Oxidation of glutathione by the superoxide radical to the disulfide and the sulfonate yielding singlet oxygen

Evidence for the role of a peroxidase compound I-type intermediate in the oxidation of glutathione, NADH, ascorbate, and dichlorofluorescin by cytochrome c/H2O2. Implications for oxidative stress during apoptosis

The release of cytochrome c from mitochondria is a crucial step in apoptosis, resulting in the activation of the caspase proteases. A further consequence of cytochrome c release is the enhanced mitochondrial production of superoxide radicals (O2.), which are converted to hydrogen peroxide by manganese-superoxide dismutase. Recently, we showed that cytochrome c is a potent catalyst of 2',7'-dichlorofluorescin oxidation to the fluorescent 2',7'-dichlorofluorescein by these species, leading to the conclusion that 2',7'-dichlorofluorescein fluorescence is a reflection of cytosolic cytochrome c concentration rather than "reactive oxygen species" levels (Burkitt, M. J., and Wardman, P. (2001) Biochem. Biophys. Res. Commun. 282, 329-333). The oxidant generated from cytochrome c has so far not been identified. Several authors have suggested that the hydroxyl radical (*OH) is generated, but others have discussed the possibility of a peroxidase compound I. By examining the effects of various antioxidants (glutathione, ascorbate, and NADH) and "hydroxyl radical scavengers" (ethanol and mannitol) on the rate of 2',7'-dichlorofluorescin oxidation by cytochrome c, together with complementary EPR spin-trapping studies, we demonstrate that the hydroxyl radical is not generated. Instead, our findings suggest the formation of a peroxidase compound I-type intermediate, in which one oxidizing equivalent is present as an oxoferryl heme species and the other as the protein tyrosyl radical previously identified (Barr, D. P., Gunther, M. R., Deterding, L. J., Tomer, K. B., and Mason, R. P. (1996) J. Biol. Chem. 271, 15498-15503). Competition studies involving spin traps indicated that the oxoferryl heme component is the active oxidant. These findings provide an improved understanding of the physicochemical basis of the redox changes that occur during apoptosis.

Dual role of organosulfur compounds in foods: a review

Organosulfur compounds present in natural food are generally considered as beneficial for health because of their antioxidant and anticarcinogenic properties. This has led to their excessive and long-term consumption. However, there is also evidence that these compounds demonstrate toxicity and adverse health effects suggesting their potential dual biological roles. Thus, they can act as double-edged biological swords.

Irreversible thiol oxidation in carbonic anhydrase III: protection by S-glutathiolation and detection in aging rats

Proteins with reactive sulfhydryls are central to many important metabolic reactions and also contribute to a variety of signal transduction systems. In this report, we examine the mechanisms of oxidative damage to the two reactive sulfhydryls of carbonic anhydrase III. Hydrogen peroxide (H2O2), peroxy radicals, or hypochlorous acid (HOCl) produced irreversibly oxidized forms, primarily cysteine sulfinic acid or cysteic acid, of carbonic anhydrase III if glutathione (GSH) was not present. When GSH was approximately equimolar to protein thiols, irreversible oxidation was prevented. H202 and peroxyl radicals both generated S-glutathiolated carbonic anhydrase III via partially oxidized protein sulfhydryl intermediates, while HOCl did not cause S-glutathiolation. Thus, oxidative damage from H202 or AAPH was prevented by protein S-glutathiolation, while a direct reaction between GSH and oxidant likely prevents HOCl-mediated protein damage. In cultured rat hepatocytes, carbonic anhydrase III was rapidly S-glutathiolated by menadione. When hepatocyte glutathione was depleted, menadione instead caused irreversible oxidation. We hypothesized that normal depletion of glutathione in aged animals might also lead to an increase in irreversible oxidation. Indeed, both total protein extracts and carbonic anhydrase III contained significantly more cysteine sulfinic acid in older rats compared to young animals. These experiments show that, in the absence of sufficient GSH, oxidation reactions lead to irreversible protein sulfhydryl damage in purified proteins, cellular systems, and whole animals.

Reactive sulfur species: an emerging concept in oxidative stress

The ingredients of oxidative stress include a variety of reactive species such as reactive oxygen and reactive nitrogen species (ROS, RNS). While sulfur is usually considered as part of cellular antioxidant systems there is mounting evidence that reactive sulfur species (RSS) with stressor properties similar to the ones found in ROS are formed under conditions of oxidative stress. Thiols as well as disulfides are easily oxidised to sulfur species with sulfur in higher oxidation states. Such agents include thiyl radicals, disulfides, sulfenic acids and disulfide-S-oxides. They rapidly oxidise and subsequently inhibit thiol-proteins and enzymes and can be considered as a separate class of oxidative stressors providing new antioxidant drug targets.

Thiols enhance the sensitivity of luminescent assays for non-cross-linked and covalently cross-linked aminophthalhydrazides

Transglutaminases catalyse an acyl-transfer reaction between the gamma-carboxamide of a protein or peptide-bound glutamine (P-CH2-gammaCH2-CO-1NH2) and the primary amino group of mono- or polyamines (R-2NH2), covalently cross-linking the reactants by an isopeptide bond: P-CH2-gammaCH2-CO-1NH2 + R-2NH2 --> P-CH2-gammaCH2-CO-2NH-R + 1NH3. We reported that N-(4-aminobutyl)-N-ethylisoluminol (ABEI) was a chemiluminescent (CL) amine substrate for transglutaminases. We now identified N-(6-aminohexyl)-N-ethylisoluminol (AHEI) as a second, less reactive, transglutaminase substrate. A structure-based explanation is offered for the lower reactivity of AHEI. Optimum CL from non-cross-linked or cross-linked ABEI or AHEI was elicited in the presence of 10 mmol/L dithiothreitol, by oxidizing with a mixture of 20 mmol/L potassium ferricyanide and 10 mmol/L hydrogen peroxide in 100 mmol/L NaOH. The limits of detection and quantitation for non-cross-linked aminophthalhydrazides obtained in this system were: 20 fmol and 60 fmol for ABEI and 10 fmol and 30 fmol for AHEI. These values represented a 500-800-fold improved sensitivity. Delayed peak CL and CL decay in the presence of dithiothreitol contributed to improving the sensitivity. The data could be useful for improving the immunoassays for aminophthalhydrazides and facilitate the development of high throughput assays for transglutaminases.

Study on glutathionesulphonic acid as biodistribution promoter: concomitant use effect on verapamil hydrochloride and tegafur

The effect of glutathionesulphonic acid (N-(N-gamma-L-glutamyl-L-beta-sulphoalanylglycine, GSO3H), which is one of the minor metabolites of glutathione (GSH), on the pharmacokinetics of verapamil hydrochloride (verapamil x HCl) and tegafur was investigated in rats. GSO3H was concomitantly used as sodium salt (GSO3Na). No significant change by the concomitant use of GSO3Na was recognized in the pharmacokinetics parameters of verapamil x HCl and tegafur, and plasma elimination of both substances was not affected by GSO3Na. The tissue-to-plasma concentration ratio (Kp) of verapamil x HCl in the lung 5 min after its administration under concomitant use of GSO3Na rose significantly, however, this effect disappeared 120 min after administration. No significant change was recognized in other organs. On the other hand, a significant difference of Kp of tegafur under a steady state concentration of GSO3Na was not recognized in any organs. It seemed that the elevation of a lipid solubility (oil water partition coefficient) of verapamil x HCl by the concomitant use of GSO3Na was related to the increase of the Kp value of verapamil x HCl in the lung. The partition coefficient of GSO3Na itself decreased when it was used concomitantly with verapamil x HCl.

Erythrocyte, plasma, and serum antioxidant activities in untreated toxic multinodular goiter patients

Erythrocyte, plasma, and serum antioxidant activities were studied in patients with newly diagnosed and untreated toxic multinodular hyperthyroid goiter and compared to healthy control subjects. Erythrocyte antioxidant enzyme activities, glutathione, malondialdehyde, and ceruloplasmin levels were significantly increased, whereas serum vitamin E, plasma vitamin C, and selenium levels were decreased in hyperthyroid patients compared to control subjects. The findings show that untreated toxic multinodular goiter causes profound alterations in components of the antioxidant system in erythrocytes indicative of increased oxidative stress. Taken together, these data suggest that hyperthyroid patients may benefit from dietary supplements of antioxidants.

Effect of sulfur dioxide inhalation on erythrocyte antioxidant status, food intake, and lipid peroxidation during aging

The effect of sulfur dioxide on red blood cell antioxidant status and lipid peroxidation was investigated in young (3 mo), middle-age (12 mo), and old (24 mo) male albino rats. Ten ppm of sulfur dioxide was administered to the rats in the sulfur dioxide groups in an exposure chamber. Exposure occurred 1 hr/d, 7 d/wk, for 6 wk; control rats were exposed to filtered air during the same time periods. Copper-zinc superoxide dismutase, glutathione peroxidase, catalase, glutathione, and glutathione-S-transferase activities were significantly decreased in the middle-aged and older groups, compared with the young group. Sulfur dioxide exposure significantly decreased copper-zinc superoxide dismutase activity in all experimental groups, compared with controls. Sulfur dioxide exposure significantly increased enzyme and glutathione activities.

Reactivity of biologically important thiol compounds with superoxide and hydrogen peroxide

The reactivities of glutathione, cysteine, cysteamine, penicillamine, N-acetylcysteine, dithiothreitol and captopril with superoxide generated from xanthine oxidase and hypoxanthine, and with reagent hydrogen peroxide, have been investigated. Rates of thiol loss on adding hydrogen peroxide, and superoxide-dependent thiol loss and oxygen uptake were measured. The relative reactivities of the different thiols with both oxidants were inversely related to the pK of the thiol group, such that at pH 7.4, penicillamine was the most reactive. N-acetylcysteine weakly reactive and no reaction was seen with captopril. For hydrogen peroxide, the calculated rate constants for the reaction with the thiolate anion all fell within the range 18-26 M(-1) s(-1). With superoxide, our results are consistent with each thiol reacting via a short chain that consumes oxygen and regenerates superoxide. Only with some of the thiols, was the consumed oxygen recovered as hydrogen peroxide. Reported values for the rate constant for the reaction of thiols with superoxide vary over four orders of magnitude, with the highest being > 10(5) M(-1) s(-1). Due to the complexity of the chain reaction, no study so far has been able to obtain accurate values and we consider the best estimates to be in the 30 to 1000 M(-1) s(-1) range.

Glutathione protects the rat liver against reperfusion injury after hypothermic preservation

BACKGROUND & AIMS

The extracellular generation of reactive oxygen species (ROS) by Kupffer cells contributes to reperfusion injury of the liver allograft. The endogenous antioxidant glutathione (GSH) can detoxify these ROS; however, this effect might be limited by the low extracellular concentration of GSH. We therefore investigated whether an increase of extracellular GSH protects the liver against reperfusion injury after cold preservation.

METHODS

Livers of male Sprague-Dawley rats subjected to 24 hours of cold ischemia in University of Wisconsin solution (4 degrees C) were reperfused for 2 hours in the absence (controls) or presence of 0.5, 1, 2, or 4 mmol/L GSH (n = 4-6 each).

RESULTS

Two hours after starting reperfusion of control livers, the sinusoidal release of lactate dehydrogenase and purine nucleoside phosphorylase increased to 247 +/- 96 and 27 +/- 13 mU. min(-1). g liver(-1), respectively, but only to 76 +/- 43 and 10 +/- 4 mU. min(-1). g liver(-1) in the presence of 4 mmol/L GSH. This cytoprotective effect was confirmed histologically by a marked reduction of trypan blue staining of hepatocytes. Compared with control livers, postischemic bile flow was significantly enhanced by GSH (0.15 +/- 0.02 vs. 0.41 +/- 0.11 microL. min(-1). g liver(-1)), indicating improved liver function. During reperfusion of control livers, intracellular GSH content declined from 4.5 +/- 0.3 to 2.3 +/- 0.1 micromol/g liver, but only to 3.8 +/- 0.4 micromol/g liver in the presence of 4 mmol/L GSH. Reperfusion of untreated livers was accompanied by a prolonged increase of portal pressure to maximally 12.5 +/- 1.9 cm H2O, which was significantly attenuated by 4 mmol/L GSH (7.2 +/- 1.4 cm H2O). Similar cytoprotective and hemodynamic effects were observed with 2 mmol/L GSH, but not with 0.5 and 1 mmol/L GSH.

CONCLUSIONS

Treatment of cold-preserved livers with GSH upon reperfusion prevents damage of hepatocytes, deterioration of the hepatic circulation, and loss of intracellular GSH. In view of these protective effects and its low toxicity in humans, GSH should be considered a candidate drug for prevention of ROS-related reperfusion injury of the liver allograft.

The role of N-acetylcysteine in protecting synovial fluid biomolecules against radiolytically-mediated oxidative damage: a high field proton NMR study

High field proton (1H) NMR spectroscopy has been employed to evaluate the abilities of the antioxidant thiol drug N-acetylcysteine and exogenous cysteine to protect metabolites present in intact inflammatory synovial fluid samples against oxidative damage arising from gamma-radiolysis (5.00 kGy) in the presence of atmospheric O2. Although oxidation of urate to allantoin by radiolytically-generated *OH radical was readily circumventable by pre-treatment of synovial fluids with N-acetylcysteine (1.00 or 3.00 x 10(-3) mol x dm(-3)) or cysteine (1.00, 2.00 or 5.00 x 10(-3) mol x dm(-3)), both thiols offered only a limited protective capacity with respect to hyaluronate depolymerisation and the production of formate from carbohydrates in general. Radiolytic products generated from the added thiols (predominantly their corresponding disulphides) were simultaneously detectable in 1H Hahn spin-echo spectra of gamma-irradiated synovial fluids, permitting a quantitative evaluation of the radioprotective capacity of these agents. It is concluded that the multicomponent analytical ability of high field 1H NMR spectroscopy provides much useful molecular information regarding mechanisms associated with the radioprotectant actions of thiols in intact biofluids.

On the path to the heat shock response: destabilization and formation of partially folded protein intermediates, a consequence of protein thiol modification

This review discusses the initial events that occur during oxidative stress that induce the synthesis of heat shock proteins. The focus is on non-native oxidation or modification of protein thiols and the destablization that can result. Proteins that contain non-native modified thiols can become destablized such that they unfold into molten globule-like intermediates at or below 37 degrees C, relieving Hsf-1 negative regulation, and inducing Hsp transcription.

Development of a liquid chromatographic method for picomole determination of S-sulfocysteine in trifluoroacetic acid extracts of neonatal rat brain

Neonatal Sprague Dawley rat brain tissue was extracted with methanol, acetonitrile, acetic acid and trifluoroacetic acids (TFA). Among the extractants tested, 0.1 M TFA gave the highest recovery, 73.4 +/- 5.2% (slope of regression of 'added' vs. 'found' and standard error of the slope) of S-sulfocysteine (SSC). The poorest recovery of SSC was found with acetonitrile and 90% methanol extractions (less than 10%). Possible reasons for the low recoveries have been explored. The recovery of SSC from aqueous standards in 0.1 M TFA is 92 +/- 5%. Detection of picomole quantities of SSC has been demonstrated with a combination of the optimized extraction procedures and our previously developed detection system. Supernatant of rat brain homogenate (0.10 M TFA as extractant) was evaporated to dryness in a vacuum centrifuge. Residues were reconstituted with deionized water. Samples were separated on a reversed phase column. The mobile phase was 20 mM aqueous acetate buffer (pH 5.2) containing 0.40 mM cetyl trimethylammonium p-toluene sulfonate and 2 vol.% methanol. Electrochemical detection used dual series gold-mercury amalgam electrodes. For the first time, S-sulfocysteine was detected in normal neonatal rat brain. Its concentration is 0.99 +/- 0.25 pmol/mg brain tissue. The results indicate that TFA, rarely reported an an extractant, efficiently recovers SSC from rat brain tissues.

The fate of the oxidizing tyrosyl radical in the presence of glutathione and ascorbate. Implications for the radical sink hypothesis

Cellular systems contain as much as millimolar concentrations of both ascorbate and GSH, although the GSH concentration is often 10-fold that of ascorbate. It has been proposed that GSH and superoxide dismutase (SOD) act in a concerted effort to eliminate biologically generated radicals. The tyrosyl radical (Tyr.) generated by horseradish peroxidase in the presence of hydrogen peroxide can react with GSH to form the glutathione thiyl radical (GS.). GS. can react with the glutathione anion (GS-) to form the disulfide radical anion (GSSG-). This highly reactive disulfide radical anion will reduce molecular oxygen, forming superoxide and glutathione disulfide (GSSG). In a concerted effort, SOD will catalyze the dismutation of superoxide, resulting in the elimination of the radical. The physiological relevance of this GSH/SOD concerted effort is questionable. In a tyrosyl radical-generating system containing ascorbate (100 microM) and GSH (8 mM), the ascorbate nearly eliminated oxygen consumption and diminished GS. formation. In the presence of ascorbate, the tyrosyl radical will oxidize ascorbate to form the ascorbate radical. When measuring the ascorbate radical directly using fast-flow electron spin resonance, only minor changes in the ascorbate radical electron spin resonance signal intensity occurred in the presence of GSH. These results indicate that in the presence of physiological concentrations of ascorbate and GSH, GSH is not involved in the detoxification pathway of oxidizing free radicals formed by peroxidases.

The significance of intraluminal prostatic crystalloids in benign needle biopsies

Intraluminal prostatic crystalloids (IPC) are more common in prostate cancer acini than in benign acini. This study was undertaken to evaluate the hypothesis that crystalloids seen in a benign biopsy may indicate an increased risk of a concomitant prostatic carcinoma. A total of 600 patients underwent more than one prostate biopsy. For 394 patients the results of the biopsy were either negative or positive for prostate cancer. After exclusion of patients whose biopsy results were considered negative but coded as high-grade prostatic intraepithelial neoplasia or were suspicious for cancer or whose slides were unavailable for review, 331 patients remained. Biopsy results for these patients were evaluated for the presence of IPC. Also, 18 completely-embedded benign prostates from cystoprostatectomy specimens from patients with bladder cancer were evaluated for the presence of IPC. Seven hundred twenty-five biopsy specimens were reviewed; 51 (7%) contained crystalloids. Thirty-two of 634 (5%) benign biopsy specimens and 19 of 91 (21%) prostatic carcinoma biopsy specimens contained crystalloids. Sixteen of 331 patients (5%) had crystalloids in the initial benign biopsy specimen; 6 patients subsequently were determined to have carcinoma (38%), and 10 continued to have negative results (62%). Three hundred fifteen initial benign biopsies did not show crystalloids; 83 (26%) patients were subsequently diagnosed as having prostatic carcinoma (p = 0.238, Fisher's Exact Test, chi-square test). The IPC were found in 5 of 18 cystoprostatectomy prostates (28%). In this study, the presence of IPC on the initial biopsy specimens was not a significant risk factor for a subsequent diagnosis of prostate cancer. The IPC were not uncommon in prostates without cancer.

Inactivation of yeast glutathione reductase by Fenton systems: effect of metal chelators, catecholamines and thiol compounds

Oxygen radical generating systems, namely, Cu(II)/ H2O2, Cu(II)/ascorbate, Cu(II)/NAD(P)H, Cu(II)/ H2O2/catecholamine and Cu(II)/H2O2/SH-compounds irreversibly inhibited yeast glutathione reductase (GR) but Cu(II)/H2O2 enhanced the enzyme diaphorase activity. The time course of GR inactivation by Cu(II)/H2O2 dependent on Cu(II) and H2O2 concentrations and was relatively slow, as compared with the effect of Cu(II)/ascorbate. The fluorescence of the enzyme Tyr and Trp residues was modified as a result of oxidative damage. Copper chelators, catalase, bovine serum albumin and HO. scavengers prevented GR inactivation by Cu(II)/H2O2 and related systems. Cysteine, N-acetylcysteine, N-(2-dimercaptopropionylglycine and penicillamine enhanced the effect of Cu(II)/H2O2 in a concentration- and time-dependent manner. GSH, Captopril, dihydrolipoic acid and dithiotreitol also enhanced the Cu(II)/H2O2 effect, their actions involving the simultaneous operation of pro-oxidant and antioxidant reactions. GSSG and trypanothione disulfide effectively protected GR against Cu(II)/H2O2 inactivation. Thiol compounds prevented GR inactivation by the radical cation ABTS.+. GR inactivation by the systems assayed correlated with their capability for HO. radical generation. The role of amino acid residues at GR active site as targets for oxygen radicals is discussed.

Oxidation of neutrophil glutathione and protein thiols by myeloperoxidase-derived hypochlorous acid

Neutrophils, when stimulated, generate reactive oxygen species including myeloperoxidase-derived HOCl. There is an associated decrease in reduced glutathione (GSH) concentration. We have shown that neutrophil GSH levels decrease on exposure to reagent HOCl, whereas the equivalent concentration of H2O2 had no effect. GSH loss occurred without cell lysis, was not reversible, and was accompanied by the loss of an equivalent proportion of the total protein thiols. No glutathione disulphide was formed. Studies with 35S-labelled cells indicated that much of the GSH lost was accounted for by mixed disulphides with protein and a product that co-migrated on HPLC with a novel compound formed in the reaction of HOCl and pure GSH. The properties of this compound are consistent with an intramolecular sulphonamide. Neutrophils stimulated with PMA lost 30-40% of their GSH and a similar proportion of protein thiols. Little glutathione disulphide was formed and the products were the same as seen with HOCl-treated cells. From the results and studies with inhibitors and scavengers, we conclude that HOCl was responsible for the GSH loss. Propargylglycine and buthionine sulphoximine, inhibitors of glutathione synthesis, enhanced GSH loss, but their effects were due to the production of long-lived chloramines that oxidized GSH with greater efficiency than HOCl, rather than to the inhibition of GSH synthesis. The lack of thiol selectivity by HOCl and irreversibility of oxidation means that GSH will provide limited antioxidant protection for thiol enzymes in stimulated neutrophils.

The protective role of thiols against nitric oxide-mediated cytotoxicity in murine macrophage J774 cells

Nitric oxide (NO) plays an important role in the cytotoxic activity of macrophages towards tumour cells and microbial pathogens. We investigated whether alteration of intracellular thiol levels modulates the cytotoxic effects of different NO donors and lipopolysaccharide-induced NO in the murine macrophage cell lin J774A.1. The NO-releasing compound S-nitroso-N-acetylpenicillamine caused a significant concentration-dependent loss of viability of the macrophages only under glucose-limiting conditions. The cytotoxic effect of S-nitroso-N-acetylpenicillamine was prevented by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO). Depletion of total glutathione before exposure to S-nitroso-N-acetylpenicillamine further decrease cell viability while pretreatment with N-acetylcysteine was protective. Comparing equimolar concentrations of various NO donors including S-nitrosoglutathione, S-nitrosocysteine and 3-morpholino-sydnonimine hydrochloride, cytotoxicity appeared to be related to the relative stability of the test compound. Both the order of stability and the order of potency for cell killing was S-nitrosoglutathione > S-nitroso-N-acetylpenicillamine > S-nitrosocysteine = 3-morpholino-sydnonimine hydrochloride. Stimulation of the macrophages with lipopolysaccharide and interferon-gamma resulted in dose-dependent cell injury and NO production. Glutathione depletion prior to stimulation considerably decreased macrophage viability as well as the NO production. In contrast to the protective effect on S-nitroso-N-acetylpenicillamine-mediated injury, pretreatment with N-acetylcysteine did not influence the lipopolysaccharide-mediated cytotoxicity. These results demonstrate that (a) reduction in the availability of glucose and intracellular glutathione renders the cells more vulnerable to the cytotoxic effects of NO donors, (b) in this model of cytotoxicity, long-lived NO donors were more cytotoxic than short-lived NO donors, (c) the differential effects of N-acetylcysteine on S-nitroso-N-acetylpenicillamine-induced and bacterial lipopolysaccharide-mediated cytotoxicity support the existence of other toxic species different from NO or NO-related compounds with a potent cytotoxic activity in immunostimulated macrophages, and (d) other non-protein thiols like N-acetylcysteine may substitute for glutathione as a major component of the cellular antioxidant defense system.

Free radical toxicology and antioxidant defence

1. A large number of compounds that have toxic effects can be metabolized to free radicals and secondary reactive oxygen species. These may be directly damaging or may affect cell function by altering regulatory mechanisms through changing redox status. 2. Protection is provided by an integrated system of antioxidant defences. This includes reduced glutathione, one of the functions of which is to scavenge free radicals. It acts by channelling radicals to superoxide so that the one enzyme, superoxide dismutase, has a major control over radical reactions in the cell.

Determination of thiols and disulfides using high-performance liquid chromatography with electrochemical detection

Low-molecular-mass thiols, such as glutathione (GSH), and their associated disulfides are ubiquitous in nature, and based upon the many known functions of these compounds, their identification and accurate measurement is essential. Our objectives were to develop a simple method for the simultaneous measurement of thiols and disulfides in biological samples using HPLC with dual electrochemical detection (HPLC-DED). Particular emphasis was placed on the applicability to a wide variety of important GSH-related thiols and disulfides, including gamma-Glu-Cys, Cys-Gly, their disulfides, and the mixed disulfide of glutathione and cysteine (CSSG), validation on different types of biological samples, maintenance of chromatographic resolution and reproducibility with routine and extended use, and enhancement of assay sensitivity. To this end, optimal HPLC conditions including mobile phase, column, and electrode polishing procedures were established and the method was applied to, and validated on a variety of biological samples. This improved methodology should prove to be a useful tool in studies on the metabolism of GSH and other thiols and disulfides and their role in cellular homeostasis and disease processes.

Does luminol chemiluminescence detect free radical scavengers?

Thiol compounds have been reported to abolish hypoxanthine/xanthine oxidase induced luminol chemiluminescence and this effect has been attributed to scavenging of superoxide (O2-)/(H2O2) produced from hypoxanthine/xanthine oxidase. Yet other workers have reported that thiol compounds have shown little, if any, reactivity towards O2-/H2O2. The aim of this study was to examine the discrepancy between these two sets of findings further. Captopril (a thiol angiotensin-converting enzyme (ACE) inhibitor) and MPG (a simple thiol) were observed to abolish hypoxanthine/xanthine oxidase induced chemiluminescence. The reactivity of captopril and MPG towards O2-/H2O2 was then determined by measurement of thiol oxidation in captopril and MPG after their incubation with hypoxanthine/xanthine oxidase. Incubation (at 10 min, 37 degrees C) with 4 mM hypoxanthine/0.03 u ml-1 xanthine oxidase resulted in 7% and 20% thiol oxidation in captopril and MPG (at 1 mM) respectively. Captopril and MPG, therefore, appeared to be ineffective scavengers of oxidants produced by hypoxanthine/xanthine oxidase. Captopril and MPG also did not affect urate production or oxygen consumption by xanthine oxidase which indicated that captopril and MPG quench luminol chemiluminescence by a mechanism that excludes the inhibition of xanthine oxidase. Hypoxanthine/xanthine oxidase induced luminol chemiluminescence may, therefore, be an unsuitable method for measuring free radical scavenging activity by drugs.

Comparison of the delivery of reduced glutathione into P388D1 cells by reduced glutathione and its mono- and diethyl ester derivatives

The effect of reduced glutathione, reduced glutathione monoethyl ester and reduced glutathione diethyl ester on the cellular concentration of reduced glutathione and cysteine in P388D1 macrophages in vitro, and the cellular and extracellular de-esterification of reduced glutathione esters, was investigated. At 1 mM reduced glutathione derivative, only reduced glutathione diester markedly increased the cellular concentration of reduced glutathione. There was little delivery of reduced glutathione monoethyl ester into the cells. Reduced glutathione, and monoethyl and diethyl ester derivatives all increased the cellular concentration of cysteine; reduced glutathione diethyl ester also increased the cellular concentration of gamma-glutamylcysteine. Reduced glutathione diethyl ester also increased the cellular concentration of gamma-glutamylcysteine. Reduced glutathione esters were de-esterified intracellularly where the diester was rapidly converted to the monoester. The diester was also converted to the monoester extracellularly by interaction with cell surface esterases and by a much slower spontaneous hydrolysis. This indicates that the diester of reduced glutathione was a much more effective vehicle for delivery of reduced glutathione into cells than the monoester. Reduced glutathione diester also increased the cellular concentrations of cysteine and gamma-glutamylcysteine, suggesting that de novo synthesis of reduced glutathione was also stimulated.

The role of 8-hydroxy-2'-deoxyguanosine in rifamycin-induced DNA damage

The effect of rifamycin SV on the formation of 8-hydroxy-2'-deoxyguanosine (8-0HdG) has been investigated in vitro and in vivo. Oxidative modification of 2'-deoxyguanosine has been measured as an indication of DNA damage using high-performance liquid chromatography with electrochemical detection. Rifamycin SV in the presence of copper(II) ions induces the formation of 8-0HdG in calf thymus DNA. The effect is enhanced by increasing the antibiotic concentration and inhibited by catalase and hydroxyl radical (.0H) scavengers, such as thiourea and ethanol, in a rifamycin SV concentration-dependent manner. The reduced glutathione (GSH) inhibits DNA damage, and this effect is proportional to the final concentration of the tripeptide in the incubation medium. A significant increase in the formation of 8-0HdG and of malondialdehyde (MDA) in rat liver DNA was observed only in GSH-depleted animals after 5 days of rifamycin SV treatment. These results support the involvement of hydrogen peroxide (H2(0)2) and .0H in the mechanism of the oxidative modification of DNA achieved by rifamycin SV. The role of other reactive species and the antioxidant properties of GSH against oxidative damage is also discussed.

Hydroxyl radical-mediated reduction of Ca(2+)-ATPase activity of masseter muscle sarcoplasmic reticulum

To understand the effect of oxygen free radicals on Ca(2+)-ATPase, we used sarcoplasmic reticulum (SR) microsomes of canine masseter muscle as a model system in which to explore the effects of oxidation on a biological membrane, and we investigated the effect of hydroxyl radicals (.OH) generated from Fenton's reagent (H2O2/FeSO4). H2O2 (10 mM) alone had no effect on Ca(2+)-ATPase activity; in the presence of FeSO4 (0.2 mM), H2O2 inhibited the enzyme activity. Oxygen free radical species generated from H2O2/FeSO4 under the conditions employed in the Ca(2+)-ATPase assay were verified by highly sensitive electron spin resonance spectroscopy and the spin-trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) in the absence of SR vesicles; the 1:2:2:1 quartet (AN = A beta H = 1.49 mT), characteristic of the DMPO-OH spin adduct, was observed. The Ca(2+)-ATPase activity was inversely correlated with the calculated signal intensity of DMPO-OH, which is indicative of the amount of .OH radical generated. The effect of Fenton's reagent was effectively inhibited by catalase, dimethylsulfoxide, and dimethylthiourea; the effect was also inhibited by sulfhydryl (SH) group reducing agents, cysteine and dithiothreitol. The SH group modifying agents, p-chloromercuric benzoate and 5,5'-dithiobis(2-nitrobenzoic acid) depressed Ca(2+)-ATPase activity; the effects of the SH group modifying agents used were potentiated in the presence of Fenton's reagent. It is suggested that .OH radical-induced oxidant injury may be caused primarily by modification of the key SH group(s) on the ATPase molecule of masseter muscle SR vesicles.

The formation of one-G deletions as a consequence of single-oxygen-induced DNA damage

Single-stranded M13mp10 DNA containing a 144-bp mutational target sequence in the lacZ alpha gene was treated with singlet oxygen (1O2) generated by thermodissociation of the endoperoxide of 3,3'-(1,4-naphthalene-1,4-diyl)dipropionate (NDPO2). After transfection to non-SOS-induced E. coli cells, 32 mutants preselected for a mutation in the 144-bp target were collected and analyzed by DNA sequencing. One-G deletions represented the predominant type of mutation accounting for 50% of the mutations analyzed. The remaining part appeared to consist of base substitutions, i.e. G-->T transversions (34%), C-->T transitions (12.5%) and one T-->C transition (3%). Sixty percent of the mutations were found in two major mutational hotspots. We conclude that the predominant one-G deletions are due to a guanine reaction product which might be specific for 1O2.

Synthesis of heat shock proteins following oxidative challenge: role of glutathione

The relationship between glutathione metabolism, menadione sodium bisulphite oxidation of protein thiols, and the synthesis of hsc70 was investigated using CHO cells. A 30-min/37 degrees C exposure to menadione, a compound which redox cycles to produce superoxide anion radicals and hydrogen peroxide, resulted in rapid accumulation of hsc70 mRNA. PAGE and Western blot analysis indicated increased synthesis such that accumulation of hsc70 occurred. These changes were preceded by rapid oxidation of GSH to GSSG, followed by GSH depletion, and subsequent protein thiol oxidation. As a test of whether a correlation existed between GSH oxidation and depletion, protein thiol oxidation and hsp synthesis, cells were exposed to menadione in the absence and presence of glucose. Synthesis of hsc70 was increased in cells exposed to menadione in the absence of glucose compared with its presence. As a further test, cells were exposed to BSO/DEM in order to deplete GSH and then exposed to menadione. The synthesis of hsc70 following exposure to menadione was greatly increased in GSH-depleted cells compared with GSH-replete cells. Experiments were conducted to determine if electroporation of cells in GSSG containing buffer affected hsp synthesis. Electroporation in glucose-free buffer containing 3 mM GSSG did not affect hsp synthesis. We interpret these results to indicate that the inability to maintain glutathione in a reduced form during menadione redox cycling resulted in protein thiol oxidation. This, in turn, resulted in accumulation of hsc70 mRNA with a subsequent increase in the synthesis of hsc70.

Sulfur-rich prostatic intraluminal crystalloids: a surgical pathologic and electron probe x-ray microanalytic study

Prostatic intraluminal crystalloids are irregular eosinophilic, non-birefringent structures increasingly recognized as potential indicators of prostatic malignancy. In a study of 250 randomly selected surgical pathology cases of prostatic tissues none of 50 cases of benign glandular hyperplasia (0%), one of 50 cases of atypical adenomatous hyperplasia, 18 of 50 cases of well-differentiated adenocarcinoma (36%), seven of 50 cases of moderately differentiated adenocarcinoma (14%), and none of 50 cases of poorly differentiated adenocarcinoma (0%) revealed intraluminal crystalloids. A histochemical and immunohistochemical staining panel indicated that the crystalloids were nonproteinaceous. Crystalloids were stained intensely with phosphotungstic acid hematoxylin and did not stain for prostatic-specific antigen or hemoglobin. Crystalloids were clearly differentiated from prostatic corpora amylacea on light microscopy, histochemistry, scanning, and transmission electron microscopy. Electron probe x-ray microanalysis of 10 cases of crystalloids revealed uniform high sulfur peaks and small sodium peaks. We conclude that intraluminal crystalloids are associated more frequently with low-grade prostatic adenocarcinoma, may occur in benign tissue bordering adenocarcinoma, are predominantly composed of inorganic sulfur, and their presence in benign and atypical prostate biopsies may be of pathologic significance and should warrant further clinical investigation and possibly repeat biopsy.

Antioxidant systems and erythrocyte life-span in mammals

1. Erythrocyte antioxidant systems--superoxide dismutase (SOD), catalase (CAT), reduced glutathione (GSH), glutathione peroxidase (GSH-Px), glutathione S-transferase (GST) and glutathione reductase (GR)--were discussed in relation to life-spans in some mammalian species. 2. The erythrocyte life-span of different mammals was found to be correlated with the levels of SOD, GSH-Px and GSH. 3. Data reviewed indicates that the erythrocyte life-span of each species is governed by both the oxygen radical formation and the efficiency of intrinsic antioxidant systems.

Effect of dietary protein and selected antioxidants on fatty liver hemorrhagic syndrome induced in Japanese quail

The effects of CP and antioxidants on fatty liver hemorrhagic syndrome (FLHS) in Japanese quail hens were studied. In Experiment 1, four treatments were arranged as a 2 x 2 factorial; dietary CP (18 or 24%) and reduced glutathione (GSH, 0 or 120 mg/kg diet) were the major variables, but cysteine and other amino acids were higher in the 24% CP diets. Negative control (NC1) and positive control (PC1) diets were also evaluated. In Experiment 2, the effects of vitamin E (VE) and GSH were evaluated in the presence and absence of adequate dietary sulfur amino acids. Negative control (NC2) and positive control (PC2) diets were used. In both experiments, liver hemorrhage was most severe in quail fed the diets that were formulated to induce hepatic steatosis and limit oxidant defense capability. Liver hemorrhage was least severe in quail fed the diets that were formulated to minimize liver lipid accumulation and support oxidant defenses. Histological evaluation of affected quail livers showed changes consistent with FLHS in chicken hens. In Experiment 1, neither CP concentration nor GSH supplementation influenced liver hemorrhage. In Experiment 2, liver hemorrhagic score was reduced from 3.8 to 2.7 (P < or = .05) by adding VE to the basal diet. The PC2 diet further depressed liver score to only 2.0 (P < or = .05). The data clearly show that Japanese quail are susceptible to FLHS and indicate that a combination of lipotropic and antioxidant nutrients is protective against hemorrhage, even when lipogenic demands are maximized by feeding diets devoid of added fat.

Mutational specificity of oxidative DNA damage

In this paper we describe our studies on the mutagenic consequences of oxidative DNA damage introduced by radiation-induced OH radicals (.OH) and by exposure to singlet oxygen (1O2), released by thermo-dissociation of the endoperoxide 3,3'-(1,4-naphthalidene) dipropionate (NDPO2). We have made use of M13mp10 bacteriophage and pUC18 plasmid DNA, containing a 144 base pair (bp) insert in the lacZ alpha gene. This 144 bp insert was used as a mutational target sequence. When dilute aqueous solutions of double-stranded (ds) M13mp10 (plus 144 bp insert) were gamma-irradiated in the presence of oxygen (O2; 100% .OH) or nitrous oxide (N2O; 90% .OH, 10% .H), very specific mutation spectra were found. Mainly bp substitutions were observed, of which C/G to G/C transversions are the predominant type. Moreover, the mutations are for the most part concentrated into two mutational hot spots: a minor and major one. Differences between the oxic (O2) and anoxic (N2O) mutation spectra could also be observed. Under N2O-1 bp deletions were detected, which are absent in the presence of O2, and in the anoxic spectrum more C/G to A/T transversions are present. To investigate whether these differences were due to the small amount of H radicals, which are formed under N2O, ds M13mp10 (plus 144 bp insert) was exposed to gamma-rays in phosphate buffer under nitrogen (55% .H, 45% .OH). Under these conditions a remarkable shift was observed from C/G-->G/C to C/G-->A/T transversions, while the mutations were far more scattered along the 144 bp sequence and no -1 bp deletions were detected. These results strongly suggest that H radicals do not cause -1 bp deletions, but may be responsible for the observed C/G to A/T transversions. The kind of bp substitution not only appeared to be dependent on the type of the water radicals, but also appeared to be strongly influenced by the replicon in which the target sequence is incorporated. When an oxygenated solution of pUC18 plasmid DNA (plus 144 bp insert) is irradiated, mainly C/G to A/T transversions were found at the same major hot spot instead of C/G to G/C transversions when the 144 bp sequence is part of M13mp10 DNA. Finally, in agreement with the observation that 1O2 reacts preferentially with guanine in DNA, a guanine is involved in most of the mutations scored after exposure of single-stranded (ss) M13mp10 DNA to NDPO2-generated 1O2.(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence that the large loss of glutathione observed in ischemia/reperfusion of the small intestine is not due to oxidation to glutathione disulfide

Reperfusion injury following ischemia is thought to be the consequence of reactive oxygen species possibly generated either by xanthine oxidase activity or by processes associated with neutrophil activation in the affected organ or tissue. The conversion of xanthine dehydrogenase to the oxidase as well as the interactions between endothelium and neutrophils in the margination and activation of the latter are all considered to be results of conditions resulting from the ischemic episode. Determination of the redox status of glutathione in an ischemic/reperfused organ is frequently employed as an indicator of oxidative stress created by the production of oxygen free radicals during the reperfusion period. In this procedure, the ratio of oxidized glutathione (GSSG) to total glutathione (GSH + GSSG) is utilized to demonstrate the proportion of glutathione oxidized during reperfusion. We determined this ratio in the rat small intestine during ischemia and reperfusion and found that while the ratio of GSSG/(GSH + GSSG) does increase, this increase was the result of GSH disappearance rather than an increase in GSSG, and that essentially all of this loss occurred during the ischemic episode. We demonstrated that no oxidation of GSH occurred that was attributable to reperfusion per se; nor was there an increase of GSSG during this reoxygenation period.

Superoxide as an intracellular radical sink

A pathway is proposed for superoxide to act as a sink for intracellularly generated radicals. A variety of radicals, either directly or via reduced glutathione (GSH) as an intermediate, can transfer their unpaired electron to oxygen to give superoxide. It is proposed that in a cellular environment, superoxide can undergo chain reactions involving GSH with or without another redox cycling agent, converting GSH to oxidized glutathione (GSSG) and oxygen to hydrogen peroxide far in excess of the initial radical. This places an oxidative stress on the cell, depleting reducing equivalents and energy reserves. Superoxide dismutase is necessary to prevent this oxidative stress, as well as any direct damage by superoxide. Through this metabolic pathway, GSH and superoxide dismutase can be linked in antioxidant function, and superoxide dismutase, by reacting with superoxide, can provide general protection against radical reactions in the cell. The pathway also provides a mechanism for superoxide and superoxide dismutase to influence the redox state of the cell and regulate functions that are under redox control.

Cellular responses to hematoporphyrin-induced photooxidative damage in Fanconi anemia, xeroderma pigmentosum and normal human fibroblasts

Several observations reported in the literature suggest that singlet oxygen (1O2) might play a role in the clastogenic process in Fanconi anemia (FA) cells, and that the antioxidant status of xeroderma pigmentosum (XP) may also be altered. In order to test the ability of FA and XP cells, relative to normal cells, to cope with 1O2 damage, the effects of photosensitization by hematoporphyrin (HP) have been determined (i) on host cell reactivation (HCR) of damaged infecting herpes simplex virus (HSV) or transfecting SV40 DNA, and (ii) on DNA template capability and clonogenicity of treated cells. Results showed no significant difference among the three types of cells, either for the survival of HP-photosensitized HSV, or for the yields of SV40 virus following transfection of cultures with damaged viral DNA. The treatment of cells with HP plus 365-nm light leads to a dose-dependent, homothetic reduction of 18S and 28S ribosomal RNA (rRNA) synthesis, presumably through a mechanism other than the formation of transcription termination sites. After a 24-h post-exposure incubation, the rate of rRNA synthesis was restored to higher than normal levels in all cell lines. Finally, two FA cell lines showed a higher survival to HP photosensitization than two normal cell lines. Another FA cell line and XP-A and XP-C cells were in the range of sensitivity of the two normal strains for this treatment. These results indicate that FA cells possess an antioxidant defense system at least as efficient as that of normal cells for processing 1O2-induced damage.

Evaluation of N-hydroxy-2-thiopyridone as a nonmetal dependent source of the hydroxyl radical (HO.) in aqueous systems

N-hydroxy-2-thiopyridone (1), an established source of the hydroxyl radical (HO., Boivin, J., Crepon, E., and Zard, S. Z. (1990) Tetrahedron Lett. 31, 6869-6872), produced HO. under conditions directly applicable to biological studies. Generation of HO. by subjecting 1 to irradiation with visible light was monitored in the following "HO." assays: deoxyribose degradation, addition to dimethyl sulfoxide, and hydroxylation of salicylate and phenol. All four assays demonstrated the production of HO. from 1 (added as a sodium salt) under mild conditions in aqueous buffer systems. An improved analysis method was developed for the phenol assay. A time course analysis demonstrated that a flux of HO. is generated from 1 throughout the irradiation period, in contrast to the classical Fenton reaction of H2O2 with a transition metal in which a burst of HO. is generated in a short time period. While a thiyl radical is generated from 1 concurrent with HO. generation, this species does not contribute to, or interfere with, any of the HO. assays, suggesting that it is weakly reactive in aqueous buffers. Thus, irradiation of 1 can be used as an alternative, complementary, approach for the unequivocal generation of the biologically significant and reactive HO..

Glutathione and tissue amino acid responses to light-exposed parenteral nutrients

Effects of infusion of light-exposed (+L) or light-protected (-L) total parenteral nutrition solutions were investigated in rats. The parenteral infusions were carried out for 7 days through jugular cannulas in freely moving rats in metabolic cages. Plasma tyrosine and citrulline, hepatic methionine, valine, isoleucine, leucine and tyrosine, and biliary cystathionine were significantly greater in the -L than +L rats, whereas biliary arginine was significantly lower in the -L compared to +L rats. Bile flow, biliary inorganic phosphate and glucose were significantly lower, whereas biliary total glutathione (GSH+GSSG) was significantly greater in the -L compared to +L animals. These data suggest adverse effects on hepatobiliary function due to light exposure of parenteral nutrients. The endogenous markers used suggest that tight junction permeability, bile acid-independent flow, glutathione and amino acid homeostasis are altered by light exposure and that these changes can be minimized by light protection. The mechanisms involved in the induction of these changes need to be elucidated. The role of light exposure of parenteral nutrients during routine clinical use in the induction of hepatic dysfunction, a common metabolic complication of parenteral nutrition, needs to be considered.

Interaction of singlet oxygen with DNA and biological consequences

To study the interaction of singlet oxygen (1O2) with DNA and the biological consequences of 1O2-induced DNA damage, we used the thermodissociable endoperoxide of 3,3'-(1,4 naphthalidene) dipropionate (NDPO2) as a generator of free 1O2 in reactions with (1) 2'-deoxynucleoside 3'-monophosphates (dNps), (2) an oligonucleotide (16-mer) having one deoxyguanine (dG), (3) native and denaturated rat kidney DNA and (4) single-stranded (ss) and double-stranded (ds) bacteriophage M13mp10 DNA. Using both anion exchange and reversed phase HPLC and 32P-postlabeling analyses, it was found that exposure of the various dNps to chemically generated 1O2 led to a detectable reaction with dGp and not with dAp, dCp, d5mCp or Tp. The reaction with dGp led to degradation of this nucleotide and the formation of a large number of reaction products, one of which could be identified as 7-hydro-8-oxo-2'-deoxyguanosine 3'-monophosphate (8-oxo-dGp). A second product could tentatively be identified as a formamido pyrimidine derivative of dGp (Fapy-dGp). When ss DNA, ds DNA or the oligonucleotide were exposed to 1O2, the formation of 8-oxo-dG could also be demonstrated. With the oligonucleotide, we found a so far unidentified reaction product. Under the same reaction conditions the yield of 8-oxo-dG was about 8-fold higher in ss DNA than in ds DNA. In ss DNA 8-oxo-dG seemed to be a more prominent product than in the case of reaction of 1O2 with free dGp. Reaction of 1O2 with ss or ds M13mp10 DNA led to biological inactivation of these DNAs, ss DNA being at least 100-fold more sensitive than ds DNA. It could be concluded that inactivation of the ss DNA must be largely due to 1O2-induced DNA lesions other than 8-oxo-dG. In agreement with the observed preferential reaction of 1O2 with dG most of the so far sequenced mutations, induced by 1O2 in a 144 bp mutation target sequence inserted in the lacZ alpha gene of ss or ds M13mp10 DNA, occurred at a G or G/C base pair respectively. A preference for G(C) to T(A) transversions can be observed for which 8-oxo-dG might have been responsible. In ss DNA a significant number of the mutations are characterized by the fact that a G is deleted.

Research note: antioxidant activity of Japanese quail liver cytosol in the absence and presence of reduced glutathione

The antioxidant activity of Japanese quail liver cytosol was assessed in the presence of .1, 1.0, or 10.0 mM reduced glutathione (GSH) using an in vitro assay system that utilized quail liver microsomes as the lipid substrate. The formation of malonaldehyde (MA), an indicator of lipid peroxidation, was reduced (P less than .01) by 1.0 and 10.0 mM GSH, even in the absence of cytosolic protein. Cytosolic protein at a level of 1 mg/mL of assay medium did not further reduce MA formation at any of the GSH concentrations tested. Increasing the cytosolic protein concentration to 6 mg/mL decreased (P less than .01) MA formation, even in the absence of added GSH.

Oxidative stress responses in Escherichia coli and Salmonella typhimurium

Oxidative stress is strongly implicated in a number of diseases, such as rheumatoid arthritis, inflammatory bowel disorders, and atherosclerosis, and its emerging as one of the most important causative agents of mutagenesis, tumorigenesis, and aging. Recent progress on the genetics and molecular biology of the cellular responses to oxidative stress, primarily in Escherichia coli and Salmonella typhimurium, is summarized. Bacteria respond to oxidative stress by invoking two distinct stress responses, the peroxide stimulon and the superoxide stimulon, depending on whether the stress is mediated by peroxides or the superoxide anion. The two stimulons each contain a set of more than 30 genes. The expression of a subset of genes in each stimulon is under the control of a positive regulatory element; these genes constitute the OxyR and SoxRS regulons. The schemes of regulation of the two regulons by their respective regulators are reviewed in detail, and the overlaps of these regulons with other stress responses such as the heat shock and SOS responses are discussed. The products of Oxy-R- and SoxRS-regulated genes, such as catalases and superoxide dismutases, are involved in the prevention of oxidative damage, whereas others, such as endonuclease IV, play a role in the repair of oxidative damage. The potential roles of these and other gene products in the defense against oxidative damage in DNA, proteins, and membranes are discussed in detail. A brief discussion of the similarities and differences between oxidative stress responses in bacteria and eukaryotic organisms concludes this review.

Oxidants and antioxidants: state of the art

Reactive oxygen species are regarded as merely pernicious. This is incorrect for they play a pivotal role in many physiologic reactions, such as cytochrome P450-mediated oxidations, regulation of the tone of smooth muscle, and killing of microorganisms. An imbalance in oxidant-antioxidant activity is involved in many free radical-mediated pathologies, e.g., ischemia-reperfusion and asthma. In an attempt to alleviate these pathologies with antioxidants, it should be noted that these compounds are neither specific nor mere antioxidants. Associated with antioxidant activity is a pro-oxidant action. In the development of new antioxidant therapies, the important question of how these drugs are incorporated in or commensurate with existing integrated physiologic radical-defense systems should be addressed.

Glutathione metabolism in activated human neutrophils: stimulation of glutathione synthesis and consumption of glutathione by reactive oxygen species

Since glutathione (GSH) is involved in the modulation of the function of polymorphonuclear leucocytes (PMN) such as phagocytosis and production of reactive oxygen species, the metabolism of GSH was studied in human PMN. The concentration of GSH in resting PMN amounted to 13.3 nmol 10(-7) PMN and remained stable over 100 min of incubation. Upon activation of PMN with phorbol myristate acetate intracellular GSH decreased to 50% of the resting concentration within 80 min. In the presence of buthionine sulfoximine, which inhibits the synthesis of GSH, the depletion of intracellular GSH was dramatically accelerated, indicating that activation of PMN is associated with a marked stimulation of GSH synthesis. Since a similar depletion of GSH was seen in the presence of propargylglycine, an inhibitor of the cystathionine pathway, most of the cysteine required for the resynthesis of GSH must originate from methionine and not from cysteine generated by the catabolism of GSH. Further studies showed that GSH is sequentially oxidized by O2-. and HOCl, first to GSSG and then to an unidentified compound, most likely a chloramine. In the presence of an adequate supply of GSH and NADPH which is required for the reduction of GSSG by glutathione reductase this further oxidation of GSSG was prevented. Thus, the highly toxic HOCl generated by PMN can be detoxified by the glutathione reducatase system. The capacity of PMN to re-synthesize GSH may be an important determinant of PMN function.