Analysis of diagnostic metabolites by capillary electrophoresis-mass spectrometry

Mass Spectrometry in Advancement of Redox Precision Medicine

Redox (portmanteau of reduction-oxidation) reactions involve the transfer of electrons between chemical species in biological processes fundamental to life. It is of outmost importance that cells maintain a healthy redox state by balancing the action of oxidants and antioxidants; failure to do so leads to a multitude of diseases including cancer, diabetes, fibrosis, autoimmune diseases, and cardiovascular and neurodegenerative diseases. From the perspective of precision medicine, it is therefore beneficial to interrogate the redox phenotype of the individual-similar to the use of genomic sequencing-in order to design tailored strategies for disease prevention and treatment. This chapter provides an overview of redox metabolism and focuses on how mass spectrometry (MS) can be applied to advance our knowledge in redox biology and precision medicine.

Cleaved DNAzyme substrate induced enzymatic cascade for the exponential amplified analysis of L-histidine

A novel strategy of cleaved DNAzyme substrate induced enzymatic cascade has been devised for the exponential amplified detection of L-histidine. The enzyme strand carries out hydrolytic cleavage of the substrate strand in the presence of L-histidine. The cleaved DNAzyme substrates introduce the polymerase/endonuclease reaction cycles as primers. The L-histidine acts as the activator for enzymatic cascade amplification generating a distinguishable fluorescence enhancement. A good nonlinear correlation (R=0.9994) between fluorescence intensity and the logarithm of the L-histidine concentration is obtained over the range from 50 nM to 1.0 mM. The detection limit was estimated as 30 nM. This efficient amplification of the fluorescence signal is attributed to the L-histidine induced cooperation of Klenow Fragment polymerase (exo(-)) and Nb.BbvCI endonuclease reaction. The activation of such enzymatic cascades through analyte-DNAzyme interactions has a substantial impact on the development of exponential amplified DNAzyme sensors.

Light and heavy dansyl reporter groups in food chemistry: amino acid assay in beverages

5-Dimethylamino-1-sulfonyl naphthalene (DNS, commonly referred as dansyl) is a functionality, bearing well-established properties in directing the fragmentation, by mass spectrometry (MS), of the corresponding ionized sulfonylated derivatives. This property is shared also by its labeled analogs. The use of d(0)/d(6) DNS derivatives is now exploited in the application of the well-established isotope dilution mass spectrometric approach in the assay of complex mixtures. A new method for the quantitation of amino acids (AAs) in beverages is therefore presented, which relies on liquid chromatographic separation of their N-dansylated derivatives followed by comparative electrospray tandem MS/MS of the d(0)/d(6) isobaric mixtures. Labeled and unlabeled DNS derivatives of the selected AAs are readily available by microwave-assisted synthetic protocols. The novelty of the method is represented by the use of heavy and light DNS-isotopologue providing suitable reporter groups. Multiple-reaction monitoring has been applied in the assay of AAs in wine, pineapple juice and bergamot juice with good-to-excellent results as proved by both relative standard deviation, lower than 15%, and by the accuracy values in the range 90-110%.

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.

Comparative metabolite profiling of carboxylic acids in rat urine by CE-ESI MS/MS through positively pre-charged and (2)H-coded derivatization

A new approach to the selective comparative metabolite profiling of carboxylic acids in rat urine was established using CE-MS and a method for positively pre-charged and (2)H-coded derivatization. Novel derivatizing reagents, N-alkyl-4-aminomethyl-pyridinum iodide (alkyl = butyl, butyl-d9 or hexyl), containing quaternary amine and stable-isotope atoms (deuterium), were introduced for the derivatization of carboxylic acids. CE separation in positive polarity showed high reproducibility (0.99-1.32% RSD of migration time) and eliminated problems with capillary coating known in CE-MS anion analyses. Essentially complete ionization and increased hydrophobicity after the derivatization also enhanced MS detection sensitivity (e.g. formic acid was detected at 0.5 pg). Simultaneous derivatization of one sample using two structurally similar reagents, N-butyl-4-aminomethyl-pyridinum iodide (BAMP) and N-hexyl-4-aminomethyl-pyridinum iodide, provided additional information for recognizing a carboxylic acid in an unknown sample. Moreover, characteristic fragmentation acquired by online CE-MS/MS allowed for identification and categorization of carboxylic acids. Applying this method on rat urine, we found 59 ions matching the characteristic patterns of carboxylic acids. From these 59, 32 ions were positively identified and confirmed with standards. For comparative analysis, 24 standard carboxylic acids were derivatized by chemically identical but isotopically distinct BAMP and N-butyl-d9-4-aminomethyl-pyridinium iodide, and their derivatization limits and linearity ranges were determined. Comparative analysis was also performed on two individual urine samples derivatized with BAMP and N-butyl-d9-4-aminomethyl-pyridinium iodide. The metabolite profiling variation between these two samples was clearly visualized.

A new method for screening and determination of diuretics by on-line CE-ESI-MS

A rapid, high-resolution and effective new method for analyzing 12 diuretics by CE-ESI-MS was established in this paper. Ten diuretics (except two neutral compounds) could be fast separated by CE with a DAD at 214 nm with a 20 kV voltage within 6 min, using a 50 microm id and 48.5 cm effective length uncoated fused-silica capillary in a 40 mM ammonium formate buffer (pH 9.40). CE was coupled to the mass spectrometer applying an orthogonal electrospray interface with a triple-tube sheath liquid arrangement. The sheath liquid was composed of isopropanol-water (1:1 v/v) containing 30 mM acetic acid with a flow rate of 4 microL/min. Mass spectrum was employed in the positive mode and both full scan mode and SIM scan mode were utilized. All 12 diuretics could be detected and confirmed by MS in a single analysis. Under optimized conditions, LODs for the 12 diuretics were in the range of 0.13-2.7 micromol/L at an S/N of 3, and the correlation coefficients R(2 )were between 0.9921 and 0.9978. The RDSs (n = 5) of the method was 0.24-0.94 % for migration times and 1.6-8.8 % for peak areas. The recoveries of spiked samples of 12 diuretics were between 72.4% and 118%. The real urine samples were injected directly for analysis, with only simple filtration through a 0.22 microm membrane filter in order to remove solid particles, which may cause capillary blockage. Based on the migration times and characteristic ions, the diuretics in urine samples were detected successfully. This CE-ESI-MS method for analyzing diuretics will hopefully be applied to doping control.

Amino acid profiling in urine by capillary zone electrophoresis - mass spectrometry

Analysis of amino acid profiles in urine and plasma is an essential part of modern clinical diagnostic routine. Here we present an approach for the analysis of amino acids in urine by capillary electrophoresis/time-of-flight (TOF) mass spectrometry. At first a method combining improved separation, high dynamic range, and high sensitivity is presented. Detection limits in the mid nM-range are achieved through the use of pH-mediated stacking injection in combination with modern TOF detection technology. The method can be easily applied to detect differences in the amino acid profile in urine in a clinical context. Moreover, beside amino acids low molecular weight amines, peptides and related metabolites can be profiled. As a proof of concept, urine samples from patients suffering from osteoarthritis have been analyzed. Finally, the introduction of multivariate data analysis in the work flow was evaluated on spiked urine samples and real clinical material.

Metabolome analysis by capillary electrophoresis-mass spectrometry

Capillary electrophoresis (CE)-mass spectrometry (MS), as an analytical platform, has made significant contributions in advancing metabolomics research, if still limited up to this time. This review, covering reports published between 1998 and 2006, describes how CE-MS has been used thus far in this field, with the majority of the works dealing with targeted metabolite analyses and only a small fraction using it in the comprehensive context. It also discusses how some of the key features of CE-MS were exploited in selected metabolomic applications.

Metabolite profiling of human urine by CE-ESI-MS using separation electrolytes at low pH

We investigated the potential of CE coupled to electrospray MS (CE-ESI-MS) in metabolite profiling of human urine without any sample prefractionation step. A heterogeneous mixture of biologically relevant compounds covering a broad range of physicochemical properties was used to optimize separation conditions in fused-silica capillaries. A running electrolyte containing 50 mM of acetic acid and 50 mM of formic acid at pH 2.5 was used for the CE separations. A sheath-flow electrospray interface was employed for CE-ESI-MS analysis. Sheath liquids containing 80:20 v/v methanol/water with 0.1% v/v of acetic acid or 60:40 v/v isopropanol/water with 0.5% v/v of ammonia were selected for optimum detection in positive and negative ESI modes, respectively. Reproducibility and sensitivity were studied, and strategies for identification of the separated urinary compounds are suggested. We report major advantages and disadvantages of CE-ESI-MS for metabolite profiling of human body fluids. This work may be regarded as a first step in the use of CE-ESI-MS for reliable differential analysis of body fluids from healthy and diseased individuals.

Direct determination of fourteen underivatized amino acids from Whitmania pigra by using liquid chromatography-evaporative light scattering detection

A new reversed phase high performance liquid chromatography-evaporative light scattering detection (RP-HPLC-ELSD) method has been developed for the direct determination of fourteen amino acids in Whitmania pigra, a commonly used traditional Chinese medicine (TCM). Simultaneous separation of these fourteen amino acids was achieved on a Prevail C18 column. Under the condition of gradient elution, the fourteen amino acids were separated within 25 min. The drift tube temperature of ELSD was set at 115 degrees C, and with the nitrogen flow rate of 2.5 l/min. All calibration curves showed good linear regression (r > 0.9975) within test ranges. The recoveries ranged from 94.8% to 104.4%. The limit of detection (LOD) for each compound was more than 20 mg/l at a signal to noise ratio (S/N) of 3. The validated method was successfully applied to quantify fourteen amino acids from Whitmania pigra, which provides a new basis of overall assessment on quality of Whitmania pigra.

Urine profiling using capillary electrophoresis-mass spectrometry and multivariate data analysis

This work presents the development of a general and fast method for metabolic profiling of urine, using capillary electrophoresis-electrospray ionisation mass spectrometry (CE-ESIMS) and multivariate data analysis (DA). Human urine samples collected before and after ingestion of paracetamol were analysed at acidic and basic CE conditions, using both positive and negative ESI-MS detection. Analysis of the entire resulting data set, with no prior knowledge of the target compounds, using pair-wise 'fuzzy' correlation and eigenvalue analysis enabled the samples to be discriminated between on the basis of blank urine and urine collected after drug intake. By generating two-dimensional loadings plots, it was also possible to identify the m/z values of the substances responsible for the differentiation between control and dosed samples.

Mass spectrometry in metabolome analysis

In the post-genomic era, increasing efforts have been made to describe the relationship between the genome and the phenotype in cells and organisms. It has become clear that even a complete understanding of the state of the genes, messages, and proteins in a living system does not reveal its phenotype. Therefore, researchers have started to study the metabolome (or the metabolic complement of functional genomics). Within this context, mass spectrometry (MS) has increasingly occupied a central position in the methodologies developed for determination of the metabolic state. This review is mainly focused on the status of MS in the metabolome field, trying to direct the reader to the main approaches for analysis of metabolites, reviewing basic methodologies in sample preparation, and the most recent MS techniques introduced. Apart from the description of the different methods, this review will try to state a general comparison between the several different techniques that involve MS and metabolite analysis, and will highlight their limitations and preferred applicability.

Analysis of carboxylic acids in biological fluids by capillary electrophoresis

This review article addresses the different capillary electrophoretic methods that are being used for the study of both short-chain organic acids (including anionic catecholamine metabolites) and fatty acids in biological samples. This work intends to provide an updated overview (including works published until November 2004) on the recent methodological developments and applications of such procedures together with their main advantages and drawbacks. Moreover, the usefulness of CE analysis of organic acids to study and/or monitor different diseases such as diabetes, new-borns diseases or metabolism disorders is examined. The use of microchip devices and CE-MS couplings for organic acid analysis is also discussed.

Micellar electrokinetic chromatographic and capillary zone electrophoretic methods for screening urinary biomarkers of human disorders: a critical review of the state-of-the-art

Human urine plays a central role in clinical diagnostic being one of the most-frequently used body fluid for detection of biological markers. Samples from patients with different diseases display patterns of biomarkers that differ significantly from those obtained from healthy subjects. The availability of fast, reproducible, and easy-to-apply analytical techniques that would allow identification of a large number of these analytes is thus highly desiderable since they may provide detailed information about the progression of a pathological process. From among the variety of methods so far applied for the determination of urinary metabolites, capillary electrophoresis, both in the capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) modes, represents a robust and reliable analytical tool widely used in this area. The aim of the present article is to focus the interest of the reader on recent applications of MEKC and CZE in the field of urinary biomarkers and to discuss advantages and/or limitations of each mode.

Evaluation of diabetes-related short-chain organic acids in rat plasma by capillary electrophoresis

A capillary zone electrophoresis method was optimised to analyse low-molecular-mass organic acids for the purpose of monitoring diabetes in rat plasma. The method included acetoacetic, 2-hydroxybutyric, lactic and uric acids. A variation in the background electrolyte allowed us to measure pyruvic acid in the same sample. Conditions have been optimised for measuring a large number of plasma samples corresponding to control and diabetic rats. Samples were mixed with acetonitrile (1:1, v/v) to precipitate proteins, centrifuged, diluted and injected. Tropic acid was chosen as an adequate internal standard. Separation was developed with reversed voltage by using a column cartridge pre-treated with polyacrylamide. Two electrophoretic buffers were employed: 0.150 M H3PO4 made up pH 6.20 with NaOH and 0.3 mM CaCl2 for acetoacetic, hydroxybutyric, lactic and uric acids, and 200 mM phosphate-10 mM acetate pH 4.0 for pyruvic acid, both with direct detection at 200 nm. The method was validated for linearity, accuracy and precision and the limits of quantification were calculated. The method was successfully applied to analyse these organic acids in control and diabetic animals. Acetoacetic and hydroxybutyric acids were clearly increased in diabetic rats, meanwhile no statistically significant difference has been found with the other acids.

Micellar electrokinetic capillary chromatography and data alignment analysis: a new tool in urine profiling

The complex nature of biofluids demands efficient, sensitive and high-resolution analytical methodologies to examine how the 'metabolic fingerprint' changes during disease. This paper describes how sulphated beta-cyclodextrin-modified micellar electrokinetic capillary chromatography (SbetaCD-MECC) has been combined with data alignment analysis and may prove a useful new tool in urine profiling, allowing for separation of over 80 urinary analytes in under 25 min. The optimised and validated SbetaCD-MECC methodology combined with data alignment analysis provides rapid identification of 'mismatches' between urine profiles which are not easily detected with the naked eye as well as a 'similarity score' which indicates the total sum of differences between one profile and another. The combination of SbetaCD-MECC with data alignment software should prove a useful alternative tool in metabonomic studies for rapid comparison of urine profiles.

Capillary electrophoresis for the determination of organic acidurias in body fluids: a review

A systematic review of the literature on capillary electrophoresis applied to short chain organic acid analysis in body fluids has been conducted with special interest on those acids related to inborn errors of metabolism. The technique is briefly described, as well as the choice of the main analytical parameters: sample pre-treatment, polarity, capillary type, background electrolyte, and detection. The applications described in the literature are listed and the main features of the technique are discussed.

Capillary electrophoresis for short-chain organic acids and inorganic anions in different samples

This review article is a comprehensive survey of capillary electrophoresis methods developed for the measurement of short-chain organic acids and inorganic anions in a wide variety of matrices, such as food and beverages, environmental, industry, and other applications, as well as clinical applications in body fluids such as urine, plasma or cerebrospinal fluid. Details of sample pretreatment and of electrophoretic conditions have been collected in tables, arranged by the type of matrix. Strategies employed for method development for the analysis of these compounds by capillary electrophoresis in real samples are discussed.

Analytical methods to investigate glutathione and related compounds in biological and pathological processes

Reduced glutathione (GSH, gamma-L-glutamyl-L-cysteinylglycine) is a fundamental low-molecular mass antioxidant that serves several biological functions. Upon enzymatic and non-enzymatic oxidation, GSH forms glutathione disulfide (GSSG) and, under particular conditions, may generate other oxidative products. The determination of GSH, its precursors, and metabolites in several bio-matrices is a useful tool in studying oxidative stress. Many separative and non-separative methods have been developed and improved for the assay of GSH and related compounds. At present, high-performance liquid chromatography and capillary electrophoresis are the most used separative techniques to determine GSH and congeners. The review will deal with analytical methods developed over the last few years for the determination of GSH and related compounds, and with the procedures performed in sample pre-treatment in order to minimize analytical errors. Since GSH, GSSG, and related compounds lack of strong chromophores or fluorophores, it is advantageous, in many assays, to derivatize the compounds in order to improve the detection limit with UV-Vis and to allow fluorescence, thus the most commonly used labeling agents are also described.

Comprehensive Screening of Urine Samples for Inborn Errors of Metabolism by Electrospray Tandem Mass Spectrometry

Background: Detection of abnormal metabolites in urine is important for the diagnosis of many inborn errors of metabolism (IEM). Rapid, comprehensive screening methods are needed.

Methods: We used electrospray ionization tandem mass spectrometry in positive- and negative-ion modes to detect selected metabolites in urine. For positive-ion analysis, samples were dried and butylated, whereas for negative-ion analysis, samples were merely diluted with the mobile phase. Analysis was by direct injection with multiple reaction monitoring for 32 metabolites in positive mode (amino acids and acylcarnitines) and 30 metabolites in negative mode (organic acids). Run time was 2.1 min in each mode.

Results: Interbatch CVs ranged from 4.8% to 32%, enabling quantification of many metabolites. The procedure was applied to controls (278 and 120 in positive- and negative-ion mode, respectively) and 108 IEM individuals representing 37 different IEM. In 105 IEM individuals, representing 36 different IEM, concentrations of one or more diagnostic metabolites were above the 99th percentiles of the control values.

Conclusions: The procedure is faster and less labor-intensive than conventional methods of testing for IEM by amino and organic acid profiling and has similar diagnostic sensitivity. The ability to include a greater range of metabolites offers the potential of a more comprehensive screening procedure.

Recent advances in amino acid analysis by capillary electrophoresis

Amino acids are studied extensively using capillary electrophoresis. In this review we will report the different researchs which have been done in the literature since 1998. We will describe the developments of, detection methods, separations of enantiomers, the new medical applications, and amino acids in food and plants.

The use of selective adsorbents in capillary electrophoresis-mass spectrometry for analyte preconcentration and microreactions: a powerful three-dimensional tool for multiple chemical and biological applications

Much attention has recently been directed to the development and application of online sample preconcentration and microreactions in capillary electrophoresis using selective adsorbents based on chemical or biological specificity. The basic principle involves two interacting chemical or biological systems with high selectivity and affinity for each other. These molecular interactions in nature usually involve noncovalent and reversible chemical processes. Properly bound to a solid support, an "affinity ligand" can selectively adsorb a "target analyte" found in a simple or complex mixture at a wide range of concentrations. As a result, the isolated analyte is enriched and highly purified. When this affinity technique, allowing noncovalent chemical interactions and biochemical reactions to occur, is coupled on-line to high-resolution capillary electrophoresis and mass spectrometry, a powerful tool of chemical and biological information is created. This paper describes the concept of biological recognition and affinity interaction on-line with high-resolution separation, the fabrication of an "analyte concentrator-microreactor", optimization conditions of adsorption and desorption, the coupling to mass spectrometry, and various applications of clinical and pharmaceutical interest.

Potential of capillary electrophoresis, tandem mass spectrometry and coupled capillary electrophoresis–tandem mass spectrometry as diagnostic tools

Urine and blood samples from patients with known metabolic disorders have been analyzed by CE, MS-MS and CE-MS-MS. For the identification of defects in acylcarnitine metabolism, blood spots on filter paper were analyzed using an MS-MS "neonatal screening" approach. Direct CE-MS-MS analysis was used for the analysis of urine samples from patients with different metabolic disorders, including galactosemia, neuroblastoma, Zellweger syndrome, propionic acidemia and alcaptonuria. The sensitivity of the CE-MS-MS method was increased by use of multiple reaction monitoring.

Recent advances in capillary electrophoresis/electrospray-mass spectrometry

In this review, the progress in hyphenation of capillary electrophoresis (CE) with electrospray ionization-mass spectrometry (ESI-MS) since the article of Banks (Banks, J. F., Electrophoresis 1997, 18, 2255-2266) is reported. In all capillary-based electromigration techniques, such as capillary gel electrophoresis (CGE), capillary isotachophoresis (CITP), capillary isoelectric focussing (CIEF), micellar electrokinetic chromatography (MEKC), affinity capillary electrophoresis (ACE), as well as in the hybrid techniques capillary electrochromatography (CEC), and pressurized capillary electrochromatography (pCEC) progress has been made in experimental setups, and for many groups of analytes, such as peptides, proteins, nucleotides, saccharides, drugs and their metabolites, CE/ESI-MS has been successfully applied. Electromigration is further miniaturized. New preconcentration methods allow the investigation of compounds, which are not sensitively detected with ESI-MS. Coordination ion spray (CIS) MS is another method for sensitivity enhancement by on-line formation of charged coordination compounds.

Separation of nicotine metabolites by capillary zone electrophoresis and capillary zone electrophoresis/mass spectrometry

The use of capillary zone electrophoresis (CZE) and capillary zone electrophoresis/mass spectrometry (CZE/MS) has been demonstrated, in principle, for the separation of nicotine and nicotine metabolites. The buffer system developed for separation and detection by CZE/UV was modified for use in CZE/MS analysis. Several of the metabolites are isobaric and tandem mass spectrometric (MS/MS) techniques have been used to differentiate such analytes.

Capillary electrophoresis and capillary electrochromatography of organic pollutants

Capillary electrophoresis (CE) has a unique capability for separation of analytes of environmental concern, particularly those that are more polar and ionic, based on the complementary separation principle of electrophoresis. In the past few years, CE has been selectively used to analyze various classes of compounds having current or potential environmental relevance. This review outlines the current status of CE for the determination of environmental pollutants, based predominantly on research results published from the beginning of 1997 to early 1999. Covered are environmental pollutants of all types except pesticides and inorganics. Certain naturally produced toxins are also covered because of their significant impacts upon human health and the environment. CE methods, as with all methods, must be judged on their ability to provide approaches that are reliable, sensitive, selective, and rapid, while meeting "green chemistry" initiatives for pollution prevention. We also compare CE methods to benchmark environmental techniques involving gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and high performance liquid chromatography (HPLC).