Estrogen down-regulates uncoupling proteins and increases oxidative stress in breast cancer

Oxidative stress has been postulated as one of the mechanisms underlying the estrogen carcinogenic effect in breast cancer. Estrogens are known to increase mitochondrial-derived reactive oxygen species (ROS) by an unknown mechanism. Given that uncoupling proteins (UCPs) are key regulators of mitochondrial energy efficiency and ROS production, our aim was to check the presence and activity of UCPs in estrogen receptor (ER)-positive and ER-negative breast cancer cells and tumors, as well as their relation to oxidative stress. Estrogen (1 nM) induced higher oxidative stress in the ER-positive MCF-7 cell line, showing increased mitochondrial membrane potential, H₂O₂ levels, and DNA and protein damage compared to ER-negative MDA-MB-231 cells. All isoforms of uncoupling proteins were highly expressed in ER-positive breast cancer cells and tumors compared to negative ones. ROS production in mitochondria isolated from MCF-7 was increased by inhibition of UCPs with GDP, but not in mitochondria from MDA-MB-231. Estrogen treatment decreased uncoupling protein and catalase levels in MCF-7 and decreased GDP-dependent ROS production in isolated mitochondria. On the whole, these results suggest that estrogens, through an ER-dependent mechanism, may increase mitochondrial ROS production by repressing uncoupling proteins, which offers a new perspective on the understanding of why estrogens are a risk factor for breast cancer.     

Plant defenses against oxidative stress

Many reactive oxygen species such as ozone, singlet oxygen, hydroxyl radical, and organic oxyradicals have been implicated in damage to plant organs and biopolymers such as chloroplasts, cell membranes, proteins, and DNA. The principal defenses against these reactive molecules and free radicals in plants include detoxifying enzymes (catalase, superoxide dismutase, etc.) and also lower molecular weight secondary products with antioxidant activity. These latter compounds include a great variety of phenolic compounds, carotenoids, nitrogenous, and sulfur-containing materials. Some of the more important mechanisms of action of the secondary compounds will be discussed, with emphasis on the use of structural and kinetic data to identify the most effective antioxidants against peroxy radical-induced damage, which is perhaps the most important of the oxidative stresses present in the usual environment of plants. © 1995 Wiley-Liss, Inc.     

Bacterial defenses against oxidative stress

Bacteria treated with low doses of oxidants such as hydrogen peroxide adapt to subsequent high doses of these oxidants by inducing the expression of numerous genes. The study of these genes and the roles they play in defending bacteria against oxidative damage has given general insights into what oxidants are hazardous to cells, what cell constituents are damaged by oxidants, and how cells sense and respond to oxidative stress.     

Molecular and structural antioxidant defenses against oxidative stress in animals

In this review, it is our aim 1) to describe the high diversity in molecular and structural antioxidant defenses against oxidative stress in animals, 2) to extend the traditional concept of antioxidant to other structural and functional factors affecting the "whole" organism, 3) to incorporate, when supportable by evidence, mechanisms into models of life-history trade-offs and maternal/epigenetic inheritance, 4) to highlight the importance of studying the biochemical integration of redox systems, and 5) to discuss the link between maximum life span and antioxidant defenses. The traditional concept of antioxidant defenses emphasizes the importance of the chemical nature of molecules with antioxidant properties. Research in the past 20 years shows that animals have also evolved a high diversity in structural defenses that should be incorporated in research on antioxidant responses to reactive species. Although there is a high diversity in antioxidant defenses, many of them are evolutionary conserved across animal taxa. In particular, enzymatic defenses and heat shock response mediated by proteins show a low degree of variation. Importantly, activation of an antioxidant response may be also energetically and nutrient demanding. So knowledge of antioxidant mechanisms could allow us to identify and to quantify any underlying costs, which can help explain life-history trade-offs. Moreover, the study of inheritance mechanisms of antioxidant mechanisms has clear potential to evaluate the contribution of epigenetic mechanisms to stress response phenotype variation.     

The rheumatoid arthritis shared epitope increases cellular susceptibility to oxidative stress by antagonizing an adenosine-mediated anti-oxidative pathway

We have recently demonstrated that the rheumatoid arthritis (RA) shared epitope (SE) acts as a ligand that triggers nitric oxide (NO) signaling in opposite cells. Given the known pro-oxidative effect of NO and the proposed role of oxidative stress in the pathogenesis of RA, this study explores whether SE-triggered signaling can increase cellular oxidative stress. cAMP levels, adenylyl cyclase activity, and protein kinase A activity were measured using commercial kits. Generation of reactive oxygen species (ROS) was quantified using the fluorochrome dichlorofluorescein diacetate. Oxidative DNA damage was quantified using the single-cell electrophoresis technique. Here, we report that cells exposed to cell surface SE-positive HLA-DR (human leukocyte antigen-DR) molecules, to cell-free recombinant proteins genetically engineered to express the SE motif, or to SE-positive synthetic peptide showed diminished cAMP-dependent signaling, increased ROS levels, and higher vulnerability to oxidative DNA damage. Introduction of single amino acid substitutions into SE-positive peptides revealed a consensus five-amino acid sequence motif of Q/R-K/R-X-X-A that is necessary and sufficient for SE-triggered signaling. The pro-oxidative effect of the SE could be reversed by inhibiting NO production. We conclude that the SE acts as a signaling ligand that activates an NO-mediated pro-oxidative pathway. The potential contribution of this signaling aberration to RA pathogenesis is discussed.     

Re-aeration-induced oxidative stress and antioxidative defenses in hypoxically pretreated lupine roots

The level of free radicals and activities of antioxidative enzymes were examined in roots of lupine seedlings (Lupinus luteus L.) that were deprived of oxygen by subjecting them to root hypoxia for 48 and 72 h and then re-aerated for up to 24 h. Using electron paramagnetic resonance (EPR), we found that the exposure of previously hypoxically grown roots to air caused the increase in free radicals level, irrespective of duration of hypoxic pretreatment. Immediately after re-aeration the level of free radicals was two times higher than in aerated control. The EPR signal with the g-values at the maximum absorption of 2.0057 and 2.0040 implied that the paramagnetic radicals are derived from a quinone. Directly after re-aeration of hypoxically pretreated roots, the activity of superoxide dismutase (SOD, EC 1.15.1.1) increased to its highest value, followed by a decline below the initial level, whereas activities of catalase (CAT, EC 1.11.1.6) and peroxidase (POX, EC 1.11.1.7) were diminished or only slightly influenced during re-aeration. The electrophoretic patterns of the soluble extracts show 4 isozymes of SOD, 4 isozymes of POX and 1 isozyme of CAT. The level of H2O2 was enhanced or lowered by re-aeration, depending on the previous duration of hypoxia. At the onset of re-aeration products of lipid peroxidation were present at a three-fourth of the levels found in aerobic control. Their levels increased after prolonged exposure to air but remained lower than those in aerobic control even after 24 h of re-aeration. Re-admission of oxygen resulted in about 20% rise in oxygen uptake by root axes segments immediately after transfer of roots from hypoxia and the high uptake rates were observed over whole re-aeration period. Oxygen consumption by root tips was significantly reduced just after transfer from hypoxic conditions as compared to aerated control but after 24 h of re-aeration even approached the control level. The results are discussed in relation to the ability of lupine roots to cope with oxidative stress caused by re-aeration following hypoxic pretreatment.     

Dapsone induces oxidative stress and impairs antioxidant defenses in rat liver

Dapsone (DDS) is currently used in the treatment of leprosy, malaria and in infections with Pneumocystis jirovecii and Toxoplasma gondii in AIDS patients. Adverse effects of DDS involve methemoglobinemia and hemolysis and, to a lower extent, liver damage, though the mechanism is poorly characterized. We evaluated the effect of DDS administration to male and female rats (30 mg/kg body wt, twice a day, for 4 days) on liver oxidative stress through assessment of biliary output and liver content of reduced (GSH) and oxidized (GSSG) glutathione, lipid peroxidation, and expression/activities of the main antioxidant enzymes glutathione peroxidase, superoxide dismutase, catalase and glutathione S-transferase. The influence of DDS treatment on expression/activity of the main DDS phase-II-metabolizing system, UDP-glucuronosyltransferase (UGT), was additionally evaluated. The involvement of dapsone hydroxylamine (DDS-NHOH) generation in these processes was estimated by comparing the data in male and female rats since N-hydroxylation of DDS mainly occurs in males. Our studies revealed an increase in the GSSG/GSH biliary output ratio, a sensitive indicator of oxidative stress, and in lipid peroxidation, in male but not in female rats treated with DDS. The activity of all antioxidant enzymes was significantly impaired by DDS treatment also in male rats, whereas UGT activity was not affected in any sex. Taken together, the evidence indicates that DDS induces oxidative stress in rat liver and that N-hydroxylation of DDS was the likely mediator. Impairment in the activity of enzymatic antioxidant systems, also associated with DDS-NHOH formation, constituted a key aggravating factor.     

Resveratrol increases vascular oxidative stress resistance

Epidemiological studies suggest that Mediterranean diets rich in resveratrol are associated with reduced risk of coronary artery disease. However, the mechanisms by which resveratrol exerts its vasculoprotective effects are not completely understood. Because oxidative stress and endothelial cell injury play a critical role in vascular aging and atherogenesis, we evaluated whether resveratrol inhibits oxidative stress-induced endothelial apoptosis. We found that oxidized LDL and TNF-alpha elicited significant increases in caspase-3/7 activity in endothelial cells and cultured rat aortas, which were prevented by resveratrol pretreatment (10(-6)-10(-4) mol/l). The protective effect of resveratrol was attenuated by inhibition of glutathione peroxidase and heme oxygenase-1, suggesting a role for antioxidant systems in the antiapoptotic action of resveratrol. Indeed, resveratrol treatment protected cultured aortic segments and/or endothelial cells against increases in intracellular H(2)O(2) levels and H(2)O(2)-mediated apoptotic cell death induced by oxidative stressors (exogenous H(2)O(2), paraquat, and UV light). Resveratrol treatment also attenuated UV-induced DNA damage (comet assay). Resveratrol treatment upregulated the expression of glutathione peroxidase, catalase, and heme oxygenase-1 in cultured arteries, whereas it had no significant effect on the expression of SOD isoforms. Resveratrol also effectively scavenged H(2)O(2) in vitro. Thus resveratrol seems to increase vascular oxidative stress resistance by scavenging H(2)O(2) and preventing oxidative stress-induced endothelial cell death. We propose that the antioxidant and antiapoptotic effects of resveratrol, together with its previously described anti-inflammatory actions, are responsible, at least in part, for its cardioprotective effects.     

Magnesium deficiency increases oxidative stress in rats

Magnesium deficiency has been implicated in the development of atherosclerosis and late diabetic complications, diseases often associated with increased oxidative stress. Present study was carried out to examine the effect of magnesium deficiency on oxidative stress and total radical trapping antioxidant parameter (calculated) in rats and correlate it with the development of free radical mediated diseases. Male Wistar rats were divided into two groups and pair fed for six weeks with low magnesium diet (70 mg/kg) and control diet (990 mg/kg) prepared synthetically. Deionized water was given ad libitum. Low magnesium diet caused a significant decrease in plasma and red blood cell magnesium levels. A marked increase in plasma malondialdehyde and corresponding decrease in total radical trapping antioxidant parameters (calculated) were observed in the low magnesium diet group than control group. The level of plasma glucose increased moderately in the low magnesium diet group. Hypertriglyceridemia and significantly decreased plasma HDL (high density lipoprotein)-cholesterol levels were observed in the low magnesium diet group. The results clearly demonstrate that magnesium deficiency is associated with increased oxidative stress through reduction in plasma antioxidants and increased lipid peroxidation suggesting that the increased oxidative stress may be due to increased susceptibility of body organs to free radical injury.     

Plant aging increases oxidative stress in chloroplasts

Aging has received considerable attention in biomedicine, but little is known about the regulatory mechanisms responsible for the aging not associated with senescence in plants. This study provides new insights into the relationship between oxidative stress and plant aging, and points out chloroplasts as one of the target organelles of age-associated oxidative stress in plants. We simultaneously analyzed lipid oxidation, photosynthesis, chlorophyll content, de-epoxidation state of the xanthophyll cycle, and levels of chloroplastic antioxidant defenses such as beta-carotene and alpha-tocopherol in leaves of the same age in 1-, 3- and 7-year-old Cistus clusii Dunal plants growing under Mediterranean field conditions. Enhanced formation of malondialdehyde in leaves (2.7-fold) and chloroplasts (2.8-fold), decreased photosynthetic activity (25%), and lower chlorophyll (ca. 20%) and chloroplastic antioxidant defense levels (ca. 25%-85%) were observed in 7-year-old plants, when compared with 1- and 3-year-old plants. The differences observed, which were associated with plant aging, were only noticeable in mature nonsenescing plants (7-year-old plants). No differences were observed between pre-reproductive (1-year-old plants) and young plants (3-year-old plants). This study shows that from a certain age, oxidative stress increases progressively in chloroplasts as plants age, whereas photosynthesis is reduced. The results indicate that the oxidative stress associated with the aging in plants accumulates progressively in chloroplasts, and that the contribution of oxidative stress to aging increases as plants age.     

Ubiquitin-proteasome pathway and cellular responses to oxidative stress

The ubiquitin-proteasome pathway (UPP) is the primary cytosolic proteolytic machinery for the selective degradation of various forms of damaged proteins. Thus, the UPP is an important protein quality control mechanism. In the canonical UPP, both ubiquitin and the 26S proteasome are involved. Substrate proteins of the canonical UPP are first tagged by multiple ubiquitin molecules and then degraded by the 26S proteasome. However, in noncanonical UPP, proteins can be degraded by the 26S or the 20S proteasome without being ubiquitinated. It is clear that a proteasome is responsible for selective degradation of oxidized proteins, but the extent to which ubiquitination is involved in this process remains a subject of debate. Whereas many publications suggest that the 20S proteasome degrades oxidized proteins independent of ubiquitin, there is also solid evidence indicating that ubiquitin and ubiquitination are involved in degradation of some forms of oxidized proteins. A fully functional UPP is required for cells to cope with oxidative stress and the activity of the UPP is also modulated by cellular redox status. Mild or transient oxidative stress up-regulates the ubiquitination system and proteasome activity in cells and tissues and transiently enhances intracellular proteolysis. Severe or sustained oxidative stress impairs the function of the UPP and decreases intracellular proteolysis. Both the ubiquitin-conjugating enzymes and the proteasome can be inactivated by sustained oxidative stress, especially the 26S proteasome. Differential susceptibilities of the ubiquitin-conjugating enzymes and the 26S proteasome to oxidative damage lead to an accumulation of ubiquitin conjugates in cells in response to mild oxidative stress. Thus, increased levels of ubiquitin conjugates in cells seem to be an indicator of mild oxidative stress.     

Decreased SIRT3 in aged human mesenchymal stromal/stem cells increases cellular susceptibility to oxidative stress

Sirtuin3 (SIRT3) is an important member of the sirtuin family of protein deacetylases that is localized to mitochondria and linked to lifespan extension in organisms ranging from yeast to humans. As aged cells have less regenerative capacity and are more susceptible to oxidative stress, we investigated the effect of ageing on SIRT3 levels and its correlation with antioxidant enzyme activities. Here, we show that severe oxidative stress reduces SIRT3 levels in young human mesenchymal stromal/stem cells (hMSCs). Overexpression of SIRT3 improved hMSCs resistance to the detrimental effects of oxidative stress. By activating manganese superoxide dismutase (MnSOD) and catalase (CAT), SIRT3 protects hMSCs from apoptosis under stress. SIRT3 expression, levels of MnSOD and CAT, as well as cell survival showed little difference in old versus young hMSCs under normal growth conditions, whereas older cells had a significantly reduced capacity to withstand oxidative stress compared to their younger counterparts. Expression of the short 28 kD SIRT3 isoform was higher, while the long 44 kD isoform expression was lower in young myocardial tissues compared with older ones. These results suggest that the active short isoform of SIRT3 protects hMSCs from oxidative injury by increasing the expression and activity of antioxidant enzymes. The expression of this short isoform decreases in cardiac tissue during ageing, leading to a reduced capacity for the heart to withstand oxidative stress.     

L-malate reverses oxidative stress and antioxidative defenses in liver and heart of aged rats

The intracellular levels of antioxidant and free radical scavenging enzymes are gradually altered during the aging process. An age-dependent increase of oxidative stress occurring throughout the lifetime is hypothesized to be the major cause of aging. The current study examined the effects of L-malate on oxidative stress and antioxidative defenses in the liver and heart of aged rats. Sprague-Dawley male rats were randomly divided into four groups, each group consisting of 6 animals. Group Ia and Group IIa were young and aged control rats. Group Ib and Group IIb were young and aged rats treated with L-malate (210 mg/kg body weight per day). L-malate was orally administrated via intragastric canula for 30 days, then the rats were sacrificed and the liver and heart were removed to determine the oxidant production, lipid peroxidation and antioxidative defenses of young and aged rats. Dietary L-malate reduced the accumulation of reactive oxygen species (ROS) and significantly decreased the level of lipid peroxidation in the liver and heart of the aged rats. Accordingly, L-malate was found to enhance the antioxidative defense system with an increased activity of antioxidant enzymes, such as superoxide dismutase (SOD) and glutathione peroxidase (GPx) and increased glutathione (GSH) levels in the liver of aged rats, a phenomenon not observed in the heart of aged rats. Our data indicate that oxidative stress was reversed and the antioxidative defense system was strengthened by dietary supplementation with L-malate.     

Tolerance to oxidative stress is associated with both oxidative stress response and inherent growth in a fungal wheat pathogen

Reactive oxygen species are toxic byproducts of aerobic respiration that are also important in mediating a diversity of cellular functions. Reactive oxygen species form an important component of plant defenses to inhibit microbial pathogens during pathogen–plant interactions. Tolerance to oxidative stress is likely to make a significant contribution to the viability and pathogenicity of plant pathogens, but the complex network of oxidative stress responses hinders identification of the genes contributing to this trait. Here, we employed a forward genetic approach to investigate the genetic architecture of oxidative stress tolerance in the fungal wheat pathogen Zymoseptoria tritici. We used quantitative trait locus (QTL) mapping of growth and melanization under axenic conditions in two cross-populations to identify genomic regions associated with tolerance to oxidative stress. We found that QTLs associated with growth under oxidative stress as well as inherent growth can affect oxidative stress tolerance, and we identified two uncharacterized genes in a major QTL associated with this trait. Our data suggest that melanization does not affect tolerance to oxidative stress, which differs from what was found for animal pathogens. This study provides a whole-genome perspective on the genetic basis of oxidative stress tolerance in a plant pathogen.     

Maternal nicotine exposure increases oxidative stress in the offspring

Fetal and neonatal nicotine exposure causes β-cell apoptosis and loss of β-cell mass, but the underlying mechanisms are unknown. The goal of this study was to determine whether maternally derived nicotine can act via the pancreatic nicotinic acetylcholine receptor (nAChR) during fetal and neonatal development to induce oxidative stress in the pancreas. Female Wistar rats were given saline or nicotine (1 mg/kg/day) via subcutaneous injection for 2 weeks prior to mating until weaning (postnatal day 21). In male offspring, nAChR subunit mRNA expression was characterized in the developing pancreas and various oxidative stress markers were measured at weaning following saline and nicotine exposure. The nAChR subunits 2-4, 6, 7, and β2–β4 were present in the pancreas during development. Fetal and neonatal exposure to nicotine significantly increased pancreatic GPx-1 and MnSOD protein expression, as well as islet ROS production. Furthermore, protein carbonyl formation was higher in nicotine-exposed offspring relative to controls, particularly within the mitochondrial fraction. There was also a nonsignificant trend toward higher serum 8-isoPG levels. These data suggest that β-cell apoptosis in the fetal and neonatal pancreas may be the result of a direct effect of nicotine via its receptor and that this effect may be mediated through increased oxidative stress.