Examination of capillary zone electrophoresis, capillary isoelectric focusing and sodium dodecyl sulfate capillary electrophoresis for the analysis of recombinant tissue plasminogen activator

Capillary electrophoresis mass spectrometry coupling with immobilized enzyme electrospray capillaries

Open tubular capillary enzyme reactors were studied for rapid protein digestion and possible on-line integration into a CE/ESI/MS system. The need to minimize the time of the analyte molecules to diffuse towards the surface immobilized enzyme and to maximize the surface-to-volume (S/V) ratio of the open tubular reactors dictated the use of very narrow bore capillaries. Extremely small protein amounts (atto-femtomoles loaded) could be digested with enzymes immobilized directly on the inside wall of a 10 microm I.D. capillary. Covalently immobilized L-1-tosylamido-2-phenylethyl chloromethyl ketone (TPCK)-trypsin and pepsin A were tested for the surface immobilization. The enzymatic activity was characterized in the flow-through mode with on-line coupling to electrospray ionization-time of flight-mass spectrometer (ESI/TOF-MS) under a range of protein concentrations, buffer pH's, temperatures and reaction times. The optimized reactors were tested as the nanospray needles for fast identification of proteins using CE-ESI/TOF-MS.

Selective ion filtering by digital thresholding: a method to unwind complex ESI-mass spectra and eliminate signals from low molecular weight chemical noise

In this work, we present a simple method by which to preferentially detect either high molecular weight or low molecular weight ions generated by electrospray ionization. This approach, termed selective ion filtering by digital thresholding (SIFdT) is demonstrated on a commercial ESI-TOF instrument that employs a fast digitizer coupled to a microchannel plate detector. The digital representation of each individual scan is digitally filtered prior to spectral coaddition. As larger, more highly charged ions induce a more intense response than low molecular weight singly charged species, a digital threshold can be set that precludes the detection of singly charged species yet permits the efficient detection of larger, more highly charged species. In this work, we demonstrate the applicability of this approach to eliminate low molecular weight chemical noise in ESI-TOF spectra of oligonucleotide and protein ions, demonstrate improved dynamic range for analyte solutions containing high levels of low MW constituents, and show that spectra acquired at different digital thresholds can be subtracted to yield spectra of low molecular weight constituents with improved mass measurement accuracies. A notional scheme is presented in which an alternative digitization approach is employed using multiple differentially thresholded data streams to allow improved internal mass calibration and higher resolution ion partitioning.

Chromatographic and electrophoretic characterization of protein variants

Almost all proteins are expressed in several variants, also known as isoforms. Individual protein variants differ by modifications of the individual amino acid side chains, or the N- or C-terminus. Typical modifications are glycosylation, phosphorylation, acetylation, methylation, deamidation or oxidation. It is of utmost interest to either get a quantitative picture of the variants of a particular protein or to separate the variants in order to be able to identify their molecular structure. Protein variants are present in native as well as in recombinant proteins. In the case of protein production it is interesting, how variants are generated during fermentation, purification processes, storage, and how present individual variants influence the biological activity. This review provides a comparison of chromatographic and electrophoretic separation methods to analyze and to prepare protein variants.

On-line chemiluminescence detection for isoelectric focusing of heme proteins on microchips

In this paper we present a sensitive chemiluminescence (CL) detection of heme proteins coupled with microchip IEF. The detection principle was based on the catalytic effects of the heme proteins on the CL reaction of luminol-H2O2 enhanced by para-iodophenol. The glass microchip and poly(dimethylsiloxane) (PDMS)/glass microchip for IEF were fabricated using micromachining technology in the laboratory. The modes of CL detection were investigated and two microchips (glass, PDMS/glass) were compared. Certain proteins, such as cytochrome c, myoglobin, and horseradish peroxidase, were focused by use of Pharmalyte pH 3-10 as ampholytes. Hydroxypropylmethylcellulose was added to the sample solution in order to easily reduce protein interactions with the channel wall as well as the EOF. The focused proteins were transported by salt mobilization to the CL detection window. Cytochrome c, myoglobin, and horseradish peroxidase were well separated within 10 min on a glass chip and the detection limits (S/N=3) were 1.2x10(-7), 1.6x10(-7), and 1.0x10(-10) M, respectively.

Isoelectric focusing in cyclic olefin copolymer microfluidic channels coated by polyacrylamide using a UV photografting method

As an alternative material to glass or silicon, microfluidic devices made from a cyclic olefin copolymer (COC) were fabricated. This material is of interest because of the relative ease of fabrication, low costs, and solvent resistance. However, as a result of the strong hydrophobic interactions normally present, COC surfaces are not suitable for protein separations. To reduce the protein adsorption and make COC suitable for protein separations, UV-initiated grafting of polyacrylamide was used to coat the surface of COC devices. The change in surface properties caused by different graft times was studied. The surface hydrophilicity and electroosmotic mobility were characterized by contact angle and electroosmosis measurements. Isoelectric focusing was performed to test protein separations in polyacrylamide-coated COC microchannels. A single protein, carbonic anhydrase, was used to analyze the focusing effects and peak capacities in uncoated and polyacrylamide-coated COC devices. Peak capacities ranging from 75 to 190 were achieved with a polyacrylamide-coated surface. A mixture of two proteins, conalbumin labeled with Alexa Fluor 488 and beta-lactoglobulin A labeled with Alexa Fluor 546, was used to test protein separations. Linear and rapid separation of proteins was achieved in the polyacrylamide-coated COC microfluidic device.

On-Chip Native Gel Electrophoresis-Based Immunoassays for Tetanus Antibody and Toxin

By integrating photopolymerized cross-linked polyacrylamide gels within a microfluidic device, we have developed a microanalytical platform for performing electrophoresis-based immunoassays. The microfluidic immunoassays are performed by gel electrophoretic separation and quantitation of bound and unbound antibody or antigen. To retain biological activity of proteins and maintain intact immune complexes, nondenaturing polyacrylamide gel electrophoresis conditions were investigated. Both direct (noncompetitive) and competitive immunoassay formats are demonstrated in microchips. A direct immunoassay was developed for detection of tetanus antibodies in buffer as well as diluted serum samples. After an off-chip incubation step, the immunoassay was completed in less than 3 min and the sigmoidal dose-response curve spanned an antibody concentration range from 0.17 to 260 nM. The minimum detectable antibody concentration was 0.68 nM. A competitive immunoassay was also developed for tetanus toxin C-fragment by allowing unlabeled and fluorescently labeled tetanus toxin C-fragment compete to bind to a limited fixed concentration of tetanus antibody. The immunoassay technique described in this work shows promise as a component of an integrated microfluidic device amenable to automation and relevant to development of clinical diagnostic devices.

Analysis of glycoproteins and the oligosaccharides thereof by high-performance capillary electrophoresis-significance in regulatory studies on biopharmaceutical products

This review describes the recent development in the analysis of glycoproteins using capillary electrophoresis with various separation techniques, and focuses especially on the analysis of recombinant glycoprotein pharmaceuticals. We include the analysis of glycoprotein multiforms (ie glycoform) as well as glycan analysis. The relationship between glycoprotein multiforms and oligosaccharide distributions in a glycoprotein sample is also discussed. Further, recent development in capillary electrophoresis-mass spectrometry is described.

Capillary electrophoretic analysis of proteins and peptides of biomedical and pharmacological interest

Capillary electrophoresis (CE) is an automated approach to electrokinetic separations that has had a deep impact in all fields of life sciences, including biomedical and biotechnological research and clinical and forensic practice. The present review highlights aspects of peptides and proteins separations, with particular emphasis on macromolecular analytes of biomedical interest. Among the various CE techniques available, a novel methodology is here illustrated consisting in separations in acidic, isoelectric buffers, which have the advantage of protonating the silica wall, thus minimizing interactions of proteinaceous material with the siliceous surface, while allowing delivery of high voltage gradients, due to their low conductivities. The review ends with applications of CE to the analysis of folding/unfolding/refolding/misfolding of proteins, a field which has deep implications in the biomedical arena, since it is connected to a host of disorders, such as prion protein diseases.

Multiple cell culture factors can affect the glycosylation of Asn-184 in CHO-produced tissue-type plasminogen activator

Human tissue-type plasminogen activator (t-PA) contains a variably occupied glycosylation site at Asn-184 in naturally produced t-PA and in t-PA produced in recombinant Chinese hamster ovary (CHO) cells. The presence of an oligosaccharide at this site has previously been shown to reduce specific activity and fibrin binding. In this report, the site occupancy of t-PA is shown to increase gradually over the course of batch and fed-batch CHO cultures. Additional cell culture factors, including butyrate and temperature, are also shown to influence the degree of glycosylation. In each of these cases, conditions with decreased growth rate correlate with increased site occupancy. Investigations using quinidine and thymidine to manipulate the cell cycle distribution of cultures further support this correlation between site occupancy and growth state. Comparison of the cell cycle distribution across the range of cell culture factors investigated shows a consistent relationship between site occupancy and the fraction of cells in the G(0)/G(1) phase of the cell cycle. These results support a correlation between growth state and site occupancy, which fundamentally differs from site occupancy trends previously observed and illustrates the importance of the growth profile of CHO cultures in producing consistently glycosylated recombinant glycoproteins.

One-step capillary isoelectric focusing for the separation of the recombinant human immunodeficiency virus envelope glycoprotein glycoforms

One-step capillary isoelectric focusing was investigated as a rapid method to resolve the glycoforms of the heterogeneous recombinant human immunodeficiency virus (HIV) envelope glycoprotein (rgp 160sMN/LAI). The separation was performed in a poly(vinyl alcohol) (PVA) coated capillary using a mixture of ampholyte of narrow and wide pH range. A combination of saccaharose and 3-(cyclohexylamino)-1-propanesulfonic acid was shown to be the most efficient additive to avoid protein precipitation which occurs at a pH close to its pI. Although the calibration curve [isoelectric point (pI) vs. migration times] showed a non-linear relationship, an adequate linearity could be yielded for short pI ranges permitting to exhibit the acidic character of the different glycoforms of the rgp 160s MN/LAI (pI from 4.00 to 4.95). Reproducibility evaluated by comparing the performance of a polyacrylamide and a PVA coated capillary showed that low RSD values were obtained for intra-day (0.5 to 1.9%) and inter-day (1.6 to 7.6%) measurements using the PVA capillary. Moreover, the long term stability of the PVA capillary was demonstrated by measuring the variation of migration times of the protein markers for a long period of use. Finally, this method was able to differentiate the glycoform pattern of two close glycoproteins such as the rgp 160 of two sub-populations of the virus HIV-1.

Fraction collection in micropreparative capillary zone electrophoresis and capillary isoelectric focusing

A new fraction collection system for capillary zone electrophoresis (CZE) and capillary isolelectric focusing (CIEF) is described. Exact timing of the collector steps was based on determining the velocity of each individual zone measured between two detection points close to the end of the capillary. Determination of the zone velocity shortly before collection overcame the need for constant analyte velocity throughout the column. Consequently, sample stacking in CZE with large injection volumes as well as zone focusing in CIEF could be utilized with high collection accuracy. Capillaries of 200 microm inner diameter (ID) were employed in CZE and 100 microm ID in CIEF for the micropreparative mode. A sheath flow fraction collector was used to maintain permanent electric current during the collection. The bulk liquid flow due to siphoning, as well as the backflow arising from the sheath flow droplet pressure, were suppressed by closing the separation system at the inlet with a semipermeable membrane. In the CZE mode, the performance of the fraction collector is demonstrated by isolation of individual peaks from a fluorescently derivatized oligosaccharide ladder. In the CIEF mode, collection of several proteins from a mixture of standards is shown, followed by subsequent analysis of each protein fraction by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS).

Applications of capillary electrophoresis in biotechnology

Capillary electrophoresis (CE)-related techniques are increasingly being used as a matter of routine practice in the biotechnology discipline. Since recombinant DNA-derived proteins and the antisense oligonucleotides constitute a large portion of the applications of these techniques, they have been emphasized in this review. Analyses by CE of Escherichia coli-derived proteins and glycosylated proteins derived from mammalian cell cultures are summarized, as well as those of the carbohydrate chains that have been enzymatically removed from the protein. Applications of CE in the analysis of the antisense oligonucleotides for the determination of purity and the analytical studies on the metabolism of these modified oligonucleotides, by CE are reviewed. The literature mainly covers the period from 1996.

Overview of capillary electrophoresis and capillary electrochromatography

This paper provides an overview on the current status of capillary electrophoresis (CE) and capillary electrochromatography (CEC). The focus is largely on the current application areas of CE where routine methods are now in place. These application areas include the analysis of DNA, clinical and forensic samples, carbohydrates, inorganic anions and metal ions, pharmaceuticals, enantiomeric species and proteins and peptides. More specific areas such the determination of physical properties, microchip CE and instrumentation developments are also covered. The application, advantages and limitations of CEC are covered. Recent review articles and textbooks are frequently cited to provide readers with a source of information regarding pioneering work and theoretical treatments.

Use of acidic and basic pH and calcium ion addition in the capillary zone electrophoretic characterization of recombinant human deoxyribonuclease, a complex phosphoglycoprotein

This paper describes the analysis of recombinant human deoxyribonuclease (rhDNAse), an acidic and complex phosphoglycoprotein, by capillary zone electrophoresis (CZE). Separation performance was found to be dramatically improved by the addition of calcium ions to the CZE running buffer, due to the influence of calcium binding on the charge and the electrophoretic behavior of rhDNAse. The pH dependent calcium binding effects on the electrophoretic separation were demonstrated at both acidic and basic pH, resulting in a two-dimensional (pH 4.8 and 8.0) calcium aided analysis that achieved multipeak resolution of the complex, glycosylation based, charge microheterogeneity of rhDNAse. Two-dimensional investigation of neuraminidase- and alkaline phosphatase-digested protein further demonstrated that the acidic pH resolved acidic charge heterogeneity and that the basic pH discriminated neutral heterogeneity. This work demonstrates the resolving power of CZE for the analysis of a complex microheterogeneous glycoprotein, and emphasizes the importance of employing multiple separation conditions in accordance with known structural characteristics of the protein.

Separation of bovine serum albumin and its monoclonal antibody from their immunocomplexes by sodium dodecyl sulfate-capillary gel electrophoresis and its application in capillary electrophoresis-based immunoassay

A non-competitive immunoassay was performed by sodium dodecyl sulfate-capillary gel electrophoresis with UV detection using bovine serum albumin (BSA) and monoclonal anti-BSA. BSA, anti-BSA and their immunocomplexes were well resolved under non-denaturing conditions. A linear calibration curve was obtained and can be used for the quantification of anti-BSA. The limit of detection of anti-BSA was 0.1 microM under the present conditions. Compared with capillary zone electrophoresis, we believed that this method has the potential to be used as a more general format for performing capillary electrophoresis-based immunoassay of medium- and large-sized analytes.

Capillary electrophoresis sodium dodecyl sulfate nongel sieving analysis of a therapeutic recombinant monoclonal antibody: a biotechnology perspective

With the increasing interest in the therapeutic use of recombinant monoclonal antibodies (rMAbs), a generic analytical approach for the analysis of size-based rMAb variants is desired. Such a method using capillary electrophoresis (CE) with laser-induced fluorescence detection is described. The assay was developed as a replacement for silver-stained SDS-PAGE and was validated according to the guidelines of the International Committee on Harmonization for use in routine lot release testing of a rMAb pharmaceutical. In this assay, the rMAb solution is first derivatized with a neutral fluorophore, e.g., 5-carboxytetramethylrhodamine succinimidyl ester. The labeled sample is then incubated with SDS, and the SDS-protein complexes are then separated by CE using a hydrophilic polymer as a sieving matrix. The precolumn labeling conditions described in this study allowed the detection of rMAb at a low-nanomolar concentration (9 ng/mL), with no apparent loss in resolution or changes to the distribution of rMAb analyte species, when compared to an unlabeled sample. In addition, the traditional practice of heating proteins at elevated temperatures in the presence of SDS to facilitate SDS-protein binding resulted in the generation of significant levels of rMAb fragmentation, and alternative conditions to minimize this artifact are discussed. Illustrations of the uses of this assay in monitoring consistency of bulk manufacture of a protein pharmaceutical, and in providing a size-based separation of product-related variants, as well as nonproduct impurities are shown. In brief, the assay described in this paper demonstrated comparable resolution and sensitivity to silver-stained SDS-PAGE but offered the advantages of enhanced precision and robustness, speed, ease of use, and on-line detection.

Monitoring recombinant human interferon-gamma N-glycosylation during perfused fluidized-bed and stirred-tank batch culture of CHO cells

Chinese hamster ovary cells producing recombinant human interferon-gamma were cultivated for 500 h attached to macroporous microcarriers in a perfused, fluidized-bed bioreactor, reaching a maximum cell density in excess of 3 x 10(7) cells (mL microcarrier)-1 at a specific growth rate (mu) of 0.010 h-1. During establishment of the culture, the N-glycosylation of secreted recombinant IFN-gamma was monitored by capillary electrophoresis of intact IFN-gamma proteins and by HPLC analysis of released N-glycans. Rapid analysis of IFN-gamma by micellar electrokinetic capillary chromatography resolved the three glycosylation site occupancy variants of recombinant IFN-gamma (two Asn sites occupied, one Asn site occupied and nonglycosylated) in under 10 min per sample; the relative proportions of these variants remained constant during culture. Analysis of IFN-gamma by capillary isoelectric focusing resolved at least 11 differently sialylated glycoforms over a pI range of 3.4 to 6.4, enabling rapid quantitation of this important source of microheterogeneity. During perfusion culture the relative proportion of acidic IFN-gamma proteins increased after 210 h of culture, indicative of an increase in N-glycan sialylation. This was confirmed by cation-exchange HPLC analysis of released, fluorophore-labeled N-glycans, which showed an increase in the proportion of tri- and tetrasialylated N-glycans associated with IFN-gamma during culture, with a concomitant decrease in the proportion of monosialylated and neutral N-glycans. Comparative analyses of IFN-gamma produced by CHO cells in stirred-tank culture showed that N-glycan sialylation was stable until late in culture, when a decline in sialylation coincided with the onset of cell death and lysis. This study demonstrates that different modes of capillary electrophoresis can be employed to rapidly and quantitatively monitor the main sources of glycoprotein variation, and that the culture system and operation may influence the glycosylation of a recombinant glycoprotein.

A tabulated review of capillary electrophoresis of carbohydrates

This review summarizes publications on capillary electrophoresis (CE) of carbohydrates, covering almost all hitherto published papers on this topic. It is designed to be a convenient tool for the literature search by providing a comprehensive table. Since CE analysis of carbohydrates is generally complicated due to the structural diversity of carbohydrate species, an attempt is made in this table to supply detailed information on the analyzed form (underivatized or derivatized, type of derivative) and analytical conditions (capillary size, state of the inner wall, composition of the electrophoretic solution, applied voltage, detection method, etc.), for each combination of carbohydrate species to be analyzed. In addition, a brief overview is presented to help in the literature search.

Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications

This review is in support of the development of selective, reproducible and validated capillary electrophoretis (CE) methods. Focusing on pharmaceutical and biological applications, the successful use of CE is demonstrated by more than 800 references, mainly from 1994 until 1998. Approximately 80 recent reviews have been catalogued. These articles sum up the existing strategies for method development in CE, especially in the search for generally accepted concepts, but also looking for new, promising reagents and ideas. General strategies for method development were derived not only with regard to selectivity and efficiency, but also with regard to precision, short analysis time, limit of detection, sample pretreatment requirements and validation. Standard buffer recipes, surfactants used in micellar electrokinetic capillary chromatography (MEKC), chiral selectors, useful buffer additives, polymeric separation media, electroosmotic flow (EOF) modifiers, dynamic and permanent coatings, actions to deal with complex matrices and aspects of validation are collected in 20 tables. Detailed schemes for the development of MEKC methods and chiral separations, for optimizing separation efficiency, means of troubleshooting, and other important information for key decisions during method development are given in 19 diagrams. Method development for peptide and protein separations, possibilities to influence the EOF and how to stabilize it, as well as indirect detection are considered in special sections.

Electrophoretic methods for process monitoring and the quality assessment of recombinant glycoproteins

In many ways electrophoretic techniques appear ideal for quality monitoring of proteins and are thus well suited for the analysis of recombinant glycoproteins. The requirements of high throughput, comparative analysis and resolution of many variants are met by several electrophoretic techniques. A wide variety of such techniques are available to biotechnologists in the rapidly developing area of recombinant glycoproteins. It is the aim of this review to specifically cover recent work which has been applied to the analysis of DNA-derived glycoproteins, both from a process control standpoint and final product validation. All major areas of electrophoresis including sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing and techniques utilizing capillary electrophoresis are covered, with emphasis on analysis of glycoforms and oligosaccharide profiles of recombinant glycoproteins. As illustration, actual examples rather than standard glycoproteins are given to indicate the potential and limitations which may be encountered. It is anticipated that this review will prove a useful and practical guide to the latest developments by indicating the relevant merits of different methods.

Recent developments in capillary electrophoresis of carbohydrate species

Carbohydrates are ubiquitous species involved in many life processes. Because of the multilateral roles of carbohydrates, their analysis has come to have increasing importance. As shown in this review, capillary electrophoresis in its various modes of operation has proved very useful in the analysis of carbohydrate species including mono- and oligosaccharides, glycoproteins, glycopeptides and glycosaminoglycans. Advances in separation approaches and applications as well as advances in detection including sensitive and selective pre-column derivatization are described. In summary, this comprehensive review is a supplement to previous reviews and covers the published work in 1996 and the first half of 1997.

Capillary electrophoresis of biotechnology-derived proteins

Applications of capillary electrophoretic techniques for the analysis of biotechnology-derived proteins continue at a steady pace. This review summarizes the analyses of these proteins achieved using capillary isoelectric focusing, micellar electrokinetic capillary chromatography, capillary electrophoresis/mass spectrometry and capillary gel electrophoresis. A very brief summary of each technique is included. Application of capillary isoelectric focusing to the analysis of recombinant tissue plasminogen activator in quality control type applications is examined in some detail. Analyses of dosage forms of biotechnology derived proteins of pharmaceutical importance as well as the identification and examination of the peptides, obtained after enzymatic cleavage of proteins, by capillary electrophoresis have been included. Examples of capillary gel electrophoresis as a substitute sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of biotechnology-derived proteins are also reviewed.

Capillary isoelectric focusing

Capillary isoelectric focusing (CIEF) provides excellent resolution of proteins with the advantage that separations are carried out in a capillary format with on-tube detection and automated analysis. Recent advances in the technique provide improved resolution, reproducibility and reliability. This review summarizes improvements in sample preparation, capillary selection, and focusing and zone mobilization procedures which have helped CIEF become a more robust analytical method. New applications are reviewed, in particular the use of CIEF in analysis of biopharmaceutical products.

Capillary zone electrophoresis of proteins

This review article with 237 references is focused on capillary zone electrophoresis (CZE) of proteins. It includes discussion of modeling electrophoretic migration of proteins, sample pretreatment before the analysis, methods reducing the sorptions of proteins on the capillary wall, and techniques for increasing selectivity by using electrolyte additives including the sieving matrices. Significant progress in detection techniques, namely in laser-induced fluorescence and mass spectrometry, is emphasized. Modifications of CZE using specific interactions, such as affinity capillary electrophoresis or capillary immunoelectrophoresis, are debated as well as combination of CZE with other separation methods such as high performance liquid chromatography (HPLC). A number of practical applications of CZE of proteins are described.

Buffer additives other than the surfactant sodium dodecyl sulfate for protein separations by capillary electrophoresis

The different compounds utilized as additives to the electrolyte solutions employed in protein capillary zone electrophoresis (CZE) for minimizing protein-capillary wall interactions, for improving selectivity and resolution and for controlling the electroosmotic flow are reviewed. The dependence of the electroosmotic flow on the different variables that can be affected by the incorporation of an additive into the electrolytic solution is discussed. A list of the most effective additives employed for protein separations by CZE is reported in Appendix A.