Evidence for free radical formation during the oxidation of 2'-7'-dichlorofluorescin to the fluorescent dye 2'-7'-dichlorofluorescein by horseradish peroxidase: possible implications for oxidative stress measurements

The roles of thiol-derived radicals in the use of 2',7'-dichlorodihydrofluorescein as a probe for oxidative stress

2',7'-Dichlorodihydrofluorescein (DCFH2) is one of the most widely used probes for detecting intracellular oxidative stress, but requires a catalyst to be oxidized by hydrogen peroxide or superoxide and reacts nonspecifically with oxidizing radicals. Thiyl radicals are produced when many radicals are "repaired" by thiols, but are oxidizing agents and thus potentially capable of oxidizing DCFH2. The aim of this study was to investigate the reactivity of thiol-derived radicals toward DCFH2 and its oxidized, fluorescent form 2',7'-dichlorofluorescein (DCF). Thiyl radicals derived from oxidation of glutathione (GSH) or cysteine (CysSH) oxidized DCFH2 with rate constants at pH 7.4 of approximately 4 or approximately 2x10(7) M(-1) s(-1), respectively. Both the rates of oxidation and the yields of DCF were pH-dependent. Glutathione-derived radicals interacted with DCF, resulting in the formation of DCFH* absorbing at 390 nm and loss of fluorescence; in contrast, cysteine-derived radicals did not cause any depletion of DCF fluorescence. We postulate that the observed apparent difference in reactivity between GS* and CysS* toward DCF is related to the formation of carbon-centered, reducing radicals from base-catalyzed isomerization of GS*. DCF formation from interaction of DCFH2 with GS* was inhibited by oxygen in a concentration-dependent manner over the physiological range. These data indicate that in applying DCFH2 to measure oxidizing radicals in biological systems, we have to consider not only the initial competition between thiols and DCFH2 for the oxidizing radicals, but also subsequent reactions of thiol-derived radicals, together with variables--including pH and oxygen concentration--which control thiyl radical chemistry.

Detection and measurement of reactive oxygen intermediates in mitochondria and cells

Reactive oxygen intermediates (ROIs) play a key role in a number of human diseases either by inducing cell death, cellular proliferation, or by acting as mediators in cellular signaling. Therefore, their measurement in vivo and in cell culture is desirable but technically difficult and often troublesome. To address some of the key methodological issues in examining the formation of ROI in cells and mitochondria, this chapter discusses the following: (a) the cellular sources of ROI and their enzymatic removal, (b) common methods used to determine cellular and mitochondrial ROI such as chemiluminescence, electron paramagnetic resonance spectroscopy, fluorescence, and enzymatic techniques, and (c) some common problems associated with these assays and the interpretation of data. We also provide some simple protocols for the estimation of ROI production in cells and mitochondria, and when measuring ROI in cells and mitochondria, we emphasize the need for thorough understanding of results obtained and their interpretation.

Reactive oxygen species and cellular oxygen sensing

Many organisms activate adaptive transcriptional programs to help them cope with decreased oxygen (O(2)) levels, or hypoxia, in their environment. These responses are triggered by various O(2) sensing systems in bacteria, yeast and metazoans. In metazoans, the hypoxia inducible factors (HIFs) mediate the adaptive transcriptional response to hypoxia by upregulating genes involved in maintaining bioenergetic homeostasis. The HIFs in turn are regulated by HIF-specific prolyl hydroxlase activity, which is sensitive to cellular O(2) levels and other factors such as tricarboxylic acid cycle metabolites and reactive oxygen species (ROS). Establishing a role for ROS in cellular oxygen sensing has been challenging since ROS are intrinsically unstable and difficult to measure. However, recent advances in fluorescence energy transfer resonance (FRET)-based methods for measuring ROS are alleviating some of the previous difficulties associated with dyes and luminescent chemicals. In addition, new genetic models have demonstrated that functional mitochondrial electron transport and associated ROS production during hypoxia are required for HIF stabilization in mammalian cells. Current efforts are directed at determining how ROS mediate prolyl hydroxylase activity and hypoxic HIF stabilization. Progress in understanding this process has been enhanced by the development of the FRET-based ROS probe, an vivo prolyl hydroxylase reporter and various genetic models harboring mutations in components of the mitochondrial electron transport chain.

Detection of Reactive Oxygen Species Induced by Radiation in Cells Using the Dichlorofluorescein Assay

The goal of this study was to determine the amount of reactive oxygen species (ROS) that arises inside cells irradiated in medium containing blood serum using the 2'7'-dichlorofluorescein (DCF) assay. DCF fluorescence in cells and medium was recorded on an MF44 Perkin Elmer fluorimeter, and fluorescence in cells only was recorded on a Partec flow-through cytometer. Human larynx tumor HEp-2 cells and lympholeukosis P388 cells were irradiated with X rays at a dose rate of 1.12 Gy/min. The factors (temperature, pH, serum concentration) affecting the oxidation of 2'7'-dichlorofluorescin (DCFH) to DCF were studied, and errors in the dichlorofluorescein assay of ROS were minimized. The amount of ROS registered by the DCF assay in cells was found to depend on the concentration of serum in the medium during irradiation. In the presence of 10% serum, radiation had no effect on the amount of detectable ROS. The effect of radiation on the formation of intracellular ROS was almost completely abolished if the irradiated medium was removed immediately after radiation exposure. The increase in the formation of ROS in cells irradiated in medium with a low serum content is due mainly to the radiolytic products of water that arise in medium and oxidize DCFH located in cells.

Positive correlation between peripheral blood granulocyte oxidative status and level of anxiety in mice

Oxidative stress is involved in many acute and chronic diseases including cancer, cardiovascular disorders and neurodegenerative diseases. We studied the relationship between the level of intracellular reactive oxygen species in peripheral granulocytes and the estimated anxiety level of mice using the behavioral light/dark choice test. Our results indicate a linear and significant relationship between the intracellular redox status of peripheral blood granulocytes and different parameters of anxiety-related behavior including latency time (R(2)=0.737, P<0.001), cumulative time spent in the lit box (R(2)=0.612, P<0.01) and number of entries into the lit box (R(2)=0.661, P<0.01). These results suggest a positive relationship between peripheral oxidative status and level of anxiety in mice.

Metal-enhanced Singlet Oxygen Generation: A Consequence of Plasmon Enhanced Triplet Yields

In this Rapid Communication, we report the first observation of Metal-Enhanced singlet oxygen generation (ME(1)O(2)). Rose Bengal in close proximity to Silver Island Films (SiFs) can generate more singlet oxygen, a three-fold increase observed, as compared to an identical glass control sample but containing no silver. The enhanced absorption of the photo-sensitizer, due to coupling to silver surface plasmons, facilitates enhanced singlet oxygen generation. The singlet oxygen yield can potentially be adjusted by modifying the choice of MEF (Metal-Enhanced Fluorescence) & MEP (Metal Enhance Phosphorescence) parameters, such as distance dependence for plasmon coupling and wavelength emission of the coupling fluorophore. This is a most helpful observation in understanding the interactions between plasmons and lumophores, and this approach may well be of significance for singlet oxygen based clinical therapy.

Evaluation of the probe dihydrocalcein acetoxymethylester as an indicator of reactive oxygen species formation and comparison with oxidative DNA base modification determined by modified alkaline elution technique

Reactive oxygen species (ROS) play a predominant role in various diseases and the development of fast and easy methods for the quantification of intracellular ROS represents an important goal. Therefore, the aim of the present study was the evaluation of the fluorogenic probe dihydrocalcein acetoxymethylester (AM) for the detection of intracellular ROS. A flow cytometric method was developed using MCF-7 cells and the kinetics of ester hydrolysis and the cellular distribution and stability of calcein were characterized using calcein AM. Then, MCF-7 cells were challenged with model agents for the generation of singlet oxygen (illumination with visible light), peroxyl and hydroxyl radicals (tert-butylhydroperoxide, tBHP), superoxide anion radicals (potassium dioxide), and the intracellular formation of superoxide anion radicals by redox cycling (menadione) and the formation of calcein was compared with the induction of oxidative DNA base modifications assessed by modified alkaline elution technique. Every model agent significantly induced formamidopyrimidine-DNA glycosylase-sensitive sites (i.e. oxidative DNA base modifications) and most also induced DNA strand breaks. In contrast, exclusively tBHP and illumination with visible light induced the intracellular formation of calcein. In conclusion, though intracellular oxidation of dihydrocalcein represents a fast screening method, it detects a limited spectrum of ROS.

Antioxidative and oxidative changes in the digestive gland cells of freshwater mussels Unio tumidus caused by selected phenolic compounds in the presence of H2O2 or Cu2+ ions

Research on biomarkers as early bioindicators of perturbation in populations and individuals has received increasing interest during recent decades. These ecotoxicity studies allow us to measure the impact of environmental stressors and to monitor and evaluate the degradation or restoration of systems. In the present study we used bivalve molluscs (mussels), which are sensitive biomarkers of aquatic ecosystem pollution, to assess the effects of three polyphenols: tannic acid, ellagic acid and gallic acid. These compounds were used in the 1-60 microM concentration range, alone and in the presence of H(2)O(2) (40 and 100 microM) or Cu(2+) ions (50 microM). The fluorescence probe dichlorofluorescein-diacetate (DCFH-DA) was used to measure reactive oxygen species (ROS). The oxidation of DCFH-DA to the fluorescent DCF (dichlorofluorescein) by the phenolic compounds was investigated spectrofluorimetrically. The results showed that the polyphenols tested can act as antioxidants against the ROS present in the digestive gland cells, but their activity is decreased after incubation with hydrogen peroxide or copper ions. SH-groups were determined spectrophotometrically using Ellman's reagent. The results showed that oxidative modification of proteins increased in a concentration-dependent manner in cells incubated with polyphenols (above 15 microM) alone. Incubation of the cells with phenolic acids and H(2)O(2) or Cu(2+) ions revealed that the phenolic acids had prooxidant properties in all concentrations used except for 1 microM tannic and ellagic acid and 40 microM H(2)O(2). DNA fragmentation was estimated by a fluorescence method using Hoechst 33258/propidium iodine binding. The data showed that the phenolic acids alone and in the presence of hydrogen peroxide or copper ions can induce apoptosis and necrosis. The methods used and results obtained indicate that the polyphenols selected can act not only as antioxidants but also as prooxidants in digestive gland cells of Unio tumidus.

Detection of reactive oxygen species and nitric oxide in vascular cells and tissues: comparison of sensitivity and specificity

Reactive oxygen and nitrogen species are thought to contribute to pathogenesis of many cardiovascular diseases including hypertension, atherosclerosis, restenosis, heart failure, and diabetic vascular complications. Some of these reactive oxygen species also play an important role in vascular signaling. In this chapter, we describe various techniques that we have successfully employed to reliably measure superoxide and hydrogen peroxide. Because reactive oxygen species are capable of rapidly inactivating nitric oxide and because endothelial function characterized by nitric oxide bioavailability is an important indicator of vascular health, we have also included novel techniques capable of directly measuring nitric oxide radical from vascular cells and tissues.

An investigation into copper catalyzed D-penicillamine oxidation and subsequent hydrogen peroxide generation

D-Penicillamine is a potent copper (Cu) chelating agent. D-Pen reduces Cu(II) to Cu(I) in the process of chelation while at the same time being oxidized to D-penicillamine disulfide. It has been proposed that hydrogen peroxide is generated during this process. However, definitive experimental proof that hydrogen peroxide is generated remains lacking. Thus, the major aims of these studies were to confirm and quantitatively assess the in vitro production of hydrogen peroxide during copper catalyzed D-penicillamine oxidation. The potential cytotoxic effect of hydrogen peroxide generation was also investigated in vitro against MCF-7 human breast cancer cells. Cell cytotoxicity resulting from the incubation of D-penicillamine with copper was compared to that of D-penicillamine, copper and hydrogen peroxide. The mechanism of copper catalyzed D-penicillamine oxidation and simultaneous hydrogen peroxide production was investigated as a function of time, concentration of cupric sulfate or ferric chloride, temperature, pH, anaerobic condition and chelators such as ethylenediaminetetraacetic acid and bathocuproinedisulfonic acid. A simple, sensitive and rapid HPLC assay was developed to simultaneously detect D-penicillamine, its major oxidation product D-penicillamine disulfide, and hydrogen peroxide in a single run. Hydrogen peroxide was shown to be generated in a concentration dependent manner as a result of D-penicillamine oxidation in the presence of cupric sulfate. Chelators such as ethylenediaminetetraacetic acid and bathocuproinedisulfonic acid were able to inhibit D-penicillamine oxidation. The incubation of MCF-7 human breast cancer cells with D-penicillamine plus cupric sulfate resulted in the production of reactive oxygen species within the cell and cytotoxicity that was comparable to free hydrogen peroxide.

Mitochondrial reactive oxygen species and nitric oxide-mediated cancer cell apoptosis in 2-butylamino-2-demethoxyhypocrellin B photodynamic treatment

Photodynamic therapy (PDT) is a novel and promising cancer treatment which employs a combination of a photosensitizing chemical and visible light to induce apoptosis in cancer cells. Singlet oxygen has been recognized as the main origin of oxidative stress in PDT. However, the precise mechanism of PDT-induced apoptosis is not well characterized, especially the dualistic role of nitric oxide (NO). To dissect the apoptosis pathways triggered by PDT, the intracellular free radicals in MCF-7 cells were investigated by examining a novel photosensitizer 2-butylamino-2-demethoxyhypocrellin B (2-BA-2-DMHB)-mediated PDT. It was found that exposure of the cells to 2-BA-2-DMHB and irradiation resulted in a significant increase of intracellular ROS in minutes, and then followed by cytoplasmic free calcium enhancement, mitochondrial nitric oxide synthase (mtNOS) activation, cytochrome c release, and apoptotic death. Scavengers of singlet oxygen or NO could attenuate PDT-induced cell viability loss, nucleus morphology changes, cytochrome c release, mitochondria swelling, and apo-apoptosis gene p53 and p21 mRNA levels. The results suggested that both ROS and NO played important roles in the apoptosis-induced by PDT.

Biomarkers of oxidative stress in critically ill patients: what should be measured, when and how?

PURPOSE OF REVIEW

This review is dedicated to updating the knowledge on oxidative stress in critically ill patients with an intense inflammatory reaction, and to link it with recent findings supporting the possible involvement of oxidative injuries in systems and organs that frequently fail in the critically ill.

RECENT FINDINGS

Some direct or indirect biomarkers of oxidative stress have been validated in critically ill patients, and further support the major role of oxidative stress in these conditions.

SUMMARY

The assessment of oxidative stress, defined as the association between an increased production of oxygen-derived species and an exhaustion of the stores of antioxidants, requires a multimodal approach. Oxidative damage itself can be much better estimated by quantifying the oxidative byproducts of the lipids and proteins associated with an evaluation of the remaining stores of the corresponding functional antioxidants, or the activity of antioxidant enzymes, than by global tests of the total oxidative damage or the total antioxidant stores. Recent clinical data confirm an important role of increased oxidative stress in the acute dysfunctions of the respiratory, renal and cerebral systems.

The mechanism of flow-induced dilation in human adipose arterioles involves hydrogen peroxide during CAD

Flow-induced dilation (FID) is an important physiological stimulus that regulates tissue blood flow and is mediated by endothelium-derived factors that play a role in vascular integrity and the development of atherosclerosis. In coronary artery disease (CAD), conduit artery FID is impaired. The purpose of this study was to determine the mechanism of FID in human visceral adipose and examine whether the presence of conduit coronary atherosclerosis is associated with altered endothelial function in visceral fat. FID was determined in isolated visceral fat arterioles from patients with and without CAD. After constriction with endothelin-1, increases in flow produced an endothelium-dependent vasodilation that was sensitive to N(omega)-nitro-l-arginine methyl ester (l-NAME) in visceral fat arterioles from patients without CAD. In contrast, l-NAME alone or in combination with indomethacin had no effect on FID in similarly located arterioles from patients with CAD. Flow increased dichlorofluorescein (DCF) and dihydroethidium fluorescence accumulation in arterioles from patients with CAD versus without, indicative of the production of oxidative metabolites and superoxide, respectively. Both the dilation and DCF fluorescence to flow were reduced in the presence of the H(2)O(2) scavenger polyethylene glycol-catalase. Exogenous H(2)O(2) elicited similar relaxations of arterioles from patients in both groups. These data indicate that FID in visceral fat arterioles is nitric oxide dependent in the absence of known CAD. However, in the presence of CAD, H(2)O(2) replaces nitric oxide as the mediator of endothelium-dependent FID. This study provides evidence that adverse microvascular changes during CAD are evident in human visceral adipose, a tissue associated with CAD.

The antioxidant role of a reagent, 2',7'-dichlorodihydrofluorescin diacetate, detecting reactive-oxygen species and blocking the induction of heme oxygenase-1 and preventing cytotoxicity

Heme oxygenase-1 (HO-1) degrades heme into biliverdin, iron and CO. The enzyme participates in adaptive and protective responses to oxidative stress and various inflammatory stimuli, and is induced in response to reactive oxygen species (ROS). 2',7'-Dichlorodihydrofluorescin diacetate (DCFH-DA) is a common reagent used to detect ROS by the oxidation of 2',7'-dichlorodihydrofluorescin (DCFH) to fluorescent dichlorodihydrofluorescein. We previously found that rapid oxidation of DCFH occurred with heme-compounds as well as ROS [Ohashi, T. et al. (2002) FEBS Lett. 511, 21-27], and then examined the effect of DCFH-DA on the induction of HO-1 expression by arsenite, cadmium and hemin, which induce oxidative stress and cytotoxicity. We found suppression of the arsenite-, cadmium- and hemin-dependent induction of HO-1 with DCFH-DA. The suppression occurred at the transcriptional level since the promoter activity of the Maf-recognition site of the HO-1 gene decreased with the DCFH-DA treatment. DCFH abolished the phosphorylation of extracellular signal-regulated kinase, the nuclear translocation of a transcriptional activator Nrf2, and cell death. An antioxidant, N-acetylcysteine (NAC), also suppressed the induction by arsenite and cadmium, but not that by hemin, indicating that DCFH blocked a different site in the stress signal pathway from NAC. Considering that the oxidation of DCFH diminishes ROS generated by various stressors, our findings provide a potential strategy for protection of cells from toxic insults using DCFH-like molecules.

Response of mitochondrial reactive oxygen species generation to steady-state oxygen tension: implications for hypoxic cell signaling

Mitochondria are proposed to play an important role in hypoxic cell signaling. One currently accepted signaling paradigm is that the mitochondrial generation of reactive oxygen species (ROS) increases in hypoxia. This is paradoxical, because oxygen is a substrate for ROS generation. Although the response of isolated mitochondrial ROS generation to [O(2)] has been examined previously, such investigations did not apply rigorous control over [O(2)] within the hypoxic signaling range. With the use of open-flow respirometry and fluorimetry, the current study determined the response of isolated rat liver mitochondrial ROS generation to defined steady-state [O(2)] as low as 0.1 microM. In mitochondria respiring under state 4 (quiescent) or state 3 (ATP turnover) conditions, decreased ROS generation was always observed at low [O(2)]. It is concluded that the biochemical mechanism to facilitate increased ROS generation in response to hypoxia in cells is not intrinsic to the mitochondrial respiratory chain alone but may involve other factors. The implications for hypoxic cell signaling are discussed.

Reactive oxygen species in the control of hypoxia-inducible factor-mediated gene expression

Reactive oxygen species (ROS) have long been considered as cytotoxic. However, recent evidence indicates a prominent role of ROS as signaling molecules in the response to hormones, growth and coagulation factors, cytokines and other factors as well as to changes in oxygen tension. The hypoxia-inducible transcription factors (HIFs) are key players in the cellular response to changes in oxygen tension. Recently, HIFs have also been shown to respond to the above-mentioned non-hypoxic stimuli. In this article, the role of ROS in the regulation of HIF-1 under hypoxic and non-hypoxic conditions is summarized.

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.

Recent advances in fluorescent probes for the detection of reactive oxygen species

Reactive oxygen species (ROS) have captured the interest of many researchers in the chemical, biological, and medical fields since they are thought to be associated with various pathological conditions. Fluorescent probes for the detection of ROS are promising tools with which to enhance our understanding of the physiological roles of ROS, because they provide spatial and temporal information about target biomolecules in in vivo cellular systems. ROS probes, designed to detect specific ROS with a high selectivity, would be desirable, since it is now becoming clear that each ROS has its own unique physiological activity. However, dihydro-compounds such as 2',7'-dichlorodihydrofluorescein (DCFH), which have traditionally been used for detecting ROS, tend to react with a wide variety of ROS and are not completely photostable. Some attractive fluorescent probes that exhibit a high degree of selectivity toward specific ROS have recently been reported, and these selective probes are expected to have great potential for elucidating unknown physiological mechanisms associated with their target ROS. This review focuses on the design, detection mechanism, and performance of fluorescent probes for the detection of singlet oxygen ((1)O(2)), hydrogen peroxide (H(2)O(2)), hydroxyl radicals ((.)OH), or superoxide anion (O(2) (-.)), a field in which remarkable progress has been achieved in the last few years.

The oxidation of 2',7'-dichlorofluorescin to reactive oxygen species: a self-fulfilling prophesy?

The oxidation of 2',7'-dichlorofluorescin (DCFH) and its diacetate form (DCFHDA) by the HRP/peroxynitrite system was investigated. Both DCFH and DCFHDA were oxidized to fluorescent products. A major anomaly, however, was the observation that fluorescence continued to build up long after peroxynitrite total decomposition and the initial HRP compound I reduction, suggesting the production of oxidants by the system. Indeed, preformed HRP compound I was instantly reduced by DCFH and DCFHDA to compound II with the obligate formation of DCF(-) semiquinone and DCFHDA-derived radicals. Catalase strongly inhibited fluorescence and EPR signals, suggesting the intermediate formation of H2O2. Taken together the data indicate that peroxynitrite rapidly oxidizes HRP to HRP compound I, which is reduced by DCFH and its diacetate form with the concomitant formation of DCF(-) semiquinone and DCFHDA-derived radicals. These are oxidized by O2, producing O2(-) (as demonstrated by EPR and oxygen consumption experiments), which dismutates to produce H2O2, which serves to fuel further DCFH/DCFHDA oxidation via HRP catalysis. Also DCFHDA was shown to be considerably more resistant to oxidation than its hydrolyzed product DCFH, presumably because of the absence of the easily oxidizable phenol moieties. DCFHDA/DCFH have been used to study free radical production in a variety of systems. Our findings demonstrate that this assay is subject to a serious artifact in that it produces what it is purported to measure; therefore, its use in biological systems should be approached with caution.

Prooxidant reactions promoted by soluble and cell-bound gamma-glutamyltransferase activity

Recent studies have provided evidence for the prooxidant roles played by molecular species originating during the catabolism of glutathione (GSH) effected by gamma-glutamyltransferase (GGT), an enzyme normally present in serum and on the outer surface of numerous cell types. The reduction of metal ions by GSH catabolites is capable of inducing the redox cycling processes, leading to the production of reactive oxygen species and other free radicals. Through the action of these reactive compounds, cell membrane GGT activity can ultimately produce oxidative modifications on a variety of molecular targets, involving oxidation and/or S-thiolation of protein thiol groups in the first place. This chapter is a survey of the procedures most suitable to reveal GGT-dependent prooxidant reactions and their effects at the cellular and extracellular level, including methods in histochemistry, cytochemistry, and biochemistry, with special reference to methods for the evaluation of protein thiol redox status.

Free radical generation during chemical depolymerization of heparin

Low-molecular weight heparins (LMWHs), as compared with unfractionated heparin (UFH), present superior bioavailability, much longer plasma half-life, and lower incidence of side effects. For these reasons, over the past two decades LMWHs have become the drugs of choice for the treatment of deep venous thrombosis, pulmonary embolism, arterial thrombosis, and unstable angina. Furthermore, their use in acute ischemic stroke is currently under study. LMWHs are obtained by UFH depolymerization, which can be performed using various methods, including nitrous acid depolymerization, cleavage by beta-elimination of benzyl ester, enzymatic depolymerization, and peroxyl radical-dependent depolymerization. This article addresses the chemical depolymerization, obtained by free radical attack (mainly hydroxyl radical), of heparin. The electron spin resonance (ESR) spectroscopy, coupled to the spin trapping technique, was employed to study this reaction. Free radical-mediated heparin depolymerization was performed under different chemical conditions. The final products of the reactions were purified and classified on the basis of their molecular weight and other characteristics. The level of heparin fragmentation was different depending on the type of depolymerization reaction used. Moreover, the level of reproducibility and the resulting radical species were different for every type of reaction performed.

Cadmium effects on ros production and DNA damage via adrenergic receptors stimulation: role of Na+/H+ exchanger and PKC

The objective of the present study was to elucidate the events that are involved in reactive oxygen species (ROS) production and DNA damage after adrenergic receptors stimulation by cadmium, in relation to cAMP, protein kinase C (PKC) and Na+/H+ exchanger (NHE). Cadmium (50 microM) caused increased levels of ROS with a concomitant increase in DNA damage in digestive gland of Mytilus galloprovincialis. Either the use of EIPA, a NHE blocker, or calphostin C, the inhibitor of PKC, reduced cadmium effects. Cells treated with alpha1-, alpha2-, beta- and beta1- adrenergic antagonists together with cadmium reversed cadmium alone effects, while the respective adrenergic agonists, phenylephrine and isoprenaline, mimic cadmium effects. Moreover, cadmium caused an increase in the levels of cAMP in digestive gland cells that were reversed after NHE and PKC inhibition as well as in the presence of each type of adrenergic antagonist. The different sensitivity of alpha1-, alpha2-, beta-, beta1- adrenergic receptors on ROS, cAMP production and DNA damage possibly leads to the induction of two signaling pathways that may be interacting or to the presence of a compensatory pathway that acts in concert with the alpha- and beta- adrenergic receptors. In these signaling pathways PKC and NHE play significant role.

Changes in Superoxide Dismutase Activity and Peroxynitrite Content in Rat Peritoneal Macrophages Exposed to He-Ne Laser Radiation

The formation of reactive oxygen and nitrogen species by rat peritoneal macrophages induced by a low-intensity He-Ne laser radiation (LR) was studied in this work. It was found that the formation of reactive oxygen species, nitric oxide, and peroxynitrite as well as changes in the activity of superoxide dismutase (SOD) depended to a large extent on the LR dose. In particular, it was found that activation of SOD at low LR doses was accompanied by nitric oxide level increase, while the level of peroxynitrite showed no significant changes. On the other hand, an enhanced LR dose inhibited the enzyme, and this was accompanied by peroxynitrite accumulation. All the measurements were carried out the day after LR treatment. The revealed regularities consequently demonstrate the existence of a deferred LR action on macrophages associated with the production of reactive oxygen and nitrogen species.

Doxorubicin increases intracellular hydrogen peroxide in PC3 prostate cancer cells

We studied the effect of doxorubicin on the production of hydrogen peroxide by PC3 human prostate cancer cells, using a sensitive assay based on aminotriazole-mediated inhibition of catalase. PC3 cells exposed to increasing concentrations of doxorubicin had an increase in intracellular hydrogen peroxide that was concentration-dependent up to 1 microM doxorubicin. The apparent hydrogen peroxide concentration in the PC3 cells was 13 +/- 4 pM under basal steady-state conditions and increased to 51 +/- 13 pM after exposure to 1 microM doxorubicin for 30 min. The level of hydrogen peroxide in the medium as measured by Amplex Red did not increase as a result of doxorubicin treatment. PC3 cells overexpressing catalase were no more resistant to doxorubicin cytotoxicity as compared to non-transduced wild-type cells; therefore, the exact role of hydrogen peroxide in anthracycline cytotoxicity remains unproven. This study demonstrates that a specific oxidative event associated with the exposure of PC3 human prostate cancer cells to anthracyclines results in an increase in intracellular hydrogen peroxide.

Fluorescence probes used for detection of reactive oxygen species

Endogenously produced pro-oxidant reactive species are essential to life, being involved in several biological functions. However, when overproduced (e.g. due to exogenous stimulation), or when the levels of antioxidants become severely depleted, these reactive species become highly harmful, causing oxidative stress through the oxidation of biomolecules, leading to cellular damage that may become irreversible and cause cell death. The scientific research in the field of reactive oxygen species (ROS) associated biological functions and/or deleterious effects is continuously requiring new sensitive and specific tools in order to enable a deeper insight on its action mechanisms. However, reactive species present some characteristics that make them difficult to detect, namely their very short lifetime and the variety of antioxidants existing in vivo, capable of capturing these reactive species. It is, therefore, essential to develop methodologies capable of overcoming this type of obstacles. Fluorescent probes are excellent sensors of ROS due to their high sensitivity, simplicity in data collection, and high spatial resolution in microscopic imaging techniques. Hence, the main goal of the present paper is to review the fluorescence methodologies that have been used for detecting ROS in biological and non-biological media.

Characterization of the Oxidase Activity in Mammalian Catalase

Catalase is a highly conserved heme-containing antioxidant enzyme known for its ability to degrade hydrogen peroxide into water and oxygen. In low concentrations of hydrogen peroxide, the enzyme also exhibits peroxidase activity. We report that mammalian catalase also possesses oxidase activity. This activity, which is detected in purified catalases, cell lysates, and intact cells, requires oxygen and utilizes electron donor substrates in the absence of hydrogen peroxide or any added cofactors. Using purified bovine catalase and 10-acetyl-3,7-dihydroxyphenoxazine as the substrate, the oxidase activity was found to be temperature-dependent and displays a pH optimum of 7-9. The Km for the substrate is 2.4 x 10(-4) m, and Vmax is 4.7 x 10(-5) m/s. Endogenous substrates, including the tryptophan precursor indole, the neurotransmitter precursor beta-phenylethylamine, and a variety of peroxidase and laccase substrates, as well as carcinogenic benzidines, were found to be oxidized by catalase or to inhibit this activity. Several dietary plant micronutrients that inhibit carcinogenesis, including indole-3-carbinol, indole-3-carboxaldehyde, ferulic acid, vanillic acid, and epigallocatechin-3-gallate, were effective inhibitors of the activity of catalase oxidase. Difference spectroscopy revealed that catalase oxidase/substrate interactions involve the heme-iron; the resulting spectra show time-dependent decreases in the ferric heme of the enzyme with corresponding increases in the formation of an oxyferryl intermediate, potentially reflecting a compound II-like intermediate. These data suggest a mechanism of oxidase activity involving the formation of an oxygen-bound, substrate-facilitated reductive intermediate. Our results describe a novel function for catalase potentially important in metabolism of endogenous substrates and in the action of carcinogens and chemopreventative agents.

15-Deoxy-delta12,14-prostaglandin J2, a neuroprotectant or a neurotoxicant?

15-Deoxy-delta12,14-prostaglandin J2 (15d-PGJ2) is a potent ligand for peroxisome proliferators-activated receptor gamma (PPARgamma). However, its various effects independent of PPARgamma have recently been observed. The effect of 15d-PGJ2 on neuronal cells is still controversial. We investigated its effect on neuronal cells (N18D3 cells). When N18D3 cells were treated with 15d-PGJ2, the viability was not changed up to 8 microM, but decreased at higher than 8 microM. The expressions of survival signals, such as p85a phosphatidylinositol 3-kinase, phospho-Akt, and phospho-glycogen synthase kinase-3 beta (Ser-9), slightly increased up to 8 microM, however, decreased at higher than 8 microM. The levels of free radicals and membrane lipid peroxidation and the expression of c-Jun N-terminal Kinase increased in a dose-dependent manner, especially at higher than 8 microM. However, the expressions of death signals, such as cytosolic cytochrome c, activated caspase-3, and cleaved poly(ADP-ribose) polymerase, decreased up to 8 microM, however, increased at higher than 8 microM. In the study to evaluate whether low dose of 15d-PGJ2, up to 8 microM, had protective effect on oxidative stress-injured N18D3 cells, compared to the cells treated with only 100 microM H2O2, the pretreatment with 8 microM 15d-PGJ2 increased the viability and the expressions of the survival signals, but decreased them of the death signals. These results indicate that 15d-PGJ2 could be a neuroprotectant or a neurotoxicant, depending on its concentration. Therefore, some specific optimum dose of 15d-PGJ2 may be a new potential therapeutic candidate for oxidative stress-injury model of neurodegenerative diseases.

Effects ofN-acylethanolamines on the respiratory chain and production of reactive oxygen species in heart mitochondria

Long-chain N-acylethanolamines (NAEs) have been found to uncouple oxidative phosphorylation and to inhibit uncoupled respiration of rat heart mitochondria [Wasilewski, M., Wieckowski, M.R., Dymkowska, D. and Wojtczak, L. (2004) Biochim. Biophys. Acta 1657, 151-163]. The aim of the present work was to investigate in more detail the mechanism of the inhibitory effects of NAEs on the respiratory chain. In connection with this, we also investigated a possible action of NAEs on the generation of reactive oxygen species (ROS) by respiring rat heart mitochondria. It was found that unsaturated NAEs, N-oleoylethanolamine (N-Ole) and, to a greater extent, N-arachidonoylethanolamine (N-Ara), inhibited predominantly complex I of the respiratory chain, with a much weaker effect on complexes II and III, and no effect on complex IV. Saturated N-palmitoylethanolamine had a much smaller effect compared to unsaturated NAEs. N-Ara and N-Ole were found to decrease ROS formation, apparently due to their uncoupling action. However, under specific conditions, N-Ara slightly but significantly stimulated ROS generation in uncoupled conditions, probably due to its inhibitory effect on complex I. These results may contribute to our better understanding of physiological roles of NAEs in protection against ischemia and in induction of programmed cell death.

Apoptosis of pancreatic cancer BXPC-3 cells induced by indole-3-acetic acid in combination with horseradish peroxidase

AIM: To explore the mechanisms underlying the apoptosis of human pancreatic cancer BXPC-3 cells induced by indole-3-acetic acid (IAA) in combination with horseradish peroxidase (HRP).

METHODS: BXPC-3 cells derived from human pancreatic cancer were exposed to 40 or 80 µmol/L IAA and 1.2 µg/mL HRP at different times. Then, MTT assay was used to detect the cell proliferation. Flow cytometry was performed to analyze cell cycle. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay was used to detect apoptosis. 2,7-Dichlorofluorescin diacetate uptake was measured by confocal microscopy to determine free radicals. Level of malondialdehyde (MDA) and activity of superoxide dismutase (SOD) were measured by biochemical methods.

RESULTS: IAA/HRP initiated growth inhibition of BXPC-3 cells in a dose- and time-dependent manner. Flow cytometry revealed that the cells treated for 48 h were arrested at G1/G0. After exposure to 80 µmol/L IAA plus 1.2 µg/mL HRP for 72 h, the apoptosis rate increased to 72.5, which was nine times that of control. Content of MDA and activity of SOD increased respectively after treatment compared to control. Meanwhile, IAA/HRP stimulated the formation of free radicals.

CONCLUSION: The combination of IAA and HRP can inhibit the growth of human pancreatic cancer BXPC-3 cells in vitro by inducing apoptosis.

Reactive oxygen species formation in the transition to hypoxia in skeletal muscle

Many tissues produce reactive oxygen species (ROS) during reoxygenation after hypoxia or ischemia; however, whether ROS are formed during hypoxia is controversial. We tested the hypothesis that ROS are generated in skeletal muscle during exposure to acute hypoxia before reoxygenation. Isolated rat diaphragm strips were loaded with dihydrofluorescein-DA (Hfluor-DA), a probe that is oxidized to fluorescein (Fluor) by intracellular ROS. Changes in fluorescence due to Fluor, NADH, and FAD were measured using a tissue fluorometer. The system had a detection limit of 1 μM H2O2 applied to the muscle superfusate. When the superfusion buffer was changed rapidly from 95% O2 to 0%, 5%, 21%, or 40% O2, transient elevations in Fluor were observed that were proportional to the rise in NADH fluorescence and inversely proportional to the level of O2 exposure. This signal could be inhibited completely with 40 μM ebselen, a glutathione peroxidase mimic. After brief hypoxia exposure (10 min) or exposure to brief periods of H2O2, the fluorescence signal returned to baseline. Furthermore, tissues loaded with the oxidized form of the probe (Fluor-DA) showed a similar pattern of response that could be inhibited with ebselen. These results suggest that Fluor exists in a partially reversible redox state within the tissue. When Hfluor-loaded tissues were contracted with low-frequency twitches, Fluor emission and NADH emission were significantly elevated in a way that resembled the hypoxia-induced signal. We conclude that in the transition to low intracellular Po2, a burst of intracellular ROS is formed that may have functional implications regarding skeletal muscle O2-sensing systems and responses to acute metabolic stress.

Effects of peroxidase substrates on the Amplex red/peroxidase assay: Antioxidant properties of anthracyclines

Oxidation of Amplex red (AR) by H(2)O(2) in the presence of horseradish peroxidase (HRP) gives rise to an intensely colored product, resorufin. This reaction has been frequently employed for measurements of low concentrations of H(2)O(2) in biological samples. In the current study, we show that alternative peroxidase substrates, such as p-hydroquinone, acetaminophen, anticancer mitoxantrone, and ametantrone, inhibit AR oxidation by consuming H(2)O(2) in a competitive process. In contrast, the anthracycline agents doxorubicin, daunorubicin, and 5-iminodaunorubicin are markedly less efficient as competitors in these reactions, as is salicylic acid. When [H(2)O(2)]>[AR], the generated resorufin was oxidized by HRP and H(2)O(2). In the presence of anthracyclines, this process was inhibited and occurred with a lag time, the duration of which depended on the concentration of anthracycline. We propose that the mechanism of this inhibition is due to the antioxidant activity of anthracyclines involving the reduction of the resorufin-derived phenoxyl radical by the drugs' hydroquinone moiety back to resorufin. In addition to HRP, lactoperoxidase, myeloperoxidase, and HL-60 cells, naturally rich in myeloperoxidase, also supported these reactions. Results of this study suggest that extra caution is needed when using AR to measure cellular H(2)O(2) in the presence of alternative peroxidase substrates. They also demonstrate that the anticancer anthracyclines may function as antioxidants.

Quantifying hydrogen peroxide in iron-containing solutions using leuco crystal violet

Hydrogen peroxide is present in many natural waters and wastewaters. In the presence of Fe(II), this species decomposes to form hydroxyl radicals, that are extremely reactive. Hence, in the presence of Fe(II), hydrogen peroxide is difficult to detect because of its short lifetime. Here, we show an expanded use of a hydrogen peroxide quantification technique using leuco crystal violet (LCV) for solutions of varying pH and iron concentration. In the presence of the biocatalyst peroxidase, LCV is oxidized by hydrogen peroxide, forming a colored crystal violet ion (CV+), which is stable for days. The LCV method uses standard equipment and allows for detection at the low microM concentration level. Results show strong pH dependence with maximum LCV oxidation at pH 4.23. By chelating dissolved Fe(II) with EDTA, hydrogen peroxide can be stabilized for analysis. Results are presented for hydrogen peroxide quantification in pyrite-water slurries. Pyrite-water slurries show surface area dependent generation of hydrogen peroxide only in the presence of EDTA, which chelates dissolved Fe(II). Given the stability of CV+, this method is particularly useful for field work that involves the detection of hydrogen peroxide.

Immune cell-induced synthesis of NO and reactive oxygen species in lymphoma cells causes their death by apoptosis

Induction of apoptosis in a lymphoma cell line using immune cell-conditioned medium, etoposide or an nitric oxide (NO) donor, resulted in the production of reactive oxygen species (ROS). Agents that inhibited NO production or scavenged ROS or species formed by reaction of NO with ROS, protected the cells from apoptosis. These data support the suggestion that immune rejection of an immunogenic derivative of this lymphoma in vivo involves the induced synthesis of both NO and ROS by the tumour cells.

Standardization of a fluorometric assay for measuring oxidative stress in irradiated cells

The present study was undertaken to standardize a dichlorofluorescein (DCF) assay for measurement of radiation-induced oxidation of dichlorofluorescin (DCFH) substrate in MCF-10 cells. This assay was highly sensitive and capable of detecting increased DCFH oxidation in the cells exposed to gamma radiation at doses as low as 1.5 cGy with linear dose-response curves. However, the slope of the dose-response curves varied considerably from one experiment to another and was influenced by the fluorescent substrate concentration and cell density. To make the assay reproducible so that results obtained from different experiments could be compared, a series of conversion factors and equations have been established to normalize the data for these variables. The results demonstrate that the DCF assay, as standardized in the present study, is highly reproducible with acceptable assay precision. The normalized results can be compared from one experiment to another even when the experiments were performed using different fluorescent substrate concentrations and/or cell densities. Since changes in DCFH oxidation may be related to changes that are indicative of oxidative stress in cells, this assay can be useful to quantify radiation-induced oxidative stress and evaluate the efficacy of antioxidant agents in protection against radiation-induced oxidative stress.

Active oxygen chemistry within the liposomal bilayer. Part IV: Locating 2',7'-dichlorofluorescein (DCF), 2',7'-dichlorodihydrofluorescein (DCFH) and 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) in the lipid bilayer

2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) is commonly used to detect the generation of reactive oxygen intermediates and for assessing the overall oxidative stress in toxicological phenomenon. It has been suggested that DCFH-DA crosses the cell membrane, subsequently undergoing deacetylation by intracellular esterases. The resulting 2',7'-dichlorodihydrofluorescein (DCFH) is proposed to react with intracellular hydrogen peroxide or other oxidizing ROS to give the fluorescent 2',7'-dichlorofluorescein (DCF). Using an NMR chemical shift-polarity correlation, we have determined that DCFH-DA and DCFH are located well within the lipid bilayer and certainly not at the interface. These results, therefore, put into serious question the proposed ability of DCFH to come in contact with the aqueous phase and thereby interact with aqueous intracellular ROS and components. However, H2O2 and superoxide can cross or at least penetrate the lipid bilayer and react with certain lipophilic substrates. This may well describe the mode of reaction of these and other ROS with DCFH.

Alaternin and emodin with hydroxyl radical inhibitory and/or scavenging activities and hepatoprotective activity on tacrine-induced cytotoxicity in HepG2 cells

The antioxidative and hepatoprotective potentials of two anthraquinones, alaternin (2-hydroxyemodin) and emodin, to scavenge and/or inhibit hydroxyl radicals generated by the Fenton reaction and to protect tacrine-induced cytotoxicity in human liver derived HepG2 cells were evaluated, respectively. The inhibitory activity on hydroxyl radical generated in a cell-free chemical system (FeSO4/H2O2) was investigated by a fluorescence spectrophotometer using a highly fluorescent probe, 2',7'-dichlorofluorescein. The hydroxyl radical scavenging activity was determined by electron spin resonance spectroscopy using 5,5-dimethy-1-pyrroline-N-oxide as hydroxyl radicals trapping agents. Tacrine-induced HepG2 cell toxicity was determined by a 3-[4,5-dimethylthiazole-2yl]-2,5-diphenyltertrazolium bromide assay. Although the scavenging activity of alaternin on hydroxyl radical was similar to that of emodin in dose-dependent patterns, the inhibitory activity exhibited by the former on hydroxyl radical generation was stronger than that of the latter, with IC50 values of 3.05 +/- 0.26 microM and 13.29 +/- 3.20 microM, respectively. In addition, the two anthraquinones, alaternin and emodin showed their hepatoprotective activities on tacrine-induced cytotoxicity, and the EC50 values were 4.02 microM and 2.37 microM, respectively. Silymarin, an antihepatotoxic agent used as a positive control exhibited the EC50 value of 2.00 microM. These results demonstrated that both alaternin and emodin had the simultaneous antioxidant and hepatoprotective activities.

N-acetylcysteine amide, a novel cell-permeating thiol, restores cellular glutathione and protects human red blood cells from oxidative stress

Oxidative stress plays an important role in the progression of neurodegenerative and age-related diseases, causing damage to proteins, DNA, and lipids. A novel thiol N-acetylcysteine amide (AD4), the amide form of N-acetylcysteine (NAC) and a Cu(2+) chelator, was assessed for its antioxidant and protective effects using human red blood cells (RBCs) as a model. AD4 was shown by flow cytometry to inhibit tert.-butylhydroxyperoxide (BuOOH)-induced intracellular oxidation in RBCs stained with the oxidant-sensitive probe 2',7'-dichlorofluorescein diacetate. In addition, AD4 retarded BuOOH-induced thiol depletion and hemoglobin oxidation. Restoration of the thiol-depleted RBCs by externally applied AD4 was significantly greater compared with NAC and, unlike NAC, was accompanied by hemoglobin protection from oxidation. In a cell-free system we have demonstrated that AD4 reacted with oxidized glutathione (GSSG) to generate reduced glutathione (GSH). The formation of GSH was determined enzymatically using GSH peroxidase and by HPLC. Based on these results a thiol-disulfide exchange between AD4 and GSSG is proposed as the mechanism underlying the antioxidant effects of AD4 on BuOOH-treated RBCs. Together, these studies demonstrate that AD4 readily crosses cell membranes, replenishes intracellular GSH, and, by incorporating into the redox machinery, defends the cell from oxidation. These results provide further evidence for the efficient membrane permeation of AD4 over NAC, and support the possibility that it could be explored for treatment of neurodegeneration and other oxidation-mediated disorders.

Effects of COX-2 inhibitors on ROS produced by Chlamydia pneumoniae-primed human promonocytic cells (THP-1)

Chronic inflammation through foam cells and macrophages is important in atherosclerosis development, and can be considered as therapeutic targets. Cyclooxygenase and NADPH-oxidase were expressed within atherosclerotic lesions. Reactive oxygen species produced by NADPH oxidase were found to trigger the cyclooxygenase-2 expression. The effects of preferential COX-2 inhibitors on ROS produced by Chlamydia-primed human monocytes (THP-1 cells) were evaluated by fluorescence, chemiluminescence, oxymetry, and EPR spin trapping. Fluorescence assays showed an increased production of ROS with Chlamydia versus cells primed by 10(-8)M PMA. COX-2 inhibitors inhibited in a dose-dependent manner the luminol-enhanced CL while ibuprofen and diclofenac increased the chemiluminescence response. By EPR spin trapping, COX-2 inhibitors, ibuprofen, and diclofenac, exhibited a dose-dependent inhibiting effect (10 and 100muM) on the EPR signal appearance. Our cell model combining EPR, chemiluminescence, and oxymetry appeared relevant to study the modulating effects of preferential COX-2 inhibitors on the cell oxidant activity and chronic inflammatory diseases.

Biodegradability of poly (2-hydroxyethyl methacrylate) in the presence of the J774.2 macrophage cell line

The degradation of cross-linked and linear poly(2-hydroxyethyl methacrylate) (pHEMA), was examined in vitro with J774.2 cells. pHEMA microbeads were prepared with both types of polymers. Only cells in contact with the microbeads increased their production of lysosomal enzymes (TRAcP and ANAE) and released large amounts of reactive oxygen species with both types of pHEMA microbeads. Electron microscopy showed that macrophages were able to erode the surface of linear pHEMA but unable to erode the surface of the cross-linked polymer. Cells appeared wrapped by the linear pHEMA surface, but those cultured on the cross-linked polymer were only laying at the surface. After cell culture, the surface roughness of pHEMA slices was observed by atomic force microscopy (AFM). There was a significant increase in roughness (R(a)) of the surface of linear pHEMA slices cultured with J774.2 cells whereas no difference in R(a) between the surface of cross-linked pHEMA slices could be measured. AFM image of the hydrated materials were done: the surface of linear pHEMA swelled considerably in saline whereas the hydrated cross-linked polymer did not differ from the air-dried appearance. In conclusion, linear pHEMA swells in biological fluids, activates macrophages in close contact with the polymer and can be progressively eroded.

Determination of mitochondrial function and site-specific defects in electron transport in duodenal mitochondria in broilers with low and high feed efficiency

Duodenal mitochondria were isolated from broiler breeder males with high (0.79+/-0.01, n = 9) and low (0.63+/-0.02, n = 9) feed efficiency (FE) to assess relationships of FE with duodenal mitochondrial function and site-specific defects in electron transport. Sequential additions of adenosine diphosphate (ADP) resulted in 1) higher respiratory control ratio (RCR; an index of respiratory chain coupling) in high FE mitochondria provided succinate, and 2) higher ADP to oxygen ratio (ADP:O; an index of oxidative phosphorylation) in low FE mitochondria provided NADH-linked substrates (malate, pyruvate, or both). Basal electron leak, measured as H2O2 production, was greater in low FE mitochondria provided succinate (P = 0.08) or NADH-linked substrates. As H2O2 levels were elevated in low FE compared with high FE mitochondria by complex I (P+/-0.07) and complex II inhibition, the higher basal electron leak in low FE mitochondria was apparently due to site-specific defects in electron transport at complexes I and II. Elevations in H2O2 above basal levels indicated that high FE mitochondria may also exhibit electron transport defects at complexes I and III. Despite an ability to produce adenosine triphosphate (ATP) that was equal or superior to that demonstrated in high FE duodenal mitochondria, low FE mitochondria exhibited a greater inherent degree of electron leak. The results provide insight into the role that duodenal mitochondria play in the phenotypic expression of FE in broilers.

Detection of intracellular superoxide formation in endothelial cells and intact tissues using dihydroethidium and an HPLC-based assay

Recently, it was demonstrated that superoxide oxidizes dihydroethidium to a specific fluorescent product (oxyethidium) that differs from ethidium by the presence of an additional oxygen atom in its molecular structure. We have adapted this new HPLC-based assay to quantify this product as a tool to estimate intracellular superoxide in intact tissues. Ethidium and oxyethidium were separated using a C-18 column and quantified using fluorescence detection. Initial cell-free experiments with potassium superoxide and xanthine oxidase confirmed the formation of oxyethidium from dihydroethidium. The formation of oxyethidium was inhibited by superoxide dismutase but not catalase and did not occur upon the addition of H(2)O(2), peroxynitrite, or hypochlorous acid. In bovine aortic endothelial cells (BAEC) and murine aortas, the redox cycling drug menadione increased the formation of oxyethidium from dihydroethidium ninefold (0.4 nmol/mg in control vs. 3.6 nmol/mg with 20 microM menadione), and polyethylene glycol-conjugated superoxide dismutase (PEG-SOD) significantly inhibited this effect. Treatment of BAEC with angiotensin II caused a twofold increase in oxyethidium formation, and this effect also was reduced by PEG-SOD (0.5 nmol/mg). In addition, in the aortas of mice with angiotensin II-induced hypertension and DOCA-salt hypertension, the formation of oxyethidium was increased in a manner corresponding to superoxide production estimated on the basis of cytochrome c reduction. Detection of oxyethidium using HPLC represents a new, convenient, quantitative method for the detection of superoxide in intact cells and tissues.

Glucose deprivation increases hydrogen peroxide level in immunostimulated rat primary astrocytes

Activated astrocytes produce a large amount of bioactive molecules, including reactive oxygen and nitrogen species. Astrocytes are in general resistant to those reactive species. However, we previously reported that immunostimulated astrocytes became highly vulnerable to metabolic insults, such as glucose deprivation. In this study, we investigated whether H(2)O(2) production was associated with the increased vulnerability. Glucose deprivation for up to 8 hr did not change the intracellular level of H(2)O(2) in astrocytes. Treatment with lipopolysaccharide plus interferon-gamma for 48 hr evoked astroglial H(2)O(2) production; however, no apparent death or injury was observed in immunostimulated astrocytes. Glucose deprivation after 48 hr of immunostimulation markedly increased H(2)O(2) level, depleted adenosine triphosphate (ATP), and enhanced lactate dehydrogenase (LDH) release. The ATP depletion and LDH release were in part prevented by catalase, mannitol, and N-acetyl-L-cysteine. The enhanced level of H(2)O(2) in glucose-deprived immunostimulated astrocytes appeared to be secondary to the depletion of reduced glutathione. 4-(2-Aminoethyl)bebzenesulfonyl fluoride (AEBSF), an inhibitor of NADPH oxidase, reduced H(2)O(2) level and LDH release in glucose-deprived immunostimulated astrocytes. H(2)O(2), either endogenously produced or exogenously added, depolarized mitochondrial transmembrane potential in glucose-deprived astrocytes, leading to their ATP depletion and death. The present results strongly indicate that glucose deprivation causes deterioration of immunostimulated astrocytes by increasing the intracellular concentration of H(2)O(2).

Measurement of exhaled hydrogen peroxide from rabbit lungs

Exhaled H2O2 is considered an indicator of lung inflammatory and oxidative stress. Moreover, H2O2 may be involved in signal transduction processes. It is not fully elucidated to what extent (i) H2O2 escapes from the intravascular compartment, and (ii) pulmonary H2O2 generation and nasopharyngeal H2O2 generation contribute to exhaled H2O2. We investigated H2O2 concentrations in breath condensate from isolated buffer-perfused and ventilated rabbit lungs, and from both intubated and spontaneously breathing rabbits with a horseradish peroxidase/2',7'dichlorofluorescin assay. For the perfused lungs, a H2O2 concentration of 58 +/- 19 nM was found. Addition of H2O2 to the buffer fluid resulted in only minute appearance in the exhaled air (<0.001%). Levels of exhaled H2O2 in intubated rabbits and perfused lungs were virtually identical. Nearly ten-fold higher levels were detected in spontaneously breathing rabbits. Decreasing the inspired oxygen concentration from 21% to 1% resulted in a tendency toward decreased H2O2 exhalation in perfused lungs. In contrast, phorbol-12-myristate-13-acetate (PMA) prompted a approximately 4-fold increase in H2O2 exhalation. We conclude that the horseradish peroxidase/2',7'dichlorofluorescin assay is a feasible technique to measure H2O2 in exhaled breath condensate in rabbits. When collecting exhaled air via the tracheal tube, the signal represents pulmonary H2O2 generation with the contribution of the remaining body being negligible.