Measurement of superoxide radical and hydrogen peroxide production in isolated cells and subcellular organelles

Quantitative Factors Introduced in the Feasibility Analysis of Reactive Oxygen Species (ROS)-Sensitive Triggers

Reactive oxygen species (ROS) are critical for cellular signaling. Various pathophysiological conditions are also associated with elevated levels of ROS. Hence, ROS-sensitive triggers have been extensively used for selective payload delivery. Such applications are predicated on two key functions: (1) a sufficient magnitude of concentration difference for the interested ROS between normal tissue/cells and intended sites and (2) appropriate reaction kinetics to ensure a sufficient level of selectivity for payload release. Further, ROS refers to a group of species with varying reactivity, which should not be viewed as a uniform group. In this review, we critically analyze data on the concentrations of different ROS species under various pathophysiological conditions and examine how reaction kinetics affect the success of ROS-sensitive linker chemistry. Further, we discuss different ROS linker chemistry in the context of their applications in drug delivery and imaging. This review brings new insights into research in ROS-triggered delivery, highlights factors to consider in maximizing the chance for success and discusses pitfalls to avoid.

Aluminum promotes changes in rice root structure and ascorbate and glutathione metabolism

In acidic soil, aluminum (Al) ionizes into trivalent cation and becomes highly toxic to plants. Thus, the objectives of this work were (i) to evaluate the Al concentration and identify sites of Al toxicity and its effect on the structure on rice root tips and (ii) to elucidate the adjustments involved in the activities/contents of enzymes/compounds in the roots against Al. For this, two genotypes with contrasting Al tolerance were used. Our results showed that the root length of the tolerant genotype was not affected after Al exposure. We also observed that both the genotypes used strategies to avoid Al uptake, such as the overlap of P and Al in the tolerant genotype and the presence of border cells in the sensitive genotype, which proved inefficient. In the tolerant genotype, other external Al detoxification mechanisms may have contributed to the lower Al concentration in roots and lower fluorescence of the Al-lumogallion complex. Additionally, both genotypes present the activation of key enzymes to decrease oxidative stress, such as CAT, POX, APX, and DHAR, and a more reducing redox environment, mainly due to the increase in the AA/DHA ratio. However, higher total ascorbate, AA, total glutathione, and GSH contents associated with higher SOD, GPX, and GR activities contributed to the reduction of oxidative stress in the tolerant genotype after Al exposure. Furthermore, there was a strong association between the sensitive genotype to Al concentration, O2 •- content, and MDA amount; therefore, these traits can be used as sensitivity indicators in Al studies.

Hydrogen Peroxide Inducible JAK3 Covalent Inhibitor: Prodrug for the Treatment of RA with Enhanced Safety Profile

Selective inhibition of Janus kinases (JAKs) is an arising strategy in drug discovery. Covalent inhibitors targeting a unique cysteine in JAK3 exhibit ultraselectivity among JAK family members. However, safety and tissue specific concerns still remain. A prodrug of a known JAK3 covalent inhibitor sensitive to H₂O₂ was designed and synthesized and its therapeutic effect was evaluated in the CIA (collagen-induced arthritis) mice model of RA (rheumatoid arthritis). The prodrug strategy relied on the introduction of a hydrogen peroxide-sensitive borate trigger group to avoid random covalent binding to thiol functionalities in biomacromolecules. The results show that the prodrug can be activated and released under pathophysiological concentration of H₂O₂. In addition, the prodrug demonstrated stability to the physiological environment. In comparison to the parent compound, the prodrug showed a similar therapeutic effect in the CIA model but notably exhibited lower toxicity and a larger therapeutic window.

Sporadic activation of an oxidative stress-dependent NRF2-p53 signaling network in breast epithelial spheroids and premalignancies

Breast and mammary epithelial cells experience different local environments during tissue development and tumorigenesis. Microenvironmental heterogeneity gives rise to distinct cell regulatory states whose identity and importance are just beginning to be appreciated. Cellular states diversify when clonal three-dimensional (3D) spheroids are cultured in basement membrane, and one such state is associated with stress tolerance and poor response to anticancer therapeutics. Here, we found that this state was jointly coordinated by the NRF2 and p53 pathways, which were costabilized by spontaneous oxidative stress within 3D cultures. Inhibition of NRF2 or p53 individually disrupted some of the transcripts defining the regulatory state but did not yield a notable phenotype in nontransformed breast epithelial cells. In contrast, combined perturbation prevented 3D growth in an oxidative stress-dependent manner. By integrating systems models of NRF2 and p53 signaling in a single oxidative stress network, we recapitulated these observations and made predictions about oxidative stress profiles during 3D growth. NRF2 and p53 signaling were similarly coordinated in normal breast epithelial tissue and hormone-negative ductal carcinoma in situ lesions but were uncoupled in triple-negative breast cancer (TNBC), a subtype in which p53 is usually mutated. Using the integrated model, we correlated the extent of this uncoupling in TNBC cell lines with the importance of NRF2 in the 3D growth of these cell lines and their predicted handling of oxidative stress. Our results point to an oxidative stress tolerance network that is important for single cells during glandular development and the early stages of breast cancer.

Is arsenite more toxic than arsenate in plants?

In order to evaluate the differential absorption and toxicity of arsenate (As^V) and arsenite (As^III), Lemna valdiviana plants were grown in a nutrient solution and subjected to 0.0 (control); 0.5; 1.0; 1.5; 2.0; 3.0; 4.0; 5.0 and 7.5 mg L^-1 of As^III or As^V for three days. Exposure to both chemical forms resulted in As bioaccumulation, although As^III-grown plants showed higher As content in tissues. In As^V-grown plants, the relative growth rate (RGR) decreased to 50%, at a concentration of 4.0 mg L^-1, while for treatments with As^III, the same decrease was observed at 1.0 mg L^-1. The tolerance index decreased with increasing concentrations, with lower values for As^III. Plants treated with As^III showed increased superoxide anion levels, whilst higher levels of hydrogen peroxide were present in AsV-treated plants. Moreover, malondialdehyde (MDA) levels were higher for plants subjected to As^III when compared to As^V at lower concentrations. Concentrations of 1 mg L^-1 of As^III and 4 mg L^-1 of As^V showed equivalent MDA levels. Superoxide dismutase and catalase activities were increased at low concentrations and were inhibited at higher concentrations of As^III and As^V, whereas peroxidase activity was positively modulated by increased As^III or As^V concentrations. In conclusion, L. valdiviana plants took up and accumulated arsenic as As^III or As^V, demonstrating the potential for phytoremediation of this metalloid. Furthermore, As^III-exposed plants showed enhanced toxicity when compared to As^V, at the same applied concentration, although toxicity was more related to internal As concentrations, regardless of the chemical form applied.

Prodrug strategies for targeted therapy triggered by reactive oxygen species

Increased levels of reactive oxygen species (ROS) have been associated with numerous pathophysiological conditions including cancer and inflammation and the ROS stimulus constitutes a potential trigger for drug delivery strategies. Over the past decade, a number of ROS-sensitive functionalities have been identified with the purpose of introducing disease-targeting properties into small molecule drugs - a prodrug strategy that offers a promising approach for increasing the selectivity and efficacy of treatments. This review will provide an overview of the ROS-responsive prodrugs developed to date. A discussion on the current progress and limitations is provided along with a reflection on the unanswered questions that need to be addressed in order to advance this novel approach to the clinic.

Synthesis and Evaluation of Hydrogen Peroxide Sensitive Prodrugs of Methotrexate and Aminopterin for the Treatment of Rheumatoid Arthritis

A series of novel hydrogen peroxide sensitive prodrugs of methotrexate (MTX) and aminopterin (AMT) were synthesized and evaluated for therapeutic efficacy in mice with collagen induced arthritis (CIA) as a model of chronic rheumatoid arthritis (RA). The prodrug strategy selected is based on ROS-labile 4-methylphenylboronic acid promoieties linked to the drugs via a carbamate linkage or a direct C-N bond. Activation under pathophysiological concentrations of H₂O₂ proved to be effective, and prodrug candidates were selected in agreement with relevant in vitro physicochemical and pharmacokinetic assays. Selected candidates showed moderate to good solubility, high chemical and enzymatic stability, and therapeutic efficacy comparable to the parent drugs in the CIA model. Importantly, the prodrugs displayed the expected safer toxicity profile and increased therapeutic window compared to MTX and AMT while maintaining a comparable therapeutic efficacy, which is highly encouraging for future use in RA patients.

Human Mn-superoxide dismutase inactivation by peroxynitrite: a paradigm of metal-catalyzed tyrosine nitration in vitro and in vivo

Nitration of human MnSOD at active site Tyr34 represents a biologically-relevant oxidative post-translational modification that causes enzyme inactivation.

The Involvement of Nitric Oxide in Integration of Plant Physiological and Ultrastructural Adjustments in Response to Arsenic

High arsenic (As) concentrations are toxic to all the living organisms and the cellular response to this metalloid requires the involvement of cell signaling agents, such as nitric oxide (NO). The As toxicity and NO signaling were analyzed in Pistia stratiotes leaves. Plants were exposed to four treatments, for 24 h: control; SNP [sodium nitroprusside (NO donor); 0.1 mg L-1]; As (1.5 mg L-1) and As + SNP (1.5 and 0.1 mg L-1, respectively). The absorption of As increased the concentration of reactive oxygen species and triggered changes in the primary metabolism of the plants. While photosynthesis and photorespiration showed sharp decrease, the respiration process increased, probably due to chemical similarity between arsenate and phosphate, which compromised the energy status of the cell. These harmful effects were reflected in the cellular structure of P. stratiotes, leading to the disruption of the cells and a possible programmed cell death. The damages were attenuated by NO, which was able to integrate central plant physiological processes, with increases in non-photochemical quenching and respiration rates, while the photorespiration level decreased. The increase in respiratory rates was essential to achieve cellular homeostasis by the generation of carbon skeletons and metabolic energy to support processes involved in responses to stress, as well to maintaining the structure of organelles and prevent cell death. Overall, our results provide an integrated view of plant metabolism in response to As, focusing on the central role of NO as a signaling agent able to change the whole plant physiology.

Thioredoxin-1 Attenuates Ventricular and Mitochondrial Postischemic Dysfunction in the Stunned Myocardium of Transgenic Mice

AIM

We evaluated the effect of thioredoxin1 (Trx1) system on postischemic ventricular and mitochondrial dysfunction using transgenic mice overexpressing cardiac Trx1 and a dominant negative (DN-Trx1) mutant (C32S/C35S) of Trx1. Langendorff-perfused hearts were subjected to 15 min of ischemia followed by 30 min of reperfusion (R). We measured left ventricular developed pressure (LVDP, mmHg), left ventricular end diastolic pressure (LVEDP, mmHg), and t63 (relaxation index, msec). Mitochondrial respiration, SERCA2a, phospholamban (PLB), and phospholamban phosphorylation (p-PLB) Thr17 expression (Western blot) were also evaluated.

RESULTS

At 30 min of reperfusion, Trx1 improved contractile state (LVDP: Trx1: 57.4 ± 4.9 vs. Wt: 27.1 ± 6.3 and DN-Trx1: 29.2 ± 7.1, p < 0.05); decreased myocardial stiffness (LVEDP: Wt: 24.5 ± 4.8 vs. Trx1: 11.8 ± 2.9, p < 0.05); and improved the isovolumic relaxation (t63: Wt: 63.3 ± 3.2 vs. Trx1: 51.4 ± 1.9, p < 0.05). DN-Trx1 mice aggravated the myocardial stiffness and isovolumic relaxation. Only the expression of p-PLB Thr17 increased at 1.5 min R in Wt and DN-Trx1 groups. At 30 min of reperfusion, state 3 mitochondrial O2 consumption was impaired by 13% in Wt and by 33% in DN-Trx1. ADP/O ratios for Wt and DN-Trx1 decrease by 25% and 28%, respectively; whereas the Trx1 does not change after ischemia and reperfusion (I/R). Interestingly, baseline values of complex I activity were increased in Trx1 mice; they were 24% and 47% higher than in Wt and DN-Trx1 mice, respectively (p < 0.01).

INNOVATION AND CONCLUSION

These results strongly suggest that Trx1 ameliorates the myocardial effects of I/R by improving the free radical-mediated damage in cardiac and mitochondrial function, opening the possibility of new therapeutic strategies in coronary artery disease. Antioxid. Redox Signal. 25, 78-88.

Endothelial Cell Seeding onto Various Biomaterials Causes Superoxide-induced Cell Death

The seeding and/or in-growth of endothelial cells on a number of blood-contacting implants are a concern for both biomaterials and tissue engineering. While endothelialization has been viewed positively, owing to their ability to regulate both smooth muscle and blood, there is evidence which suggests that endothelial cells on a nonoptimized surface may be counterproductive. The present study describes the experimentation designed to elucidate the effect of culture substrate on intracellular superoxide (SO) levels, a marker for endothelial cell dysfunction. The adaptation of the use of dihydroethidium under physiologically relevant shearing conditions is also reported.

The present study describes a standardized method for the use of dihydroethidium as a marker for intracellular oxidative stress under physiologic shear. Levels of hydrogen peroxide (oxidative stress producing agent) are optimized to a minimum of 60 μM (under static conditions) to allow for the detection of SO within the free radical scavenging environment. A flow rate of 24.4 mL/min is applied and found to produce physiologically relevant shear stress (8.2 dynes/cm2) within the system under study. Dihydroethidium is a useful marker for assessing intracellular oxidative stress in studies that require shear.

Different effects of H2O2 treatment on cervical squamous carcinoma cells and adenocarcinoma cells

INTRODUCTION

This study aims to compare the antioxidant abilities of cervical squamous carcinoma cells and cervical adenocarcinoma cells and to study the related mechanisms.

MATERIAL AND METHODS

Cervical squamous carcinoma and adenocarcinoma cells were treated with H2O2. Cell proliferation was determined with the MTT assay. The reactive oxygen species (ROS) level was detected by the 2',7'-dichlorofluorescein-diacetate (DCFH-DA) method. The 5,5'-dithiobis-2-nitrobenzoic acid (DTNB) method was performed to measure intracellular concentrations of reduced glutathione (GSH) and oxidized glutathione (GSSG). The nitrite formation method, the molybdate colorimetric method, and the DTNB colorimetric method were used to determine activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), respectively.

RESULTS

Compared with untreated control cells, cell proliferation of cervical squamous carcinoma cells and cervical adenocarcinoma cells was significantly inhibited by H2O2 treatment (p < 0.05). Reactive oxygen species levels and GSSG levels were significantly increased (p < 0.01), whereas GSH levels were significantly decreased (p < 0.05 or 0.01) in both cells after H2O2 treatment. Thus the ratio of GSH/GSSG was significantly decreased by H2O2 treatment in both cells (p < 0.01). In addition, H2O2 treatment significantly increased activities of SOD, CAT, and GPx in both cells (p < 0.05 or 0.01). Furthermore, the above-mentioned changes induced by H2O2 treatment were more dramatic in cervical squamous carcinoma cells.

CONCLUSIONS

The antioxidant ability of cervical squamous carcinoma cells is lower than that of cervical adenocarcinoma cells, which may be related to the increased ROS levels in cervical squamous carcinoma cells induced by H2O2 treatments.

Diffused Intra-Oocyte Hydrogen Peroxide Activates Myeloperoxidase and Deteriorates Oocyte Quality

Hydrogen peroxide (H2O2) is a relatively long-lived signaling molecule that plays an essential role in oocyte maturation, implantation, as well as early embryonic development. Exposure to relatively high levels of H2O2 functions efficiently to accelerate oocyte aging and deteriorate oocyte quality. However, little precise information exists regarding intra-oocyte H2O2 concentrations, and its diffusion to the oocyte milieu. In this work, we utilized an L-shaped amperometric integrated H2O2-selective probe to directly and quantitatively measure the real-time intra-oocyte H2O2 concentration. This investigation provides an exact measurement of H2O2 in situ by reducing the possible loss of H2O2 caused by diffusion or reactivity with other biological systems. This experiment suggests that the intra-oocyte H2O2 levels of oocytes obtained from young animals are reasonably high and remained constant during the procedure measurements. However, the intra-oocyte H2O2 concentration dropped significantly (40-50% reduction) in response to catalase pre-incubation, suggesting that the measurements are truly H2O2 based. To further confirm the extracellular diffusion of H2O2, oocytes were incubated with myeloperoxidase (MPO), and the diffused H2O2 triggered MPO chlorinating activity. Our results show that the generated hypochlorous acid (HOCl) facilitated the deterioration in oocyte quality, a process that could be prevented by pre-incubating the oocytes with melatonin, which was experimentally proven to be oxidized utilizing HPLC methods. This study is the first to demonstrate direct quantitative measurement of intracellular H2O2, and its extracellular diffusion and activation of MPO as well as its impact on oocyte quality. These results may help in designing more accurate treatment plans in assisted reproduction under inflammatory conditions.

Sulfur metabolism: different tolerances of two aquatic macrophytes exposed to arsenic

The toxicity of arsenic (As) and the mechanisms of response to this pollutant were analyzed in two aquatic plant species, one sensitive and one tolerant to the pollutant, Salvinia minima and Lemna gibba, respectively. The plants, grown in nutrient solution at pH 6.5, were exposed to As concentrations of 0.0 and 1.0mgL(-1) for 3 days. Both species accumulated As in their tissues, which resulted in increases in H2O2 production. L. gibba accumulated eleven times more As than S. minima. However, L. gibba was more tolerant, as shown by the absence of cell membrane damage and, despite greater accumulation, smaller growth reduction than S. minima. Indeed, the index of tolerance to As was twenty percent higher in L. gibba than in S. minima, which most likely results from the presence of a more efficient defense system. This defense system in L. gibba is most likely based on sulfate absorption, assimilation and metabolism. L. gibba showed an increase in sulfate absorption and adenosine-5'-triphosphate (ATP) sulfurylase activity (the first enzyme of the inorganic sulfate assimilation pathway) following exposure to As. Consequently, the plant produced greater concentrations of sulfur-containing compounds that are involved in cellular detoxification, such as glutathione and non-protein thiols, and demonstrated greater enzymatic activity of γ-glutamylcysteine synthetase, glutathione S-transferase and glutathione reductase. Therefore, the plant׳s ability to increase absorption, assimilation and metabolism of sulfur are key steps for tolerance to oxidative stress triggered by metals.

Effects of adding nitroprusside on arsenic stressed response of Pistia stratiotes L. under hydroponic conditions

Effect of nitric oxide (NO) in mitigating stress induced by arsenic (As) was assessed in Pistia stratiotes, with NO supplied as sodium nitroprusside (SNP). Plants were exposed to four treatments: control, SNP (0.1 mg L(-1)), As (1.5 mg L(-1)), As + SNP (1.5 and 0.1 mg L(-1)), for seven days (analyses of growth, absorption of As and mineral nutrients) and for 24 h (analyses of concentration of reactive oxygen intermediates (ROIs), antioxidant capacity and photosynthesis). P. stratiotes accumulated high concentrations of As and this accumulation wasn't affected by the addition of SNP, but the tolerance index of the plant to As increased. SNP attenuated effects of As on the absorption of mineral nutrients (Ca, Fe, Mn, and Mg), but not for phosphorus, and maintained concentrations of ROIs to normal levels, probably due to the increase in antioxidant capacity. The As damaged the photosynthesis by the decrease in pigment contents and by disturbance the photochemical (loss of PSII efficiency and increases in non-photochemical quenching coefficient) and biochemical (reductions in carbon assimilation, increase in the C(i)/C(a) and phi(PSII)/phi(CO2) ratios) steps. The addition of SNP restored these parameters to normal levels. Thus, NO was able to increasing the resistance of P. stratiotes to As.

Cross-linking of thioredoxin reductase by the sulfur mustard analogue mechlorethamine (methylbis(2-chloroethyl)amine) in human lung epithelial cells and rat lung: selective inhibition of disulfide reduction but not redox cycling

Oxidative stress plays a key role in mechlorethamine (methylbis(2-chloroethyl)amine, HN2) toxicity. The thioredoxin system, consisting of thioredoxin reductase (TrxR), thioredoxin, and NADPH, is important in redox regulation and protection against oxidative stress. HN2 contains two electrophilic side chains that can react with nucleophilic sites in proteins, leading to changes in their structure and function. We report that HN2 inhibits the cytosolic (TrxR1) and mitochondrial (TrxR2) forms of TrxR in A549 lung epithelial cells. TrxR exists as homodimers under native conditions; monomers can be detected by denaturing and reducing SDS-PAGE followed by western blotting. HN2 treatment caused marked decreases in TrxR1 and TrxR2 monomers along with increases in dimers and oligomers under reducing conditions, indicating that HN2 cross-links TrxR. Cross-links were also observed in rat lung after HN2 treatment. Using purified TrxR1, NADPH reduced, but not oxidized, enzyme was inhibited and cross-linked by HN2. LC-MS/MS analysis of TrxR1 demonstrated that HN2 adducted cysteine- and selenocysteine-containing redox centers forming monoadducts, intramolecule and intermolecule cross-links, resulting in enzyme inhibition. HN2 cross-links two dimeric subunits through intermolecular binding to cysteine 59 in one subunit of the dimer and selenocysteine 498 in the other subunit, confirming the close proximity of the N- and C-terminal redox centers of adjacent subunits. Despite cross-linking and inhibition of TrxR activity by HN2, TrxR continued to mediate menadione redox cycling and generated reactive oxygen species. These data suggest that disruption of the thioredoxin system contributes to oxidative stress and tissue injury induced by HN2.

Peroxynitrite formation in nitric oxide-exposed submitochondrial particles: detection, oxidative damage and catalytic removal by Mn-porphyrins

Peroxynitrite (ONOO(-)) formation in mitochondria may be favored due to the constant supply of superoxide radical (O(2)(∙-)) by the electron transport chain plus the facile diffusion of nitric oxide ((∙)NO) to this organelle. Herein, a model system of submitochondrial particles (SMP) in the presence of succinate plus the respiratory inhibitor antimycin A (to increase O(2)(∙-) rates) and the (∙)NO-donor NOC-7 was studied to directly establish and quantitate peroxynitrite by a multiplicity of methods including chemiluminescence, fluorescence and immunochemical analysis. While all the tested probes revealed peroxynitrite at near stoichiometric levels with respect to its precursor radicals, coumarin boronic acid (a probe that directly reacts with peroxynitrite) had the more straightforward oxidation profile from O(2)(∙-)-forming SMP as a function of the (∙)NO flux. Interestingly, immunospintrapping studies verified protein radical generation in SMP by peroxynitrite. Substrate-supplemented SMP also reduced Mn(III)porphyrins (MnP) to Mn(II)P under physiologically-relevant oxygen levels (3-30 μM); then, Mn(II)P were capable to reduce peroxynitrite and protect SMP from the inhibition of complex I-dependent oxygen consumption and protein radical formation and nitration of membranes. The data directly support the formation of peroxynitrite in mitochondria and demonstrate that MnP can undergo a catalytic redox cycle to neutralize peroxynitrite-dependent mitochondrial oxidative damage.

The epinephrine assay for superoxide: why dopamine does not work

Superoxide oxidizes epinephrine to a semiquinone, initiating a series of reactions leading to the colored product adrenochrome. This popular assay for superoxide is more sensitive at higher pH, and it does not work if dopamine is used instead of epinephrine. A kinetic analysis shows that these effects can be explained by competing reactions that lower the yield of the observed product. The catecholamine quinone may cyclize to form the absorbing product, or it may be reduced back to the semiquinone by superoxide. For epinephrine, the quinone cyclizes quickly and adrenochrome formation dominates, but for dopamine, the quinone cyclizes slowly and the back reaction prevails. The yield of adrenochrome increases if the epinephrine semiquinone reacts with O(2) to form more superoxide, but this reaction competes with disproportionation of the semiquinone. Because disproportionation slows as pH increases, both superoxide formation and the yield of adrenochrome increase at higher pH.

Hypoxia-inducible factor 2alpha regulates expression of the mitochondrial aconitase chaperone protein frataxin

Mice lacking Epas1, encoding the transcription factor Hypoxia-inducible Factor 2alpha (HIF-2alpha), exhibit an apparent mitochondrial disease state. Similarities between knock-outs of Epas1 and of Sod2, encoding the mitochondrial antioxidant enzyme manganese superoxide dismutase, led to the identification of Sod2 as a HIF-2alpha target gene. However, Sod2 levels in Epas1(-)(/)(-) liver are intermediate between that of Sod(+)(/)(-) and Sod2(-)(/)(-) mice, which have subtle or severe phenotypes, respectively. This suggests that additional HIF-2alpha target genes besides Sod2 contribute to the Epas1(-)(/)(-) mitochondrial disease state. To define the nature of the mitochondrial defect in Epas1(-)(/)(-) liver, we performed biophysical, biochemical, and molecular studies. In the setting of decreased Sod2 levels and increased oxidative stress, we found reduced respiration, sensitized mitochondrial permeability transition pore opening, intact electron transport chain activities, and impaired mitochondrial aconitase activity. Mitochondrial aconitase protein levels were preserved, whereas mRNA and protein levels for frataxin, the oxidative stress-regulated mitochondrial aconitase chaperone protein, were markedly reduced in Epas1(-)(/)(-) livers. The mouse Fxn promoter was preferentially activated by HIF-2alpha through a consensus HIF-responsive enhancer element. In summary, the studies reveal that Fxn, like Sod2, is a nuclear-encoded, mitochondrial-localized HIF-2alpha target gene required for optimal mitochondrial homeostasis. These findings expand upon the previously defined role of HIF-2alpha in the cellular response to oxidative stress and identify a novel link of HIF-2alpha with mitochondrial homeostasis.

Up-regulation of alpha1-microglobulin by hemoglobin and reactive oxygen species in hepatoma and blood cell lines

alpha(1)-Microglobulin is a 26-kDa glycoprotein synthesized in the liver, secreted to the blood, and rapidly distributed to the extravascular compartment of all tissues. Recent results show that alpha(1)-microglobulin has heme-binding and heme-degrading properties and it has been suggested that the protein is involved in the defense against oxidation by heme and reactive oxygen species. In the present study the influence of hemoglobin and reactive oxygen species (ROS) on the cellular expression of alpha(1)-microglobulin was investigated. Oxy- and methemoglobin, free heme, and Fenton reaction-induced hydroxyl radicals induced a dose-dependent up-regulation of alpha(1)-microglobulin on both mRNA and protein levels in hepatoma cells and an increased secretion of alpha(1)-microglobulin. The up-regulation was reversed by the addition of catalase and ascorbate, and by reacting hemoglobin with cyanide which prevents redox reactions. Furthermore, the blood cell lines U937 and K562 expressed alpha(1)-microglobulin at low levels, and this expression increased up to 11-fold by the addition of hemoglobin. These results suggest that alpha(1)-microglobulin expression is induced by ROS, arising from redox reactions of hemoglobin or from other sources and are consistent with the hypothesis that alpha(1)-microglobulin participates in the defense against oxidation by hemoglobin, heme, and reactive oxygen species.

Use of spectroscopic probes for detection of reactive oxygen species

The detection and quantitation of reactive oxygen species (ROS) receives a great deal of interest because of their importance in a wide range of physiological and pathogenic events. Probe-assisted spectroscopy (electron spin resonance, spectrophotometry, fluorescence and luminescence) is the main tool for this application. This review discusses the properties of spectroscopic probes most commonly used for ROS detection and highlights their limitations in cellular systems. These include poor stability of some probes and/or products that may be subjected to cellular metabolism and lack of specificity in their reactions with oxidants or reductants. Additional problems often arise from undesired reactions of the probes and from their non-homogeneous distribution in the studied system, production of ROS by the probes themselves, perturbation of the systems under investigation by the probes, and artifacts due to the presence of ROS in the reaction medium. The limits imposed by these difficulties on the precise evaluation of the amounts and rates of formation of ROS are discussed critically.

Hydrogen peroxide: a signaling messenger

Hydrogen peroxide (H2O2) is a well-documented component of living cells. It plays important roles in host defense and oxidative biosynthetic reactions. In addition there is growing evidence that at low levels, H2O2 also functions as a signaling agent, particularly in higher organisms. This review evaluates the evidence that H2O2 functions as a signaling agent in higher organisms in light of the known biology and biochemistry of H2O2. All aerobic organisms studied to date from prokaryotes to humans appear to tightly regulate their intracellular H2O2 concentrations at relatively similar levels. Multiple biochemical strategies for rapidly reacting with these low endogenous levels of H2O2 have been elucidated from the study of peroxidases and catalases. Well-defined biochemical pathways involved in the response to exogenous H2O2 have been described in both prokaryotes and yeast. In animals and plants, regulated enzymatic systems for generating H2O2 have been described. In addition oxidation-dependent steps in signal transduction pathways are being uncovered, and evidence is accumulating regarding the nature of the specific reactive oxygen species involved in each of these pathways. Application of physiologic levels of H2O2 to mammalian cells has been shown to stimulate biological responses and to activate specific biochemical pathways in these cells.

Kinetic analysis of thapsigargin-induced thymocyte apoptosis

Thapsigargin addition to thymocytes increased cytosolic Ca2+ by a factor of 8.5 with a time for half maximal effect (t1/2) of 2.5 min. Calcium signaling increased mitocondrial and endoplasmic reticulum nitric oxide synthase (NOS) activities by five and six times, with t1/2 of 16 and 48 min, respectively, followed by increases of 140% in intracellular [H2O2], 73% in hydroperoxide content, and 250% in thiobarbituric reactive substance content, with t1/2 of 13, 27, and 30 min, respectively. Mitochondrial dysfunction followed, and was characterized by decreased respiratory control, membrane depolarization, and decrease cytochrome c content release, processes with t1/2 of 101, 129, and 133 min, respectively. Increased UDP-GT gene expression, observed by mRNA synthesis, and the enzymatic activity of this protein had t1/2 of 52 and 187 min, respectively. These events were followed by caspase-3 activation (t1/2 = 210 min) and DNA laddering (t1/2 = 260 min) at the completion of the cell death program. Preincubation of thymocytes with NOS inhibitors (NG-methyl-L-arginine and L-Nomega-nitro-L-arginine methylester) halted the whole process through inhibition of mitochondrial and endoplasmic reticulum NOS activities and of DNA laddering.

Role of oxidative modifications in atherosclerosis

This review focuses on the role of oxidative processes in atherosclerosis and its resultant cardiovascular events. There is now a consensus that atherosclerosis represents a state of heightened oxidative stress characterized by lipid and protein oxidation in the vascular wall. The oxidative modification hypothesis of atherosclerosis predicts that low-density lipoprotein (LDL) oxidation is an early event in atherosclerosis and that oxidized LDL contributes to atherogenesis. In support of this hypothesis, oxidized LDL can support foam cell formation in vitro, the lipid in human lesions is substantially oxidized, there is evidence for the presence of oxidized LDL in vivo, oxidized LDL has a number of potentially proatherogenic activities, and several structurally unrelated antioxidants inhibit atherosclerosis in animals. An emerging consensus also underscores the importance in vascular disease of oxidative events in addition to LDL oxidation. These include the production of reactive oxygen and nitrogen species by vascular cells, as well as oxidative modifications contributing to important clinical manifestations of coronary artery disease such as endothelial dysfunction and plaque disruption. Despite these abundant data however, fundamental problems remain with implicating oxidative modification as a (requisite) pathophysiologically important cause for atherosclerosis. These include the poor performance of antioxidant strategies in limiting either atherosclerosis or cardiovascular events from atherosclerosis, and observations in animals that suggest dissociation between atherosclerosis and lipoprotein oxidation. Indeed, it remains to be established that oxidative events are a cause rather than an injurious response to atherogenesis. In this context, inflammation needs to be considered as a primary process of atherosclerosis, and oxidative stress as a secondary event. To address this issue, we have proposed an "oxidative response to inflammation" model as a means of reconciling the response-to-injury and oxidative modification hypotheses of atherosclerosis.

Antioxidant defences and homeostasis of reactive oxygen species in different human mitochondrial DNA-depleted cell lines

Three pairs of parental (rho+) and established mitochondrial DNA depleted (rho0) cells, derived from bone, lung and muscle were used to verify the influence of the nuclear background and the lack of efficient mitochondrial respiratory chain on antioxidant defences and homeostasis of intracellular reactive oxygen species (ROS). Mitochondrial DNA depletion significantly lowered glutathione reductase activity, glutathione (GSH) content, and consistently altered the GSH2 : oxidized glutathione ratio in all of the rho0 cell lines, albeit to differing extents, indicating the most oxidized redox state in bone rho0 cells. Activity, as well as gene expression and protein content, of superoxide dismutase showed a decrease in bone and muscle rho0 cell lines but not in lung rho0 cells. GSH peroxidase activity was four times higher in all three rho0 cell lines in comparison to the parental rho+, suggesting that this may be a necessary adaptation for survival without a functional respiratory chain. Taken together, these data suggest that the lack of respiratory chain prompts the cells to reduce their need for antioxidant defences in a tissue-specific manner, exposing them to a major risk of oxidative injury. In fact bone-derived rho0 cells displayed the highest steady-state level of intracellular ROS (measured directly by 2',7'-dichlorofluorescin, or indirectly by aconitase activity) compared to all the other rho+ and rho0 cells, both in the presence or absence of glucose. Analysis of mitochondrial and cytosolic/iron regulatory protein-1 aconitase indicated that most ROS of bone rho0 cells originate from sources other than mitochondria.

Role of oxidative stress in intermittent hypoxia-induced immediate early gene activation in rat PC12 cells

Intermittent hypoxia (IH) occurs in many pathophysiological conditions. The molecular mechanisms associated with IH, however, have received little attention. Previous studies have reported that the c-fos gene via formation of activator protein-1 (AP-1) transcription factor contributes to adaptive responses to continuous hypoxia. In the present study, using a cell culture model we examined whether IH activates c-fos and AP-1 and if so, by what mechanisms. Experiments were performed on rat phaeochromocytoma cells exposed to 21% O(2) (normoxia) or 60 and 120 cycles of IH, each cycle consisting 15 s of hypoxia followed by 4 min of normoxia. IH resulted in a significant elevation of c-fos mRNA as well as transcriptional activation. IH was more potent and induced a longer lasting activation of c-fos than comparable cumulative duration of continuous hypoxia. IH increased AP-1 activity and tyrosine hydroxylase (TH) mRNA, an AP-1-regulated downstream gene, and these effects were prevented by antisense c-fos. Superoxide dismutase mimetic, a potent scavenger of superoxide anions, prevented IH-induced c-fos, AP-1 and TH activations. IH increased superoxide anion levels in mitochondria as evidenced by decreased aconitase enzyme activity and increased levels of hydrogen peroxide, a stable dismutated product of superoxide anions. Complex I of the mitochondrial electron transport chain was markedly inhibited in IH exposed cells. Pharmacological inhibitors of complex I mimicked the effects of IH during normoxia and occluded the effects of IH on c-fos activation, suggesting the involvement of the mitochondrial electron transport chain in the generation of superoxide anions during IH. These results suggest IH-induced c-fos-mediated transcriptional activation involves oxidative stress.

An assessment of proposed mechanisms for sensing hydrogen peroxide in mammalian systems

Despite much recent interest in the biochemistry of reactive oxygen species, the mechanisms by which hydrogen peroxide (H2O2) functions in mammalian cells remain poorly defined. Proposed mechanisms for sensing H2O2 in mammalian cells include inactivation of protein tyrosine phosphatases and dual specificity phosphatases as well as inactivation of peroxiredoxins. In this critical review, proteins proposed to serve as sensors for H2O2 in mammals will be compared to peroxidases, catalases, and the bacterial H2O2 sensor OxyR for their ability to react with H2O2, in the context of our current knowledge concerning the concentrations of H2O2 present in cells.

Multiple organ pathology, metabolic abnormalities and impaired homeostasis of reactive oxygen species in Epas1-/- mice

Hypoxia-inducible factor (HIF) transcription factors respond to multiple environmental stressors, including hypoxia and hypoglycemia. We report that mice lacking the HIF family member HIF-2alpha (encoded by Epas1) have a syndrome of multiple-organ pathology, biochemical abnormalities and altered gene expression patterns. Histological and ultrastructural analyses showed retinopathy, hepatic steatosis, cardiac hypertrophy, skeletal myopathy, hypocellular bone marrow, azoospermia and mitochondrial abnormalities in these mice. Serum and urine metabolite studies showed hypoglycemia, lactic acidosis, altered Krebs cycle function and dysregulated fatty acid oxidation. Biochemical assays showed enhanced generation of reactive oxygen species (ROS), whereas molecular analyses indicated reduced expression of genes encoding the primary antioxidant enzymes (AOEs). Transfection analyses showed that HIF-2alpha could efficiently transactivate the promoters of the primary AOEs. Prenatal or postnatal treatment of Epas1-/- mice with a superoxide dismutase (SOD) mimetic reversed several aspects of the null phenotype. We propose a rheostat role for HIF-2alpha that allows for the maintenance of ROS as well as mitochondrial homeostasis.

The role of hydrogen peroxide in endothelial proliferative responses

Hydrogen peroxide (H2O2) is a recently recognized second messenger regulating proliferation in mammalian cells. Endothelial cells possess NADPH oxidases, which produce the H202 precursor superoxide (.O2-) in response to receptor-mediated signaling. Multiple physiologic agents have been shown to stimulate endothelial cells to produce .O2-/H2O2, including growth factors, such as vascular endothelial growth factor and transforming growth factor-beta1, and alterations in biomechanical forces, such as shear stress and cyclic strain. Downstream effects of these stimuli can often be inhibited by scavenging H2O2. Low concentrations of H2O2 stimulate proliferation or enhanced survival in a wide variety of cell types. Also, low concentrations of H2O2 stimulate endothelial migration as well as tube formation in an in vitro model of angiogenesis. Although low concentrations of H2O2 have been shown to be involved in numerous signal transduction pathways and to independently stimulate mitogenesis, there has been little information presented on precisely how mammalian cells respond biochemically to these low concentrations of H2O2. Recently a functional proteomics approach has been utilized to identify proteins responsive to low concentrations of H2O2 in human endothelial cells.

Kidney mitochondrial nitric oxide synthase

Nitric oxide synthase activity was recognized in rat renal cortex mitochondria (mtNOS) with nitric oxide (NO) production rates of 0.14-0.78 nmol/min/mg of protein. Rat pretreatment with enalapril (30 mg/kg/day i.p., up to 15 days) increased NO production in kidney, liver, and heart mitochondria. In kidney, mtNOS activity and mtNOS protein, measured by western blot densitometry, were 5 and 2.3 times increased, respectively. Electron paramagnetic resonance analysis with the probe N-methyl-D-glucamine dithiocarbamate/FeSO(4) detected NO production in mitochondria isolated from enalapril-treated rats, but not in control untreated animals. Polyclonal antibodies anti-iNOS and anti-nNOS detected kidney mtNOS in western blots and inhibited mtNOS biochemical activity. The enzymatic activity of kidney mtNOS generates intramitochondrial NO concentrations that regulate mitochondrial functions: state 3 respiration was decreased by 12-28%, and state 4 hydrogen peroxide production was increased 12-35%.