until delivery the developing embryo encounters changing environmental conditions such as varying levels of oxygen, which can give rise to reactive oxygen species (ROS). These challenges are met by the embryo with metabolic adaptations and by an array of anti-oxidative mechanisms. ROS can be deleterious by modifying biological molecules including lipids, proteins, and nucleic acids and may induce abnormal development or even embryonic lethality. On the other hand ROS are vital players of various signaling cascades that affect the balance between cell growth, differentiation, and death. An imbalance or dysregulation of these biological processes may generate cells with abnormal growth and is therefore potentially teratogenic and tumorigenic. Thus, a precise balance between processes generating ROS and those decomposing ROS is critical for normal embryo development. One tier of the cellular protective system against ROS constitutes the family of selenium-dependent glutathione peroxidases (GPx). These enzymes reduce hydroperoxides to the corresponding alcohols at the expense of reduced glutathione. Of special interest within this protein family is the moonlighting enzyme glutathione peroxidase 4 (Gpx4). This enzyme is a scavenger of lipophilic hydroperoxides on one hand, but on the other hand can be transformed into an enzymatically inactive cellular structural component. GPx4 deficiency - in contrast to all other GPx family members - leads to abnormal embryo development and finally produces a lethal phenotype in mice. This review is aimed at summarizing the current knowledge on GPx isoforms during embryo development and tumor development with an emphasis on GPx4.

The neural stem/progenitor cell marker nestin is expressed in proliferative endothelial cells, but not in mature vasculature

Nestin is an intermediate filament protein that is known as a neural stem/progenitor cell marker. It is expressed in undifferentiated central nervous system (CNS) cells during development, but also in normal adult CNS and in CNS tumor cells. Additionally, nestin is expressed in endothelial cells (ECs) of CNS tumor tissues and of adult tissues that replenish by angiogenesis. However, the regulation of nestin expression in vascular endothelium has not been analyzed in detail. This study showed that nestin expression was observed in proliferating endothelial progenitor cells (EPCs), but not in mature ECs. In adherent cultured cells derived from bone marrow cells, EPCs that highly expressed nestin also expressed the endothelial marker CD31 and the proliferation marker Ki67. ECs cultured without growth factors showed attenuated nestin immunoreactivity as they matured. Transgenic mice that carried the enhanced green fluorescent protein under the control of the CNS-specific second intronic enhancer of the nestin gene showed no reporter gene expression in EPCs. This indicated that the mechanisms of nestin gene expression were different in EPCs and CNS cells. Immunohistochemistry showed nestin expression in neovascular cells from two distinct murine models. Our results demonstrate that nestin can be used as a marker protein for neovascularization.

The Role of Nrf2 in Cellular Innate Immune Response to Inflammatory Injury

Nuclear factor erythroid derived 2-related factor-2 (Nrf2) is a master transcription regulator of antioxidant and cytoprotective proteins that mediate cellular defense against oxidative and inflammatory stresses. Disruption of cellular stress response by Nrf2 deficiency causes enhanced susceptibility to infection and related inflammatory diseases as a consequence of exacerbated immuneediated hypersensitivity and autoimmunity. The cellular defense capacity potentiated by Nrf2 activation appears to balance the population of CD4⁺ and CD8⁺ of lymph node cells for proper innate immune responses. Nrf2 can negatively regulate the activation of pro-inflammatory signaling molecules such as p38 MAPK, NF-KB, and AP-1. Nrf2 subsequently functions to inhibit the production of pro-inflammatory mediators including cytokines, chemokines, cell adhesion molecules, matrix metalloprotein-ases, COX-2 and iNOS. Although not clearly elucidated, the antioxidative function of genes targeted by Nrf2 may cooperatively regulate the innate immune response and also repress the expression of proinflammatory mediators.

Drug targets for traumatic brain injury from poly(ADP-ribose)polymerase pathway modulation

The deleterious pathophysiological cascade induced after traumatic brain injury (TBI) is initiated by an excitotoxic process triggered by excessive glutamate release. Activation of the glutamatergic N-methyl-D-aspartate receptor, by increasing calcium influx, activates nitric oxide (NO) synthases leading to a toxic production of NO. Moreover, after TBI, free radicals are highly produced and participate to a deleterious oxidative stress. Evidence has showed that the major toxic effect of NO comes from its combination with superoxide anion leading to peroxynitrite formation, a highly reactive and oxidant compound. Indeed, peroxynitrite mediates nitrosative stress and is a potent inducer of cell death through its reaction with lipids, proteins and DNA. Particularly DNA damage, caused by both oxidative and nitrosative stresses, results in activation of poly(ADP-ribose) polymerase (PARP), a nuclear enzyme implicated in DNA repair. In response to excessive DNA damage, massive PARP activation leads to energetic depletion and finally to cell death. Since 10 years, accumulating data have showed that inactivation of PARP, either pharmacologically or using PARP null mice, induces neuroprotection in experimental models of TBI. Thus TBI generating NO, oxidative and nitrosative stresses promotes PARP activation contributing in post-traumatic motor, cognitive and histological sequelae. The mechanisms by which PARP inhibitors provide protection might not entirely be related to the preservation of cellular energy stores, but might also include other PARP-mediated mechanisms that needed to be explored in a TBI context. Ten years of experimental research provided rational basis for the development of PARP inhibitors as treatment for TBI.

Glutathione peroxidases in different stages of carcinogenesis

Cancer cells produce high amounts of reactive oxygen species (ROS) and evade apoptosis. Hydroperoxides support proliferation, invasion, migration and angiogenesis, but at higher levels induce apoptosis, thus being pro- and anti-carcinogenic. Accordingly, glutathione peroxidases (GPxs) regulating hydroperoxide levels might have dual roles too. GPx1, clearly an antioxidant enzyme, is down-regulated in many cancer cells. Its main role would be prevention of cancer initiation by ROS-mediated DNA damage. GPx2 is up-regulated in cancer cells. GPx1/GPx2 double knockout mice develop colitis and intestinal cancer. However, GPx2 knockdown cancer cells grow better in vitro and in vivo probably reflecting the physiological role of GPx2 in intestinal mucosa homeostasis. GPx2 counteracts COX-2 expression and PGE(2) production, which explains its potential to inhibit migration and invasion of cultured cancer cells. Overexpression of GPx3 inhibits tumor growth and metastasis. GPx4 is decreased in cancer tissues. GPx4-overexpressing cancer cells have low COX-2 activity and tumors derived therefrom are smaller than from control cells and do not metastasize. Collectively, GPxs prevent cancer initiation by removing hydroperoxides. GPx4 inhibits but GPx2 supports growth of established tumors. Metastasis, but also apoptosis, is inhibited by all GPxs. GPx-mediated regulation of COX/LOX activities may be relevant to early stages of inflammation-mediated carcinogenesis.

Cellular glutathione peroxidase in human brain: cellular distribution, and its potential role in the degradation of Lewy bodies in Parkinson's disease and dementia with Lewy bodies

Glutathione peroxidase (GPx-1) is regarded as one of the mammalian cell's main antioxidant enzymes inactivating hydrogen peroxide and protecting against oxidative stress. Using control, Parkinson's disease (PD), and dementia with Lewy bodies tissue (DLB) we have shown that GPx-1 is a 21-kD protein under reducing conditions in all tissues examined but is not in high abundance in human brain. Using immunohistochemistry we have mapped the cellular distribution of GPx-1 and have shown it to be in highest levels in microglia and with lower levels in neurons. Only a trace amount was detectable in astrocytes using immunofluorescence and GPx-1 was not detectable in oligodendrocytes. GPx-1 positive microglia were hypertrophied and more abundant in PD and DLB tissues and were seen to be making multiple contacts with neurons. In some cases neurons containing Lewy bodies were surrounded by microglia. Unstructured Lewy bodies were enveloped with a layer of GPx-1 that was partially colocalized with alpha-synuclein whereas concentric Lewy bodies had discrete deposits of GPx-1 around the periphery which appeared to be involved in the degradation of the Lewy bodies. These results suggest that abnormal alpha-synuclein as found in Lewy bodies produce hydrogen peroxide and these neurons are capable of directing antioxidant enzymes to regions of oxidative stress. These results also suggest that GPx-1 positive microglia are involved in neuroprotection in PD and DLB and that GPx-1 is an important antioxidant enzyme in neuronal defences.

Decreased cardiac glutathione peroxidase levels and enhanced mandibular apoptosis in malformed embryos of diabetic rats

OBJECTIVE

To characterize normal and malformed embryos within the same litters from control and diabetic rats for expression of genes related to metabolism of reactive oxygen species (ROS) or glucose as well as developmental genes.

RESEARCH DESIGN AND METHODS

Embryos from nondiabetic and streptozotocin-induced diabetic rats were collected on gestational day 11 and evaluated for gene expression (PCR) and distribution of activated caspase-3 and glutathione peroxidase (Gpx)-1 by immunohistochemistry.

RESULTS

Maternal diabetes (MD group) caused growth retardation and an increased malformation rate in the embryos of MD group rats compared with those of controls (N group). We found decreased gene expression of Gpx-1 and increased expression of vascular endothelial growth factor-A (Vegf-A) in malformed embryos of diabetic rats (MDm group) compared with nonmalformed littermates (MDn group). Alterations of messenger RNA levels of other genes were similar in MDm and MDn embryos. Thus, expression of copper zinc superoxide dismutase (CuZnSOD), manganese superoxide dismutase (MnSOD), and sonic hedgehog homolog (Shh) were decreased, and bone morphogenetic protein-4 (Bmp-4) was increased, in the MD embryos compared with the N embryos. In MDm embryos, we detected increased activated caspase-3 immunostaining in the first visceral arch and cardiac area and decreased Gpx-1 immunostaining in the cardiac tissue; both findings differed from the caspase/Gpx-1 immunostaining of the MDn and N embryos.

CONCLUSIONS

Maternal diabetes causes growth retardation, congenital malformations, and decreased general antioxidative gene expression in the embryo. In particular, enhanced apoptosis of the first visceral arch and heart, together with decreased cardiac Gpx-1 levels, may compromise the mandible and heart and thus cause an increased risk of developing congenital malformation.

Cysteinyl leukotriene receptor 1 partially mediates brain cryoinjury in mice

AIM

To determine whether the cysteinyl leukotriene receptor 1 (CysLT1 receptor) modulates brain cryoinjury and whether the CysLT1 receptor antagonist pranlukast exerts a time-dependent protective effect on cryoinjury in mice.

METHODS

Brain cryoinjury was induced by applying a liquid nitrogen-cooled metal probe to the surface of the skull for 30 s. Brain lesion, neuron density, and endogenous IgG exudation were observed 24 h after cryoinjury. Transcription and the expression of the CysLT1 receptor were detected by RT-PCR and immunoblotting, and the localization of the receptor protein by double immunofluorescence.

RESULTS

The mRNA and protein expressions of the CysLT1 receptor were upregulated in the brain 6-24 h after cryoinjury, and the CysLT1 receptor protein was primarily localized in the neurons, not in the astrocytes or microglia. Pre-injury treatments with multi-doses and a single dose of pranlukast (0.1 mg/kg) attenuated cryoinjury; postinjury single dose (0.1 mg/kg) at 30 min (not 1 h) after cryoinjury was also effective.

CONCLUSION

The CysLT1 receptor modulates cryoinjury in mice at least partly, and postinjury treatment with its antagonist pranlukast exerts the protective effect with a therapeutic window of 30 min.

Glutathione peroxidase 1 and a high cellular glutathione concentration are essential for effective organic hydroperoxide detoxification in astrocytes

Organic hydroperoxides are produced in the eicosanoid metabolism and by lipid peroxidation. To examine the contribution of glutathione peroxidase-1 (GPx1) and glutathione (GSH) in the disposal of organic hydroperoxides in brain astrocytes, primary astrocyte cultures from wild type or GPx1-deficient (GPx1(-/-)) mice were exposed to cumene hydroperoxide (CHP). After application of 100 microM CHP, the peroxide disappeared quickly from the incubation medium of wild type cells with a half-life of 9 min, whereas CHP clearance was strongly retarded in GPx1(-/-) astrocytes. Depletion of GSH by pre-incubation with buthionine sulfoximine (BSO) significantly slowed CHP clearance by wild type astrocytes, while almost completely preventing peroxide disposal by GPx1(-/-) cells. In contrast, the catalase inhibitor 3-aminotriazole (3AT) had no effect on CHP clearance. Application of CHP to wild type astrocytes was followed by a rapid and transient accumulation of GSSG, whereas in GPx1(-/-) cells no increase in the GSSG content was detected. Astrocytes from both mouse lines remained viable for up to 24 h following CHP exposure, however depletion of cellular GSH by pre-treatment with BSO compromised the viability of astrocytes, an effect that was stronger in GPx1(-/-) than in wild type cells. This cell death was almost completely prevented by iron chelators, whereas pre-incubation with iron increased CHP toxicity. These novel data demonstrate that the toxicity of organic hydroperoxides in astrocytes is iron-mediated, and that an intact GSH system is required for the effective removal of organic hydroperoxides and for protection from these peroxides.

Glutathione peroxidase 1 and glutathione are required to protect mouse astrocytes from iron-mediated hydrogen peroxide toxicity

The enzyme glutathione peroxidase 1 (GPx1) is involved in the cellular detoxification of peroxides. To test for the consequences of GPx deficiency in astrocytes, astrocyte-rich primary cultures from wild-type and GPx1-deficient [GPx1(-/-)] mice were exposed to H(2)O(2). In GPx1(-/-) astrocytes, the clearance rate of H(2)O(2) was slower than in wild-type cells. In contrast to GPx1-deficient astrocytes, wild-type cells exhibited, within 2 min of H(2)O(2) application, a rapid and transient accumulation of cellular glutathione disulfide that amounted to 60% of total glutathione. The peroxide treatment did not affect the viability of wild-type astrocytes, whereas 45% of the GPx1(-/-) cells died within 8 hr. However, the viability of both types of astrocytes was strongly compromised by lowering cellular glutathione content before peroxide application. In contrast, inactivation of catalase caused substantial cell death only in GPx1(-/-) cells but not in wild-type astrocytes. The cell death observed was prevented by the iron chelators deferoxamine, 1,10-phenathroline, or 2,2'-dipyridyl, whereas preincubation with ferric ammonium citrate increased the toxicity of peroxide treatments. These results demonstrate that GPx1 contributes to the rapid clearance of H(2)O(2) by mouse astrocytes and that both GPx1 and a high concentration of glutathione are required to protect these cells from iron-dependent peroxide damage.

Caffeic acid attenuates neuronal damage, astrogliosis and glial scar formation in mouse brain with cryoinjury

Traumatic brain injury induces neuron damage in early phase, and astrogliosis and the formation of the glial scar in late phase. Caffeic acid (3, 4-dihydroxycinnamic acid), one of the natural phenolic compounds, exerts neuroprotective effects against ischemic brain injuries with anti-oxidant and anti-inflammatory properties, and by scavenging reactive species. However, whether caffeic acid has protective effects against traumatic brain injury is unknown. Therefore, we determined the effect of caffeic acid on the lesion in the early (1 day) and late phases (7 to 28 days) of cryoinjury in mice. We found that caffeic acid (10 and 50 mg/kg, i.p., for 7 days after cryoinjury) reduced the lesion area and attenuated the neuron loss around the lesion core 1 to 28 days, but attenuated the neuron loss in the lesion core only 1 day after cryoinjury. Moreover, caffeic acid attenuated astrocyte proliferation, glial scar wall formation and glial fibrillary acidic protein (GFAP) protein expression in the late phase of cryoinjury (7 to 28 days). Caffeic acid also inhibited the reduction of superoxide dismutase activity and the increase in malondialdehyde content in the brain 1 day after cryoinjury. These results indicate that caffeic acid exerts a protective effect in traumatic brain injury, especially on glial scar formation in the late phase, which at least is associated with its anti-oxidant ability.

Glutathione-peroxidase-1 null muscle progenitor cells are globally defective

Mice lacking glutathione peroxidase-1 (Gpx1) have decreased resistance to systemically administered oxidants as well as infections, and sustain increased damage after ischemia-reperfusion injuries. However, stem or progenitor cell function in these animals has not been studied. We characterized patterns of proliferation, apoptosis, and differentiation of primary muscle progenitor cells (myoblasts) from Gpx1(-/-) mice. Myoblasts are the transit amplifying compartment of skeletal muscle. All aspects of myoblast biology are negatively affected by deletion of Gpx1. In particular, passaged, proliferating Gpx1(-/-) myoblasts, when induced to differentiate into fused multinucleated myotubes, show significant impairment, and form only a few immature myotubes. This defect occurs despite increased expression of the core regulators of muscle differentiation, the myogenic basic helix-loop-helix (bHLH) transcription factors, in the Gpx1(-/-) myoblasts. Furthermore, Gpx1(-/-) myoblasts exhibited decreased proliferation and increased apoptosis compared to wild-type cells. In vivo, muscle fiber areas are decreased in Gpx1(-/-) vs wild-type mice. These data suggest that Gpx1 is important for adult muscle progenitor cell function at many levels, is necessary for integrity of muscle differentiation, and that quiescent resident stem cell populations may be particularly vulnerable to peroxide-mediated damage.

Glutathione peroxidase-1 contributes to the protection of glutamine synthetase in astrocytes during oxidative stress

Glutamine synthetase (GS) is an astrocytic enzyme that is essential for the glutamate-glutamine cycle between neurons and astrocytes. To measure the effects of oxidative stress on the activity of GS in astrocytes, astrocyte-rich primary cultures from the brains of wild-type and glutathione peroxidase-1 deficient mice (GPx1(-/-)) were exposed to a chronic hydrogen peroxide-generating system consisting of xanthine oxidase, hypoxanthine and superoxide dismutase. The specific activity of GS was strongly diminished by chronic exposure to hydrogen peroxide in astrocytes cultured from both mouse lines. After 60 min of oxidative stress in the presence of 5 mU/mL, 10 mU/mL and 20 mU/mL of xanthine oxidase, the specific GS activity of wild-type astrocytes was reduced to 47%, 22% and 13% of the initial activity, respectively. For all activities of xanthine oxidase applied, astrocytes from GPx1(-/-) mice experienced a significantly greater rate of GS inactivation compared to their wild-type counterparts. These results confirm that GS is sensitive to inactivation by chronic peroxide stress in viable astrocytes and show that glutathione peroxidase-1 helps to protect GS from inactivation by oxidative stress.

Overexpression of human GPX1 modifies Bax to Bcl-2 apoptotic ratio in human endothelial cells

As they scavenge reactive oxygen species, antioxidants were studied for their ability to interfere with apoptotic processes. However, their mechanisms of action remain unclear. In this study, we measured the expression of two Bcl-2 family members, Bax and Bcl-2, in a human endothelial like cell-line overexpressing the organic hydroperoxide-scavenging enzyme glutathione peroxidase (GPX1), in the absence of any apoptotic/oxidant stimulus. ECV304 were stably transfected with the GPX1 cDNA and used for quantification of Bax (pro-apoptotic) and Bcl-2 (antiapoptotic) mRNA and protein levels, by quantitative RT-PCR and Western-blot. We found that, compared to control cells, cells from a clone showing a 13.2 fold increase in GPX1 activity had unchanged mRNA or protein Bcl-2 levels but expressed 42.6% and 46.1% less Bax mRNA and Bax protein respectively. Subsequently to Bax decrease, the Bax/Bcl-2 ratio, reflecting the apoptotic state of the cells, was also lower in cells overexpressing GPX1. Noticeably, the mRNA and the protein level of the cell-cycle protein p53, known to activate Bax expression, was unchanged. Our study showed that overexpressing an antioxidant gene such as GPX1 in endothelial cells is able to change the basal mRNA and protein Bax levels without affecting those of p53 and Bcl-2. This phenomenon could be useful to antiatherogenic therapies which use antioxidants with the aim of protecting the vascular wall against oxidative stress injury.

Lack of glutathione peroxidase-1 exacerbates Abeta-mediated neurotoxicity in cortical neurons

The aetiologies of Alzheimer's disease (AD) are complex and multifactorial. Current therapies are largely ineffective, as the pathophysiological pathways are poorly understood. Observations in AD autopsies, as well as in vivo and in vitro observations in transgenic mice, have implicated oxidative stress as pathogenic in AD. This study used the Glutathione Peroxidase-1 knockout mouse (Gpx1--/--) model to investigate the role of antioxidant disparity in neuropathologies. Cultured neurons from control and Gpx1--/-- embryos were treated with AD-related peptides and the degree of cell loss compared. Results show that antioxidant disparity makes Gpx1--/-- cells more susceptible to Abeta toxicity. Surrogate replacement of Gpx1 with the reactive oxygen species scavenger N-acetyl cysteine and the Gpx1 mimetic ebselen, reverses the Gpx1--/-- increased susceptibility to Abeta toxicity. Such results support a role for oxidative stress in AD-related neuronal loss. This study is the first to report such findings using the Gpx1--/-- model, and supports a role for oxidative stress as one of the contributing factors, in development of AD-like pathologies.

Peroxide detoxification by brain cells

Peroxides are generated continuously in cells that consume oxygen. Among the different peroxides, hydrogen peroxide is the molecule that is formed in highest quantities. In addition, organic hydroperoxides are synthesized as products of cellular metabolism. Generation and disposal of peroxides is a very important process in the human brain, because cells of this organ consume 20% of the oxygen used by the body. To prevent cellular accumulation of peroxides and damage generated by peroxide-derived radicals, brain cells contain efficient antioxidative defense mechanisms that dispose of peroxides and protect against oxidative damage. Cultured brain cells have been used frequently to investigate peroxide metabolism of neural cells. Efficient disposal of exogenous hydrogen peroxide was found for cultured astrocytes, oligodendrocytes, microglial cells, and neurons. Comparison of specific peroxide clearance rates revealed that cultured oligodendrocytes dispose of the peroxide quicker than the other neural cell cultures. Both catalase and the glutathione system contribute to the clearance of hydrogen peroxide by brain cells. For efficient glutathione-dependent reduction of peroxides, neural cells contain glutathione in high concentration and have substantial activity of glutathione peroxidase, glutathione reductase, and enzymes that supply the NADPH required for the glutathione reductase reaction. This article gives an overview on the mechanisms involved in peroxide detoxification in brain cells and on the capacity of the different types of neural cells to dispose of peroxides.

Impact of oxidative stress on neuronal survival

1. Reactive oxygen species and oxidative state are slowly gaining acceptance in having a physiological relevance rather than just being the culprits in pathophysiological processes. The control of the redox environment of the cell provides for additional regulation in relation to signal transduction pathways. Conversely, aberrant regulation of oxidative state manifesting as oxidative stress can predispose a cell to adverse outcome. 2. The phosphatidylinositol 3-kinase/akt pathway is one such pathway that is partially regulated via oxidative state and, in an oxidative stress paradigm such as ischaemic-reperfusion injury, may be inactivated, which can lead to exacerbation of cell death. 3. Activation of nuclear factor (NF)-kappaB has been associated with oxidative stress. The role of NF-kappaB in neuronal cell death is widely debated, with major studies highlighting both a pro- and anti-apoptotic role for NF-kappaB, with the outcome being region, stimulus, dose and duration specific. 4. Oxidative state plays a key role in the regulation and control of numerous signal transduction pathways in the cell. Elucidating the mechanisms behind oxidative stress-mediated neuronal cell death is important in identifying potential putative targets for the treatment of diseases such as stroke.

Akt phosphorylation and NFκB activation are counterregulated under conditions of oxidative stress

This study was designed to elucidate the mechanisms involved in elevated cell death arising from an altered endogenous oxidant state. Increased levels of cell death were detected in cells lacking Gpx1 following the addition of exogenous H2O2. This increased apoptosis correlated with a down-regulation in the activation of the PI(3)K-Akt survival pathway. The importance of this pathway in protecting against H2O2-induced cell death was highlighted by the increased susceptibility of wild-type cells to apoptosis when treated with the PI(3)K inhibitor, LY294002. Activation of the oxidative stress sensitive transcription factor, NFkappaB, was elevated in the Gpx1-/- cells. Significantly, NFkappaB activation could be increased in wild-type cells through the addition of dominant-negative Akt. Therefore, our results suggest that the increased susceptibility of Gpx1-/- cells to H2O2-induced apoptosis can be attributed in part to diminished activation of Akt despite an up-regulation in the activation of the prosurvival NFkappaB. Thus, the PI(3)K-Akt and NFkappaB pathways can act independently of each other in an endogenous model of oxidative stress.

Selenium and selenoproteins in the brain and brain diseases

Over the past three decades, selenium has been intensively investigated as an antioxidant trace element. It is widely distributed throughout the body, but is particularly well maintained in the brain, even upon prolonged dietary selenium deficiency. Changes in selenium concentration in blood and brain have been reported in Alzheimer's disease and brain tumors. The functions of selenium are believed to be carried out by selenoproteins, in which selenium is specifically incorporated as the amino acid, selenocysteine. Several selenoproteins are expressed in brain, but many questions remain about their roles in neuronal function. Glutathione peroxidase has been localized in glial cells, and its expression is increased surrounding the damaged area in Parkinson's disease and occlusive cerebrovascular disease, consistent with its protective role against oxidative damage. Selenoprotein P has been reported to possess antioxidant activities and the ability to promote neuronal cell survival. Recent studies in cell culture and gene knockout models support a function for selenoprotein P in delivery of selenium to the brain. mRNAs for other selenoproteins, including selenoprotein W, thioredoxin reductases, 15-kDa selenoprotein and type 2 iodothyronine deiodinase, are also detected in the brain. Future research directions will surely unravel the important functions of this class of proteins in the brain.