Purification and immunoelectron microscopic localization of cellular glutathione peroxidase in rat hepatocytes: quantitative analysis by postembedding method

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.

The Interaction between Dietary Selenium Intake and Genetics in Determining Cancer Risk and Outcome

There is considerable interest in the trace element selenium as a possible cancer chemopreventive dietary component, but supplementation trials have not indicated a clear benefit. Selenium is a critical component of selenium-containing proteins, or selenoproteins. Members of this protein family contain selenium in the form of selenocysteine. Selenocysteine is encoded by an in-frame UGA codon recognized as a selenocysteine codon by a regulatory element, the selenocysteine insertion sequence (SECIS), in the 3′-untranslated region of selenoprotein mRNAs. Epidemiological studies have implicated several selenoprotein genes in cancer risk or outcome based on associations between allelic variations and disease risk or mortality. These polymorphisms can be found in or near the SECIS or in the selenoprotein coding sequence. These variations both function to control protein synthesis and impact the efficiency of protein synthesis in response to the levels of available selenium. Thus, an individual’s genetic makeup and nutritional intake of selenium may interact to predispose them to acquiring cancer or affect cancer progression to lethality.

GPX1 Localizes to the Nucleus in Prostate Epithelium and its Levels are not Associated with Prostate Cancer Recurrence

Glutathione peroxidase 1 (GPX1) is an extensively studied selenium-dependent protein that reduces hydrogen and lipid peroxides to water. Because of its antioxidant function and its responsiveness to dietary intakes of selenium, an essential trace element whose levels are inversely associated with prostate cancer risk, GPX1 levels were assessed in a prostate cancer tissue microarray, comparing cases of recurrent prostate cancer following prostatectomy to non-recurrent controls. While GPX1 is generally considered as a protein that resides in both the cytoplasm and mitochondria, we detected strong nuclear staining by immunofluorescence using GPX1-specific antibodies. Nuclear localization of GPX1 was also observed in both primary prostate epithelial cells and the immortalized prostate-derived cell line RWPE-1, but not in LNCaP or PC3 prostate tumor-derived cell lines. Quantification of GPX1 levels in the entire cell, the cytoplasm, and the nucleus did not indicate any association of either its levels or subcellular distribution with prostate cancer recurrence. While GPX1 levels may not have an impact on survival among men with prostate cancer, the data indicates that this extensively characterized protein may have a novel function in the nucleus of prostate epithelial cells.

Manganese superoxide dismutase and glutathione peroxidase-1 contribute to the rise and fall of mitochondrial reactive oxygen species which drive oncogenesis

Reactive oxygen species (ROS) largely originating in the mitochondria play essential roles in the metabolic and (epi)genetic reprogramming of cancer cell evolution towards more aggressive phenotypes. Recent studies have indicated that the activity of superoxide dismutase (SOD2) may promote tumor progression by serving as a source of hydrogen peroxide (H₂O₂). H₂O₂ is a form of ROS that is particularly active as a redox agent affecting cell signaling due to its ability to freely diffuse out of the mitochondria and alter redox active amino acid residues on regulatory proteins. Therefore, there is likely a dichotomy whereas SOD2 can be considered a protective antioxidant, as well as a pro-oxidant during cancer progression, with these effects depending on the accumulation and detoxification of H₂O₂. Glutathione peroxidase-1 GPX1, is a selenium-dependent scavenger of H₂O₂ which partitions between the mitochondria and the cytosol. Epidemiologic studies indicated that allelic variations in the SOD2 and GPX1 genes alter the distribution and relative concentrations of SOD2 and GPX1 in mitochondria, thereby affecting the dynamic between the production and elimination of H₂O₂. Experimental and epidemiological evidence supporting a conflicting role of SOD2 in tumor biology, and epidemiological evidence that SOD2 and GPX1 can interact to affect cancer risk and progression indicated that it is the net accumulation of mitochondrial H₂O₂ (mtH₂O₂) resulting from of the balance between the activities SOD2 and anti-oxidants such as GPX1 that determines whether SOD2 prevents or promotes oncogenesis. In this review, research supporting the idea that GPX1 is a gatekeeper restraining the oncogenic power of mitochondrial ROS generated by SOD2 is presented. This article is part of a Special Issue entitled Mitochondria in Cancer, edited by Giuseppe Gasparre, Rodrigue Rossignol and Pierre Sonveaux.

Iron as a catalyst of human low-density lipoprotein oxidation: Critical factors involved in its oxidant properties

Iron-induced human LDL oxidation, which is relevant to atherosclerosis, has not yet been properly investigated. We addressed such issue using iron(II) and (III) basically in the presence of phosphates, which are present in vivo and influence iron oxidative properties, at pH 4.5 and 7.4, representative, respectively, of the lysosomal and plasma environment. In 10mM phosphate buffered saline (PBS), iron(II) induces substantial LDL oxidation at pH 4.5 at low micromolar concentrations, while at pH 7.4 has low oxidative effects; iron(III) promotes small LDL oxidation only at pH 4.5. In 10mM sodium acetate/NaCl buffer, pH 4.5, iron-induced LDL oxidation is far higher than in PBS, highlighting the relevance of phosphates in the inhibitory modulation of iron-induced LDL oxidation. LDL oxidation is related to iron binding to the protein and lipid moiety of LDL, and requires the presence of iron(II) bound to LDL together with iron(III). Chemical modification of LDL carboxyl groups, which could bind iron especially at pH 4.5, decreases significantly iron binding to LDL and iron-induced LDL oxidation. Hydroxyl radical scavengers are ineffective on iron-induced LDL oxidation, which is inhibited by metal chelation, scavengers of alkoxyl/peroxyl radicals, or removal of LDL lipid hydroperoxides (LOOH). Overall, substantial human LDL oxidation is induced LOOH-dependently by iron(II) at pH 4.5 even in the presence of phosphates, suggesting the occurrence of iron(II)-induced LDL oxidation in vivo within lysosomes, where pH is about 4.5, iron(II) and phosphates coexist, plasma with its antioxidants is absent, and glutathione peroxidase is poorly expressed resulting in LOOH accumulation.

The subcellular location of selenoproteins and the impact on their function

Most human selenium containing proteins contain selenium in the form of the amino acid selenocysteine, which is encoded in the corresponding mRNA as a UGA codon. Only a few non-selenocysteine containing selenoproteins are present and the nature of the association with selenium is not well understood. This review focuses on two selenocysteine-containing proteins that are members of the glutathione peroxidase family, GPx-1 and GPx-4, and the selenium-associated protein referred to as Selenium Binding Protein 1. Each of these proteins have been described to reside in two or more cellular compartments, and in the case of GPx-1 and SBP1, interact with each other. The enzymatic activity of GPx-1 and GPx-4 have been well described, but it is less clear how their cellular location impacts the health related phenotypes associated with activities, while no catalytic function is assigned to SBP1. The distribution of these proteins is presented as is the possible consequences of that compartmentalization.

Ultrasensitive response motifs: basic amplifiers in molecular signalling networks

Multi-component signal transduction pathways and gene regulatory circuits underpin integrated cellular responses to perturbations. A recurring set of network motifs serve as the basic building blocks of these molecular signalling networks. This review focuses on ultrasensitive response motifs (URMs) that amplify small percentage changes in the input signal into larger percentage changes in the output response. URMs generally possess a sigmoid input–output relationship that is steeper than the Michaelis–Menten type of response and is often approximated by the Hill function. Six types of URMs can be commonly found in intracellular molecular networks and each has a distinct kinetic mechanism for signal amplification. These URMs are: (i) positive cooperative binding, (ii) homo-multimerization, (iii) multistep signalling, (iv) molecular titration, (v) zero-order covalent modification cycle and (vi) positive feedback. Multiple URMs can be combined to generate highly switch-like responses. Serving as basic signal amplifiers, these URMs are essential for molecular circuits to produce complex nonlinear dynamics, including multistability, robust adaptation and oscillation. These dynamic properties are in turn responsible for higher-level cellular behaviours, such as cell fate determination, homeostasis and biological rhythm.

Cerebral antioxidant enzyme increase associated with learning deficit in type 2 diabetes rats

In this study, we examined alterations in the enzymatic antioxidant defenses associated with learning deficits induced by type 2 diabetes, and studied the effects of the peroxisome proliferator-activated receptor γ agonist pioglitazone on these learning deficits. Learning ability was assessed by visual discrimination tasks in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, as a model of spontaneous type 2 diabetes. Levels of the antioxidant enzymes glutathione peroxidase (GPx), Cu(2+)-Zn(2+) superoxide dismutase (CuZn-SOD) and manganese SOD were measured in the cortex, hippocampus and striatum. Half the rats received oral pioglitazone (20mg/kg/day) from the early stage of diabetes (22 weeks old) to 27 weeks old. OLETF rats showed learning deficits compared with control, Long-Evans Tokushima Otsuka (LETO) rats. GPx levels in the cortex and hippocampus were increased in OLETF rats compared with LETO rats, with an inverse correlation between GPx in the hippocampus and learning score. CuZn-SOD levels were also increased in the hippocampus in OLETF rats. Pioglitazone reduced blood glucose and increased serum adiponectin levels, but had no effect on learning tasks or antioxidant enzymes, except for CuZn-SOD. These results suggest that an oxidative imbalance reflected by increased brain antioxidant enzymes plays an important role in the development of learning deficits in type 2 diabetes. Early pioglitazone administration partly ameliorated diabetic symptoms, but was unable to completely recover cerebral oxidative imbalance and functions. These results suggest that diabetes-induced brain impairment, which results in learning deficits, may have occurred before the appearance of the symptoms of overt diabetes.

Mitochondrial targeting of peroxiredoxin 5 is preserved from annelids to mammals but is absent in pig Sus scrofa domesticus

Peroxiredoxin 5 (PRDX5) is a thioredoxin peroxidase able to reduce hydrogen peroxide, alkyl hydroperoxides and peroxynitrite. In human, PRDX5 was reported to be localized in the cytosol, the mitochondria, the peroxisomes and the nucleus. Mitochondrial localization results from the presence of an N-terminal mitochondrial targeting sequence (MTS). Here, we examined the conservation of mitochondrial localization of PRDX5 in animal species. We found that PRDX5 MTS is present and functional in the annelid lugworm Arenicola marina. Surprisingly, although mitochondrial targeting is well conserved among animals, PRDX5 is missing in mitochondria of domestic pig. Thus, it appears that mitochondrial targeting of PRDX5 may have been lost throughout evolution in animal species, including pig, with unknown functional consequences.

Oxidative stress and oxidative damage in chemical carcinogenesis

Reactive oxygen species (ROS) are induced through a variety of endogenous and exogenous sources. Overwhelming of antioxidant and DNA repair mechanisms in the cell by ROS may result in oxidative stress and oxidative damage to the cell. This resulting oxidative stress can damage critical cellular macromolecules and/or modulate gene expression pathways. Cancer induction by chemical and physical agents involves a multi-step process. This process includes multiple molecular and cellular events to transform a normal cell to a malignant neoplastic cell. Oxidative damage resulting from ROS generation can participate in all stages of the cancer process. An association of ROS generation and human cancer induction has been shown. It appears that oxidative stress may both cause as well as modify the cancer process. Recently association between polymorphisms in oxidative DNA repair genes and antioxidant genes (single nucleotide polymorphisms) and human cancer susceptibility has been shown.

Oxidative stress and oxidative damage in carcinogenesis

Carcinogenesis is a multistep process involving mutation and the subsequent selective clonal expansion of the mutated cell. Chemical and physical agents including those that induce reative oxygen species can induce and/or modulate this multistep process. Several modes of action by which carcinogens induce cancer have been identified, including through production of reactive oxygen species (ROS). Oxidative damage to cellular macromolecules can arise through overproduction of ROS and faulty antioxidant and/or DNA repair mechanisms. In addition, ROS can stimulate signal transduction pathways and lead to activation of key transcription factors such as Nrf2 and NF-kappaB. The resultant altered gene expression patterns evoked by ROS contribute to the carcinogenesis process. Recent evidence demonstrates an association between a number of single nucleotide polymorphisms (SNPs) in oxidative DNA repair genes and antioxidant genes with human cancer susceptibility. These aspects of ROS biology will be discussed in the context of their relationship to carcinogenesis.

A systems biology perspective on Nrf2-mediated antioxidant response

Cells in vivo are constantly exposed to reactive oxygen species (ROS) generated endogenously and exogenously. To defend against the deleterious consequences of ROS, cells contain multiple antioxidant enzymes expressed in various cellular compartments to scavenge these toxic species. Under oxidative stresses, these antioxidant enzymes are upregulated to restore redox homeostasis. Such an adaptive response results from the activation of a redox-sensitive gene regulatory network mediated by nuclear factor E2-related factor 2. To more completely understand how the redox control system is designed by nature to meet homeostatic goals, we have examined the network from a systems perspective using engineering approaches. As with man-made control devices, the redox control system can be decomposed into distinct functional modules, including transducer, controller, actuator, and plant. Cells achieve specific performance objectives by utilizing nested feedback loops, feedforward control, and ultrasensitive signaling motifs, etc. Given that endogenously generated ROS are also used as signaling molecules, our analysis suggests a novel mode of action to explain oxidative stress-induced pathological conditions and diseases. Specifically, by adaptively upregulating antioxidant enzymes, oxidative stress may inadvertently attenuate ROS signals that mediate physiological processes, resulting in aberrations of cellular functions and adverse consequences. Lastly, by simultaneously considering the two competing cellular tasks-adaptive antioxidant defense and ROS signaling-we re-examine the premise that dietary antioxidant supplements is generally beneficial to human health. Our analysis highlights some possible adverse effects of these widely consumed antioxidants.

Molecular mechanisms by which selenoproteins affect cancer risk and progression

Selenoproteins comprise a unique class of proteins that contain selenium in the form of selenocysteine. Several selenoproteins have been implicated in the risk or development of cancers in humans by genetic data. These include Selenoprotein P, 3 members of the glutathione peroxidase family of anti-oxidant enzymes and Sep15. At-risk alleles in the germline indicate a likely role in determining susceptibility to cancer, while loss of heterozygosity or chromosomal epigenetic silencing indicate that the reduction in the levels of the corresponding proteins contribute to malignant progression. Lower levels of these proteins are likely to be detrimental due to the resulting cellular stress and perturbations in important regulatory signaling pathways. The genetic data indicating the involvement of these selenoproteins in cancer etiology are discussed, as are the possible mechanisms by which these genes might promote carcinogenesis.

Dose response relationship in anti-stress gene regulatory networks

To maintain a stable intracellular environment, cells utilize complex and specialized defense systems against a variety of external perturbations, such as electrophilic stress, heat shock, and hypoxia, etc. Irrespective of the type of stress, many adaptive mechanisms contributing to cellular homeostasis appear to operate through gene regulatory networks that are organized into negative feedback loops. In general, the degree of deviation of the controlled variables, such as electrophiles, misfolded proteins, and O₂, is first detected by specialized sensor molecules, then the signal is transduced to specific transcription factors. Transcription factors can regulate the expression of a suite of anti-stress genes, many of which encode enzymes functioning to counteract the perturbed variables. The objective of this study was to explore, using control theory and computational approaches, the theoretical basis that underlies the steady-state dose response relationship between cellular stressors and intracellular biochemical species (controlled variables, transcription factors, and gene products) in these gene regulatory networks. Our work indicated that the shape of dose response curves (linear, superlinear, or sublinear) depends on changes in the specific values of local response coefficients (gains) distributed in the feedback loop. Multimerization of anti-stress enzymes and transcription factors into homodimers, homotrimers, or even higher-order multimers, play a significant role in maintaining robust homeostasis. Moreover, our simulation noted that dose response curves for the controlled variables can transition sequentially through four distinct phases as stressor level increases: initial superlinear with lesser control, superlinear more highly controlled, linear uncontrolled, and sublinear catastrophic. Each phase relies on specific gain-changing events that come into play as stressor level increases. The low-dose region is intrinsically nonlinear, and depending on the level of local gains, presence of gain-changing events, and degree of feedforward gene activation, this region can appear as superlinear, sublinear, or even J-shaped. The general dose response transition proposed here was further examined in a complex anti-electrophilic stress pathway, which involves multiple genes, enzymes, and metabolic reactions. This work would help biologists and especially toxicologists to better assess and predict the cellular impact brought about by biological stressors.

To maintain a stable intracellular environment, cells are equipped with multiple specialized defense programs that are launched in response to various external chemical and physical stressors. These anti-stress mechanisms comprise primarily gene regulatory networks, and like many manmade control devices, such as thermostats and automobile cruise controls, they are often organized into negative feedback circuits. A quantitative understanding of how these control circuits operate in the cell can help us to assess and predict more accurately the cellular impacts brought about by perturbing stressors, such as environmental toxicants. Using control theory and computer simulations, we explored nature's design principle for anti-stress gene regulatory networks, and the manner in which cells respond and adapt to perturbations. We showed that cells can exploit multiple mechanisms, such as protein homodimerization, cooperative binding, and auto-regulation, to enhance the feedback loop gain, which, according to control theory, is a basic principle for effective perturbation resistance. We also illustrated that the steady-state dose response curve is likely to transition through multiple phases as stressor level increases, and that the low-dose region is inherently nonlinear. Our results challenge the common practice of linear extrapolation for evaluating the low-dose effect, and would lead to improved human health risk assessment for exposures to environmental toxicants.

Plant peroxisomes as a source of signalling molecules

Peroxisomes are pleiomorphic, metabolically plastic organelles. Their essentially oxidative function led to the adoption of the name 'peroxisome'. The dynamic and diverse nature of peroxisome metabolism has led to the realisation that peroxisomes are an important source of signalling molecules that can function to integrate cellular activity and multicellular development. In plants defence against predators and a hostile environment is of necessity a metabolic and developmental response--a plant has no place to hide. Mutant screens are implicating peroxisomes in disease resistance and signalling in response to light. Characterisation of mutants disrupted in peroxisomal beta-oxidation has led to a growing appreciation of the importance of this pathway in the production of jasmonic acid, conversion of indole butyric acid to indole acetic acid and possibly in the production of other signalling molecules. Likewise the role of peroxisomes in the production and detoxification of reactive oxygen, and possibly reactive nitrogen species and changes in redox status, suggests considerable scope for peroxisomes to contribute to perception and response to a wide range of biotic and abiotic stresses. Whereas the peroxisome is the sole site of beta-oxidation in plants, the production and detoxification of ROS in many cell compartments makes the specific contribution of the peroxisome much more difficult to establish. However progress in identifying peroxisome specific isoforms of enzymes associated with ROS metabolism should allow a more definitive assessment of these contributions in the future.

Mitochondrial metabolism of reactive oxygen species

Oxidative stress is considered a major contributor to etiology of both "normal" senescence and severe pathologies with serious public health implications. Mitochondria generate reactive oxygen species (ROS) that are thought to augment intracellular oxidative stress. Mitochondria possess at least nine known sites that are capable of generating superoxide anion, a progenitor ROS. Mitochondria also possess numerous ROS defense systems that are much less studied. Studies of the last three decades shed light on many important mechanistic details of mitochondrial ROS production, but the bigger picture remains obscure. This review summarizes the current knowledge about major components involved in mitochondrial ROS metabolism and factors that regulate ROS generation and removal. An integrative, systemic approach is applied to analysis of mitochondrial ROS metabolism, which is now dissected into mitochondrial ROS production, mitochondrial ROS removal, and mitochondrial ROS emission. It is suggested that mitochondria augment intracellular oxidative stress due primarily to failure of their ROS removal systems, whereas the role of mitochondrial ROS emission is yet to be determined and a net increase in mitochondrial ROS production in situ remains to be demonstrated.

Redox system expression in the motor neurons in amyotrophic lateral sclerosis (ALS): immunohistochemical studies on sporadic ALS, superoxide dismutase 1 (SOD1)-mutated familial ALS, and SOD1-mutated ALS animal models

Peroxiredoxin-ll (Prxll) and glutathione peroxidase-l (GPxl) are regulators of the redox system that is one of the most crucial supporting systems in neurons. This system is an antioxidant enzyme defense system and is synchronously linked to other important cell supporting systems. To clarify the common self-survival mechanism of the residual motor neurons affected by amyotrophic lateral sclerosis (ALS), we examined motor neurons from 40 patients with sporadic ALS (SALS) and 5 patients with superoxide dismutase 1 (SOD1)-mutated familial ALS (FALS) from two different families (frame-shift 126 mutation and A4 V) as well as four different strains of the SOD1-mutated ALS models (H46R/G93A rats and G1H/G1L-G93A mice). We investigated the immunohistochemical expression of Prxll/GPxl in motor neurons from the viewpoint of the redox system. In normal subjects, Prxll/GPxl immunoreactivity in the anterior horns of the normal spinal cords of humans, rats and mice was primarily identified in the neurons: cytoplasmic staining was observed in almost all of the motor neurons. Histologically, the number of spinal motor neurons in ALS decreased with disease progression. Immunohistochemically, the number of neurons negative for Prxll/GPxl increased with ALS disease progression. Some residual motor neurons coexpressing Prxll/GPxl were, however, observed throughout the clinical courses in some cases of SALS patients, SOD1-mutated FALS patients, and ALS animal models. In particular, motor neurons overexpressing Prxll/GPxl, i.e., neurons showing redox system up-regulation, were commonly evident during the clinical courses in ALS. For patients with SALS, motor neurons overexpressing Prxll/GPxl were present mainly within approximately 3 years after disease onset, and these overexpressing neurons thereafter decreased in number dramatically as the disease progressed. For SOD1-mutated FALS patients, like in SALS patients, certain residual motor neurons without inclusions also overexpressed Prxll/GPxl in the short-term-surviving FALS patients. In the ALS animal models, as in the human diseases, certain residual motor neurons showed overexpression of Prxll/GPxl during their clinical courses. At the terminal stage of ALS, however, a disruption of this common Prxll/GPxl-overexpression mechanism in neurons was observed. These findings lead us to the conclusion that the residual ALS neurons showing redox system up-regulation would be less susceptible to ALS stress and protect themselves from ALS neuronal death, whereas the breakdown of this redox system at the advanced disease stage accelerates neuronal degeneration and/or the process of neuronal death.

Plasma proteome of severe acute respiratory syndrome analyzed by two-dimensional gel electrophoresis and mass spectrometry

We have investigated the plasma proteome by using 2D gel electrophoresis and MS from patients with severe acute respiratory syndrome (SARS). A complete proteomic analysis was performed on four patients with SARS in different time courses, and a total of 38 differential spots were selected for protein identification. Most of the proteins identified are acute phase proteins, and their presence represents the consequence of serial cascades initiated by SARS-coronavirus infection. There are several proteins that have never been identified in plasma before using 2D gel electrophoresis, among which peroxiredoxin II was chosen for further study by analyzing additional 20 plasma samples from patients with probable and suspected SARS and patients with fever, respectively. The results showed that the level of plasma peroxiredoxin II in patients with SARS is significantly high and could be secreted by T cells. Taken together, our findings indicate that active innate immune responses, along with the oxidation-associated injuries, may play a major role in the pathogenesis of SARS.

Induction of glutathione peroxidase in response to inactivation by nitric oxide

To determine effect of nitric oxide (NO) on cellular glutathione peroxidase (GPX) level in living cells, we measured the activity, protein and mRNA of GPX in rat kidney (KNRK) cells under a high NO condition. Combined treatment of lipopolysaccharide (LPS, 1 microgram/ml) and tumor necrosis factor-alpha (TNF-alpha, 50 ng/ml) synergistically enhanced (23-folds) nitrite production from KNRK cells. This was suppressed by an inducible NO synthase (iNOS) inhibitor (aminoguanidine, N-nitro-L-arginine methylester hydrochloride) and arginase. iNOS expression was detected by RT-PCR in the treated cells. GPX was inactivated irreversibly when the cells had been homogenized before exposure to a NO donor, S-nitroso-N-acetylpenicillamine (SNAP). In living KNRK cells, SNAP and LPS + TNF-alpha exerted a transient effect on the GPX activity. The treatment with SNAP (200 microM) or sodium nitroprusside (200 microM) enhanced GPX gene expression, which was blocked by a NO scavenger, 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-oxide. GPX mRNA was markedly increased by the treatment with LPS + TNF-alpha, and aminoguanidine blocked the effect. In cells metabolically labeled with 75Se, LPS + TNF-alpha accelerated the incorporation of radioactivity into GPX molecule by 2.1-fold. These results suggest that inactivation of GPX by NO triggers a signal for inducing GPX gene expression in KNRK cells, thereby restoring the intracellular level of this indispensable enzyme.

Induction of peroxiredoxin gene expression by oxygen in lungs of newborn primates

Peroxiredoxin (Prx) is an important antioxidant defense enzyme that reduces hydrogen peroxide to molecular oxygen by using reducing equivalents from thioredoxin. We report that lung Prx I messenger RNA (mRNA) is specifically upregulated by oxygen. Throughout the third trimester, mRNA for Prx I was expressed constitutively at low levels in fetal baboon lung. However, after premature birth (125 or 140 d gestation), lung Prx I mRNA increased rapidly with the onset of oxygen exposure. Premature animals (140 d) breathing 100% O(2) developed chronic lung disease within 7 to 14 d. These animals had greater lung Prx I mRNA after 1, 6, or 10 d of life than did fetal controls. In 140-d animals given lesser O(2) concentrations (as needed) that did not develop chronic lung disease, lung Prx I mRNA also was increased on Days 1 and 6, but not Day 10. In fetal distal lung explant culture, Prx I mRNA was elevated in 95% O(2), relative to 1% oxygen, and remained elevated at 24 h. Prx protein activity increased in 140-d premature baboons exposed to as-needed oxygen. By contrast, there was a decrease in Prx activity in 140-d premature baboons exposed to 100% oxygen. In the lung explants from prematures (140 d), there was no significant increase in Prx activity in response to 24 h exposure to hyperoxia, whereas exposure of explants to 48 h hyperoxia caused a nonsignificant decrease in Prx activity. Treatment of lung explants with actinomycin D inhibited Prx mRNA increases in 95% oxygen, indicating transcriptional regulation. In cellular signaling studies we demonstrated that protein kinase (PK) C activity increased when A549 cells were exposed to 95% oxygen, compared with 21% oxygen exposure. In lung explant cultures, specific PKC inhibitors calphostin C or GF109203X inhibited the increase in Prx I mRNA with 95% oxygen exposure, indicating PKC-mediated signaling. The acute increase in gene expression of Prx I in response to oxygen suggests an important role for this protein during the transition from relatively anaerobic fetal life to oxygen-breathing at birth.

Chronic ethanol consumption alters the glutathione/glutathione peroxidase-1 system and protein oxidation status in rat liver

BACKGROUND

Alcohol-induced liver damage is associated with oxidative stress, which might be linked to disturbances in liver antioxidant defense mechanisms. The effect of chronic ethanol consumption on the mitochondrial and cytosolic glutathione/glutathione peroxidase-1 (GSHPx-1) system and oxidative modification of proteins was therefore studied in the rat.

METHODS

Male Sprague-Dawley rats were fed liquid diets that provided 36% total calories as ethanol for at least 31 days. Pair-fed controls received isocaloric diets with ethanol calories substituted with maltose-dextrins. Mitochondrial and cytosolic fractions were prepared from livers and assayed for GSHPx-1 and glutathione reductase activities and total and oxidized concentrations of glutathione. Catalase activity was measured in the postmitochondrial supernatant. Levels of GSHPx-1, lactate dehydrogenase, and the beta subunit of the F1 portion of the ATP synthase protein were determined by western blot analysis. Concentrations of mitochondrial and cytosolic protein carbonyls were measured to assess ethanol-induced oxidation of proteins.

RESULTS

Chronic ethanol consumption significantly decreased cytosolic and mitochondrial GSHPx-1 activities by 40% and 30%, respectively. Levels of GSHPx-1 protein in cytosol were unaffected by ethanol feeding, whereas there was a small decrease in GSHPx-1 protein levels in mitochondria isolated from ethanol-fed rats. Glutathione reductase activities were increased in both intracellular compartments and catalase activity was increased as a consequence of ethanol exposure. Cytosolic total glutathione was mildly decreased, whereas ethanol feeding increased mitochondrial levels of total glutathione. Chronic ethanol feeding significantly increased both cytosolic and mitochondrial concentrations of protein carbonyls by 30% and 60%, respectively.

CONCLUSIONS

This study demonstrates that chronic ethanol-induced alterations in the glutathione/GSHPx-1 antioxidant system might promote oxidative modification of liver proteins, namely those of the mitochondrion, which could contribute to the adverse effects of ethanol on the liver.

Effect of obesity and troglitazone on expression of two glutathione peroxidases: cellular and extracellular types in serum, kidney and adipose tissue

To determine the effect of obesity on expression of cellular- (C-) and extracellular (EC-) glutathione peroxidase (GPX) in serum, kidney and adipose tissue, we measured GPX in serum, kidneys and adipose tissue of the obese Otsuka-Long-Evans-Tokushima Fatty (OLETF) rat and its lean counterpart (LETO). We also investigated the effect of troglitazone. Five each of OLETF and LETO rats were fed diet with or without 0.2% troglitazone for 10 days. Final body weight, kidney weight, blood glucose and serum tumor necrosis factor-alpha (TNF-alpha) level were higher in OLETF rats than in LETO rats. Serum and kidney GPX activities were higher, but adipose tissue GPX activity was lower, in OLETF rats than in LETO rats. Troglitazone treatment decreased adipose tissue GPX activity and abolished overproduction of TNF-alpha in OLETF rats. Immunoblot analysis, for the first time, revealed that both obesity and troglitazone suppressed the protein signals for C-GPX and EC-GPX in adipose tissue. Serum protein carbonyl groups were increased in OLETF rats and troglitazone completely blocked this increase. Increased serum GPX activity in obese rat was due to the increased secretion of EC-GPX from the kidney. Troglitazone protected against the enhanced oxidative stress induced by obesity independently of the serum GPX concentration.

Different generation of inhibitors against gallic acid-induced apoptosis produces different sensitivity to gallic acid

Gallic acid (3,4,5-trihydroxybenzoic acid), a naturally occurring plant phenol, showed selective cytotoxicity against tumor cells with higher sensitivity than normal cells such as hepatocytes and keratinocytes. To elucidate the difference in sensitivity between normal and tumor cells to gallic acid, we studied whether the inhibitor of gallic acid-induced apoptosis existed or not. A serum-free conditioned medium, prepared from high density rat primary cultured hepatocytes and cytoplasm of hepatocytes, prevented gallic acid-induced apoptosis. In contrast, hepatomas and hepatic cell lines such as dRLh-84, PLC/PRF/5, HLE, and HUH and two other kinds of tumor cell, HeLa and KB, scarcely generated such an inhibitor in either their conditioned medium or their cells. Biochemical characterization of the inhibitors revealed that the inhibitor in the hepatocyte conditioned medium was completely inactivated by heating at 65 degrees C for 10 min. Its molecular weight was estimated at 150-250 kDa by gel filtration column chromatography, indicating that the inhibitor may be a protein-like substance. These results suggest that the generation of a large amount of the inhibitor may endow hepatocytes with insensitivity to gallic acid. In conclusion, the difference in the amount of the inhibitors generated by hepatocytes and tumor cells should contribute to the underlying mechanism in the difference in sensitivity of cells to gallic acid.

Characterization of three isoforms of mammalian peroxiredoxin that reduce peroxides in the presence of thioredoxin

A peroxidase from yeast that reduces H2O2 with the use of electrons provided by thioredoxin (Trx) together with homologs from a wide variety of species constitute the peroxiredoxin (Prx) family of proteins. Twelve mammalian Prx members have been previously identified in association with various cellular functions apparently unrelated to peroxidase activity. These mammalian proteins have now been divided into three distinct types, Prx I, II, and III, on the basis of their deduced amino acid sequences and immunological reactivity. With the use of recombinant proteins, Prx I, II, and III have now been shown to possess peroxidase activity and to rely on Trx as a source of reducing equivalents. None of the three proteins exhibited peroxidase activity in the presence of glutaredoxin. All three enzymes showed similar kinetic properties: the Vmax was 6-13 micromol/min per mg at 37 degrees C, the Km for Trx was 3-6 microM, and the Km for H2O2 was < 20 microM. Immunoblot analysis of various rat tissues and cultured cells indicated that most cell types contain the three Prx isoforms, the sum of which amounts to approximately 1-10 microg per milligram of soluble protein. Prx I and II are cytosolic proteins, whereas Prx IlI is localized in mitochondria. These results suggest that, together with glutathione peroxidase and catalase, Prx enzymes likely play an important role in eliminating peroxides generated during metabolism as well as during stimulation of cell surface receptors.

Effect of peroxisome proliferator on extracellular glutathione peroxidase in rat

Glutathione peroxidase (GPX) activity measured using tert-butyl hydroperoxide as a substrate detects solely cellular/classical GPX (cGPX) in rat liver and kidney, and extracellular/plasma glutathione peroxidase (EC-GPX) in rat serum. To investigate the effect of peroxisome proliferator on EC-GPX, we measured activities of GPX and catalase in rat liver, kidney and serum, and then we performed immunoblot and Northern blot analyses in the kidney. Rats were fed on a diet containing either 2% (w/w) di-2-ethylhexyl phthalate (DEHP) or 0.25% (w/w) clofibrate for two or three weeks, respectively. Catalase activity was increased 1.4-fold (p < 0.001) in the treated liver, but not in the kidney. GPX activity was decreased to 59.2% (DEHP) and 70.4% (clofibrate) of the control (p < 0.001) in the serum but was unaltered in the liver and kidney. The immunoreactivity for EC-GPX was also significantly decreased in the DEHP-treated kidney compared with the control. The mRNA levels of EC-GPX and cGPX were unaltered. The immunostaining for 4-hydroxy-2-nonenal, a maker of lipid peroxide, was more intense in the treated kidney compared with the control. These results suggest that EC-GPX is post-transcriptionally decreased by peroxisome proliferator through the oxidative stress in the renal tubules. This may be a new deleterious effect of an endocrine disruptor DEHP.

Manganese superoxide dismutase in rat liver peroxisomes: biochemical and immunochemical evidence

By using highly purified peroxisomes from rat liver, we have shown that peroxisomes contain manganese superoxide dismutase (MnSOD) activity and a 23 kDa protein immunoreactive with antibodies against purified mitochondrial MnSOD. Immunocytochemical studies have also revealed immunoreaction (immunogold) with MnSOD antibodies in mitochondria and peroxisomes. Studies of the intraperoxisomal localization of MnSOD have shown that in peroxisomes MnSOD is a component of the peroxisomal limiting membranes and dense core. Furthermore, the MnSOD level in peroxisomes was modulated by oxidative stress conditions such as ischemia-reperfusion or the treatment with ciprofibrate, a peroxisomal proliferator. These findings suggest that MnSOD in peroxisomes may play an important role in the dismutation of superoxide generated on the peroxisomal membrane for keeping the delicate balance of the redox state.

Effect of selenium deficiency on cellular and extracellular glutathione peroxidases: immunochemical detection and mRNA analysis in rat kidney and serum

To determine the effect of selenium (Se) deficiency on expression of glutathione peroxidase (GSH-Px) 1 and 2, we measured GSH-Px activity in rat serum, liver and kidneys, serum immunoreactive GSH-Px 2, and the mRNAs of kidney GSH-Px 1 and 2. We purified rat GSH-Px 2 and raised polyclonal antibodies. Immunoreactive GSH-Px 2 was measured by rocket immunoelectrophoresis. GSH-Px 2 was purified 1470-fold with a specific activity of 250 units/mg. Immunoblotting detected only GSH-Px 2 in rat serum, and much less GSH-Px 2 than GSH-Px 1 in kidney. Immunoblot signal of kidney GSH-Px 1 and 2 decreased progressively in Se deficient rats. Serum GSH-Px activity in Se deficient rats at 1, 2, 3, and 4 weeks declined to 33, 20, 10, and 9% of the control, while the serum level of immunoreactive GSH-Px 2 was 58, 24, 15, and 10% of the control, suggesting the presence of an inactive protein at week 1. GSH-Px activity declined to 4 and 11% of the control in the liver and kidney at 4 weeks. The mRNAs of kidney GSH-Px 1 and 2 showed similar decreases, and were 24 and 23% of the control at 4 weeks. GSH-Px mRNA levels were better preserved than GSH-Px activity, suggesting that GSH-Px expression was regulated at both pre-translational and translational levels.

Mammalian peroxiredoxin isoforms can reduce hydrogen peroxide generated in response to growth factors and tumor necrosis factor-alpha

Mammalian tissues express three immunologically distinct peroxiredoxin (Prx) proteins (Prx I, II, and III), which are the products of distinct genes. With the use of recombinant proteins Prx I, II, and III, all have now been shown to possess peroxidase activity and to rely on Trx as a source of reducing equivalents for the reduction of H2O2. Prx I and II are cytosolic proteins, whereas Prx III is localized in mitochondria. Transient overexpression of Prx I or II in cultured cells showed that they were able to eliminate the intracellular H2O2 generated in response to growth factors. Moreover, the activation of nuclear factor kappaB (NFkappaB) induced by extracellularly added H2O2 or tumor necrosis factor-alpha was blocked by overproduction of Prx II. These results suggest that, together with glutathione peroxidase and catalase, Prx enzymes likely play an important role in eliminating peroxides generated during metabolism. In addition, Prx I and II might participate in the signaling cascades of growth factors and tumor necrosis factor-alpha by regulating the intracellular concentration of H2O2.

The Gpx1 gene encodes mitochondrial glutathione peroxidase in the mouse liver

Mitochondria have GPX and PHGPX activity. It has been an unsettled issue whether mitochondrial GPX is encoded by Gpx1. Unlike the Gpx4 gene which encodes PHGPX with alternative transcription and translation start sites determining the subcellular localization of PHGPX, the Gpx1 gene appears to have a single translation start site. Additionally, mitochondrial GPX has been shown to have different chromatographic and kinetic properties from the cytosolic GPX1. We studied mouse liver mitochondrial GPX activity in homozygous Gpx1-knockout mice. Mitochondria were enriched at the density of 1.10 g/ml in the Percoll gradients as shown by electron microscopy. The H2O2-reducing GPX activity in the highly enriched mitochondrial fraction of wild-type mouse liver is 2700 mU/mg which is about one-half of specific activity found in cytosol. There is less than 0.5% GPX activity in the cytosol and no GPX activity in the mitochondria of Gpx1-knockout mouse liver compared to the cytosol of wild-type mouse liver using H2O2 or cumene hydroperoxide as the substrate. The fact that the knockout mice express normal levels of plasma GPX as well as testis and liver PHGPX activity indicates that animals are not selenium-deficient. Based on these observations, we concluded that mitochondrial GPX is the product of the Gpx1 gene.

Methods for purification of glutathione peroxidase and related enzymes

The different preparative techniques and related analytical methods used for purification of glutathione peroxidase, glutathione transferase and glutathione reductase, described in papers published in the last ten years, have been reviewed in this article. Among the different purification techniques, chromatography has played a relevant role, being reported in all the papers reviewed, whereas other preparative techniques such as electrophoresis and isoelectric focusing were less employed and have been reported in only ca. 3% of cases. Frequently, several different chromatographic modes and several rechromatography steps have been employed. The use of at least three different chromatographic modes has been reported in 53% of total reviewed papers, whereas 41% of them employed two differents modes and in only 6% a single preparative chromatographic step was used. To evaluate losses and improve recovery, analytical methods for quantitation of protein and assay of enzymatic activity must be used in each purification step. Among these analytical techniques, gel electrophoresis, under denaturing conditions, has been widely used to assess purity of enzyme preparation. A discussion of the different activity assay methods used for these three enzymes is also presented in this article.

Ethanol-induced oxidative stress and enzymatic defenses in cultured fetal rat hepatocytes

Previously, we have documented an ethanol (E)-induced oxidative stress (OS) in cultured fetal rat hepatocytes (FRH). The cause of this is uncertain, but an inhibition of key antioxidant enzymes could be a/the factor. OS was also observed in fetal liver (FL) during in utero E exposure, but not in maternal liver, a difference that might be related to selectively lower enzymatic defenses in the fetus. Here, we record effects of E on activities of catalase (Cat), superoxide dismutase (Cu, Zn SOD and Mn SOD), glutathione peroxidase (GPX), and glutathione-S-transferase (GST) in FRH isolated from 20-day-old fetuses and exposed to E (2 mg/ml) for up to 24 h and we compare these to adult rat liver data. E treatment decreased fetal liver reduced glutathione (GSH) pools by 23% (p < 0.05) and increased malondialdehyde (MDA) by 14% (p < 0.05) within 24 h of E exposure. E caused an increase in fetal liver Cat by 18%, 32%, and 47% by 3, 6, and 24 h of E, respectively (p < 0.05). A 24-h E exposure increased Cu, Zn SOD by 22% (p < 0.05) and Mn SOD by 21% (p < 0.05). A 24 h E treatment increased GPX by 18% (p < 0.05) and GST by 17% (p < 0.05). Cat in whole FL was 26% of adult (p < 0.05) whereas Cu, Zn SOD and Mn SOD in whole FL were 12% and 11% of adult levels (p < 0.05). GPX and GST in FL were 11% and 28% of adult values (p < 0.05). It is concluded that in FRH, E-induced OS is not caused by impaired activities of these enzymes, but their low basal activities (vs. adult) may predispose the fetus to OS.

Immunolocalization of cellular glutathione peroxidase in adult rat lungs and quantitative analysis after postembedding immunogold labeling

To determine the distribution of cellular glutathione peroxidase in rat lungs, the tissues were stained immunohistochemically. Quantitative analysis was performed in certain cell types of alveolar linings, after the ultrathin sections were stained by a postembedding immunogold technique. Immunoblot analysis revealed that homogenates of rat liver, heart, and lungs all gave a single band. Under the light microscope, the following tissues were stained intensely: epithelial cells, smooth muscle cells and glands of bronchi and bronchioles, type II alveolar cells, and alveolar macrophages. Under immunoelectron microscopy, type II alveolar cells and macrophages were abundant in mitochondria. The mitochondria, nucleus, and cytoplasm of macrophages were labeled almost twice as densely as the respective compartments of type II alveolar cells. Within cell types, the mitochondria were labeled twice as densely as the nuclei. The other particles were less than half as densely labeled as the nuclei. The labeling was slightly less dense in the cytoplasm than in the nucleus. The present study revealed that glutathione peroxidase occurred predominantly in the epithelial linings and metabolically active sites in rat lungs. The tissues that were previously found to be rich in superoxide dismutases were also rich in glutathione peroxidase.

Immunohistochemical localization and quantitative analysis of cellular glutathione peroxidase in foetal and neonatal rat tissues: fluorescence microscopy image analysis

To quantitate the developmental changes in selenium-dependent cellular glutathione peroxidase during the perinatal period, tissue sections from foetal (day 12 to day 22) and neonatal (day 6) rats were stained immunohistochemically using specific polyclonal antiserum. The intensity of the staining was quantified by fluorescence microscopy image analysis. There was a general trend of enriched glutathione peroxidase in the epithelial linings and metabolically active sites. Significant fluorescence was detected in cardiomyocytes, hepatocytes, renal tubular epithelium, bronchiolar epithelium and intestinal epithelium at day 15. The intensity increased in a stepwise manner thereafter. The overall increase in the intensity of staining in the heart, liver, kidneys, lungs and intestine was 1.5-, 2.3-, 1.6-, 1.7- and 3.0-fold, respectively. The phase of most rapid increase occurred during the foetal period in the liver, intestine and heart. In the kidneys and lungs, glutathione peroxidase increased significantly during foetal life, and to a similar extent postnatally. These results suggest that the intracellular H2O2-scavenging system develops during the foetal period as an essential mechanism for living under atmospheric oxygen conditions. The late development observed in the kidneys and lungs is consistent with the relative biological immaturity of these organs in full-term neonates.