Simultaneous detection of reduced and oxidized glutathione in tissues and mitochondria by capillary electrophoresis

We have developed a rapid and precise method for glutathione quantitation by capillary electrophoresis, that allows a low amount of both redox forms to be measured. Small fragments of rat heart or liver tissues (20 mg wet weight) and the corresponding mitochondria (1 mg protein) were homogenized in 1% perchloric acid and the acid-soluble phase ultrafiltered by centrifugation with a microconcentrator (M_r cut-off 3000 Da). The analysis was performed at a constant temperature (28°C) using a Beckman P/ACE System 2100, equipped with a UV absorbance detector set to 200 nm. The limit of quantitation in heart tissue was 1.8 μM for GSH and 1.2 μM for GSSG. Myocardial concentrations of GSH and GSSG were 8.1±2.6 and 0.45±0.15 (nmol/mg protein±S.D.), respectively. The ratio of GSH to GSSG was 17.8±1.3 for heart tissue, whereas it was much higher (>100) in the mitochondria. An oxidative stress decreased the myocardial tissue GSH/GSSG ratio, indicating that the CE analysis of both glutathione forms is also a useful method to study biological redox modification.     

Inhibition of glutathione disulfide reductase by glutathione

Rat-liver glutathione disulfide reductase is significantly inhibited by physiological concentrations of the product, glutathione. GSH is a noncompetitive inhibitor against GSSG and an uncompetitive inhibitor against NADPH at saturating concentrations of the fixed substrate. In both cases, the inhibition by GSH is parabolic, consistent with the requirement for 2 eq. of GSH in the reverse reaction. The inhibition of GSSG reduction by physiological levels of the product, GSH, would result in a significantly more oxidizing intracellular environment than would be realized in the absence of inhibition. Considering inhibition by the high intracellular concentration of GSH, the steady-state concentration of GSSG required to maintain a basal glutathione peroxidase flux of 300 nmol/min/g in rat liver is estimated at 8-9 microM, about 1000-fold higher than the concentration of GSSG predicted from the equilibrium constant for glutathione reductase. The kinetic properties of glutathione reductase also provide a rationale for the increased glutathione (GSSG) efflux observed when cells are exposed to oxidative stress. The resulting decrease in intracellular GSH relieves the noncompetitive inhibition of glutathione reductase and results in an increased capacity (Vmax) and decreased Km for GSSG.     

Analysis of glutathione in rat airway surface liquid by capillary zone electrophoresis with conductivity detection

Glutathione (GSH) is an important component of antioxidant defenses in airway surface liquid (ASL), a thin layer (10-30 microm) of liquid covering the epithelial cells lining the airways of the lung. Decreased levels of ASL GSH have been reported in cystic fibrosis (CF), potentially contributing to the severe oxidative stress seen in this disease. To help investigate the role of GSH in ASL, we developed a technique suitable for analysis of GSH and its oxidized form (GSSG) in microliter samples using capillary sampling followed by capillary zone electrophoresis (CZE) analysis with conductivity detection. CZE was carried out in 100 mM CHES and 40 mM lithium hydroxide with 5 mM spermine at pH 9.1 under an applied electric field of -416 V cm(-1). To prevent any autooxidation of GSH during sample manipulations, the samples were treated with N-ethylmaleimide (50 mM) to alkylate free thiol (-SH). Under these conditions, GSH and GSSG were cleanly separated without interference from common anions (e.g. Cl(-), PO(4)(3-), HCO(3)(-), etc.) and the limit of detection for ASL analysis was 11 microM for GSH and 8 microM for GSSG (S/N=3). GSH and GSSG were also measured in rat plasma. Baseline values of 897+/-210 microM (GSH) and 215+/-61 microM (GSSG) were obtained for rat ASL (n=8), whereas 12.4+/-2.7 microM (GSH) and 14.8+/-6.7 microM (GSSG) were obtained for rat plasma (n=5).     

Cigarette smoke irreversibly modifies glutathione in airway epithelial cells

In patients with chronic obstructive pulmonary disease (COPD), an imbalance between oxidants and antioxidants is acknowledged to result in disease development and progression. Cigarette smoke (CS) is known to deplete total glutathione (GSH + GSSG) in the airways. We hypothesized that components in the gaseous phase of CS may irreversibly react with GSH to form GSH derivatives that cannot be reduced (GSX), thereby causing this depletion. To understand this phenomenon, we investigated the effect of CS on GSH metabolism and identified the actual GSX compounds. CS and H(2)O(2) (control) deplete reduced GSH in solution [Delta = -54.1 +/- 1.7 microM (P < 0.01) and -39.8 +/- 0.9 microM (P < 0.01), respectively]. However, a significant decrease of GSH + GSSG was observed after CS (Delta = -75.1 +/- 7.6 microM, P < 0.01), but not after H(2)O(2). Exposure of A549 cells and primary bronchial epithelial cells to CS decreased free sulfhydryl (-SH) groups (Delta = -64.2 +/- 14.6 microM/mg protein, P < 0.05) and irreversibly modified GSH + GSSG (Delta = -17.7 +/- 1.9 microM, P < 0.01) compared with nonexposed cells or H(2)O(2) control. Mass spectrometry (MS) showed that GSH was modified to glutathione-aldehyde derivatives. Further MS identification showed that GSH was bound to acrolein and crotonaldehyde and another, yet to be identified, structure. Our data show that CS does not oxidize GSH to GSSG but, rather, reacts to nonreducible glutathione-aldehyde derivatives, thereby depleting the total available GSH pool.     

Determination of reduced and oxidized glutathione in erythrocytes by high-performance liquid chromatography with ultraviolet absorbance detection

A method is described for simultaneous quantitation of reduced (GSH) and oxidized (GSSG) glutathione in erythrocytes by HPLC. They were determined by standard addition method. Blood samples were collected in tubes containing 1,10-phenanthroline. The separated erythrocytes were hemolyzed with water containing standard. After deproteinization, GSH and GSSG were converted to N-(2,4-dinitrophenyl) derivatives and analyzed by HPLC with UV detection. The coefficients of variation of GSH and GSSG on replicate assays were 6% and 8%, respectively. The stabilities of GSH and GSSG and of the derivatives were also examined. The present method appears to be satisfactory for determination of these physiological concentrations in erythrocytes.     

Genetic analysis of tissue glutathione concentrations and redox balance

Glutathione redox balance—defined as the ratio GSH/GSSG—is a critical regulator of cellular redox state, and declines in this ratio are closely associated with oxidative stress and disease. However, little is known about the impact of genetic variation on this trait. Previous mouse studies suggest that tissue GSH/GSSG is regulated by genetic background and is therefore heritable. In this study, we measured glutathione concentrations and GSH/GSSG in liver and kidney of 30 genetically diverse inbred mouse strains. Genetic background caused an approximately threefold difference in hepatic and renal GSH/GSSG between the most disparate strains. Haplotype association mapping determined the loci associated with hepatic and renal glutathione phenotypes. We narrowed the number of significant loci by focusing on those located within protein-coding genes, which we now consider to be candidate genes for glutathione homeostasis. No candidate genes were associated with both hepatic and renal GSH/GSSG, suggesting that genetic regulation of GSH/GSSG occurs predominantly in a tissue-specific manner. This is the first quantitative trait locus study to examine the genetic regulation of glutathione concentrations and redox balance in mammals. We identified novel candidate genes that have the potential to redefine our knowledge of redox biochemistry and its regulation and inform future therapeutic applications.     

Validation of high-performance liquid chromatography-boron-doped diamond detection for assessing hepatic glutathione redox status

Glutathione redox status is a commonly used oxidative stress biomarker. High-performance liquid chromatography-ultraviolet (HPLC-UV) and HPLC-electrochemical detection (HPLC-ECD) have been used to assess glutathione status but have potential limitations due to challenging sample preparation procedures or electrochemical signal degradation. Thus, this study aimed to validate an HPLC-ECD approach using boron-doped diamond (BDD), a novel electrode material exhibiting excellent electrochemical stability. Liver homogenates from obese (ob/ob) mice and their lean littermates (n = 4/genotype) as well as from rats fed high- or low-fat diets (n = 8/treatment) were analyzed in parallel by HPLC-BDD and -UV. HPLC-BDD responses for reduced glutathione (GSH) and oxidized glutathione (GSSG) were linear over more than four orders of magnitude at 1475 mV, the optimal oxidation potential. Within- and between-day precision values of GSH, GSSG, and GSH/GSSG were 2.1% to 7.9%, and accuracy values of GSH and GSSG were 96% and 105%, respectively. Electrochemical responses were stable up to 48 h of continuous system use. Using HPLC-BDD and -UV, hepatic GSH, GSSG, and GSH/GSSG from mice (r = 0.64-0.94) and rats (r = 0.79-0.92) were well correlated (P < 0.05), and no significant differences in thiol levels were observed between detection methods. Collectively, our findings support HPLC-BDD as a relatively simple, accurate, and validated approach for evaluating hepatic glutathione redox status.     

Detection of oxidized and reduced glutathione with a recycling postcolumn reaction

A rapid, sensitive, and selective method for the quantitation of both oxidized (GSSG) and reduced (GSH) glutathione in biological materials is described. Oxidized and reduced glutathione are resolved by anion-exchange high-performance liquid chromatography and detected with an in-line, recycling postcolumn reaction. The recycling reaction specifically amplifies the response to oxidized and reduced glutathione 20-100 times over that obtained with a stoichiometric reaction, permitting the detection of 2 pmol glutathione. Oxidized and reduced glutathione levels were measured in rat liver and in dog heart mitochondria. Special precautions are necessary to avoid artifacts which lead to either underestimation or overestimation of GSSG levels. GSH/GSSG ratios of approximately 100-300 were observed in samples prepared from rapidly frozen rat liver. Somewhat higher GSH/GSSG ratios were observed in isolated dog heart mitochondria.     

Determining glutathione and glutathione disulfide using the fluorescence probe o-phthalaldehyde

Because of the importance of glutathione (GSH) and glutathione disulfide (GSSG) in cellular signal transduction, gene regulation, redox regulation, and biochemical homeostasis, accurate determination of cellular glutathione levels is critical. Several procedures have been developed, but many suffer from overestimating GSSG or from cellular substances interfering or competing with GSH determination. Assays based on HPLC, with enzymatic reduction of GSSG by glutathione reductase and NADPH, appear to be valid but are limited in sample throughput and availability of equipment. The fluorescence probe o-phthalaldehyde (OPA, phthalic dicarboxaldehyde) reacts with GSH and has a high quantum yield, yet its use has been limited due to unidentified interfering and fluorescence-quenching substances in liver. This paper describes assay conditions under which these limitations are avoided. By using a phosphate-buffered assay at lower pH, interference with nonspecific reactants is minimal. Since enzymatic reduction is not possible due to the reaction of OPA with NAD(P)H and other stronger reducing agents, leading to an overestimation of GSSG levels, dithionite was used to reduce GSSG. High sample throughput combined with sensitive (20-pmol limit of detection) and accurate determination of GSH and GSSG using OPA is achievable with any monochromatographic spectrofluorometer. Sample preparation and storage conditions are described that return the same levels of GSH and GSSG for at least 4 weeks.     

Acetaldehyde does not inhibit glutathione peroxidase and glutathione reductase from mouse liver in vitro

Acetaldehyde, the primary ethanol metabolite, has been implicated in the pathogenesis of alcoholic liver disease, but the mechanism involved is still under investigation. This study aims at the search for direct in vitro effects of different concentrations of acetaldehyde (30, 100 and 300microM) on the activities of glutathione reductase (GR), glutathione peroxidase (GPx) from liver supernatants, and the thiol-peroxidase activity of ebselen. They did not change after pre-incubation with acetaldehyde, which suggests that acetaldehyde does not have any direct effect. Nor were direct effects of acetaldehyde toward thiols, such as dithioerythritol and glutathione (GSH), observed either, even though GSH - measured as non-protein thiols from liver supernatants - were oxidized in the presence of acetaldehyde. In addition, acetaldehyde (up to 300microM) significantly oxidized GSH when incubated in the presence of commercially available gamma-glutamyltranspeptidase (GGT), but not in the presence of glutathione-S-transferase. The interaction between ebselen and GSH was also evaluated in an attempt to better understand the possible link between acetaldehyde and nucleophilic selenol groups. The formation and stability of ebselen intermediaries, produced in the chemical interaction between GSH and ebselen, were not affected by acetaldehyde either. Overall, the acetaldehyde oxidation of hepatic low-molecular thiols depends on mouse liver constituents and GGT is proposed as an important enzyme involved in this phenomenon. Thiol depletion, a phenomenon usually observed in the livers of alcoholic patients, can be related to GSH metabolism, and the involvement of GGT may reflect a molecular mechanism involved in thiol oxidation.     

Parameters related to oxygen free radicals in erythrocytes,plasma and epidermis of the hairless rat

The following parameters related to oxygen free radicals (OFR) were determined in erythrocytes and the epidermis of hairless rats: catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), reduced (GSH) and oxidized (GSSG) glutathione, glutathione S-transferase (GST), superoxide dismutase (SOD) and thiobarbituric acid reactive substances (TBARS). GSH, GSSG and TBARS were also analyzed in plasma. In erythrocytes, the Pearson correlation coefficients (r) were significant (p < 0.001) between glutathione and other parameters as follows: GSH correlated negatively with GSSG (r = -0.665) and TBARS (r = -0.669); GSSG correlated positively with SOD (r = 0.709) and TBARS (r = 0.752). Plasma GSSG correlated negatively with erythrocytic thermostable GST activity (r = -0.608; p=0.001) and with erythrocytic total GST activity (r = -0.677; p < 0.001). In epidermis (p < 0.001 in all cases), GSH content correlated with GSSG (r = 0.682) and with GPx (r = 0.663); GSSG correlated with GPx (r = 0.731) and with GR (r = 0.794). By multiple linear regression analysis some predictor variables (R(2)) were found: in erythrocytes, thermostable GST was predicted by total GST activity and GSSG, GSSG content was predicted by GSH and by the GSH/GSSG ratio and GPx activity was predicted by GST, CAT and SOD activities; in epidermis, GSSG was predicted by GR and SOD activities and GR was predicted by GSSG, TBARS and GPx. It is concluded that the hairless rat is a good model for studying OFR-related parameters simultaneously in blood and skin, and that it may provide valuable information about other animals under oxidative stress.     

Fast liquid chromatography-mass spectrometry glutathione measurement in whole blood: micromolar GSSG is a sample preparation artifact

We describe a new, fast (6 min) and reliable method to measure reduced or oxidized glutathione (GSH) or (GSSG) in whole blood. The method is based on a LC/MS measurement in positive electrospray ionization mode after a chromatographic separation on a specific column which does not need any counter-ion in the mobile phase, improving the sensitivity of detection. A 50 microl sample of whole blood is sufficient for analysis. We demonstrate that the lack of an alkylating agent during the sample preparation brings out an underestimation of GSH and an artefactual production of GSSG, corresponding to 2-3% of GSH. The simultaneous use of N-ethyl-maleimide and a strong deproteinising acid prevents these two drawbacks. This efficient and new method of preparation and analysis lets us show that, unexpectedly, GSH is stable in whole blood for some hours and that deproteinised samples can be stored without GSH loss for at least three weeks at -20 or -80 degrees C. The reference interval, measured on 22 volunteers, on blood samples collected either with heparin or with EDTA, is 1310 +/- 118 microM for GSH and 0.62 microM for GSSG. The within-run precision of this method, with gamma glutamyl-glutamic acid as an internal standard, evaluated in three successive series (n = 30), lies between 2.1 and 4.8% for a GSH level at 580 or 1150 microM. The one step sample preparation we propose seems well suited for GSH routine measurements in hospital laboratories and avoids any underestimation of GSH, a now well accepted biomarker of oxidative stress.     

Preferential transport of glutathione versus glutathione disulfide in rat liver microsomal vesicles

A bi-directional, saturable transport of glutathione (GSH) was found in rat liver microsomal vesicles. GSH transport could be inhibited by the anion transport blockers flufenamic acid and 4, 4'-diisothiocyanostilbene-2,2'-disulfonic acid. A part of GSH taken up by the vesicles was metabolized to glutathione disulfide (GSSG) in the lumen. Microsomal membrane was virtually nonpermeable toward GSSG; accordingly, GSSG generated in the microsomal lumen could hardly exit. Therefore, GSH transport, contrary to previous assumptions, is preferred in the endoplasmic reticulum, and GSSG entrapped and accumulated in the lumen creates the oxidized state of its redox buffer.     

Redox state of glutathione in human plasma

Thiol and disulfide forms of glutathione (GSH) and cysteine (Cys) were measured in plasma from 24 healthy individuals aged 25-35 and redox potential values (E(h)) for thiol/disulfide couples were calculated using the Nernst equation. Although the concentration of GSH (2.8 +/- 0.9 microM) was much greater than that of GSSG (0.14 +/- 0.04 microM), the redox potential of the GSSG/2GSH pool (-137 +/- 9 mV) was considerably more oxidized than values for tissues and cultured cells (-185 to -258 mV). This indicates that a rapid oxidation of GSH occurs upon release into plasma. The difference in values between individuals was remarkably small, suggesting that the rates of reduction and oxidation in the plasma are closely balanced to maintain this redox potential. The redox potential for the Cys and cystine (CySS) pool (-80 +/- 9 mV) was 57 mV more oxidized, showing that the GSSG/2GSH and the CySS/2Cys pools are not in redox equilibrium in the plasma. Potentials for thiol/disulfide couples involving CysGly were intermediate between the values for these couples. Regression analyses showed that the redox potentials for the different thiol/disulfide couples within individuals were correlated, with the E(h) for CySS-mono-Gly/(Cys. CysGly) providing the best correlation with other low molecular weight pools as well as protein disulfides of GSH, CysGly and Cys. These results suggest that E(h) values for GSSG/2GSH and CySS-mono-Gly/(Cys. CysGly) may provide useful means to quantitatively express the oxidant/antioxidant balance in clinical and epidemiologic studies.     

Assay for quantitative determination of glutathione and glutathione disulfide levels using enzymatic recycling method

The spectrophotometric/microplate reader assay method for glutathione (GSH) involves oxidation of GSH by the sulfhydryl reagent 5,5'-dithio-bis(2-nitrobenzoic acid) (DTNB) to form the yellow derivative 5'-thio-2-nitrobenzoic acid (TNB), measurable at 412 nm. The glutathione disulfide (GSSG) formed can be recycled to GSH by glutathione reductase in the presence of NADPH. The assay is composed of two parts: the preparation of cell cytosolic/tissue extracts and the detection of total glutathione (GSH and GSSG). The method is simple, convenient, sensitive and accurate. The lowest detection for GSH and GSSG is 0.103 nM in a 96-well plate. This method is rapid and the whole procedure takes no longer than 15 min including reagent preparation. The method can assay GSH in whole blood, plasma, serum, lung lavage fluid, cerebrospinal fluid, urine, tissues and cell extracts and can be extended for drug discovery/pharmacology and toxicology protocols to study the effects of drugs and toxic compounds on glutathione metabolism.     

Blood glutathione redox status in gestational hypertension

Gestational hypertension during the third trimester reflects an exaggerated maternal inflammatory response to pregnancy. We hypothesized that oxidative stress present even in normal pregnancy becomes uncompensated in hypertensive patients. A glucose-6-phosphate dehydrogenase (G6PD) activity sufficient to meet the increased reductive equivalent need of the cells is indispensable for defense against oxidative stress. The erythrocyte glutathione redox system was studied, where G6PD is the only NADPH source. The glutathione (GSH) redox status was measured both in vivo and after an in vitro oxidative challenge in pregnant women with gestational hypertension (n = 19) vs. normotensive pregnant subjects (n = 18) and controls (n = 20). An erythrocyte GSH depletion with an increase in the oxidized form (GSSG) resulted in an elevated ratio GSSG/GSH (0.305 +/- 0.057; mean +/- SD) in hypertensive pregnant women vs. normotensive pregnant or control subjects (0.154 +/- 0.025; 0.168 +/- 0.073; p <.001). In hypertensive pregnant patients, a "GSH stability" decrease after an in vitro oxidative challenge suggested a reduced GSH recycling capacity resulting from an insufficient NADPH supply. The erythrocyte GSSG/GSH ratio may serve as an early and sensitive parameter of the oxidative imbalance and a relevant target for future clinical trials to control the effects of antioxidant treatment in women at increased risk of the pre-eclampsia syndrome.     

Role of S-adenosylmethionine on the hepatobiliary homeostasis of glutathione during cyclosporine A treatment

The effects of cyclosporine A (CyA) treatment on the hepatic content and biliary output of reduced (GSH) and oxidized (GSSG) glutathione and lipid peroxidation in the liver, and the ability of S-adenosylmethionine (SAMe) to antagonize the CyA-induced alterations were studied in male Wistar rats. To evaluate the efficacy of SAMe, three CyA and SAMe protocols were used: cotreatment with SAMe plus CyA, pretreatment with SAMe before starting cotreatment, and post-treatment with SAMe after beginning treatment with CyA alone. CyA treatment for one and four weeks depleted liver GSH, decreased the GSH/GSSG ratio and significantly reduced GSH and GSSG biliary concentrations and secretion rates. Additionally, long-term treatment enhanced lipid peroxidation. By contrast, when the rats were treated with CyA plus SAMe using any of the administration protocols, SAMe was seen to be efficient in antagonizing the GSH hepatic depletion, the changes in hepatic GSH/GSSG ratio and the increase induced by CyA in lipid peroxidation. Furthermore, SAMe also abolished the effects of CyA on the biliary secretion rates of GSH and GSSG. The efficacy of SAMe was similar, regardless of the administration protocols used. In conclusion, our results clearly demonstrate that SAMe is good for preventing, antagonizing and reversing the CyA-induced alterations in the hepatobiliary homeostasis of glutathione.     

Upregulation of cerebral cortical glutathione synthesis by ammonia in vivo and in cultured glial cells: the role of cystine uptake

Glutathione (GSH) is a major antioxidant in the brain and ammonia neurotoxicity is associated with oxidative stress. In this study, we show that intracerebral administration of ammonium chloride (“ammonia”, final concentration 5 mM) via a microdialysis probe, increases by 80% the glutathione content in cerebral cortical microdialysates, and tends to increase its content in striatal microdialysates. Treatment with ammonia in vitro dose-dependently increased the glutathione content in cultured cerebral cortical astrocytes and a C6 glioma cell line. Significant effects have been observed after 1 h (astrocytes) or 3 h (C6 cells) of exposure and were sustained up to 72 h of incubation. A gradual decrease of the GSH/GSSG ratio noted during 3 h (astrocytes) or 24 h (C6 cells) of exposure, was followed by an partial recovery after 24 h of incubation, the latter phase possibly reflecting increased availability of de novo synthesized glutathione. In our hands, cystine, the precursor for astrocytic glutathione synthesis, was transported to astrocytes almost exclusively by system X_AG⁻, while in C6 cells the transport engaged both system x_c⁻ (60% of uptake) and X_AG⁻ (40% of uptake). Ammonia in either cell type stimulated cystine uptake without changing the relative contribution of the uptake systems. The results are consistent with the concept of increased astrocytic glutathione synthesis as an adaptive response of the brain to ammonia challenge, and emphasize upregulation of cystine uptake as a factor contributing to this response.     

Effect of 1-methyl-4-phenylpyridinium on glutathione in rat pheochromocytoma PC 12 cells

We investigated the effect of the selective dopaminergic neurotoxin 1-methyl-4-phenylpyridinium (MPP+) on glutathione redox status and the generation of reactive oxygen intermediates (ROI) in rat pheochromocytoma PC 12 cells in vitro. Treatment with MPP+ (250 microM) led to a 63% increase of reduced glutathione (GSH) after 24 h, while a 10-fold higher concentration of MPP+ (2.5 mM) depleted cellular GSH to 12.5% of control levels within that time. Similarly, the complex I-inhibitor rotenone induced a time-dependent loss of GSH at 1 and 10 microM, whereas treatment with lower concentrations of rotenone (0.1, 0.01 microM) increased cellular GSH. Both MPP+ and rotenone increased cellular levels of oxidised glutathione (GSSG) and the higher concentrations of both compounds led to an elevated ratio of oxidised glutathione (GSSG) vs total glutathione (GSH + GSSG) indicating a shift in cellular redox balance. MPP+ or rotenone did not induce the generation of ROI or significant elevation of intracellular levels of thiobabituric acid reactive substances (TBARS) for up to 48 h. Our data suggest that MPP+ has differential effects on glutathione homeostasis depending on the degree of complex I-inhibition and that inhibition of complex I is not sufficient to generate ROI in this paradigm.