Analysis of glutathione by capillary electrophoresis based on sample stacking

Determination of glutathione in blood via capillary electrophoresis with pH-mediated stacking

A new approach has been developed for the direct determination of reduced (glutathione [GSH]) and oxidized (glutathione disulfide [GSSG]) GSH in whole blood by means of capillary electrophoresis. Its features include GSH-stabilizing sample preparation, the use of an internal standard, and pH-mediated stacking. Blood stabilized with acid citrate and K₃ EDTA was treated with acetonitrile with N-ethylmaleimide, and then the analytes were extracted with diethyl ether. The total analysis time was 8 min using a 50-µm (i.d.) by 32.5-cm (eff. length) silica capillary. The background electrolyte was 0.075-M citrate Na pH 5.8 with 200-µM cetyltrimethylammonium bromide and 5-µM sodium dodecyl sulfate, and the separation voltage was -14 kV. The quantification limit (S/N = 15) of the method was 1.5 µM for GSSG. The accuracy levels of GSH and GSSG analysis were 104% and 103%, respectively, and between-run precision levels were 2.6% and 3.2%, respectively. Analysis of blood samples from healthy volunteers (N = 24) showed that the levels of GSH and GSSG and the GSH/GSSG ratio in the whole blood were 1.05 ± 0.14 mM, 3.9 ± 1.25 µM, and 256 ± 94, respectively. Thus, the presented approach can be used in clinical and laboratory practice.

Simultaneous Determination of Ciprofloxacin and Ofloxacin in Animal Tissues with the Use of Capillary Electrophoresis with Transient Pseudo-Isotachophoresis

We have developed a precise and accurate method for the determination of ciprofloxacin and ofloxacin in meat tissues. Our method utilizes capillary electrophoresis with a transient pseudo-isotachophoresis mechanism and liquid–liquid extraction during sample preparation. For our experiment, a meat tissue sample was homogenized in pH 7.00 phosphate buffer at a ratio of 1:10 (tissue mass: buffer volume; g/mL). The extraction of each sample was carried out twice for 15 min with 600 µL of a mixture of dichloromethane and acetonitrile at a 2:1 volume ratio. We then conducted the electrophoretic separation at a voltage of 16 kV and a temperature of 25 °C using a background electrolyte of 0.1 mol/L phosphate–borate (pH 8.40). We used the UV detection at 288 nm. The experimentally determined LOQs for ciprofloxacin and ofloxacin were 0.27 ppm (0.8 nmol/g tissue) and 0.11 ppm (0.3 nmol/g tissue), respectively. The calibration curves exhibited linearity over the tested concentration range of 2 to 10 nmol/g tissue for both analytes. The relative standard deviation of the determination did not exceed 15%, and the recovery was in the range of 85–115%. We used the method to analyze various meat tissues for their ciprofloxacin and ofloxacin contents.

Glutathione

Glutathione is an endogenous peptide with antioxidant and other metabolic functions. The nomenclature, formulae, elemental composition, and appearance and uses of the drug are included. The methods used for the synthesis and biosynthesis of glutathione are described. This profile contains the physical characteristics of the drug including: solubility, X-ray powder diffraction pattern, crystal structure, melting point, and differential scanning calorimetry. The spectral methods that were used for both the identification and analysis of glutathione include ultraviolet spectrum, vibrational spectrum, 1H and 13C nuclear magnetic resonance spectra, and mass spectrum. The profile also includes the compendial methods of analysis and the other methods of analysis that are reported in the literature. These other methods of e-analysis are: potentiometric, voltammetric, amperometric, spectrophotometric, specrtofluorometric, chemiluminescence, chromatographic and immunoassay methods. The stability of and several reviews on drug are also provided. More than 170 references are listed at the end this comprehensive profile on glutathione.

Differential rates of glutathione oxidation for assessment of cellular redox status and antioxidant capacity by capillary electrophoresis-mass spectrometry: an elusive biomarker of oxidative stress

Glutathione metabolism plays a fundamental role in maintaining homeostasis and regulating the redox environment of a cell. Despite the widespread interest in quantifying glutathione metabolites in oxidative stress research, conventional techniques are hampered by complicated sample handling procedures to prevent significant oxidation artifacts generated during sample collection, sample pretreatment, and/or chemical analysis. In this report, a simple and validated method for glutathione analysis from filtered red blood cell (RBC) lysates was developed using capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) in conjunction with fingerprick microsampling and ultrafiltration. About a 3-fold improvement in precision with nanomolar detection limits was achieved when using online sample preconcentration with CE-ESI-MS via a modified injection sequence, which permitted accurate determination of the intracellular reduced/oxidized glutathione ratio (GSH/GSSG), as well as other glutathione species, including protein-bound glutathione mixed disulfide (PSSG), free glutathione mixed disulfides (GSSR) and glutathione thioether conjugates (GSX). In this work, the redox status of filtered hemolysates was determined by the equilibrium half-cell reduction potential for glutathione (E(GSSG/2GSH)), whereas its intrinsic antioxidant capacity was assessed by the apparent rate of metal-catalyzed oxidation of glutathione. In-vitro incubation studies of intact RBCs with 1-chloro-2,4-dinitrobenzene (CDNB) and N-acetyl-L-cysteine (NAC) were found to significantly alter E(GSSG/2GSH) and/or glutathione oxidation kinetics (e.g., k(GSSG)) relative to normal controls based on their function as a toxic electrophilic compound and a competitive free radical scavenging/reducing agent, respectively. Differential rates of glutathione oxidation (DIRGO) using CE-ESI-MS offers a novel strategy for global assessment of the impact of intrinsic metabolite constituents (i.e., metabolome) and/or extrinsic perturbants on cellular redox status that is relevant to improved understanding of aging and the pathogenesis of acute or chronic disease states.

Simultaneous determination of oxidized and reduced glutathione in eel's (Monopterus albus) plasma by transient pseudoisotachophoresis coupled with capillary zone electrophoresis

Both the reduced form of glutathione (GSH) and the oxidized form of glutathione (GSSG) in eel's ( Monopterus albus) plasma were for the first time determined by transient pseudoisotachophoresis coupled with capillary zone electrophoresis. The method of transient pseudoisotachophoresis coupled with capillary zone electrophoresis has been thoroughly optimized and adequately evaluated for the simultaneous determination of GSH and GSSG in eel's plasma. The detection limits (S/N = 3) of the method developed were 0.2 and 0.05 micromol/L for GSH and GSSG, respectively. The linearity of the calibration curves was valid in the range of 0-10 micromol/L GSH and 0-0.70 micromol/L GSSG. The method was simple, fast, and reproducible. It was found that the respective concentrations of GSH and GSSG were in the range of 9.1-14.5 and 0.31-0.58 micromol/L in the adult eel's plasma, and 10.8-17.9 and 0.49 - 0.68 micromol/L in the juvenile eel's plasma of the three populations determined. Each blood sample was a composite of five eels. For each of the three populations, the concentrations of GSH and GSSG in the adult eel's plasma were lower than those in the juvenile eel's plasma, and the concentrations of GSH and GSSG in the plasma of population 1 (deep yellow finless eels) were higher than those in populations 2 (light yellow finless eels) and 3 (green finless eels) for either the adult or the juvenile eels.

Sample preparation

A panorama of sample preparation methods has been composed from 481 references, with a highlight of some promising methods fast developed during recent years and a somewhat brief introduction on most of the well-developed methods. All the samples were commonly referred to molecular composition, being extendable to particles including cells but not to organs, tissues and larger bodies. Some criteria to evaluate or validate a sample preparation method were proposed for reference. Strategy for integration of several methods to prepare complicated protein samples for proteomic studies was illustrated and discussed.

Online acid barrage stacking anti-salt injection for capillary electrophoresis of 9-fluorenylmethylchloroformate-derivatized amino acids in high ionic strength solutions by UV detection

An acid barrage stacking (ABS) method has been shown to be feasible for online anti-salt injection in CE of 9-fluorenylmethyl chloroformate (FMOC)-labeled amino acids (AAs) detected by common UV absorption. The operation was performed on normal polar CE by sucking in an extra plug of acid following a sample zone, serving as a selective acid barrage to block the backward migration of weak anionic analytes due to a sudden mobility reduction via acid-base reaction which does not affect strong co-ions such as Cl(-) to penetrate the barrage freely. By CE-UV of FMOC-AAs in various NaCl solutions, the effectiveness of ABS was firmly validated, able to stand up to 500 mM NaCl and to stack analytes by 10(3)-fold calculated from the UV detection limits, that is 0.01 microM for ABS and 10 microM for non-stacking injection. The method was also validated by determining trace Glu and Asp in real samples of rat brain microdialysate, rat serum and human saliva. The intraday RSDs were 0.33-4.9% for migration time and 1.8-9.6% for peak area. The recoveries measured by spiking technique were 82-115% for Glu and 86-116% for Asp. Working equations were obtained by plotting peak height vs. concentration at 0.1-50 microM, with correlation coefficients of >0.999. The contents of Glu and Asp were thus found at 0.26-0.83 microM and 0.24-0.64 microM respectively, in rat brain microdialyste; 37-40 microM and 8.4-10 microM, respectively, in rat serum; and 3.5-5.8 microM and 1.0-4.1 microM, respectively in human saliva. They were consistent with the data from other methods.

Sample enrichment techniques in capillary electrophoresis: Focus on peptides and proteins

Compared to chromatography-based techniques, the concentration limits of detection (CLOD) associated with capillary electrophoresis are worse, and these have largely precluded their use in many practical applications. To overcome this limitation, researchers from various disciplines have exerted tremendous efforts toward developing strategies for increasing the concentration sensitivities of capillary electrophoresis (CE) systems, via the so-called sample enrichment techniques. This review highlights selected developments and advances in this area as applied to the analyses of proteins and peptides in the last 5 years.

Transient pseudo-isotachophoretic stacking in analysis of plasma for homocysteine by capillary zone electrophoresis

An analytical procedure enabling routine analysis of human plasma for total homocysteine has been developed and validated. The method includes reduction of homocysteine disulfides to thiol with tris 2-carboxyethylphosphine, derivatization of the thiol with 2-chloro-1-methylquinolinium tetrafluoroborate, separation of homocysteine 2-S-quinolinium derivative from those of plasma endogenous and exogenous thiol derivatives by capillary zone electrophoresis, and quantitation with the use of ultraviolet detection based on acetonitrile stacking. Method performance characteristics, for example recovery, calibration, precision, limit of detection, and limit of quantitation, are presented. The procedure was applied to analysis of plasma samples donated by apparently healthy volunteers.

Recent advances of transient isotachophoresis-capillary electrophoresis in the analysis of small ions from high-conductivity matrices

Since its invasion into the field of small ion analysis, quantitation of trace ionic analytes has always been a challenging task for CE, especially when dealing with highly saline samples. This review summarizes the method's progress and significant developments in the area due to its combination with on-line preconcentration by transient ITP (tITP). Principles of tITP stacking in high-conductivity solutions and operational preconcentration modes are considered. The most important application areas covered in this review include the analysis of seawater and biological fluids (urine, serum, etc.). Examples cited in this review demonstrate that tITP-CE is now on a certain way of becoming a recognized technique when the determination of trace ionic species in loaded matrices is the aim.

Progress in capillary electrophoresis of biomarkers and metabolites between 2002 and 2005

Biomarker discovery and metabolite research is a fast-growing and extremely important domain not only for the early detection of certain diseases but also for controlling its progress as well as in pharmaceutical investigations. For the analytical separation and identification, CE plays an indisputable role. Capillary systems enhancing different selectivity are applied and connected to different kind of detection systems. As the choice of buffer and its composition is responsible for a successful separation, special emphasis is put on solvent effects in this review. Altogether the most important capillary electrophoretic techniques applied for biomarker and metabolites analysis published between 2002 and 2005 are summarized and discussed.

Capillary electrophoresis of glutathione to monitor oxidative stress and response to antioxidant treatments in an animal model

Glutathione plays a central role in metabolism and antioxidant defence. Several factors can influence the analytical efficiency and rapidity of the quantitative determination of glutathione. Procedures in sample pre-treatment have been compared in order to minimize analytical errors. Capillary electrophoresis has been chosen as a more adequate technique for obtaining a rapid and simple method for glutathione and glutathione disulfide determination in the blood and liver of the rat. The methods, once optimised, have been validated and applied for monitoring the oxidative stress in an animal model, such as the rat made diabetic by streptozotocin injection, when the animals are treated with antioxidants and compared with the corresponding controls.

Optimization stacking by transient pseudo-isotachophoresis for capillary electrophoresis: example analysis of plasma glutathione

Low concentrations of both reduced form glutathione (GSH) and oxidized form glutathione (GSSG) in diabetic nephropathy (DN) patient's plasma were measured with transient pseudo-isotachophoresis. The plasma samples were deproteined with acetonitrile and centrifuged. The method was performed at constant voltage of 5 kV using a 300 mM borate buffer (pH 8.0), with a fused-silica capillary of 21 cm x 75 microm. The sample length can reach 25% of the efficient length of the capillary, and the sensitivities of GSH and GSSG increased 15-20-fold. The method was also systematically optimized, and the results show that this type of stacking offers good repeatability for routine clinical assay of glutathione in DN plasmas.

Automated large-volume sample stacking procedure to detect labeled peptides at picomolar concentration using capillary electrophoresis and laser-induced fluorescence detection

We have developed an automated large-volume sample stacking (LVSS) procedure to detect fluorescein isothiocyanate-labeled peptides in the picomolar range. The injection duration is 10 min at 50 mbar to fill 62% of the capillary volume to the detection cell. The calculated limit of detection (S/N=3), filling 1% of the capillary volume, is 74 pM for bradykinin and 45 pM for L-enkephalin with samples diluted in water and analyzed in a 50 mM borate buffer, pH 9.2. With the automated LVSS system, the limits of detection are 7 pM for bradykinin, 3 pM for L-enkephalin and 2 pM for substance P. LVSS is shown to be quantitative from 500 to 10 pM.