Thermosensitive phenotype of transgenic mice overproducing human glutathione peroxidases

Selenium-dependent glutathione peroxidase 1 regulates transcription of elongase 3 in murine tissues

We have previously shown dysregulated lipid metabolism in tissues of glutathione peroxidase 1 (GPX1) overexpressing (OE) or deficient (KO) mice. This study explored underlying mechanisms of GPX1 in regulating tissue fatty acid (FA) biosynthesis. GPX1 OE, KO, and wild-type (WT) mice (n = 5, male, 3-6 months old) were fed a Se-adequate diet (0.3 mg/kg) and assayed for liver and adipose tissue FA profiles and mRNA levels of key enzymes of FA biosynthesis and redox-responsive transcriptional factors (TFs). These three genotypes of mice (n = 5) were injected intraperitoneally with diquat, ebselen, and N-acetylcysteine (NAC) at 10, 50, and 50 mg/kg of body weight, respectively, and killed at 0 and 12 h after the injections to detect mRNA levels of FA elongases and desaturases and the TFs in the liver and adipose tissue. A luciferase reporter assay with targeted deletions of mouse Elovl3 promoter was performed to determine transcriptional regulations of the gene by GPX1 mimic ebselen in HEK293T cells. Compared with WT, GPX1 OE and KO mice had 9-42% lower (p < 0.05) and 36-161% higher (p < 0.05) concentrations of C20:0, C22:0, and C24:0 in these two tissues, respectively, along with reciprocal increases and decreases (p < 0.05) of Elovl3 transcripts. Ebselen and NAC decreased (p < 0.05), whereas diquat decreased (p < 0.05), Elovl3 transcripts in the two tissues. Overexpression and knockout of GPX1 decreased (p < 0.05) and increased (p < 0.05) ELOVL3 levels in the two tissues, respectively. Three TFs (GABP, SP1, and DBP) were identified to bind the Elovl3 promoter (-1164/+33 base pairs). Deletion of DBP (-98/-86 base pairs) binding domain in the promoter attenuated (13%, p < 0.05) inhibition of ebselen on Elovl3 promoter activation. In summary, GPX1 overexpression down-regulated very long-chain FA biosynthesis via transcriptional inhibition of the Elovl3 promoter activation.

Interdependencies of Gene Expression and Function between Two Redox Enzymes and REG Family Proteins in Murine Pancreatic Islets and Human Pancreatic Cells

Our laboratory previously revealed that regenerating islets-derived protein 2 (REG2) was diminished in pancreatic islets of glutathione peroxidase-1-overexpressing mice (Gpx1-OE). It remained unknown if there is an inverse relationship between the expression and function of all Reg family genes and antioxidant enzymes in the pancreatic islets or human pancreatic cells. This research was to determine how altering the Gpx1 and superoxide dismutase-1 (Sod1) genes alone or together (dKO) affected the expression of all seven murine Reg genes in murine pancreatic islets. In Experiment 1, Gpx1-/-, Gpx1-OE, their wild-type (WT), Sod1-/-, dKO, and their WT (male, 8-wk old, n = 4–6) were fed a Se-adequate diet and their islets were collected to assay the mRNA levels of Reg family genes. In Experiment 2, islets from the six groups of mice were treated with phosphate-buffered saline (PBS), REG2, or REG2 mutant protein (1 µg/mL), and/or GPX mimic (ebselen, 50 µM) and SOD mimic (copper [II] diisopropyl salicylate, CuDIPS, 10 µM) for 48 h before the proliferation assay using bromodeoxyuridine (BrdU). In Experiment 3, human pancreatic cells (PANC1) were treated with REG2 (1 µg/mL) and assayed for REG gene expression, GPX1 and SOD1 activities, viability, and responses to Ca2+. Compared with the WT, knockouts of Gpx1 and/or Sod1 up-regulated (p < 0.05) the mRNA levels of most of the murine Reg genes in islets whereas the Gpx1 overexpression down-regulated (p < 0.05) Reg mRNA levels. REG2, but not the REG2 mutant, inhibited islet proliferation in Gpx1 or Sod1-altered mice. Such inhibition was abolished by co-incubation the Gpx1-/- islets with ebselen and the Sod1-/- islets with CuDIPS. Treating PANC1 cells with murine REG2 protein induced expression of its human orthologue REG1B and three other REG genes, but decreased SOD1 and GPX1 activities and cell viability. In conclusion, our results revealed an interdependence of REG family gene expression and/or function on intracellular GPX1 and SOD1 activities in murine islets and human pancreatic cells.

iTRAQ-based quantitative proteomic analyses the cycle chronic heat stress affecting liver proteome in yellow-feather chickens

Heat stress (HS) is one of the main environmental factors affecting the efficiency of poultry production. The yellow-feather chickens (YFC) as an indigenous strain of chicken is a popular poultry breed in China. Our previous study used the RNA-seq to analyze the gene expression profiles of male YFC under HS and showed that the lipid and energy metabolism pathways are activated in livers of YFC exposed to acute HS (38°C, 4 h and 25°C recovery 2 h). In this study, we used quantitative proteome analysis based on iTRAQ to study the liver response of YFC to cycle chronic HS (38 ± 1°C, 8 h/d, 7 d, CyCHS). The male YFCs treatment used the CyCHS from 22 to 28 days of age. The liver tissue samples were collected at 28 d old. A total of 39,327 unique peptides matches were detected using iTRAQ analysis and 4,571 proteins exhibited a false discovery rate of 1% or less. Forty-six significant differentially expressed proteins (DEPs) were detected in the CyCHS group compared with the control group for the liver samples, including up- and down-regulated DEPs were 18 and 28, respectively. We found that the enriched biological process terms of the DEPs expressed in the liver were related to DNA metabolic process, oxidation-reduction process, oxidative stress and gluconeogenesis. In KEGG pathway analysis. Most of the hepatic DEPs were annotated to glutathione metabolism and TCA cycle in response to CyCHS. The up-regulation of 5 DEPs (GPX1, GSTT1, GSTT1L, RRM2, and LOC100859645) in the glutathione metabolism pathway likely reflects an attempt to deal with oxidative damage by CyCHS. The down-regulation of 3 DEPs (Isocitrate dehydrogenase [IDH3A], IDH3B, and phosphoenolpyruvate carboxykinase 1) in the TCA cycle pathway contributes to the regulation mechanism of energy metabolism and probably to cope with the balance of heat production and dissipation during CyCHS in order to adapt to high temperature environments. Our results provide insights into the potential molecular mechanism in heat-induced oxidative stress and energy in YFCs and future studies will investigate the functional genes associated with the response to HS.

Extracellular Glutathione Peroxidase GPx3 and Its Role in Cancer

Mammalian cells possess a multifaceted antioxidant enzyme system, which includes superoxide dismutases, catalase, the peroxiredoxin/thioredoxin and the glutathione peroxidase systems. The dichotomous role of reactive oxygen species and antioxidant enzymes in tumorigenesis and cancer progression complicates the use of small molecule antioxidants, pro-oxidants, and targeting of antioxidant enzymes as therapeutic approaches for cancer treatment. It also highlights the need for additional studies to investigate the role and regulation of these antioxidant enzymes in cancer. The focus of this review is on glutathione peroxidase 3 (GPx3), a selenoprotein, and the only extracellular GPx of a family of oxidoreductases that catalyze the detoxification of hydro- and soluble lipid hydroperoxides by reduced glutathione. In addition to summarizing the biochemical function, regulation, and disease associations of GPx3, we specifically discuss the role and regulation of systemic and tumor cell expressed GPx3 in cancer. From this it is evident that GPx3 has a dichotomous role in different tumor types, acting as both a tumor suppressor and pro-survival protein. Further studies are needed to examine how loss or gain of GPx3 specifically affects oxidant scavenging and redox signaling in the extracellular tumor microenvironment, and how GPx3 might be targeted for therapeutic intervention.

Glutathione peroxidase-1 inhibits transcription of regenerating islet-derived protein-2 in pancreatic islets

Our group previously demonstrated that overexpression of selenium-dependent glutathione peroxidase-1 (GPX1) in mice (OE) led to escalated glucose-stimulated insulin secretion and hyperinsulinemia. Because we found a strong correlation of this phenotype with a diminished expression of regenerating islet-derived protein 2 (REG2) in the OE pancreatic islets, the present study was to reveal underlying mechanisms for that down-regulation of REG2 by GPX1 as a major scavenger of reactive oxygen species. We first treated the OE and wild-type (WT) mice and their islets with ROS-generating diquat, streptozotocin, and H₂O₂ and ROS-scavenging ebselen and N-acetylcysteine (NAC). Their effects on pancreatic and islet REG2 protein and(or) secretion were opposite (P < 0.05). Thereafter, we identified 13 transcriptional factors with putative binding sites in the Reg2 proximate promoter, and found that only activator protein-1 (AP-1) and albumin D box-binding protein (DBP) mRNA and protein levels were affected (elevated) (P < 0.05) by the GPX1 overproduction in the OE pancreatic islets compared with the WT islets. Contrary to that of Reg2 expression, their mRNA abundances in the cultured islets were elevated (P < 0.05) by ebselen and NAC, but decreased (P < 0.05) by H₂O_2. Both AP-1 and DBP could bind to the Reg2 promoter at the location of -168 to 0 base pair (bp) in the OE islets. Deleting the AP-1 (-143/-137 and -60/-57 bp) and(or) DBP (-35/-29 bp) binding domains in the Reg2 promoter attenuated and(or) abolished the inhibition of Reg2 promoter activation by ebselen as the GPX1 mimic in βTC-3 cells. In conclusion, the down-regulation of Reg2 expression in the GPX1-overproducing pancreatic islets was mediated by a transcriptional inhibition of the gene through two ROS responsive transcription factors AP-1 and DBP. Our findings reveal GPX1 as a novel regulator of Reg2 expression, and linking these two previously-unrelated proteins will have broad biomedical implications.

Beneficial and paradoxical roles of selenium at nutritional levels of intake in healthspan and longevity

Accumulation of genome and macromolecule damage is a hallmark of aging, age-associated degeneration, and genome instability syndromes. Although processes of aging are irreversible, they can be modulated by genome maintenance pathways and environmental factors such as diet. Selenium (Se) confers its physiological functions mainly through selenoproteins, but Se compounds and other proteins that incorporate Se nonspecifically also impact optimal health. Bruce Ames proposed that the aging process could be mitigated by a subset of low-hierarchy selenoproteins whose levels are preferentially reduced in response to Se deficiency. Consistent with this notion, results from two selenotranscriptomic studies collectively implicate three low-hierarchy selenoproteins in age or senescence. Experimental evidence generally supports beneficial roles of selenoproteins in the protection against damage accumulation and redox imbalance, but some selenoproteins have also been reported to unexpectedly display harmful functions under sporadic conditions. While longevity and healthspan are usually thought to be projected in parallel, emerging evidence suggests a trade-off between longevity promotion and healthspan deterioration with damage accumulation. We propose that longevity promotion under conditions of Se deficiency may be attributed to 1) stress-response hormesis, an advantageous event of resistance to toxic chemicals at low doses; 2) reduced expression of selenoproteins with paradoxical functions to a lesser extent. In particular, selenoprotein H is an evolutionally conserved nuclear selenoprotein postulated to confer Se functions in redox regulation, genome maintenance, and senescence. This review highlights the need to pinpoint roles of specific selenoproteins and Se compounds in healthspan and lifespan for a better understanding of Se contribution at nutritional levels of intake to healthy aging.

Reductive Stress in Inflammation-Associated Diseases and the Pro-Oxidant Effect of Antioxidant Agents

Abstract: Reductive stress (RS) is the counterpart oxidative stress (OS), and can occur in response to conditions that shift the redox balance of important biological redox couples, such as the NAD⁺/NADH, NADP⁺/NADPH, and GSH/GSSG, to a more reducing state. Overexpression of antioxidant enzymatic systems leads to excess reducing equivalents that can deplete reactive oxidative species, driving the cells to RS. A feedback regulation is established in which chronic RS induces OS, which in turn, stimulates again RS. Excess reducing equivalents may regulate cellular signaling pathways, modify transcriptional activity, induce alterations in the formation of disulfide bonds in proteins, reduce mitochondrial function, decrease cellular metabolism, and thus, contribute to the development of some diseases in which NF-κB, a redox-sensitive transcription factor, participates. Here, we described the diseases in which an inflammatory condition is associated to RS, and where delayed folding, disordered transport, failed oxidation, and aggregation are found. Some of these diseases are aggregation protein cardiomyopathy, hypertrophic cardiomyopathy, muscular dystrophy, pulmonary hypertension, rheumatoid arthritis, Alzheimer's disease, and metabolic syndrome, among others. Moreover, chronic consumption of antioxidant supplements, such as vitamins and/or flavonoids, may have pro-oxidant effects that may alter the redox cellular equilibrium and contribute to RS, even diminishing life expectancy.

Exogenous antioxidants--Double-edged swords in cellular redox state: Health beneficial effects at physiologic doses versus deleterious effects at high doses

The balance between oxidation and antioxidation is believed to be critical in maintaining healthy biological systems. Under physiological conditions, the human antioxidative defense system including e.g., superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione (GSH) and others, allows the elimination of excess reactive oxygen species (ROS) including, among others superoxide anions (O₂^.-), hydroxyl radicals (OH.), alkoxyl radicals (RO.) and peroxyradicals (ROO.). However, our endogenous antioxidant defense systems are incomplete without exogenous originating reducing compounds such as vitamin C, vitamin E, carotenoids and polyphenols, playing an essential role in many antioxidant mechanisms in living organisms. Therefore, there is continuous demand for exogenous antioxidants in order to prevent oxidative stress, representing a disequilibrium redox state in favor of oxidation. However, high doses of isolated compounds may be toxic, owing to prooxidative effects at high concentrations or their potential to react with beneficial concentrations of ROS normally present at physiological conditions that are required for optimal cellular functioning. This review aims to examine the double-edged effects of dietary originating antioxidants with a focus on the most abundant compounds, especially polyphenols, vitamin C, vitamin E and carotenoids. Different approaches to enrich our body with exogenous antioxidants such as via synthetic antioxidants, diets rich in fruits and vegetables and taking supplements will be reviewed and experimental and epidemiological evidences discussed, highlighting that antioxidants at physiological doses are generally safe, exhibiting interesting health beneficial effects.

Paradoxical Roles of Antioxidant Enzymes: Basic Mechanisms and Health Implications

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.

Impact of glutathione peroxidase-1 deficiency on macrophage foam cell formation and proliferation: implications for atherogenesis

Clinical and experimental evidence suggests a protective role for the antioxidant enzyme glutathione peroxidase-1 (GPx-1) in the atherogenic process. GPx-1 deficiency accelerates atherosclerosis and increases lesion cellularity in ApoE^−/− mice. However, the distribution of GPx-1 within the atherosclerotic lesion as well as the mechanisms leading to increased macrophage numbers in lesions is still unknown. Accordingly, the aims of the present study were (1) to analyze which cells express GPx-1 within atherosclerotic lesions and (2) to determine whether a lack of GPx-1 affects macrophage foam cell formation and cellular proliferation. Both in situ-hybridization and immunohistochemistry of lesions of the aortic sinus of ApoE^−/− mice after 12 weeks on a Western type diet revealed that both macrophages and – even though to a less extent – smooth muscle cells contribute to GPx-1 expression within atherosclerotic lesions. In isolated mouse peritoneal macrophages differentiated for 3 days with macrophage-colony-stimulating factor (MCSF), GPx-1 deficiency increased oxidized low density-lipoprotein (oxLDL) induced foam cell formation and led to increased proliferative activity of peritoneal macrophages. The MCSF- and oxLDL-induced proliferation of peritoneal macrophages from GPx-1^−/−ApoE^−/− mice was mediated by the p44/42 MAPK (p44/42 mitogen-activated protein kinase), namely ERK1/2 (extracellular-signal regulated kinase 1/2), signaling pathway as demonstrated by ERK1/2 signaling pathways inhibitors, Western blots on cell lysates with primary antibodies against total and phosphorylated ERK1/2, MEK1/2 (mitogen-activated protein kinase kinase 1/2), p90RSK (p90 ribosomal s6 kinase), p38 MAPK and SAPK/JNK (stress-activated protein kinase/c-Jun N-terminal kinase), and immunohistochemistry of mice atherosclerotic lesions with antibodies against phosphorylated ERK1/2, MEK1/2 and p90RSK. Representative effects of GPx-1 deficiency on both macrophage proliferation and MAPK phosphorylation could be abolished by the GPx mimic ebselen. The present study demonstrates that GPx-1 deficiency has a significant impact on macrophage foam cell formation and proliferation via the p44/42 MAPK (ERK1/2) pathway encouraging further studies on new therapeutic strategies against atherosclerosis.

Hyperthermia induces injury to the intestinal mucosa in the mouse: evidence for an oxidative stress mechanism

Loss of the intestinal barrier is critical to the clinical course of heat illness, but the underlying mechanisms are still poorly understood. We tested the hypothesis that conditions characteristic of mild heatstroke in mice are associated with injury to the epithelial lining of the intestinal tract and comprise a critical component of barrier dysfunction. Anesthetized mice were gavaged with 4 kDa FITC-dextran (FD-4) and exposed to increasing core temperatures, briefly reaching 42.4°C, followed by 30 min recovery. Arterial samples were collected to measure FD-4 concentration in plasma (in vivo gastrointestinal permeability). The small intestines were then removed to measure histological evidence of injury. Hyperthermia resulted in a ≈2.5-fold elevation in plasma FD-4 and was always associated with significant histological evidence of injury to the epithelial lining compared with matched controls, particularly in the duodenum. When isolated intestinal segments from control animals were exposed to ≥41.5°C, marked increases in permeability were observed within 60 min. These changes were associated with release of lactate dehydrogenase, evidence of protein oxidation via carbonyl formation and histological damage. Coincubation with N-acetylcysteine protected in vitro permeability during hyperthermia and reduced histological damage and protein oxidation. Chelation of intracellular Ca(2+) to block tight junction opening during 41.5°C exposure failed to reduce the permeability of in vitro segments. The results demonstrate that hyperthermia exposure in mouse intestine, at temperatures at or below those necessary to induce mild heatstroke, cause rapid and substantial injury to the intestinal lining that may be attributed, in part, to oxidative stress.

Heat induction of reporter gene expression via the gadd153 promoter and its possible application to hyperthermia treatment of cancer

The use of the gadd153promoter to induce expression of a reporter geneunder heat stress conditions was investigated,since the results of previous studies have suggestedthat the gadd153promoter is likely to be activated by the indirecteffects of hyperthermia, that is, by DNA damage thatoccurs when reactive oxygen species are produced byheat stress. The optimum temperature for a significantinduction was found to be between 41 and 43 degrees C andincreased expression of the reporter gene was observedat about 24 h after the heat treatment. Under theseconditions, the cell integrity was not alteredmorphologically and the growth stopped temporarily,while the viability was maintained. A second increasein expression occurred at a later stage when the cellswere severely damaged at 43-45 degrees C. Atthese temperatures, the cellular morphology showedsignificant alteration and the growth was stronglyarrested. This is likely to be due to a differentmechanism which could involve DNA repair processes. Itis expected that this method of induction can beexploited to drive the production of a protein ofinterest in a cancer treatment program that includes hyperthermia.

Glutathione peroxidase 1 deficiency attenuates allergen-induced airway inflammation by suppressing Th2 and Th17 cell development

Engagement of T cell receptor (TCR) triggers signaling pathways that mediate activation, proliferation, and differentiation of T lymphocytes. Such signaling events are mediated by reactive oxygen species (ROS), including hydrogen peroxide and lipid peroxides, both of which are reduced by glutathione peroxidase 1 (GPx1). We have now examined the role of GPx1 in the activation, differentiation, and functions of CD4(+) T helper (Th) cells. TCR stimulation increased the intracellular ROS concentration in Th cells in a time-dependent manner, and such TCR-induced ROS generation was found to promote cell proliferation. GPx1-deficient Th cells produced higher levels of intracellular ROS and interleukin-2 than wild-type Th cells and proliferated at a faster rate than did wild-type cells. Moreover, differentiation of GPx1-deficient Th cells was biased toward Th1, and Th17 cell development was also impeded by GPx1 depletion. Consistent with these findings, GPx1-null mice were protected from the development of ovalbumin-induced allergic asthma. Eosinophil infiltration, goblet cell hyperplasia, collagen deposition, and airway hyperresponsiveness were thus all attenuated in the lungs of GPx1-null mice. These data indicate that GPx1-dependent control of intracellular ROS accumulation is important not only for regulation of Th cell proliferation but for modulation of differentiation into Th1, Th2, and Th17 cells.

Glutathione peroxidase overexpression does not rescue impaired neurogenesis in the injured immature brain

Traumatic brain injury (TBI) is a leading cause of disability among young children and is associated with long-term cognitive deficits. These clinical findings have prompted an investigation of the hippocampus in an experimental model of trauma to the developing brain at postnatal day (p21). Previous studies using this model have revealed a progressive loss of neurons in the hippocampus as brain-injured animals mature to young adulthood. Here we determined whether this hippocampal vulnerability is likewise reflected in altered neurogenesis and whether the antioxidant glutathione peroxidase (GPx) modulates neurogenesis during maturation of the injured immature brain. Male transgenic mice that overexpress GPx and wild-type littermates were subjected to controlled cortical impact or sham surgery on p21. At 2 weeks postinjury, the numbers of proliferating cells and immature neurons within the subgranular zone were measured by using Ki-67 and doublecortin, respectively. Bromodeoxyuridine (BrdU) was used to label dividing cells beginning 2 weeks postinjury. Survival (BrdU(+)) and neuronal differentiation (BrdU(+)/NeuN(+)) were then measured 4 weeks later via confocal microscopy. Two-way ANOVA revealed no significant interaction between genotype and injury. Subsequent analysis of the individual effects of injury and genotype, however, showed a significant reduction in subgranular zone proliferation (Ki-67) at 2 weeks postinjury (P = 0.0003) and precursor cell survival (BrdU(+)) at 6 weeks postinjury (P = 0.016) and a trend toward reduced neuronal differentiation (BrdU(+)/NeuN(+)) at 6 weeks postinjury (P = 0.087). Overall, these data demonstrate that traumatic injury to the injured immature brain impairs neurogenesis during maturation and suggest that GPx cannot rescue this reduced neurogenesis.

Validation of candidate causal genes for obesity that affect shared metabolic pathways and networks

A major task in dissecting the genetics of complex traits is to identify causal genes for disease phenotypes. We previously developed a method to infer causal relationships among genes through the integration of DNA variation, gene transcription, and phenotypic information. Here we validated our method through the characterization of transgenic and knockout mouse models of candidate genes that were predicted to be causal for abdominal obesity. Perturbation of eight out of the nine genes, with Gas7, Me1 and Gpx3 being novel, resulted in significant changes in obesity related traits. Liver expression signatures revealed alterations in common metabolic pathways and networks contributing to abdominal obesity and overlapped with a macrophage-enriched metabolic network module that is highly associated with metabolic traits in mice and humans. Integration of gene expression in the design and analysis of traditional F2 intercross studies allows high confidence prediction of causal genes and identification of involved pathways and networks.

Redox regulation in the extracellular environment

The oxidizing nature of the extracellular environment is vastly different from the highly reducing nature of the intracellular compartment. The redox potential of the cytosolic compartment of the intracellular environment limits disulfide bond formation, whereas the oxidizing extracellular environment contains proteins rich in disulfide bonds. If not for an extracellular antioxidant system to eliminate reactive oxygen and nitrogen species, lipid peroxidation and protein oxidation would become excessive, resulting in cellular damage. Many reviews have focused on the role of intracellular antioxidants in the elimination of oxidative stress, but this one will focus on the coordinated action of both intracellular and extracellular antioxidants in limiting cellular oxidant stress.

Overexpression of glutathione peroxidase attenuates myocardial remodeling and preserves diastolic function in diabetic heart

Oxidative stress plays an important role in the structural and functional abnormalities of diabetic heart. Glutathione peroxidase (GSHPx) is a critical antioxidant enzyme that removes H(2)O(2) in both the cytosol and mitochondia. We hypothesized that the overexpression of GSHPx gene could attenuate left ventricular (LV) remodeling in diabetes mellitus (DM). We induced DM by injection of streptozotocin (160 mg/kg ip) in male GSHPx transgenic mice (TG+DM) and nontransgenic wildtype littermates (WT+DM). GSHPx activity was higher in the hearts of TG mice compared with WT mice, with no significant changes in other antioxidant enzymes. LV thiobarbituric acid-reactive substances measured in TG+DM at 8 wk were significantly lower than those in WT+DM (58 +/- 3 vs. 71 +/- 5 nmol/g, P < 0.05). Heart rate and aortic blood pressure were comparable between groups. Systolic function was preserved normal in WT+DM and TG+DM mice. In contrast, diastolic function was impaired in WT+DM and was improved in TG+DM as assessed by the deceleration time of peak velocity of transmitral diastolic flow and the time needed for relaxation of 50% maximal LV pressure to baseline value (tau; 13.5 +/- 1.2 vs. 8.9 +/- 0.7 ms, P < 0.01). The TG+DM values were comparable with those of WT+Control (tau; 7.8 +/- 0.2 ms). Improvement of LV diastolic function was accompanied by the attenuation of myocyte hypertrophy, interstitial fibrosis, and apoptosis. Overexpression of GSHPx gene ameliorated LV remodeling and diastolic dysfunction in DM. Therapies designed to interfere with oxidative stress might be beneficial to prevent cardiac abnormalities in DM.

Superoxide dismutase expression attenuates cigarette smoke- or elastase-generated emphysema in mice

RATIONALE

Oxidants are believed to play a major role in the development of emphysema.

OBJECTIVES

This study aimed to determine if the expression of human copper-zinc superoxide dismutase (CuZnSOD) within the lungs of mice protects against the development of emphysema.

METHODS

Transgenic CuZnSOD and littermate mice were exposed to cigarette smoke (6 h/d, 5 d/wk, for 1 yr) and compared with nonexposed mice. A second group was treated with intratracheal elastase to induce emphysema.

MEASUREMENTS

Lung inflammation was measured by cell counts and myeloperoxidase levels. Oxidative damage was assessed by immunofluorescence for 3-nitrotyrosine and 8-hydroxydeoxyguanosine and lipid peroxidation levels. The development of emphysema was determined by measuring the mean linear intercept (Lm).

MAIN RESULTS

Smoke exposure caused a fourfold increase in neutrophilic inflammation and doubled lung myeloperoxidase activity. This inflammatory response did not occur in the smoke-exposed CuZnSOD mice. Similarly, CuZnSOD expression prevented the 58% increase in lung lipid peroxidation products that occurred after smoke exposure. Most important, CuZnSOD prevented the onset of emphysema in both the smoke-induced model (Lm, 68 exposed control vs. 58 exposed transgenic; p < 0.04) and elastase-generated model (Lm, 80 exposed control vs. 63 exposed transgenic; p < 0.03). These results demonstrate for the first time that antioxidants can prevent smoke-induced inflammation and can counteract the proteolytic cascade that leads to emphysema formation in two separate animal models of the disease.

CONCLUSIONS

These findings indicate that strategies aimed at enhancing or supplementing lung antioxidants could be effective for the prevention and treatment of this disease.

New roles for an old selenoenzyme: evidence from glutathione peroxidase-1 null and overexpressing mice

Cellular glutathione peroxidase-1 (GPX1) is the first identified and the most abundant selenoprotein in mammals. Although GPX1 has been widely considered to be a major antioxidant enzyme, there has been no direct evidence for such role in vivo until GPX1 transgenic and null mice became available 10 y ago. Using these new models, we demonstrated that GPX1 protects against oxidative stress mediated by reactive oxygen species (ROS), and the physiologic importance of this protection varies with insult level and body Se status. Full expression of GPX1 is needed, and overexpression of GPX1 is beneficial for Se-adequate mice to defend against severe oxidative stress. This function of GPX1 is associated with attenuating the prooxidant-induced oxidation of NADPH, NADH, lipid, and protein in various tissues. In Se-deficient mice, a minute amount of GPX1 activity (4% of adequate levels) protects against hepatic aponecrosis induced by mild oxidative stress. In contrast, knockout of GPX1 renders mice and their hepatocytes resistant to oxidative stress related to reactive nitrogen species (RNS). More intriguingly, mice overexpressing GPX1 develop insulin resistance and obesity, accompanied by a downregulation of insulin-mediated phosphorylations of insulin receptor and Akt protein. In conclusion, GPX1 seems to play contrasting roles in coping with ROS vs. RNS, and its metabolic functions extend beyond redox regulation.

Overexpression of glutathione peroxidase protects immature murine neurons from oxidative stress

Neuronal enzyme systems involved in free radical detoxification are developmentally regulated such that intracellular glutathione peroxidase (GPx-1) activity is low in the newborn mouse brain. We hypothesized that neurons expressing a higher level of GPx-1 will be more resistant to hydrogen peroxide (H(2)O(2)) exposure. We show a dose-dependent protection against H(2)O(2) in primary neuronal cultures from fetuses overexpressing human GPx-1 compared to wild types of the same genetic background. Exogenous antioxidants completely protected neurons, even at extremely high H(2)O(2 )concentrations and regardless of the genotype. Specific depletion of glutathione with buthionine sulfoximine increased cell death in transgenic cultures exposed to 200 microM H(2)O(2), reducing protection afforded by increased GPx-1 activity. Increased GPx-1 expression in immature cortical neurons confers protection from oxidative stress, but availability of reducing equivalents determines susceptibility to oxidative cell death.

Overexpression of Superoxide Dismutase or Glutathione Peroxidase Protects against the Paraquat + Maneb-induced Parkinson Disease Phenotype

Oxidative stress has been implicated in the pathogenesis of Parkinson disease based on its role in the cascade of biochemical changes that lead to dopaminergic neuronal death. This study analyzed the role of oxidative stress as a mechanism of the dopaminergic neurotoxicity produced by the combined paraquat and maneb model of the Parkinson disease phenotype. Transgenic mice overexpressing either Cu,Zn superoxide dismutase or intracellular glutathione peroxidase and non-transgenic mice were exposed to saline, paraquat, or the combination of paraquat + maneb twice a week for 9 weeks. Non-transgenic mice chronically exposed to paraquat + maneb exhibited significant reductions in locomotor activity, levels of striatal dopamine and metabolites, and dopaminergic neurons in the substantia nigra pars compacta. In contrast, no corresponding effects were observed in either Cu,Zn superoxide dismutase or glutathione peroxidase transgenic mice. Similarly, the increase in levels of lipid hydroperoxides in the midbrain and striatum of paraquat + maneb-treated non-transgenic mice was not detected in either Cu,Zn superoxide dismutase or glutathione peroxidase transgenic mice. To begin to determine critical pathways of paraquat + maneb neurotoxicity, the functions of cell death-inducing and protective mechanisms were analyzed. Even a single injection of paraquat + maneb in the non-transgenic treated group modulated several key pro- and anti-apoptotic proteins, including Bax, Bad, Bcl-xL, and upstream stress-induced cascade. Collectively, these findings support the assertion that protective mechanisms against paraquat + maneb-induced neurodegeneration could involve modulation of the level of reactive oxygen species and alterations of the functions of specific signaling cascades.

Increased susceptibility of glutathione peroxidase-1 transgenic mice to kainic acid-related seizure activity and hippocampal neuronal cell death

Glutathione peroxidase (GSHPx) has been demonstrated in several in vivo studies to reduce both the risk and severity of oxidatively-induced tissue damage. The seizure-inducing neurotoxin kainic acid (KA) has been suggested to elicit its toxic effects in part via generation of oxidative stress. In this study, we report that expression of elevated levels of murine GSHPx-1 in transgenic mice surprisingly results in increased rather than decreased KA susceptibility including increased seizure activity and neuronal hippocampal damage. Isolated transgenic primary hippocampal culture neurons also display increased susceptibility to KA treatment compared with those from wildtype animals. This could be due to alterations in the redox state of the glutathione system resulting in elevated glutathione disulfide (GSSG) levels which, in turn, may directly activate NMDA receptors or enhanced response of the NMDA receptor.

Regulation of the multidrug resistance transporter P-glycoprotein in multicellular prostate tumor spheroids by hyperthermia and reactive oxygen species

Hyperthermia is an important component of many cancer treatment protocols. In our study the regulation of the multidrug resistance (MDR) transporter P-glycoprotein by hyperthermia was studied in multicellular prostate tumor spheroids. Hyperthermia treatment of small (50-100 microm) tumor spheroids significantly increased P-glycoprotein and mdr-1 mRNA expression with a maximum effect at 42 degrees C, whereas only moderate elevation of P-glycoprotein was found in large (350-450 microm) tumor spheroids. Hyperthermia caused an elevation of intracellular reactive oxygen species (ROS). Inhibition of ROS generation with NADPH-oxidase inhibitors diphenylen iodonium (DPI) and 4-(2-aminoethyl)benzenesulfonyl fluoride (AEBSF) abolished P-glycoprotein expression but did not affect its transcript levels following heat treatment. This indicates that P-glycoprotein levels are controlled by regulating its translation rate or stability. Hyperthermia incubation resulted in a differential activation of p38 mitogen-activated protein kinase (MAPK), extracellular regulated kinase 1,2 (ERK1,2), and c-jun N-terminal kinase (JNK) immediately, 4 hr and 24 hr after treatment. Furthermore, upregulation of hypoxia-inducible factor 1alpha (HIF-1alpha) was observed. Elevation of HIF-1alpha and P-glycoprotein expression following hyperthermia treatment were abolished upon coadministration of the p38 inhibitor SB203580. In contrast the JNK inhibitor SP600125 and the ERK1,2 inhibitor UO126 resulted in increase of HIF-1alpha and P-glycoprotein in the control as well as the hyperthermia-treated samples, indicating negative regulation of intrinsic HIF-1alpha and P-glycoprotein expression by ERK1,2 and JNK signaling cascades. In summary our data demonstrate that hyperthermia-induced upregulation of P-glycoprotein and HIF-1alpha is mediated by activation of p38, whereas ERK1,2 and JNK are involved in repression of P-glycoprotein and HIF-1alpha under control conditions.

Overexpression of Glutathione Peroxidase Prevents Left Ventricular Remodeling and Failure After Myocardial Infarction in Mice

Background— Oxidative stress plays an important role in the pathophysiology of heart failure. We determined whether the overexpression of glutathione peroxidase (GSHPx) could attenuate left ventricular (LV) remodeling and failure after myocardial infarction (MI).

Methods and Results— We created MI in 12- to 16-week-old, male GSHPx transgenic mice (TG+MI) and nontransgenic wild-type littermates (WT+MI) by ligating the left coronary artery. GSHPx activity was increased in the hearts of TG mice, with no significant changes in other antioxidant enzymes. LV concentrations of thiobarbituric acid–reactive substances measured in TG+MI at 4 weeks were significantly lower than those in WT+MI. The survival rate during 4 weeks of MI was significantly higher in TG+MI than in WT+MI, although the infarct size was comparable. LV cavity dilatation and dysfunction were significantly attenuated in TG+MI. LV end-diastolic pressure was increased in WT+MI and reduced in TG+MI. Improvement of LV function in TG+MI was accompanied by a decrease in myocyte hypertrophy, apoptosis, and interstitial fibrosis in the noninfarcted LV. Myocardial matrix metalloproteinase-9 zymographic and protein levels were increased in WT+MI after 3 days but were attenuated in TG+MI.

Conclusions— Overexpression of GSHPx inhibited LV remodeling and failure after MI. Therapies designed to interfere with oxidative stress might be beneficial to prevent cardiac failure.

Glutathione peroxidase inhibits cell death and glial activation following experimental stroke

Stroke is a leading cause of morbidity and mortality in major industrial countries. Many factors contribute to the cellular damage resulting from ischemia-reperfusion (I-R). Growing evidence indicates that reactive oxygen species (ROS) contribute significantly to this process, though their exact mechanism of action is mostly unknown. We have examined the mechanism of protection against I-R injury in transgenic mice that overexpress human glutathione peroxidase (hGPx1), using a focal cerebral I-R model. In this model, transgenic animals show significant reduction of necrotic as well as apoptotic cell death in vulnerable brain regions as demonstrated by TUNEL staining, DNA laddering and ELISA assays. We also observed decreased astrocytic and microglial activation in ischemic brains of animals overexpressing hGPx1. In wild-type mice, neuronal cell death was accompanied with compromise of vascular integrity, edema and neutrophil infiltration, whereas GPx1 mice revealed significant preservation of tissue structure and decreased infiltration of acute inflammatory cells. These results indicate that glutathione peroxidase-sensitive ROS play an important role in regulation of cell death during cerebral I-R as well as in brain inflammatory reactions.

Oxidative stress and aging: beyond correlation

The oxidative stress theory of aging has become increasingly accepted as playing a role in the aging process, based primarily on a substantial accumulation of circumstantial evidence. In recent years, the hypothesis that mitochondrially generated reactive oxygen species play a role in organismal aging has been directly tested in both invertebrate and mammalian model systems. Initial results imply that oxidative damage, specifically the level of superoxide, does play a role in limiting the lifespans of invertebrates such as Drosophila melanogaster and Caenorhabditis elegans. In mammalian model systems, the effect of oxidative stress on lifespan is less clear, but there is evidence that antioxidant treatment protects against age-related dysfunction, including cognitive decline.

Regional distribution of heme oxygenase, HSP70, and glutathione in brain: relevance for endogenous oxidant/antioxidant balance and stress tolerance

It is generally recognized that lipid peroxides play an important role in the pathogenesis of several diseases and that sulfhydryl groups are critically involved in cellular defense against endogenous or exogenous oxidants. Recent evidence indicates that lipid peroxides directly participate in induction of cytoprotective proteins, such as heat shock proteins (Hsps), which play a central role in the cellular mechanisms of stress tolerance. Heme oxygenase (HO) is a stress protein that has been implicated in defense mechanisms against agents that may induce oxidative injury, such as endotoxins, cytokines and heme and its induction represents a common feature in a number of neurodegenerative diseases. In the present report we studied regional distribution of heme oxygenase (HO) activity and protein expression, together with that of Hps70, in brain of C57BL6 mice. Endogenous lipid peroxidation was investigated on the basis of the analysis of ultra weak chemiluminescence, hydro peroxides and lipid soluble fluorescent products, and compared to the regional distribution of thiols, antioxidant enzymes and trace metals. Our results show that levels of HO activity and expression of inducible Hsp70 and the ratio of GSH/GSSG in the different brain regions examined were positively correlated with the content of peroxides. Substantia Nigra was the brain area exhibiting the highest levels of HO-2, constitutive and inducible Hsp70, GSSG, peroxides, iron, and calcium, in contrast with the lowest content in GSH, GSH/GSSG ratio and glutathione reductase activity, compared to the other cerebral regions examined. Among these, cortex showed the lowest levels of HO-2, Hsp70, GSSG and peroxides that were associated with the highest levels of GSH and GSH/GSSG ratio. These data support the hypothesis that the glutathione redox state and basal peroxides can directly participate in the signaling pathways of heat shock protein expression and hence of stress tolerance.

Inflammatory response and glutathione peroxidase in a model of stroke

Stroke is one of the leading causes of death in major industrial countries. Many factors contribute to the cellular damage resulting from ischemia/reperfusion (I/R). Experimental data indicate an important role for oxidative stress and the inflammatory cascade during I/R. We are testing the hypothesis that the mechanism of protection against I/R damage observed in transgenic mice overexpressing human antioxidant enzymes (particularly intracellular glutathione peroxidase) involves the modulation of inflammatory response as well as reduced sensitivity of neurons to cytotoxic cytokines. Transgenic animals show significant reduction of expression of chemokines, IL-6, and cell death-inducing ligands as well as corresponding receptors in a focal cerebral I/R model. Reduction of DNA binding activity of consensus and potential AP-1 binding sites in mouse Fas ligand promoter sequence was observed in nuclear extracts from transgenic mice overexpressing intracellular glutathione peroxidase compared with normal animals following I/R. This effect was accompanied by modulation of the c-Jun N-terminal kinase/stress-activated protein kinase pathway. Cultured primary neurons from the transgenic mice demonstrated protection against hypoxia/reoxygenation injury as well as cytotoxicity after TNF-alpha and Fas ligand treatment. These results indicate that glutathione peroxidase-sensitive reactive oxygen species play an important role in regulation of cell death during cerebral I/R by modulating intrinsic neuronal sensitivity as well as brain inflammatory reactions.

Endotoxemia in transgenic mice overexpressing human glutathione peroxidases

In response to endotoxemia induced by administration of lipopolysaccharide, a complex series of reactions occurs in mammalian tissues. During this inflammation response, cells produce different mediators, such as reactive oxygen species, a number of arachidonic acid metabolites, and cytokines. The reactive oxygen species thus generated have been suggested to produce tissue injury as a result of macromolecular damage or by interfering with regulatory processes. They may also act as important signaling molecules to induce redox-sensitive genes. We report here that transgenic mice overexpressing 2 major forms of human glutathione peroxidases (GPs), intra- and extracellular GP, are able to modulate host response during endotoxemic conditions. We show that these animals have a decreased hypotension and increased survival rate after administration of a high dosage of lipopolysaccharide. Overexpression of GPs alters vascular permeability and production of cytokines (interleukin-1 beta and tumor necrosis factor-alpha) and NO, affects arachidonic acid metabolism, and inhibits leukocyte migration. These results suggest an important role for peroxides in pathogenesis during endotoxemia, and GPs, by regulating their level, may prove to be good candidates for antioxidant therapy to protect against such injury.

Free radicals and antioxidants in the year 2000. A historical look to the future

In the late 1950's free radicals and antioxidants were almost unheard of in the clinical and biological sciences but chemists had known about them for years in the context of radiation, polymer and combustion technology. Daniel Gilbert, Rebeca Gerschman and their colleagues related the toxic effects of elevated oxygen levels on aerobes to those of ionizing radiation, and proposed that oxygen toxicity is due to free radical formation, in a pioneering paper in 1956. Biochemistry owes much of its early expansion to the development and application of chromatographic and electrophoretic techniques, especially as applied to the study of proteins. Thus, superoxide dismutase (SOD) enzymes (MnSOD, CuZnSOD, FeSOD) were quickly identified. By the 1980's Molecular Biology had evolved from within biochemistry and microbiology to become a dominant new discipline, with DNA sequencing, recombinant DNA technology, cloning, and the development of PCR representing milestones in its advance. As a biological tool to explore reaction mechanisms, SOD was a unique and valuable asset. Its ability to inhibit radical reactions leading to oxidative damage in vitro often turned out to be due to its ability to prevent reduction of iron ions by superoxide. Nitric oxide (NO.) provided the next clue as to how SOD might be playing a critical biological role. Although NO. is sluggish in its reactions with most biomolecules it is astoundingly reactive with free radicals, including superoxide. Overall, this high reactivity of NO. with radicals may be beneficial in vivo, e.g. by scavenging peroxyl radicals and inhibiting lipid peroxidation. If reactive oxygen species are intimately involved with the redox regulation of cell functions, as seems likely from current evidence, it may be easier to understand why attempts to change antioxidant balance in aging experiments have failed. The cell will adapt to maintain its redox balance. Indeed, transgenic animals over-expressing antioxidants show some abnormalities of function. There must therefore be a highly complex interrelationship between dietary, constitutive, and inducible antioxidants with the body, under genetic control. The challenge for the new century is to be able to understand these relationships, and how to manipulate them to our advantage to prevent and treat disease.

Impairment of synaptic transmission by transient hypoxia in hippocampal slices: improved recovery in glutathione peroxidase transgenic mice

There is increasing evidence that oxygen free radicals contribute to ischemic brain injury. It is unclear, however, to what extent specific antioxidant enzymes can prevent or reverse the impairment of synaptic function caused by transient hypoxia. In this study, we investigated in transgenic (Tg) mice whether a moderate increase in glutathione peroxidase-1 (GPx1) may improve the capacity of CA1 pyramidal cells to recover synaptic transmission after a short period of hypoxia in vitro. In control hippocampal slices, transient hypoxia (7-9 min) produced irreversible loss of excitatory postsynaptic potentials. Complete recovery of synaptic transmission was observed with homozygous Tg-MT-GPx-6 mice after reoxygenation, and, after repeated episodes of hypoxia, synaptic transmission was still viable in most Tg slices, in contrast to non-Tg slices. Moreover, hypoxic episodes abolished the capacity of hippocampal slices to generate long-term potentiation in area CA1 of control mice, whereas a significant extent of long-term potentiation expression was still preserved in Tg tissues. We also demonstrated that susceptibility to N-methyl-d-aspartate-mediated oxidative injury was reduced in Tg hippocampal slices. In conclusion, our results suggest that a moderate GPx increase can be sufficient to prevent irreversible functional damage produced by transient hypoxia in the hippocampus and to help maintain basic electrophysiological mechanisms involved in memory formation.

Management of oxidative stress in the CNS: the many roles of glutathione

An outline is given of mechanisms that generate oxidative stress and inflammation. Considered are the metabolic mechanisms that give rise to peroxides, the source of strong oxidants; the production of dicarbonyls that interact with macromolecules to form advanced glycation endproducts; and the role that activation of the transcription factor NF(Kappa)B has in the expression of pro-inflammatory genes. Management of oxidative stress is considered by outlining the central role of reduced glutathione (GSH) in peroxide scavenging, dicarbonyl scavenging and activation of NF(Kappa)B. Cellular GSH levels are dictated by the balance between consumption, oxidation of GSH, reduction of oxidized-glutathione, and synthesis. The rate-limiting enzyme in GSH synthesis is L-gamma-glutamyl-L-cysteine synthase, a phase II enzyme. Phase II enzyme inducers are found in many fruits and vegetables. It is suggested that dietary phase II enzyme inducers be investigated for their potential for preventing or retarding the development of degenerative diseases that have an underlying oxidative stress and inflammatory component.

Rapid degradation of PrxI and PrxII induced by silica in Rat2 cells

Peroxidases of the peroxiredoxin (Prx) family catalyze the reduction of H(2)O(2) and lipid peroxides. The effects of H(2)O(2), 12-O-tetradecanoylphorbol 13-acetate (TPA), and silica on the abundance of two cytosolic isoforms of Prx (PrxI and PrxII) were examined in Rat2 cells. TPA induces the production of reactive oxygen species (ROS) in various mammalian cell types, and silica induces the production of ROS in Rat2 cells. Whereas H(2)O(2) and TPA did not affect the concentration of PrxI or Prx II, silica triggered a rapid degradation of both Prx enzymes. Silica also induced degradation of the NF-kappaB inhibitor IkappaB-alpha. N-Acetylcysteine and diphenyleneiodonium, both of which inhibit the accumulation of intracellular ROS, each blocked silica-induced degradation of IkappaB-alpha but had no effect on that of the Prx enzymes, suggesting that ROS do not contribute to Prx proteolysis. The silica-induced degradation of Prx enzymes was also insensitive to the proteasome inhibitors MG132 and lactacystin, whereas IkappaB-alpha proteolysis was completely blocked by these inhibitors. Experiments with the Ca(2+) ionophore A23187 indicated that a Ca(2+)-dependent protease such as calpain might contribute substantially to silica-induced degradation of PrxII, but only moderately to that of PrxI. These results indicate that silica increases cellular oxidative stress not only by inducing ROS production, but also by triggering the degradation of Prx enzymes that are responsible for elimination of cellular ROS. Such aggravated oxidative stress might be important in the initial pathogenesis of silica-associated pulmonary diseases.

Modulation of Chemokine Expression During Ischemia/Reperfusion in Transgenic Mice Overproducing Human Glutathione Peroxidases

Renal ischemia/reperfusion (I/R) injury is a major cause of kidney damage. There is accumulating evidence that inflammatory reactions are involved in the pathogenesis of this process. Our studies demonstrate that transgenic mice overexpressing human extracellular and intracellular glutathione peroxidases (GP) are protected against kidney I/R injury. Importantly, significant reduction in neutrophil migration was observed in GP mice compared with nontransgenic mice. Analysis of signaling molecules mediating neutrophil activation and recruitment indicates reduction in the level of KC and macrophage inflammatory protein-2 chemokine expression in transgenic animals. The molecular mechanism mediating this effect appears to involve repression of NF-κB activation at the level of IκBα and IκBβ degradation. In the case of IκBα, no apparent phosphorylation was detected. These results suggest that IκBα proteolysis is triggered during the renal I/R pro-oxidant state by a still unknown mechanism, which might be different from other stimuli. A central role of NF-κB in CXC chemokine activation was demonstrated in cell culture anoxia/ATP repletion experiments as a model of I/R. The data presented indicate the important role of GP-sensitive signal transduction pathways in the development of inflammatory response and tissue injury during I/R.

Synergism between mild hyperthermia and interferon-beta gene expression

In the present study, the synergistic effect of mild hyperthermia in combination with gene expression of interferon-beta (IFN-beta) was examined in vitro in the human glioma cell line U87MG. The cells transiently expressed the IFN-beta gene under the control of the mouse mammary tumor virus promoter and were then subjected to temperature elevation (41 degrees C for 1 h). In terms of the cell killing effect, the optimum scheme was obtained by transfection for 4 days before hyperthermia, i.e. rate in the time course of IFN-beta gene expression. The relative specific growth rate decreased to 32% compared with the control while it was only 40% under the hyperthermic conditions. These observations suggest that IFNbeta expression was able to enhance the sensitivity of transfected glioma cells to mild hyperthermia.

Splanchnic tissues undergo hypoxic stress during whole body hyperthermia

Exposure of conscious animals to environmental heat stress increases portal venous radical content. The nature of the observed heat stress-inducible radical molecules suggests that hyperthermia produces cellular hypoxic stress in liver and intestine. To investigate this hypothesis, conscious rats bearing in-dwelling portal venous and femoral artery catheters were exposed to normothermic or hyperthermic conditions. Blood gas levels were monitored during heat stress and for 24 h following heat exposure. Hyperthermia significantly increased arterial O2 saturation, splanchnic arterial-venous O2 difference, and venous PCO2, while decreasing venous O2 saturation and venous pH. One hour after heat exposure, liver glycogen levels were decreased approximately 20%. Two hours after heat exposure, the splanchnic arterial-venous O2 difference remained elevated in heat-stressed animals despite normal Tc. A second group of rats was exposed to similar conditions while receiving intra-arterial injections of the hypoxic cell marker [3H]misonidazole. Liver and intestine were biopsied, and [3H]misonidazole content was quantified. Heat stress increased tissue [3H]misonidazole retention 80% in the liver and 29% in the small intestine. Cellular [3H]misonidazole levels were significantly elevated in intestinal epithelial cells and liver zone 2 and 3 hepatocytes and Kupffer cells. This effect was most prominent in the proximal small intestine and small liver lobi. These data provide evidence that hyperthermia produces cellular hypoxia and metabolic stress in splanchnic tissues and suggest that cellular metabolic stress may contribute to radical generation during heat stress.

Acetaminophen toxicity. Opposite effects of two forms of glutathione peroxidase

Acetaminophen is one of the most extensively used analgesics/antipyretics worldwide, and overdose or idiopathic reaction causes major morbidity and mortality in its victims. Research into the mechanisms of toxicity and possible therapeutic intervention is therefore essential. In this study, the response of transgenic mice overexpressing human antioxidant enzymes to acute acetaminophen overdose was investigated. Animals overexpressing superoxide dismutase or plasma glutathione peroxidase demonstrated dramatic resistance to acetaminophen toxicity. Intravenous injection of glutathione peroxidase provided normal mice with nearly complete protection against a lethal dose of acetaminophen. Surprisingly, animals overexpressing intracellular glutathione peroxidase in the liver were significantly more sensitive to acetaminophen toxicity compared with nontransgenic littermates. This sensitivity appears to be due to the inability of these animals to efficiently recover glutathione depleted as a result of acetaminophen metabolism. Finally, the results suggest that glutathione peroxidase overexpression modulates the synthesis of several acetaminophen metabolites. Our results demonstrate the ability of glutathione peroxidase levels to influence the outcome of acetaminophen toxicity.

In utero methylmercury exposure differentially affects the activities of selenoenzymes in the fetal mouse brain

Pregnant ICR mice were subcutaneously injected with 0,5, or 3x3 mg Hg/kg of methylmercury (MeHg) on days 12,13, and 14(G12-14) of gestation and were sacrificed on G17. Activity of selenoenzymes, including glutathione peroxidase (GPx) and 5'- or 5-iodothyronine deiodinases (5'-DI, 5-DI), was determined in fetal brain and placenta. MeHg did not affect the concentration of Se in these tissues, while it significantly inhibited the activity of GPx in the fetal brain and placenta, but not in the maternal brain. Although the levels of thyroid hormones in the maternal and fetal plasma were not affected by MeHg, 5-DI decreased and 5'-DI increased in the fetal brain, as if they had responded to hypothyroidism. Because the level of T4 in the fetal plasma was not affected by MeHg, these changes in enzymatic activities may result in a harmful excess of T3 in the fetal brain. In addition, 5-DI activity was increased in the placenta of MeHg-treated mice. These effects of prenatal MeHg exposure on fetal and placental DIs differed from those of dietary-induced Se deficiency, where the activities of DIs were decreased or not affected. Further evaluation of the effect of MeHg on selenoenzymes, especially 5-DIs, is warranted.

The nature of antioxidant defense mechanisms: a lesson from transgenic studies

Reactive oxygen species (ROS) have been implicated in the pathogenesis of many clinical disorders such as adult respiratory distress syndrome, ischemia-reperfusion injury, atherosclerosis, neurodegenerative diseases, and cancer. Genetically engineered animal models have been used as a tool for understanding the function of various antioxidant enzymes in cellular defense mechanisms against various types of oxidant tissue injury. Transgenic mice overexpressing three isoforms of superoxide dismutase, catalase, and the cellular glutathione peroxidase (GSHPx-1) in various tissues show an increased tolerance to ischemia-reperfusion heart and brain injury, hyperoxia, cold-induced brain edema, adriamycin, and paraquat toxicity. These results have provided for the first time direct evidence demonstrating the importance of each of these antioxidant enzymes in protecting the animals against the injury resulting from these insults, as well as the effect of an enhanced level of antioxidant in ameliorating the oxidant tissue injury. To evaluate further the nature of these enzymes in antioxidant defense, gene knockout mice deficient in copper-zinc superoxide dismutase (CuZnSOD) and GSHPx-1 have also been generated in our laboratory. These mice developed normally and showed no marked pathologic changes under normal physiologic conditions. In addition, a deficiency in these genes had no effects on animal survival under hyperoxida. However, these knockout mice exhibited a pronounced susceptibility to paraquat toxicity and myocardial ischemia-reperfusion injury. Furthermore, female mice lacking CuZnSOD also displayed a marked increase in postimplantation embryonic lethality. These animals should provide a useful model for uncovering the identity of ROS that participate in the pathogenesis of various clinical disorders and for defining the role of each antioxidant enzyme in cellular defense against oxidant-mediated tissue injury.

Attenuation of 6-OHDA-induced neurotoxicity in glutathione peroxidase transgenic mice

Normal cellular metabolism produces oxidants which are neutralized within cells by antioxidant enzymes and other antioxidants. An imbalance between oxidants and antioxidants has been postulated to lead to the degeneration of specific populations of neurons in neurodegenerative diseases, e.g. Parkinson's disease. The present study investigates whether overexpression of glutathione peroxidase, the enzyme which metabolizes hydrogen peroxide to water, can prevent or slow down neuronal injury in an animal model of Parkinson's disease. Transgenic mice overexpressing the human glutathione peroxidase gene under the control of the mouse hydroxymethylglutaryl-coenzyme A promoter and genetically matched control mice were injected intracerebroventricularly with the dopaminergic neurotoxin 6-hydroxydopamine. Seven days after injection, the number of tyrosine hydroxylase-positive nigral dopaminergic neurons was decreased by 52.4% and 20.5% in 6-hydroxydopamine-injected control and glutathione peroxidase transgenic mice, respectively. Similarly, 3 days after injection of the neurotoxin, striatal dopamine was decreased by 71.2% and 56.5%, respectively. Overexpression of glutathione peroxidase therefore partially protects dopaminergic neurons against 6-hydroxydopamine-induced toxicity.

Cellular glutathione peroxidase is the mediator of body selenium to protect against paraquat lethality in transgenic mice

The antioxidative role of Se-dependent cellular glutathione peroxidase (EC 1.11.1.9, GPX1) in vivo has not been established. Our objective was to determine the effects of GPX1 knockout or overexpression on the susceptibility of mice to paraquat toxicity and the contributions of GPX1, compared with other selenoproteins and vitamin E, to body defenses against such acute oxidative stress. Four experiments were conducted using 111 GPX1 knockout or overexpressing mice and the respective controls. Mice were fed diets supplemented with Se (as sodium selenite) at 0-0.4 mg/kg and/or all-rac-alpha-tocopheryl acetate at 0-75 mg/kg before intraperitoneal injections of 12.5, 50 or 125 mg paraquat/kg body weight. All mice that received 50 or 125 mg paraquat/kg died spontaneously, and the survival time of mice was (independent of dietary levels of Se per se or alpha-tocopheryl acetate) solely a function of tissue GPX1 activity (P < 0.001). Severe acute pulmonary interstitial necrosis was found only in the GPX1 overexpressing mice and the controls that had extended survival time. Thiobarbituric acid reacting substances in postmortem liver inversely correlated with the tissue GPX1 activity and dietary levels of Se and/or alpha-tocopheryl acetate. In contrast, all mice that received 12.5 mg paraquat/kg survived and were killed 2 wk after the injection for tissue collection. Compared with the saline injection, this low dose of paraquat resulted in greater (P < 0.001) liver and lung F2-isoprostanes in both the GPX1 knockout mice and the controls. However, there was no difference in plasma alanine transaminase (EC 2.6.1.2) activity or overt injuries in liver, lung and kidney in either group. Our data indicate that GPX1 is the major, if not the only, metabolic form of body Se that protects mice against the lethal oxidative stress caused by high levels of paraquat; it seems less important, however, in protecting mice against the moderate oxidative stress by the low level of paraquat.

Comparison of formation of D2/E2-isoprostanes and F2-isoprostanes in vitro and in vivo--effects of oxygen tension and glutathione

The isoprostanes (IsoPs) are bioactive prostaglandin-like compounds derived from the free-radical-catalyzed peroxidation of arachidonic acid in vitro and in vivo. IsoPs possessing either an F-type prostane ring (F2-IsoPs) or D/E-type prostane rings (D2/E2-IsoPs) are formed depending on whether IsoP endoperoxide intermediates undergo reduction or isomerization, respectively. Little, however, is known regarding factors influencing the formation of various classes of IsoPs, particularly D2/E2-IsoPs. Thus, studies were undertaken to examine the formation of D2/E2-IsoPs in relation to F2-Isops both in vitro and in vivo. In peroxidizing rat liver microsomes, the formation of D2/E2-IsoPs increased in a time- and oxygen-dependent manner and correlated with F2-IsoP generation and loss of precursor arachidonic acid, although the absolute amount of D2/E2-IsoPs formed exceeded by over 5-fold the levels of F2-IsoPs formed. Surprisingly, however, in liver tissue from rats exposed to an oxidant stress, levels of F2-IsoPs were up to 10-fold greater than those of D2/E2-IsoPs, suggesting that an endogenous process causes IsoP endoperoxide reduction in vivo. Addition of glutathione (GSH) to peroxidizing microsomes at concentrations from 0.01 to 5 mM increased the formation of F2-IsoPs at the expense of D2/E2-IsoPs. Boiling of microsomes did not alter the effect of GSH. Formation of D2/E2-IsoPs in liver tissue in vivo was greatly enhanced compared to F2-IsoPs in rats depleted of GSH. Thus, GSH modulates the formation of different classes of IsoPs in vitro and in vivo. Other thiols, including beta-mercaptoethanol, dithiothreitol, and cysteine, were able to substitute for GSH. These studies indicate that GSH promotes F2-IsoP formation and diminishes D2/E2-IsoP levels in vitro and in vivo by causing reduction of IsoP endoperoxides.

Overexpression of human glutathione peroxidase protects transgenic mice against focal cerebral ischemia/reperfusion damage

As stroke is a major cause of disability and death in the western world, there is great interest in the basic mechanisms by which ischemia/reperfusion (I/R) causes damage. To this end, extensive research has been carried out which identifies reactive oxygen species (ROS) as key participants in brain damage resultant from I/R. Brain tissue is protected from ROS damage by antioxidant enzymes, such as superoxide dismutase (SOD) and glutathione peroxidase (GP). Overexpression of SOD in transgenic mice has already been demonstrated to confer protection against I/R damage in murine stroke models. We are using transgenic mice overexpressing the intracellular form of glutathione peroxidase (GP1) to determine the protective capacity of overexpression of this enzyme on stroke damage. 1 h of focal cerebral ischemia followed by 24 h of reperfusion was induced using the intraliminal suture method. Volume of infarction was reduced by 48% in GP1 mice compared to nontransgenic littermates. Brain edema was reduced by 33%. Behavioral deficits agreed with histologic data. Overexpression of glutathione peroxidase confers significant protection against I/R damage in our stroke model possibly through direct scavenging of ROS or through the influencing of signalling mechanisms which lead to tissue damage.

Deficiency of selenium enhances the K+-induced release of dopamine in the striatum of mice

To determine whether a selenium (Se) deficiency in the brain leads to a functional change in dopaminergic transmission in the striatum, in vivo microdialysis was conducted in mice fed a low-Se diet. After 11-13 weeks of the diet regimen, the activity of glutathione peroxidase (GPx) in the Se-deficient brain was reduced to 60% of the control brain. A high K+ perfusion (100 mM) increased the level of dopamine in the dialysate to 67 +/- 16 times the basal level; the increase was significantly greater than that observed in the control group (28 +/- 4 times). Such a between-group difference was not observed after 4-5 weeks of the Se-diet. These results indicated that prolonged Se deficiency altered the function of striatal dopaminergic neurons in mice. A possible contribution of enhanced oxidative stress due to the reduced GPx activity is discussed.

Overexpression of antioxidant enzymes in transgenic mice decreases cellular ploidy during liver regeneration

Reactive oxygen species (ROS) and antioxidant enzymes have been implicated in control mechanisms of cellular growth and proliferation. We investigated the influence of levels of endogenous antioxidant enzymes on liver regeneration in transgenic mice overexpressing human Cu,Zn-superoxide dismutase (SOD) and intracellular glutathione peroxidase (GP1) as a model system. After a two-thirds partial hepatectomy (PH), no significant difference was observed in rate of liver mass restoration among nontransgenic, SOD, and GP1 mice. In contrast, the level of polyploidization was significantly reduced in transgenic animals after PH, with a concomitant increase in 2N nuclei. The portion of 8N nuclei after 72 h reached 33.1, 15.8, and 22.1%, whereas the portion of 2N nuclei reached 7.5, 13.8, and 12.3% in nontransgenic, SOD, and GP1 mice, respectively. A similar effect was observed in another model of liver proliferation, during normal development around weaning time. Measurements of ROS production during PH indicate that overexpression of SOD leads to the decreased production of O2- and elevation of H2O2. Unexpectably, overexpression of GP in transgenic mice also results in increased production of H2O2 in hepatocytes. Finally, our data demonstrate that levels of endogenous antioxidant enzymes might influence the rate of hepatocyte polyploidization during liver proliferation.

Intestinal ischemia and reperfusion injury in transgenic mice overexpressing copper-zinc superoxide dismutase

Superoxide dismutase (SOD) scavenges oxygen radicals that are implicated in the pathogenesis of intestinal ischemia-reperfusion injury. The effect of intestinal ischemia and reperfusion was investigated in transgenic mice overexpressing human Cu-Zn SOD. Ischemia was induced by occluding the superior mesenteric artery. Myeloperoxidase activity was determined as an index of neutrophil infiltration, and malondialdehyde levels were measured as an indicator of lipid peroxidation. Forty-five minutes of intestinal ischemia followed by 4 h of reperfusion caused an increase in intestinal levels of malondialdehyde in both nontransgenic and transgenic mice, but the concentration of malondialdehyde was significantly greater in nontransgenic mice. Intestinal ischemia-reperfusion also caused an increase in intestinal and pulmonary myeloperoxidase activity in nontransgenic and transgenic mice, but the transgenic mice had significantly lower levels of myeloperoxidase activity than nontransgenic mice. Transgenic mice had higher levels of intestinal SOD activity than nontransgenic mice. There were no significant differences in the catalase or glutathione peroxidase activities. In conclusion, our study demonstrates that the overexpression of SOD protects tissues from neutrophil infiltration and lipid peroxidation during intestinal ischemia-reperfusion.

Mice deficient in cellular glutathione peroxidase develop normally and show no increased sensitivity to hyperoxia

Glutathione peroxidase, a selenium-containing enzyme, is believed to protect cells from the toxicity of hydroperoxides. The physiological role of this enzyme has previously been implicated mainly using animals fed with a selenium-deficient diet. Although selenium deficiency also affects the activity of several other cellular selenium-containing enzymes, a dramatic decrease of glutathione peroxidase activity has been postulated to play a role in the pathogenesis of a number of diseases, particularly those whose progression is associated with an overproduction of reactive oxygen species, found in selenium-deficient animals. To further clarify the physiological relevance of this enzyme, a model of mice deficient in cellular glutathione peroxidase (GSHPx-1), the major isoform of glutathione peroxidase ubiquitously expressed in all types of cells, was generated by gene-targeting technology. Mice deficient in this enzyme were apparently healthy and fertile and showed no increased sensitivity to hyperoxia. Their tissues exhibited neither a retarded rate in consuming extracellular hydrogen peroxide nor an increased content of protein carbonyl groups and lipid peroxidation compared with those of wild-type mice. However, platelets from GSHPx-1-deficient mice incubated with arachidonic acid generated less 12-hydroxyeicosatetraenoic acid and more polar products relative to control platelets at a higher concentration of arachidonic acid, presumably reflecting a decreased ability to reduce the 12-hydroperoxyeicosatetraenoic acid intermediate. These results suggest that the contribution of GSHPx-1 to the cellular antioxidant mechanism under normal animal development and physiological conditions and to the pulmonary defense against hyperoxic insult is very limited. Nevertheless, the potential antioxidant role of this enzyme in protecting cells and animals against the pathogenic effect of reactive oxygen species in other disorders remains to be defined. The knockout mouse model described in this report will also provide a new tool for future study to distinguish the physiological role of this enzyme from other selenium-containing proteins in mammals under normal and disease states.

Overexpression of cellular glutathione peroxidase does not affect expression of plasma glutathione peroxidase or phospholipid hydroperoxide glutathione peroxidase in mice offered diets adequate or deficient in selenium

Selenium-dependent cellular glutathione peroxidase (GPX1) overexpressing [GPX1(+)] mice were derived by microinjecting a 5.3-kb cloned entire mouse GPX1 genomic DNA into fertilized eggs. The objective of this study was to determine the effect of GPX1 overexpression and dietary selenium on the expression of selenoperoxidases and the status of lipid peroxidation of these transgenic animals. An experiment with a 2 x 2 factorial arrangement of treatments with 15 GPX1(+) and 15 control mice (2 mo old) was conducted for 8 wk. Ten mice of each group (half males and females) were fed a Se-deficient, Torula yeast basal diet (0.02 mg Se/kg, no supplemental vitamin E) and five mice (three males and two females) were fed the basal diet supplemented with 0.51 mg Se/kg as Na2SeO3. The GPX1(+) mice had greater GPX1 activities (one- to sixfold, P < 0.0001) than the control mice at both levels of dietary selenium in all tissues except for liver, in which such difference (100%, P < 0.05) was observed only in Se-deficient mice. The GPX1 mRNA level in kidney and in lung of the Se-deficient GPX1(+) mice was 81% and 7.5-fold greater (P < 0.003) than the respective control level. Overexpression of GPX1 did not alter phospholipid hydroperoxide glutathione peroxidase (GPX4) activities and mRNA levels or glutathione S-transferase (GST) activities in most of the tissues, plasma glutathione peroxidase (GPX3) activity or plasma Se concentrations. No differences in lipid peroxidation in kidney, lung or intestine were observed between the Se-deficient GPX1(+) and control mice. In conclusion, the overexpression of the GPX1 gene in these mice was tissue specific and did not affect the expression of GPX3, GPX4 or GST and plasma Se levels; dietary Se appeared to affect the GPX1 overexpression at its mRNA level.