Showing papers in "Free Radical Research in 1999"

Glutathione and glutathione-dependent enzymes represent a co-ordinately regulated defence against oxidative stress

Abstract: Increases in the intracellular levels of reactive oxygen species (ROS), frequently referred to as oxidative stress, represents a potentially toxic insult which if not counteracted will lead to membrane dysfunction, DNA damage and inactivation of proteins. Chronic oxidative stress has numerous pathological consequences including cancer, arthritis and neurodegenerative disease. Glutathione-associated metabolism is a major mechanism for cellular protection against agents which generate oxidative stress. It is becoming increasingly apparent that the glutathione tripeptide is central to a complex multifaceted detoxification system, where there is substantial inter-dependence between separate component members. Glutathione participates in detoxification at several different levels, and may scavenge free radicals, reduce peroxides or be conjugated with electrophilic compounds. Thus, glutathione provides the cell with multiple defences not only against ROS but also against their toxic products. This article discusses how glutathione biosynthesis, glutathione peroxidases, glutathione S-transferases and glutathione S-conjugate efflux pumps function in an integrated fashion to allow cellular adaption to oxidative stress. Co-ordination of this response is achieved, at least in part, through the antioxidant responsive element (ARE) which is found in the promoters of many of the genes that are inducible by oxidative and chemical stress. Transcriptional activation through this enhancer appears to be mediated by basic leucine zipper transcription factors such as Nrf and small Maf proteins. The nature of the intracellular sensor(s) for ROS and thiol-active chemicals which induce genes through the ARE is described. Gene activation through the ARE appears to account for the enhanced antioxidant and detoxification capacity of normal cells effected by many cancer chemopreventive agents. In certain instances it may also account for acquired resistance of tumours to cancer chemotherapeutic drugs. It is therefore clear that determining the mechanisms involved in regulation of ARE-driven gene expression has enormous medical implications.

Antioxidant defence mechanisms: from the beginning to the end (of the beginning).

Abstract: When life first evolved on Earth, there was little oxygen in the atmosphere. Evolution of antioxidant defences must have been closely associated with the evolution of photosynthesis and of O2-dependent electron transport mechanisms. Studies with mice lacking antioxidant defences confirm the important roles of MnSOD and transferrin in maintaining health, but show that glutathione peroxidase (GPX) and CuZnSOD are not essential for everyday life (at least in mice). Superoxide can be cytotoxic by several mechanisms: one is the formation of hydroxyl radicals. There is good evidence that OH* formation occurs in vivo. Other important antioxidants may include thioredoxin, and selenoproteins other than GPX. Nitric oxide may be an important antioxidant in the vascular system. Diet-derived antioxidants are important in maintaining human health, but recent studies employing "biomarkers" of oxidative DNA damage are questioning the "antioxidant" roles of beta-carotene and ascorbate. An important area of future research will be elucidation of the reasons why levels of steady-state oxidative damage to DNA and lipids vary so much between individuals, and their predictive value for the later development of human disease.

Endogenous nitric oxide synthesis: Biological functions and pathophysiology

Abstract: Modern molecular biology has revealed vast numbers of large and complex proteins and genes that regulate body function. By contrast, discoveries over the past ten years indicate that crucial features of neuronal communication, blood vessel modulation and immune response are mediated by a remarkably simple chemical, nitric oxide (NO). Endogenous NO is generated from arginine by a family of three distinct calmodulin- dependent NO synthase (NOS) enzymes. NOS from endothelial cells (eNOS) and neurons (nNOS) are both constitutively expressed enzymes, whose activities are stimulated by increases in intracellular calcium. Immune functions for NO are mediated by a calcium-independent inducible NOS (iNOS). Expression of iNOS protein requires transcriptional activation, which is mediated by specific combinations of cytokines. All three NOS use NADPH as an electron donor and employ five enzyme cofactors to catalyze a five-electron oxidation of arginine to NO with stoichiometric formation of citrulline. The highest levels of NO throughout the body are found in neurons, where NO functions as a unique messenger molecule. In the autonomic nervous system NO functions NO functions as a major non-adrenergic non-cholinergic (NANC) neurotransmitter. This NANC pathway plays a particularly important role in producing relaxation of smooth muscle in the cerebral circulation and the gastrointestinal, urogenital and respiratory tracts. Dysregulation of NOS activity in autonomic nerves plays a major role in diverse pathophysiological conditions including migraine headache, hypertrophic pyloric stenosis and male impotence. In the brain, NO functions as a neuromodulator and appears to mediate aspects of learning and memory. Although endogenous NO was originally appreciated as a mediator of smooth muscle relaxation, NO also plays a major role in skeletal muscle. Physiologically muscle-derived NO regulates skeletal muscle contractility and exercise-induced glucose uptake. nNOS occurs at the plasma membrane of skeletal muscle which facilitates diffusion of NO to the vasculature to regulate muscle perfusion. nNOS protein occurs in the dystrophin complex in skeletal muscle and NO may therefore participate in the pathophysiology of muscular dystrophy. NO signalling in excitable tissues requires rapid and controlled delivery of NO to specific cellular targets. This tight control of NO signalling is largely regulated at the level of NO biosynthesis. Acute control of nNOS activity is mediated by allosteric enzyme regulation, by posttranslational modification and by subcellular targeting of the enzyme. nNOS protein levels are also dynamically regulated by changes in gene transcription, and this affords long-lasting changes in tissue NO levels. While NO normally functions as a physiological neuronal mediator, excess production of NO mediates brain injury. Overactivation of glutamate receptors associated with cerebral ischemia and other excitotoxic processes results in massive release of NO. As a free radical, NO is inherently reactive and mediates cellular toxicity by damaging critical metabolic enzymes and by reacting with superoxide to form an even more potent oxidant, peroxynitrite. Through these mechanisms, NO appears to play a major role in the pathophysiology of stroke, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis.

The sugar moiety is a major determinant of the absorption of dietary flavonoid glycosides in man

Abstract: Flavonoids are antioxidants present in plant foods. They occur mainly as glycosides, i.e. linked with various sugars. It is uncertain to what extent dietary flavonoid glycosides are absorbed from the gut. We investigated how the nature of the sugar group affected absorption of one major flavonoid, quercetin. Quercetin linked with glucose, i.e. quercetin glucoside and quercetin linked with rutinose, i.e. quercetin rutinoside, both occur widely in foods. When we fed these compounds to nine volunteers, the peak concentration of quercetin (Cmax) in plasma was 20 times higher and was reached (Tmax) more than ten times faster after intake of the glucoside (Cmax = 3.5 ± 0.6 μM (mean ± SE); Tmax < 0.5 h) than after the rutinoside (Cmax = 0.18 ± 0.04 μM; Tmax = 6.0 ± 1.2 h). The bioavailability of the rutinoside was only 20% of that of the glucoside. We suggest that quercetin glucoside is actively absorbed from the small intestine, whereas quercetin rutinoside is absorbed from the colon after deglycosylation. Abso...

The polyphenolic content of fruit and vegetables and their antioxidant activities. What does a serving constitute

Abstract: Analysis of the major flavone, flavonol, anthocyanidin and hydroxycinnamic acid constituents (and their glycosides) of onion, tomato, egg plant and apple has been undertaken and the antioxidant act...

Regulatory mechanisms of cellular response to oxidative stress.

Abstract: An antioxidant responsive element (ARE) or electrophile responsive element (EpRE) mediates the transcriptional activation of genes encoding phase II drug metabolizing enzymes. The ARE consensus sequence shows high similarity to an erythroid gene regulatory element, and based on the observation, we have recently found that transcription factor Nrf2 is essential for the coordinate induction of phase II detoxifying enzymes. The expression of anti-oxidative stress enzyme genes is also regulated by Nrf2. Detailed analysis of the regulatory mechanisms of Nrf2 activity has ultimately led us to the identification of a new protein, which we have named Keap1, that suppresses Nrf2 activity by specific binding to its evolutionarily-conserved N-terminal Neh2 regulatory domain.

Nitric oxide and peroxynitrite. The ugly, the uglier and the not so good: a personal view of recent controversies.

Abstract: Nitric oxide, a gaseous free radical, is poorly reactive with most biomolecules but highly reactive with other free radicals. Its ability to scavenge peroxyl and other damaging radicals may make it an important antioxidant in vivo, particularly in the cardiovascular system, although this ability has been somewhat eclipsed in the literature by a focus on the toxicity of peroxynitrite, generated by reaction of O2*- with NO* (or of NO- with O2). On balance, experimental and theoretical data support the view that ONOO- can lead to hydroxyl radical (OH*) generation at pH 7.4, but it seems unlikely that OH* contributes much to the cytotoxicity of ONOO-. The cytotoxicity of ONOO- may have been over-emphasized: its formation and rapid reaction with antioxidants may provide a mechanism of using NO* to dispose of excess O2*-, or even of using O2*- to dispose of excess NO*, in order to maintain the correct balance between these radicals in vivo. Injection or instillation of "bolus" ONOO- into animals has produced tissue injury, however, although more experiments generating ONOO- at steady rates in vivo are required. The presence of 3-nitrotyrosine in tissues is still frequently taken as evidence of ONOO- generation in vivo, but abundant evidence now exists to support the view that it is a biomarker of several "reactive nitrogen species". Another under-addressed problem is the reliability of assays used to detect and measure 3-nitrotyrosine in tissues and body fluids: immunostaining results vary between laboratories and simple HPLC methods are susceptible to artefacts. Exposure of biological material to low pH (e.g. during acidic hydrolysis to liberate nitrotyrosine from proteins) or to H2O2 might cause artefactual generation of nitrotyrosine from NO2- in the samples. This may be the origin of some of the very large values for tissue nitrotyrosine levels quoted in the literature. Nitrous acid causes not only tyrosine nitration but also DNA base deamination at low pH: these events are relevant to the human stomach since saliva and many foods are rich in nitrite. Several plant phenolics inhibit nitration and deamination in vitro, an effect that could conceivably contribute to their protective effects against gastric cancer development.

The heme oxygenase pathway and its interaction with nitric oxide in the control of cellular homeostasis

Abstract: Heme oxygenase is the rate limiting enzyme in heme degradation to carbon monoxide (CO), iron and bilirubin. The inducible isoform of the protein, heme oxygenase-1 (HO-1), is susceptible to up-regulation by a diverse variety of conditions and agents in mammalian tissue, leading to the common conception that HO-1 is a stress related enzyme. However, as attempts are made to unravel the mechanisms by which HO-1 is induced and as we discover that CO, iron and bilirubin may be important effector molecules, we are learning to appreciate that heme oxygenases may be central to the regulation of many physiological and pathophysiological processes besides their established function in heme catabolism. One such process may be closely linked to nitric oxide (NO). It has been demonstrated that NO and NO donors are capable of inducing HO-1 protein expression, in a mechanism depending on the de novo synthesis of RNA and protein. Thus, it is postulated that NO may serve as a signaling molecule in the modulation of the tis...

Health effects and bioavailability of dietary flavonols

Abstract: Flavonoids are polyphenolic compounds that are ubiquitously present in foods of plant origin. Flavonoids are categorised into flavonols, flavones, catechins, flavanones, anthocyanidins, and isoflavonoids. They may have beneficial health effects because of their antioxidant properties and their inhibitory role in various stages of tumour development in animal studies. It is estimated that the human intake of all flavonoids is a few hundreds of milligram per day. Flavonoids present in foods used to be considered non-absorbable because they are bound to sugars as beta-glycosides. However, we found that human absorption of the quercetin glycosides from onions (52%) is far better than that of the pure aglycone (24%). The sugar moiety is an important determinant of their absorption and bioavailability. Flavonol glycosides might contribute to the antioxidant defences of blood. The average intake of the flavonols quercetin, myricetin and kaempferol and the flavones luteolin and apigenin in the Netherlands was 23 mg/day. The intake of these flavonols and flavones was inversely associated with subsequent coronary heart disease in some but not all prospective epidemiological studies. A protective effect of flavonols on cancer was found in one prospective study; two others showed no association. Thus the epidemiological evidence does not yet allow a decision on the involvement of flavonols in the etiology of either cardiovascular diseases or cancer.

Treatment of diabetic polyneuropathy with the antioxidant thioctic acid (alpha-lipoic acid): a two year multicenter randomized double-blind placebo-controlled trial (ALADIN II). Alpha Lipoic Acid in Diabetic Neuropathy.

Abstract: Short-term trials with the antioxidant thioctic acid (TA) appear to improve neuropathic symptoms in diabetic patients, but the long-term response remains to be established. Therefore, Type 1 and Ty...

Total antioxidant potential of resinous exudates from Heliotropium species, and a comparison of the ABTS and DPPH methods.

Abstract: Total reactive antioxidant potential (TRAP) of resinous exudates from Heliotropium species was evaluated by measuring the bleaching of stable free radicals. The antioxidant capacity of the resinous exudates in Trolox equivalents, evaluated from the bleaching of ABTS derived radical cations, ranged from 2.0 M (H. huascoense) to 5.2 M (H. stenophyllum), indicating a very high concentration of phenolic compounds. Considerably smaller values were obtained by measuring the bleaching of DPPH radicals. The ratio between the values obtained employing ABTS derived radicals and DPPH, ranged from 37 (H. megalanthum) to 4.5 (H. chenopodiaceum variety typica). The magnitude of the difference can be considered as an indication of the relative reactivity of the antioxidants present in the exudates. Similar ratios were observed when stoichiometric coefficients were evaluated for representative purified flavonoids obtained from the resinous exudates.

Differential response of antioxidative enzymes of chloroplasts and mitochondria to long-term NaCl stress of pea plants.

Abstract: In this work the activity of superoxide dismutase (SOD) and the enzymes of the ascorbate-glutathione (ASC-GSH) cycle were investigated in chloroplasts and mitochondria from leaves of Pisum sativum L. cv. Puget after 15 days treatment with 0-130 mM NaCl. The main chloroplastic SOD activity was due to CuZn-SOD II, which was increased significantly (about 1.7-fold) by NaCl, although during severe NaCl stress (110-130 mM) chloroplastic Fe-SOD exhibited a stronger enhancement in its activity (about 3.5-fold). A sudden induction in chloroplastic APX, DHAR and GR was also caused by NaCl (70-110 mM), but not by the highest salt concentration (130 mM), at which GR and DHAR activities were similar to the control values and APX decreased. In addition, the H2O2 concentration and lipid peroxidation of membranes increased significantly, 3.5- and 7-fold, respectively, in chloroplasts under severe NaCl stress. In purified mitochondria DHAR and GR were significantly induced only at 90 and 130 mM NaCl, respectively, although DHAR activity was below control values in the highest NaCl concentrations. APX and MDHAR activities started their response to salt in mild NaCl conditions (70 mM) and increased significantly with the severity of the stress. Mn-SOD was induced only under severe NaCl concentrations. The mitochondrial H2O2 and lipid peroxidation were increased at the highest NaCl concentration although to a lesser extent (about 2-2.5-fold) than in chloroplasts, whereas the increase in carbonyl protein contents was higher in mitochondria. The results suggest that the degree of enhanced tolerance to NaCl seems to require the induction of specific isoforms, depending on the different organelles.

Lycopene and beta-carotene protect against oxidative damage in HT29 cells at low concentrations but rapidly lose this capacity at higher doses.

Abstract: Epidemiological studies have clearly demonstrated a link between dietary carotenoids and the reduced incidence of certain diseases, including some cancers. However recent intervention studies (e.g. ATBC, CARET and others) have shown that β-carotene supplementation has little or no beneficial effect and may, in fact, increase the incidence of lung cancers in smokers. This presents a serious dilemma for the scientific community — are carotenoids at high concentrations actually harmful in certain circumstances?Currently, a significant number of intervention studies are on-going throughout the world involving carotenoids (of both natural and synthetic origin). Our approach has been to study the ability of supplementary carotenoids in protecting cells against oxidatively-induced DNA damage (as measured by the comet assay), and membrane integrity (as measured by ethidium bromide uptake). Both lycopene and β-carotene only afforded protection against DNA damage (induced by xanthine/xanthine oxidase) at relatively...

Overexpression of glutathione S-transferase pi enhances the adduct formation of cisplatin with glutathione in human cancer cells.

Abstract: In this paper, we provide direct evidence that glutathione S-transferase pi (GSTpi) detoxifies cisplatin (CDDP). We used human colonic cancer HCT8 cells sensitive and resistant to CDDP, the level of cisplatin-glutathione adduct (DDP-GSH) being higher in the resistant cells. There was an overexpression of GSTpi mRNA in these CDDP-resistant cells. Incubation of the cells with CDDP resulted in the formation of DDP-GSH dependent on the CDDP concentration and the incubation time. The formation of DDP-GSH was abolished when the cells were pre-treated with ethacrynic acid or ketoprofen, inhibitors of GSTpi. Purified GSTpi also catalyzed the formation of DDP-GSH in vitro, with an apparent Km of 0.23 mM for CDDP and an apparent Vmax of 4.9 nmol/min/mg protein. The increase in DDP-GSH produced by GSTpi was linear with incubation time up to 3 h and optimal of pH 7.4. A GSTpi transfectant cell line was constructed in HCT8 cells using a pcDNA3.1 (-)/Myc-His B with an expression vector containing cDNA for GSTpi. Transfection of GSTpi cDNA into HCT8 cells resulted in an increase in the expression of GSTpi by 1.4-fold in parallel with an augmentation of the formation of DDP-GSH. These results suggest that GSTpi plays a role in the formation of DDP-GSH and the acquisition of resistance to CDDP in cancer cells.

Methods to measure the antioxidant activity in plant material. A comparative discussion.

Abstract: Methods to determine total antioxidant activity (TAA) are generally based on the inhibition of certain reactions by the presence of antioxidants. The most widely used methods are those that involve the generation of radical compounds, and it is the presence of antioxidants that determines the disappearance of these radicals. Strategies for measuring TAA are discussed, particularly the different methodological and instrumental approaches used. In addition, our own methods are presented in order to facilitate and speed up the manipulation of biological material. The values of TAA by different compounds are presented and compared.

Hydrogen peroxide-induced apoptosis in HL-60 cells requires caspase-3 activation

Abstract: Apoptosis has been associated with oxidative stress in biological systems. Caspases have been considered to play a pivotal role in the execution phase of apoptosis. However, which caspases function as executioners in reactive oxygen species (ROS)-induced apoptosis is not known. The present study was performed to identify the major caspases acting in ROS-induced apoptosis. Treatment of HL-60 cells with 50 microM hydrogen peroxide (H2O2) for 4 h induced the morphological changes such as condensed and/or fragmented nuclei, increase in caspase-3 subfamily protease activities, reduction of the procaspase-3 and a DNA fragmentation. To determine the role of caspases in H2O2-induced apoptosis, caspase inhibitors, acetyl-Tyr-Val-Ala-Asp-chloromethyl ketone (Ac-YVAD-cmk), acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-CHO) and acetyl-Val-Glu-Ile-Asp-aldehyde (Ac-VEID-CHO), selective for caspase-1 subfamily, caspase-3 subfamily and caspase-6, respectively, were loaded into the cells using an osmotic lysis of pinosomes method. Of these caspase inhibitors, only Ac-DEVD-CHO completely blocked morphological changes, caspase-3 subfamily protease activation and DNA ladder formation in H2O2-treated HL-60 cells. This inhibitory effect was dose-dependent. These results suggest that caspase-3, but not caspase-1 is required for commitment to ROS-triggered apoptosis.

Antioxidant actions of plant foods: use of oxidative DNA damage as a tool for studying antioxidant efficacy.

Abstract: Plant-food-derived antioxidants and active principles such as flavonoids, hydroxycinnamates (ferulic acid, chlorogenic acids, vanillin etc.), β-carotene and other carotenoids, vitamin E, vitamin C, or rosemary, sage, tea and numerous extracts are increasingly proposed as important dietary antioxidant factors. In this endeavor, assays involving oxidative DNA damage for characterizing the potential antioxidant actions are suggested as in vitro screens of antioxidant efficacy. The critical question is the bioavailability of the plant-derived antioxidants.

Reactive oxygen intermediates regulate cellular response to apoptotic stimuli: an hypothesis.

Abstract: Production of reactive oxygen intermediates (ROI) has been thought for a long time to adversely affect the physiology and survival of a cell. There is now a growing body of evidence to suggest that ROI such as superoxide anion (O2*-) and hydrogen peroxide (H2O2) can influence the growth, as well as death, of animal cells in vitro. The observation that cells release O2*- or its dismutation product H2O2, either constitutively in the case of tumor cells or following cytokine stimulation, has led to the speculation that they might possibly serve as intercellular messengers to stimulate proliferation via mechanisms common to natural growth factors. However, as the balance between cell populations in an organism is tightly controlled by the rate of proliferation and death of constituent cells, an increase in cell numbers could reciprocally be viewed as deregulation of cell death. Hence, it is equally important to decipher how ROI influence the response of cells to signals that activate cell death pathway(s). We propose that ROI not only regulate proliferation but also affect cell sensitivity to triggers which activate the cellular suicide program (apoptosis) versus those that cause accidental (necrotic) cell death.

Cadmium toxicity and oxidative metabolism of pea leaf peroxisomes

Abstract: The effect of growing pea plants with 50 microM CdCl2 on the activated oxygen metabolism was studied at subcellular level in peroxisomes isolated from pea leaves. Cadmium treatment produced proliferation of peroxisomes as well as an increase in the content of H2O2 in peroxisomes from pea leaves, but in peroxisomal membranes no significant effect on the NADH-dependent O2*- production was observed. The rate of lipid peroxidation of membranes was slightly decreased in peroxisomes from Cd-treated plants. This could be due to the Cd-induced increase in the activity of some antioxidative enzymes involved in H2O2 removal, mainly ascorbate peroxidase and glutathione reductase, as well as the NADP-dependent dehydrogenases present in these organelles. The activity of xanthine oxidase did not experiment changes by Cd treatment and this suggests that O2*- production in the peroxisomal matrix is not involved in Cd toxicity. This was supported by the absence of changes in plants treated with Cd in the Mn-SOD activity, responsible for O2*- removal in the peroxisomal matrix. Results obtained indicate that toxic Cd levels induce imbalances in the activated oxygen metabolism of pea leaf peroxisomes, but its main effect is an enhancement of the H2O2 concentration of these organelles. Peroxisomes respond to Cd toxicity by increasing the activity of antioxidative enzymes involved in the ascorbate-glutathione cycle and the NADP-dependent dehydrogenases located in these organelles.

Regeneration of phenolic antioxidants from phenoxyl radicals: An ESR and electrochemical study of antioxidant hierarchy

Abstract: Radicals from the flavonoids quercetin, (+)-catechin, (+/-)-taxifolin and luteolin, and from all-rac-alpha-tocopherol have been generated electrochemically by one-electron oxidation in deaerated dimethylformamide (DMF), and characterised by electron spin resonance spectroscopy (ESR) after spin-trapping by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Simulations of the ESR spectrum based on estimated coupling constants of the spin-trapped quercetin radical, confirmed that this antioxidant radical is oxygen-centered. The complex mixture of radicals, quinoid intermediates and stable two-electron oxidation products, were for each antioxidant allowed to react with each of the four other antioxidants, and the progression of reaction followed by ESR after addition of DMPO, and the product solution further analysed by HPLC. All-rac-alpha-tocopherol was found to be most efficient in regenerating each of the other antioxidants from their oxidation products with a regeneration index (defined as moles regenerated of the oxidised phenolic antioxidant divided with moles of all-rac-alpha-tocopherol consumed) of 0.90+/-0.16 for quercetin, 0.48+/-0.11 for (+)-catechin, 0.48+/-0.06 for (+/-)-taxifolin and 0.50+/-0.10 for luteolin in equimolar 1.00 mM solution. Quercetin was found to have the highest regeneration index among the flavonoids: 0.88+/-0.13 for (+/-)-catechin, 0.41+/-0.03 for (+/-)-taxifolin and 0.41+/-0.02 for luteolin. The antioxidant hierarchy based on the reduction potentials determined by cyclic voltammetry under similar conditions (0.93 V for all-rac-alpha-tocopherol, 1.07 V for quercetin, 1.15 V for luteolin, 1.16V for (+)-catechin and 1.20 V for (+/-)-taxifolin) is compared with the observed over-all regeneration (34% for quercetin, 34% for (+)-catechin, 52% for (+/-)-taxifolin and 43% for luteolin by all-rac-alpha-tocopherol).

Assaying for hydroxyl radicals: hydroxylated terephthalate is a superior fluorescence marker than hydroxylated benzoate.

Abstract: Generation of hydroxyl radicals in terephthalate (benzene-1,4-dicarboxylic acid) solution yields fluorescent 2-hydroxy-terephthalate. The reaction product is stable for hours and can readily be assessed using standard fluorimeters. The efficiency, i.e. the relative increase of fluorescence per *OH radical, is about three times higher than that of the formation of salicylate (2-hydroxy-benzoate) from benzoic acid and approximately hundred-fold higher than that of the hydroxylation of phenylalanine. As the terephthalate molecule is symmetric with respect to ring-hydroxylation, only one isomer is formed; hence, mechanistic interpretation of the hydroxylation reaction is facilitated. The scavenging rate constant of terephthalate for *OH yielding the hydroxycyclohexadienyl adduct as first intermediate is close to the diffusion controlled limit (k = 3.3 x 10(9) M(-1) s(-1)). Therefore, competition of the detector molecule with biomolecules being present under physiological conditions is expected to be efficient. The assay can be used to detect 'free' *OH radicals produced by the radiolysis of water as well as 'hydroxyl analogous species' that have been suggested to arise from the interaction of complex-bound reduced metal with either oxygen or hydrogen peroxide, e.g. from Fenton reactions. Based on calibration with radiolytically generated hydroxyl radicals the detection limit of the method is estimated to be around 50 nmol/dm3. Terephthalate is classified non-toxic and hence may also prove useful for microdialysis and continuous flow experiments as observation of fluorescence is 'non-destructive' and the reporter substance does not necessarily have to be subjected to HPLC.

Oxidative Stress-inducible Proteins in Macrophages.

Abstract: Macrophages produce reactive oxygen species such as O2-, H2O2 and *OH that contribute to the pathogenesis of diseases such as inflammation and atherosclerosis. The cells have multiple defense systems against those reactive oxygen species, and we describe here such an oxidative stress-inducible defense system. Upon exposure to reactive oxygen species and electrophilic agents, murine peritoneal macrophages induce stress proteins to protect themselves. Using differential screening, we cloned two novel proteins designated MSP23 and A170 that are induced in the cells by low levels of reactive oxygen species, electrophilic agents and other oxidative stress agents. MSP23 is murine peroxiredoxin I having a thioredoxin peroxidase activity and A170 is known as an ubiquitin- and PKC xi-binding protein. In addition to these two proteins, heme oxygenase-1 (HO-1) and cystine transport activity are also induced in the cells under oxidative stress conditions. Using nrf2-deficient macrophages, we found that transcription factor Nrf2, which is known to interact with antioxidant responsive elements (AREs) in the regulatory sequences of the genes, plays an important role in the oxidative stress-inducible response in the cells.

Aggrecan degradation in chondrocytes is mediated by reactive oxygen species and protected by antioxidants.

Abstract: Reactive oxygen species (ROS) are implicated in aging of cartilage and in the pathogenesis of osteoarthritis. However, the biological role of chondrocytes-derived ROS has not been elucidated. An in-vitro model was developed to study the role of chondrocyte-derived ROS in cartilage matrix degradation. The primary articular chondrocytes were cultured and the aggrecan matrix was radiolabeled with 35-sulfate. The labeled aggrecan matrix was washed to remove unincorporated label and chondrocytes were returned to serum free balanced salt solution. The cell-monolayer-matrix sensitivity to oxidative damage due to either hydrogen peroxide or glucose oxidase was established by monitoring the release of labeled aggrecan into the medium. Lipopolysaccharide (LPS) treatment of chondrocyte-monolayer enhanced the release of labeled aggrecan. Catalase significantly prevented the release of labeled aggrecan in LPS-chondrocyte cultures, suggesting a role for chondrocyte-derived hydrogen peroxide in aggrecan degradation. Superoxide dismutase or boiled catalase had no such inhibitory effect. The effect of several antioxidants on LPS-chondrocyte-dependent aggrecan degradation was examined. Hydroxyl radical scavengers (mannitol and thiourea) significantly decreased aggrecan degradation. A spin trapping agent N-tert-butyl-phenylnitrone (but not its inactive analog tert-butyl-phenylcarbonate) significantly decreased aggrecan degradation. Butylated hydroxytoluene also inhibited aggrecan degradation, whereas the other lipophilic antioxidant tested, propyl gallate, had a marked dose-dependent inhibitory effect. These data indicate that general antioxidants, hydroxyl radical scavengers, antioxidant vitamins, iron chelating agents, lipophilic antioxidants, and spin trapping agents can influence chondrocyte-dependent aggrecan degradation. These studies support the role of a chondrocyte-dependent oxidative mechanism in aggrecan degradation and indicate that antioxidants can prevent matrix degradation and therefore may have a preventive or therapeutic value in arthritis. The enhancement of oxidative activity in chondrocytes and its damaging effect on matrix may be an important mechanism of matrix degradation in osteoarthritis.

The redox pathway of S-nitrosoglutathione, glutathione and nitric oxide in cell to neuron communications.

Abstract: Recent results demonstrated that S-nitrosoglutathione (GSNO) and nitric oxide (*NO) protect brain dopamine neurons from hydroxyl radical (*OH)-induced oxidative stress in vivo because they are potent antioxidants. GSNO and *NO terminate oxidant stress in the brain by (i) inhibiting iron-stimulated hydroxyl radicals formation or the Fenton reaction, (ii) terminating lipid peroxidation, (iii) augmenting the antioxidative potency of glutathione (GSH), (iv) mediating neuroprotective action of brain-derived neurotrophin (BDNF), and (v) inhibiting cysteinyl proteases. In fact, GSNO--S-nitrosylated GSH--is approximately 100 times more potent than the classical antioxidant GSH. In addition, S-nitrosylation of cysteine residues by GSNO inactivates caspase-3 and HIV-1 protease, and prevents apoptosis and neurotoxicity. GSNO-induced antiplatelet aggregation is also mediated by S-nitrosylation of clotting factor XIII. Thus the elucidation of chemical reactions involved in this GSNO pathway (GSH GS* + *NO-->[GSNO]-->GSSG + *NO-->GSH) is necessary for understanding the biology of *NO, especially its beneficial antioxidative and neuroprotective effects in the CNS. GSNO is most likely generated in the endothelial and astroglial cells during oxidative stress because these cells contain mM GSH and nitric oxide synthase. Furthermore, the transfer of GSH and *NO to neurons via this GSNO pathway may facilitate cell to neuron communications, including not only the activation of guanylyl cyclase, but also the nitrosylation of iron complexes, iron containing enzymes, and cysteinyl proteases. GSNO annihilates free radicals and promotes neuroprotection via its c-GMP-independent nitrosylation actions. This putative pathway of GSNO/GSH/*NO may provide new molecular insights for the redox cycling of GSH and GSSG in the CNS.

Protective effect of ozone treatment on the injury associated with hepatic ischemia-reperfusion: antioxidant-prooxidant balance.

Abstract: The effects of ozone treatment on the injury associated to hepatic ischemia-reperfusion (I/R) was evaluated. Ozone treatment (1 mg/kg daily during 10 days by rectal insufflation) is shown to be protective as it attenuated the increases in transaminases (AST, ALT) and lactate levels observed after I/R. I/R leads to a decrease in endogenous antioxidant (SOD and glutathione) and an increase in reactive oxygen species (H2O2) with respect to the control group. However, ozone treatment results in a preservation (glutathione) or increase (SOD) in antioxidant defense and maintains H2O2 at levels comparable to those in the control group. The present study reports a protective effect of ozone treatment on the injury associated to hepatic I/R. The effectiveness of ozone could be related to its action on endogenous antioxidants and prooxidants balance in favour of antioxidants, thus attenuating oxidative stress.

Recent advances in understanding the origin of the apoplastic oxidative burst in plant cells.

Abstract: The origin of the oxidative burst during plant-pathogen interactions remains controversial. A number of possibilities have been identified, which involve the protoplast, plasmalemma or apoplast. The apoplastic production of H2O2 requires three components, an extracellular peroxidase, ion fluxes leading to extracellular alkalinisation and release of a substrate. Fatty acids are the major compounds that appear in the apoplast following elicitation, which can activate H2O2 production by peroxidases in vitro. However, the reaction with peroxidases appears to be novel and is uncharacterised at present. The apoplastic mechanism also cannot be readily distinguished from the operation of a plasma membrane NADPH oxidase system by the use of the inhibitors diphenylene iodonium and N,N diethyl-dithiocarbamate since it is also inhibited by these. These inhibitors have often in the past been used to define the involvement of the latter in the oxidative burst. In common with the NADPH oxidase system, the peroxidase responsible has been cloned but unlike the NADPH oxidase it has been shown to function in vitro to generate H2O2. In vivo studies of the oxidative burst have shown that the alkalinisation is essential and the underlying ion fluxes may be regulated by cAMP. Calcium fluxes are also essential. Although the oxidative activity of peroxidase requires calcium the fluxes have obvious other function. These may include activation of release of substrate and through the activation of a CDPK, regulation of enzymes involved in phytoalexin and cell wall phenolic production such as PAL.

Redox regulation and oxidant activation of heme oxygenase-1.

Abstract: The ultraviolet A (UVA, 320-400 nm) component of sunlight has the potential to generate an oxidative stress in cells and tissue so that antioxidants (both endogenous and exogenous) strongly influence the biological effects of UVA. The expression of several genes (including heme oxygenase-1, HO-1; collagenase; the CL100 phosphatase and the nuclear oncogenes, c-fos and c-jun) is induced following physiological doses of UVA to cells and this effect can be strongly enhanced by removing intracellular glutathione or enhancing singlet oxygen lifetime. We have observed that heme is released from microsomal heme-containing proteins by UVA and other oxidants and that activation of HO-1 expression by UVA correlates with levels of heme release. UVA radiation also leads to an increase in labile iron pools (either directly or via HO-1) and eventual increases in ferritin levels. The role of heme oxygenase in protection of skin fibroblasts is probably an emergency inducible defense pathway to remove heme liberated by oxidants. The slower increase in ferritin levels is an adaptive response which serves to keep labile iron pools low and thereby reduce Fenton chemistry and oxidant-induced chain reactions involving lipid peroxidation. In keratinocytes, the primary target of UVA radiation, heme oxygenase levels are constitutively high (because of HO-2 expression). Since there is a corresponding increase in basal levels of ferritin the epidermis appears to be well protected constitutively against the oxidative stress generated by UVA.

Mechanism of copper-catalyzed autoxidation of cysteine.

Abstract: The kinetics of copper-catalyzed autoxidation of cysteine and its derivatives were investigated using oxygen consumption, spectroscopy and hydroxyl radical detection by fluorescence of a coumarin probe. The process has complex two-phase kinetics. During the first phase a stoichiometric amount of oxygen (0.25 moles per mole of thiol) is consumed without production of hydroxyl radicals. In the second reaction phase excess oxygen is consumed in a hydrogen peroxide-mediated process with significant *OH production. The reaction rate in the second phase is decreased for cysteine derivatives with a free aminogroup and increased for compounds with a modified aminogroup. The kinetic data suggest the catalytic action of copper in the form of a cysteine complex. The reaction mechanism consists of two simultaneous reactions (superoxide-dependent and peroxide-dependent) in the first phase, and peroxide-dependent in the second phase. The second reaction phase begins after oxidation of free thiol. This consists of a Fenton-type reaction between cuprous-cysteinyl complex and following oxidation of cysteinyl radical to sulfonate with the consumption of excessive oxygen and significant production of hydroxyl radicals.

Generation of hydrogen peroxide by “Antioxidant” beverages and the effect of milk addition. Is cocoa the best beverage?

Abstract: The ability of several beverages to generate hydrogen peroxide was demonstrated by direct measurement using the ferrous ion oxidation-xylenol orange (FOX) assay. Tea and coffee could generate H2O2 to achieve levels over 100 microM, but cocoa did not. Milk decreased net H2O2 production by beverages and showed some ability to remove H2O2 itself, apparently not because of catalase activity. Hence several of the beverages commonly drunk by humans show a complex mixture of anti- and pro-oxidant abilities.

Nitric oxide generation by soybean embryonic axes. Possible effect on mitochondrial function.

Abstract: Nitric oxide (NO) generation and its effect on mitochondrial enzymes were investigated in soybean embryonic axes at the onset of germination. NO was detected in homogenates from soybean embryonic axes by EPR. Enzymatic sources of NO, such as nitrate reductase activity and nitric oxide synthase, assessed as NADPH-diaphorase activity, were measured in homogenates incubated up to 48 h. Both NO content and the activity of the enzymes showed a similar profile as function of the imbibition time, with maximal levels at 15-24h. Total O2 consumption in enriched-mitochondrial fraction was inhibited by NO in a concentration-dependent manner. O2 consumption dependent on cytochrome oxidase activity was more sensitive than alternative oxidase pathway to NO exposure. Half maximal effects of NO at 0.3 and 3.6 microM were measured for cytochrome oxidase and alternative oxidase, respectively. Enriched-mitochondrial fractions from soybean embryonic axes treated with NO (up to 1 microM) showed increased H2O2 production. The data presented suggest that NO could modulate O2 consumption in soybean embryonic axes. This process could affect the pro-oxidant/antioxidant balance and the cellular energy yield in the germinating embryonic axes, and could have a role in soybean germination.