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

Capillary electrophoresis study on the base-catalyzed formation of bioactive oxidized metabolites of 20-hydroxyecdysone

A novel capillary electrophoretic method was developed for the analysis and monitoring of the base-catalyzed autoxidation of 20-hydroxyecdysone, a worldwide used non-hormonal anabolic food supplement. An effective separation of the starting material and its bioactive oxidized derivatives was achieved by using sulfobutyl-β-cyclodextrin as selector at pH 11 and by fixing the separation voltage at +30kV. Only a dilution step was inserted before injecting the sample, taken from the crude reaction mixture, to the capillary electrophoresis instrument. The same alkaline pH was used for the analysis as for the reaction, unlike the previously reported HPLC study where sample neutralization was required prior to the measurement. Due to the very short analysis time (6min) in capillary electrophoresis, more frequent sampling and more detailed time scale analysis could be carried out. Furthermore, in contrast with the preceding HPLC results, the previously unobserved calonysterone could also be detected by capillary electrophoresis as a minor primary product. Our novel method demonstrated higher resolution than the one before. Baseline separation could be achieved and the resolution values were in the range of 1.9-7.0. The limit of detection was below 71μg/ml, the relative standard deviation values of the migration time and peak area for intra- and inter-day precision were less than 10%. The more precise, direct monitoring of the time dependency of the oxidation process is expected to have a significant impact on yield optimization initiatives to allow related pharmacological studies in the near future.

Capillary Electrophoresis in Metabolomics

Metabolomics is an analytical toolbox to describe (all) low-molecular-weight compounds in a biological system, as cells, tissues, urine, and feces, as well as in serum and plasma. To analyze such complex biological samples, high requirements on the analytical technique are needed due to the high variation in compound physico-chemistry (cholesterol derivatives, amino acids, fatty acids as SCFA, MCFA, or LCFA, or pathway-related metabolites belonging to each individual organism) and concentration dynamic range. All main separation techniques (LC-MS, GC-MS) are applied in routine to metabolomics hyphenated or not to mass spectrometry, and capillary electrophoresis is a powerful high-resolving technique but still underused in this field of complex samples. Metabolomics can be performed in the non-targeted way to gain an overview on metabolite profiles in biological samples. Targeted metabolomics is applied to analyze quantitatively pre-selected metabolites. This chapter reviews the use of capillary electrophoresis in the field of metabolomics and exemplifies solutions in metabolite profiling and analysis in urine and plasma.

Affinity monolith preconcentrators for polymer microchip capillary electrophoresis

Developments in biology are increasing demands for rapid, inexpensive, and sensitive biomolecular analysis. In this study, polymer microdevices with monolithic columns and electrophoretic channels were used for biological separations. Glycidyl methacrylate-co-ethylene dimethacrylate monolithic columns were formed within poly(methyl methacrylate) microchannels by in situ photopolymerization. Flow experiments in these columns demonstrated retention and then elution of amino acids under conditions optimized for sample preconcentration. To enhance analyte selectivity, antibodies were immobilized on monoliths, and subsequent lysozyme treatment blocked nonspecific adsorption. The enrichment capability and selectivity of these affinity monoliths were evaluated by purifying fluorescently tagged amino acids from a mixture containing green fluorescent protein (GFP). Twenty-fold enrichment and 91% recovery were achieved for the labeled amino acids, with a >25 000-fold reduction in GFP concentration, as indicated by microchip electrophoresis analysis. These devices should provide a simple, inexpensive, and effective platform for trace analysis in complex biological samples.

Development of a capillary electrophoresis-mass spectrometry method using polymer capillaries for metabolomic analysis of yeast

Metabolomics is an emerging field in analytical biochemistry, and the development of such a method for comprehensive and quantitative analysis of organic acids, carbohydrates, and nucleotides is a necessity in the era of functional genomics. When a concentrated yeast extract was analyzed by CE-MS using a successive multiple ionic-polymer layer (SMIL)-coated capillary, the adsorption of the contaminants on the capillary wall caused severe problems such as no elution, band-broadening, and asymmetric peaks. Therefore, an analytical method for the analysis of anionic metabolites in yeast was developed by pressure-assisted CE using an inert polymer capillary made from poly(ether etherketone) (PEEK) and PTFE. We preferred to use the PEEK over the PTFE capillary in CE-MS due to the easy-to-use PEEK capillary and its high durability. The separation of anionic metabolites was successfully achieved with ammonium hydrogencarbonate/formate buffer (pH 6.0) as the electrolyte solution. The use of 2-propanol washing after every electrophoresis run not only eliminated wall-adsorption phenomena, but allowed for good repeatability to be obtained for migration times in the metabolomic analysis.

Electrophoretic migration of proteins in semidilute polymer solutions

We present a systematic study of the electrophoretic migration of 10-200 kDa protein fragments in dilute-polymer solutions using microfluidic chips. The electrophoretic mobility and dispersion of protein samples were measured in a series of monodisperse polydimethylacrylamide (PDMA) polymers of different molecular masses (243, 443, and 764 kDa, polydispersivity index <2) of varying concentration. The polymer solutions were characterized using rheometry. Prior to loading onto the microchip, the polymer solution was mixed with known concentrations of SDS (SDS) surfactant and a staining dye. SDS-denatured protein samples were electrokinetically injected, separated, and detected in the microchip using electric fields ranging from 100 to 300 V/cm. Our results show that the electrophoretic mobility of protein fragments decreases exponentially with the concentration c of the polymer solution. The mobility was found to decrease logarithmically with the molecular weight of the protein fragment. In addition, the mobility was found to be independent of the electric field in the separation channel. The dispersion is relatively independent of polymer concentration and it first increases with protein size and then decreases with a maximum at about 45 kDa. The resolution power of the device decreases with concentration of the PDMA solution but it is always better than 10% of the protein size. The protein migration does not seem to correspond to the Ogston or the reptation models. A semiempirical expression for mobility given by van Winkle fits the data very well.

Determination of uric acid in plasma and allantoic fluid of chicken embryos by capillary electrophoresis

Capillary electrophoresis with diode array detection (DAD) was used to determine uric acid (UA) in chicken plasma and the allantoic fluid of chicken embryos. Complete separation of uric and ascorbic acids was attained in less than 10 min in the optimized BGE containing 60 mM MES + 30 mM Tris + 0.001% (w/v) polybrene (pH 6.1). The limit of UA detection (0.2 mg/L) was found to be low enough for sensitive analysis of native plasma and allantoic fluid samples. Range of linearity (1-200 mg/L), repeatability for peak area (CV <4.1%) and migration time (CV < 2.5%), as well as recovery of UA from biological samples (97-100%), were found to be satisfactory. The method was applied to detect the elevated UA concentrations (hyperuricemia) in chicken embryos with induced unilateral renal agenesis. CE/DAD analysis of the chicken plasma can be carried out with a relatively small volume of samples (1 microL).

Peptidomic analysis of rat urine using capillary electrophoresis coupled to mass spectrometry

We have established and validated a protocol for the peptidomic analysis of rat urine using CE coupled to MS (CE-MS). In the first experiments, the reproducibility of the CE-MS set-up and of the established preparation procedure were assessed. To establish a first rat urinary peptidome map, samples were also analyzed using CE-FT-ICR. The subsequent analysis of independent samples from two different strains (WISTAR and CD) indicated strain-specific differences, which were validated in a blinded assessment. MS/MS revealed the presence of specific fragments from well-known urinary rat peptides, such as collagens, alpha-1-antitrypsin, and serum albumin. The CE-MS-based peptidomics platform may provide novel insights into body fluids of animal models, such as rat or mice. Together with peptide identification, the technology appears to be an excellent, complimentary, and non-invasive tool to analyze toxicological or other (patho)physiological effects of pharmaceutical compounds in animal models.

CE – a multifunctional application for clinical diagnosis

CE has been used widely as an analytical tool with high separation power taking advantage of size, charge-to-size ratio, or isoelectric point of various analytes. In combination with detection methods, such as UV absorption, electrochemical detection, fluorescence, or mass spectrometry (MS), it allows the separation and detection of inorganic and organic ions, as well as complex compounds, such as polypeptides, nucleic acids, including PCR amplicons from viruses or bacteria. Recent interest in identification of biomarkers of diseases using body fluids leads to development of CE-MS techniques. These applications allowed identification of new potential biomarkers for clinical diagnosis and monitoring of therapeutic interventions. In this report, we present a technical overview of various CE techniques and discuss their applications in clinical medicine.

An electrical pumping approach to eliminate sample bias in capillary electrokinetic injection

A general pumping injection (PI), which involves the use of two capillaries with different diameters, was taken to evaluate systematically the effects on eliminating sample bias associated with the electrokinetic injection process in CE. One end of the separation capillary of the smaller diameter was inserted into another pumping capillary of larger diameter. When a high voltage was applied to the pumping capillary, the EOF generated inside will act as a pump to drive the solution stream in the separation capillary. The results have demonstrated that PI is suitable for both normal and reverse EOF situations. Second, the bias degree (BD) and SD of bias we presented were used to evaluate the degree of the bias under different conditions, and the factors of bias elimination have been investigated. Under optimal conditions, the bias was satisfactorily eliminated by PI. This EOF pumping system was successfully applied to the analysis of samples in CEC for a bias-free injection. Moreover, this two-capillary pumping system did not significantly affect the EOF, current, and the column efficiency of the separation process. Finally, a PI with grounded electrode was proposed and shown to be suitable for samples with low conductivity and ions with different mobility.

Stacking and separation of fluorescent derivatives of amino acids by micellar electrokinetic chromatography in the presence of poly(ethylene oxide)

A new approach for the analysis of large-volume naphthalene-2,3-dicarboxaldehyde (NDA) derivatives of amino acids by micellar electrokinetic chromatography (MEKC) in conjunction with a purple light-emitting diode-induced fluorescence detection is described. In order to optimize resolution, speed, and stacking efficiency, a discontinuous condition is essential for the analysis of NDA-amino acid derivatives. The optimum conditions use 2.0M TB (pH 10.0) buffer containing 40mM sodium dodecyl sulfate (SDS) to fill the capillary, deionized water to dilute samples, and 200mM TB (pH 9.0) containing 10mM SDS to prepare 0.6% poly(ethylene oxide) (PEO). Once high voltage is applied, PEO solution enters the capillary via electroosmotic flow and SDS micelles interact and thus sweep the NDA-amino acid derivatives having smaller electrophoretic mobilities than that of SDS micelles in the sample zone. When the aggregates between SDS micelles and NDA amino acid derivatives enter PEO zone, they are stacked due to decrease in electric field and increases in viscosity. Under the optimum conditions, the concentration and separation of 0.53-microL 13 NDA-amino acid derivatives that are negatively charged has been demonstrated by using a 60-cm capillary, with the efficiencies 0.3-9.0x10(5) theoretical plates and the LODs at signal-to-noise ratio 3 ranging from 0.30 to 2.76nM. When compared to standard injection (30-cm height for 10s), the approach allows the sensitivity enhancements over the range of 50-800 folds for the derivatives. The new approach has been applied to the analysis of a red wine sample, with great linearity of fluorescent intensity against concentrations (R(2)>0.98) and the RSD (three repetitive runs in one day) values of the migration times for the ten identified amino acids less than 2.8%.

Application of CE for determination of DNA base composition

DNA base composition expressed as mol% of guanine plus cytosine (% GC) or GC content is a key parameter of bacterial taxonomy and genomic analyses. Direct chemical determination methods such as HPLC as well as indirect methods based on physical properties of deoxyribonucleic acid (DNA), melting point (T(m)), and buoyant density (B(d)) have been conventionally applied to determine the GC content. However, these methods require relatively large amounts of sample DNA, time, and labor. We have developed a protocol to determine the GC content by fine separation of nucleosides with CZE. Genomic DNAs with known GC content from 23 bacterial strains were determined by CE at the optimized conditions of 27 degrees C, 20 kV in 50 mM of NaHCO(3) (pH 9.0) and 70 mM SDS added. Nucleosides from <1 microg of DNA hydrolyzed with nuclease-P1 and bacterial alkaline phosphatase were separated in a 75 microm wide and 80 cm long silica capillary. The nucleoside peak areas were determined at 254 nm in less than 12 min. The CE-based determination of GC content requires only small amounts of DNA, and thus should be applicable to environmental genomics (metagenomics), as >90% of environmental micro-organisms are nonculturable and produce only small amounts of genomic DNA.

CZE of human alpha-1-acid glycoprotein for qualitative and quantitative comparison of samples from different pathological conditions

Alpha-1-acid glycoprotein (AGP) presents different forms, which may arise from differences in the amino acid sequence and/or in the glycosidic part of the protein. Changes in forms of AGP have been described in literature as a possible tumor marker. While most previous works have approached the study of glycopeptides and/or glycans obtained after fragmentation of the protein, in this work, a CZE method is developed to separate up to eleven peaks of intact forms of AGP. A computer program developed in our laboratory is used to select the migration parameters that make possible an accurate assignment of AGP peaks. Electropherograms of AGP samples purified from sera of cancer patients and healthy donors are qualitatively and quantitatively compared. Percentages of correct assignment of AGP peaks close to 100% are achieved by using either the migration time of each peak relative to that of the EOF marker or the effective electrophoretic mobility of the peaks. The computer program permits to select, among different hypotheses for peak allotment, that one providing the highest accuracy of assignment. In this way, some peaks with different charge-to-mass ratio and a different distribution of area percentage of AGP forms are observed when comparing samples from sick and healthy individuals. Thus, a method that permits to compare AGP forms existing in sera of individuals with different pathophysiological situations has been developed. A potential for using AGP forms analyzed by CZE as a disease marker and for using this technique for screening purposes is envisaged.

Efficient and highly reproducible capillary electrophoresis-mass spectrometry of peptides using Polybrene-poly(vinyl sulfonate)-coated capillaries

The potential of capillaries noncovalently coated with a bilayer of oppositely charged polymers for the analysis of peptides by CE-MS was investigated. Bilayer coatings were produced by subsequently rinsing fused-silica capillaries with a solution of Polybrene (PB) and poly(vinyl sulfonate) (PVS). The PB-PVS coating showed to be fully compatible with MS detection causing no ionization suppression or background signals. The bilayer coating provided a considerable EOF at low pH, thereby facilitating the fast separation of peptides using a BGE of formic acid (pH 2.5). Under optimized CE-MS conditions, for enkephalin peptides high separation efficiencies were obtained with plate numbers in the range of 300,000-500,000. It is demonstrated that both the cancellation of the hydrodynamic capillary flow induced by the nebulizer gas and a sufficiently high-data acquisition rate are crucial for achieving these efficiencies. The overall performance of the CE-MS system using PB-PVS-coated capillaries was evaluated by the analysis of a tryptic digest of cytochrome c. The system provided an efficient separation of the peptide mixture, which could be effectively monitored by MS/MS detection allowing identification of at least 13 peptides within a time interval of 1.5 min. In addition, the PB-PVS coating proved to be very consistent yielding stable CE-MS patterns with highly favorable migration time reproducibilities (RSDs < 1% over a 3-day period).

Capillary electrophoresis-based separation techniques for the analysis of proteins

CE offers the advantages of high speed, great efficiency, as well as the requirement of minimum amounts of sample and buffer for the analysis of proteins. In this review, we summarize the CE-based techniques coupled with absorption, LIF, and MS detection systems for the analysis of proteins mostly within the past 5 years. The basic principle of each technique and its advantages and disadvantages for protein analysis are discussed in brief. Advanced CE techniques, including on-column concentration techniques and high-efficiency multidimensional separation techniques, for high-throughput protein profiling of complex biological samples and/or of single cells are emphasized. Although the developed techniques provide improved peak capacity, they have not become practical tools for proteomics, mainly because of poor reproducibility, low-sample lading capacity, and low throughput due to ineffective interfaces between two separation dimensions and that between separation and MS systems. In order to identify the complexities and dynamics of the proteomes expressed by cells, tissues, or organisms, techniques providing improved analytical sensitivity, throughput, and dynamic ranges are still demanded.