Reversed-phase chromatographic method for specific determination of glutathione in cultured malignant cells

Role of quinones in the ascorbate reduction rates of S-nitrosoglutathione

Quinones are one of the largest classes of antitumor agents approved for clinical use, and several antitumor quinones are in various stages of clinical and preclinical development. Many of these are metabolites of, or are, environmental toxins. Because of their chemical structure they are known to enhance electron transfer processes such as ascorbate oxidation and NO reduction. The paraquinones 2,6-dimethyl-1,4-benzoquinone (DMBQ), 1,4-benzoquinone, methyl-1,4-benzoquinone, 2,6-dimethoxy-1,4-benzoquinone, 2-hydroxymethyl-6-methoxy-1,4-benzoquinone, trimethyl-1,4-benzoquinone, tetramethyl-1,4-benzoquinone, and 2,3-dimethoxy-5-methyl-1,4-benzoquinone; the paranaphthoquinones 1,4-naphthoquinone, menadione, 1,4-naphthoquinone-2-sulfonate, 2-ethylsulfanyl-3-methyl-1,4-naphthoquinone and juglone; and phenanthraquinone (PHQ) all enhance the anaerobic rate of ascorbate reduction of GSNO to produce NO and GSH. Rates of this reaction were much larger for p-benzoquinones and PHQ than for p-naphthoquinone derivatives with similar one-electron redox potentials. The quinone DMBQ also enhances the rate of NO production from S-nitrosylated bovine serum albumin upon ascorbate reduction. Density functional theory calculations suggest that stronger interactions between p-benzo- or phenanthrasemiquinones and GSNO than between p-naphthosemiquinones and GSNO are the major causes of these differences. Thus, quinones, and especially p-quinones and PHQ, could act as enhancers of NO release from GSNO in biomedical systems in the presence of ascorbate. Because quinones are exogenous toxins that could enter the human body via a chemotherapeutic application or as an environmental contaminant, they could boost the release of NO from S-nitrosothiol storages in the body in the presence of ascorbate and thus enhance the responses elicited by a sudden increase in NO levels.

Chromatographic and mass spectrometric analysis of glutathione in biological samples

Biological thiol compounds are classified into high-molecular-mass protein thiols and low-molecular-mass free thiols. Endogenous low-molecular-mass thiol compounds, namely, reduced glutathione (GSH) and its corresponding disulfide, glutathione disulfide (GSSG), are very important molecules that participate in a variety of physiological and pathological processes. GSH plays an essential role in protecting cells from oxidative and nitrosative stress and GSSG can be converted into the reduced form by action of glutathione reductase. Measurement of GSH and GSSG is a useful indicator of oxidative stress and disease risk. Many publications have reported successful determination of GSH and GSSG in biological samples. In this article, we review newly developed techniques, such as liquid chromatography coupled with mass spectrometry and tandem mass spectrometry, for identifying GSH bound to proteins, or for localizing GSH in bound or free forms at specific sites in organs and in cellular locations.

Nicotinamide adenine dinucleotide phosphate-regenerating system coupled to a glutathione-reductase microtiter method for determination of total glutathione concentrations in adherent growing cancer cell lines

Improvements in the traditional glutathione (GSH)-reductase recycling method for determining total glutathione levels in adherent growing cells have been achieved by eliminating the direct use of expensive nicotinamide adenine dinucleotide phosphate (NADPH) and normalizing the levels of GSH to moles/liter instead of the more usual but more error-prone method of normalizing with cellular protein. A glucose-6-phosphate-dehydrogenase auxiliary reaction has been added to the microtiter-adapted enzyme method of Tietze; thus NADP(+) and glucose-6-phosphate replace NADPH in the method. This modification lowers the possibility for substrate inhibition of the reductase by high levels of NADPH during the initial phase of the reaction while at the same time reducing the assay costs by 75-85%. To calculate the cellular concentration of GSH, the number of cells used for the GSH determination, estimated by counting cell nuclei of benzalkonium chloride-lysed cells with a Coulter Counter Z2, and the average cell volume, also determined with the Coulter Counter, are multiplied to give the total sample volume. The quotient of the amount of GSH found in the cells and the total sample volume yields the GSH concentration in moles/liter. The assay has been validated with respect to precision (+/-2.6%), relative accuracy (-4.2 %), linearity (r(2)=0.98), linear range (0.5-10 microM), and limit of detection (80 pmol). Recovery was cell line dependent and ranged between 70 and 103% in the six cell lines. As an application of this method, the GSH concentrations in six human cancer cell lines were determined, without and with a 24-h preincubation with 200 microM D,L-buthionine-S,R-sulfoximine (BSO), an inhibitor of GSH biosynthesis. As expected, BSO lowered GSH levels on the average 85%.

A simultaneous liquid chromatography/mass spectrometric assay of glutathione, cysteine, homocysteine and their disulfides in biological samples

A liquid chromatography/mass spectrometric (LC/MS) method was developed for simultaneous detection and quantitation of glutathione (GSH), glutathione disulfide (GSSG), cysteine (CysSH), homocysteine (HCysSH) and homocystine in biological samples (rat brain, lung, liver, heart, kidneys, erythrocytes and plasma). Thiols were derivatized with a large excess of Ellman's reagent, a thiol-specific reagent, to ensure an instantaneous and complete derivatization. The derivatization blocked the oxidation of the thiols to disulfides, preventing errors caused by thiol oxidation. The samples were then analyzed by LC/MS. The method provides a highly selective and sensitive assay for these endogenous thiols and their corresponding disulfides. The detection limits for GSH, GSSG, CysSH, HCysSH and homocystine were 3.3, 3.3, 16.5, 29.6 and 14.9 pmol, respectively. An attempt for cystine analysis was unsuccessful due to earlier elution of the compound and strong interferences caused by other endogenous compounds. This method will be a useful tool in the investigation of the roles of these important thiol-containing compounds and their corresponding disulfides in physiological and pathological processes.

Sulfur K-edge x-ray absorption spectroscopy: a spectroscopic tool to examine the redox state of S-containing metabolites in vivo

The sulfur K-edge x-ray absorption spectra for the amino acids cysteine and methionine and their corresponding oxidized forms cystine and methionine sulfoxide are presented. Distinct differences in the shape of the edge and the inflection point energy for cysteine and cystine are observed. For methionine sulfoxide the inflection point energy is 2.8 eV higher compared with methionine. Glutathione, the most abundant thiol in animal cells, also has been investigated. The x-ray absorption near-edge structure spectrum of reduced glutathione resembles that of cysteine, whereas the spectrum of oxidized glutathione resembles that of cystine. The characteristic differences between the thiol and disulfide spectra enable one to determine the redox status (thiol to disulfide ratio) in intact biological systems, such as unbroken cells, where glutathione and cyst(e)ine are the two major sulfur-containing components. The sulfur K-edge spectra for whole human blood, plasma, and erythrocytes are shown. The erythrocyte sulfur K-edge spectrum is similar to that of fully reduced glutathione. Simulation of the plasma spectrum indicated 32% thiol and 68% disulfide sulfur. The whole blood spectrum can be simulated by a combination of 46% disulfide and 54% thiol sulfur.

General strategies and selection of derivatization reactions for liquid chromatography and capillary electrophoresis

The general strategies, reasons and the different possibilities for the derivatization of biomedically important compounds are reviewed. Different approaches apply for small versus large analyte molecules, different advantages and disadvantages are visualized with pre- and post-column arrangements. Particular interest is focused upon solid-phase derivatization reagents.

Simultaneous high-performance capillary electrophoretic determination of reduced and oxidized glutathione in red blood cells in the femtomole range

This paper describes a high-performance capillary electrophoretic (HPCE) method which allows a quick, simultaneous and quantitative determination of reduced (GSH) and oxidized (GSSG) glutathione in mammalian red blood cells using a Supelco-bonded hydrophilic phase capillary CElect-P150. The extraction procedure of GSH and GSSG from erythrocytes using Microcon-10 membranes is very simple and allows a correct evaluation of these compounds present in the red blood cells. Furthermore, the HPCE method does not require removal of the excess N-ethylmaleimide used to block the glutathione in its reduced state, making the simultaneous evaluation of GSH and GSSG possible in a very short time (ca. 4 min), with a sensitivity at femtomole level.

Glutathione and glutathione linked enzymes in human small cell lung cancer cell lines

Glutathione levels and several glutathione-linked enzyme activities have been variably correlated with cisplatin chemosensitivity in cultured neoplastic cells. In order to determine the relative contribution of the glutathione-linked enzymes towards mediating inherent cisplatin resistance in cancer cells, we have measured the chemosensitivity to cisplatin, glutathione levels and activities of glutathione S-transferase, glutathione peroxidase, glutathione reductase and glucose-6-phosphate dehydrogenase in 8 cultured human small cell lung cancer (SCLC) cell lines with widely differing cisplatin sensitivities. Of these parameters, only glutathione S-transferase activity correlated with degree of cisplatin resistance in a linear fashion.