Capillary electrophoresis of intact basic proteins using noncovalently triple-layer coated capillaries

Investigating cationic and zwitterionic successive multiple ionic-polymer layer coatings for protein separation by capillary electrophoresis

Successive multiple ionic-polymer layers (SMILs) have long since proved their worth in capillary electrophoresis as they ensure stable electroosmotic flow (EOF) and relatively high separation efficiency. Recently, we demonstrated that plotting the plate height (H) against the solute migration velocity (u) enabled a reliable quantitative evaluation of the coating performances in terms of separation efficiency. In this work, various physicochemical and chemical parameters of the SMIL coating were studied and optimized in order to decrease the slope of the ascending part of the H vs u curve, which is known to be controlled by the homogeneity in charge of the coating surface and by the possible residual solute adsorption onto the coating surface. SMILs based on poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium styrene sulfonate) (PSS) were formed and the effect of each polyelectrolyte molar mass and of the number of polyelectrolyte layers (up to 21 layers) was studied. The use of polyethylene imine as an anchoring first layer was considered. More polyelectrolyte couples based on PDADMAC, polybrene, PSS, poly(vinyl sulfate), and poly(acrylic acid) were tested. Finally, zwitterionic polymers based on the poly(α-l-lysine) scaffold were synthesized and used as the last layer of SMILs, illustrating their ability to finetune the EOF, while maintaining good separation efficiency.

Critical parameters for highly efficient and reproducible polyelectrolyte multilayer coatings for protein separation by capillary electrophoresis

Since the introduction of polyelectrolyte multilayers to protein separation in capillary electrophoresis (CE), some progress has been made to improve separation efficiency by varying different parameters, such as buffer ionic strength and pH, polyelectrolyte nature and number of deposited layers. However, CE is often overlooked as it lacks robustness compared to other separation techniques. In this work, critical parameters for the construction of efficient and reproducible Successive multiple ionic-polymer layers (SMIL) coatings were investigated, focusing on experimental conditions, such as vial preparation and sample conservation which were shown to have a significant impact on separation performances. In addition to repeatability, intra- and inter-capillary precision were assessed, demonstrating the improved capability of poly(diallyldimethylammonium chloride) / poly(sodium styrene sulfonate) (PDADMAC / PSS) coated capillaries to separate model proteins in a 2 M acetic acid background electrolyte when all the correct precautions are put in place (with run to run%RSD(t_m) < 1.8%, day to day%RSD(t_m) < 3.2% and cap to cap%RSD(t_m) < 4.6%). The approach recently introduced to calculate retention factors was used to quantify residual protein adsorption onto the capillary wall and to assess capillary coating performances. 5-layer PDADAMAC / PSS coatings led to average retention factors for the five model proteins of ∼4×10^-2. These values suggest a relatively low residual protein adsorption leading to reasonably flat plate height vs linear velocity curves, obtained by performing electrophoretic separations at different electrical voltages (-10 to -25 kV).

Method development for quantitative monitoring of monoclonal antibodies in upstream cell-culture process samples with limited sample preparation - An evaluation of various capillary coatings

Monoclonal antibodies (mAbs) have become an important class of biopharmaceuticals used for the treatment of various diseases. Their quantification during the manufacturing process is important. In this work, a capillary zone electrophoresis (CZE) method was developed for the monitoring of the mAb concentration during cell-culture processes. CZE method development rules are outlined, particularly discussing various capillary coatings, such as a neutral covalent polyvinyl alcohol coating, a dynamic successive multiple ionic-polymer coating, and dynamic coatings using background electrolyte additives such as triethanolamine (T-EthA) and triethylamine. The dynamic T-EthA coating resulted in most stable electro-osmotic flows and most efficient peak shapes. The method is validated over the range 0.1-10 mg/ml, with a linear range of 0.08-1.3 mg/ml and an extended range of 1-10 mg/ml by diluting samples in the latter concentration range 10-fold in water. The intraday precision and accuracy were 2%-12% and 88%-107%, respectively, and inter-day precision and accuracy were 4%-9% and 93%-104%, respectively. The precision and accuracy of the lowest concentration level (0.08 mg/ml) were slightly worse and still well in scope for monitoring purposes. The presented method proved applicable for analysing in-process cell-culture samples from different cell-culture processes and is possibly well suited as platform method.

Determination of human insulin and its six therapeutic analogues by capillary electrophoresis - mass spectrometry

In this work, human insulin and its 6 analogues were separated and determined using CZE-MS. Three different capillaries (bare fused silica, successive multiple ionic-polymer layer (SMIL) and static linear polyacrylamide (LPA) coated) were compared based on their separation performances in their optimal operating conditions. Coated capillaries demonstrated slightly better separation of the components, although some components showed wide, distorted peaks. The highest plate number could be obtained in the SMIL capillary (192 000/m). For UV and ESI-MS detection relatively similar LOD values were obtained (0.3-1.2 mg/L and 1.0-3.4 mg/L, respectively). The application of MS detection provided useful structural information and unambiguous identification for insulins having similar or the same molecular mass. This work is considered to be important not only for the investigation of insulins but also for its potential contribution to the top-down analysis of proteins using CE-MS.

Polyelectrolyte Multilayers in Capillary Electrophoresis

Capillary electrophoresis (CE) has been proven to be a performant analytical method to analyze both small and macro molecules. Indeed, it is capable of separating compounds of the same nature according to differences in their charge to size ratios, particularly proteins, monoclonal antibodies and peptides. However, one of the major obstacles to reach high separation efficiency remains the adsorption of solutes on the capillary wall. Among the different coating approaches used to control and minimize solute adsorption, polyelectrolyte multilayers can be applied to CE as a versatile approach. These coatings are made up of alternating layers of polycations and polyanions, and may be used in acidic, neutral or basic conditions depending on the solutes to be analyzed. This Review provides an overview of Successive Multiple Ionic-polymer Layer (SMIL) coatings used in CE, looking at how different parameters induce variations on the electro-osmotic flow (EOF), separation efficiency and coating stability, as well as their promising applications in the biopharmaceutical field.

Protein mapping of peanut extract with capillary electrophoresis

Protein separation can be achieved with different modes of capillary electrophoresis, such as with capillary gel electroporesis (CGE) or with capillary zone electrophoresis (CZE). CZE protein mapping of peanut extract was approached in four different ways, combining neutral-coated or multilayer-coated capillaries with pHs well over or under the isoelectric point range of the proteins of interest. At acidic pHs, the mobility ranges of the major peanut allergens Ara h1, Ara h2, Ara h3, and Ara h6 were identified. Although the pH is a major factor in CZE separation, buffers with different compositions but with the same pH and ionic strength showed significantly different resolutions. Different components of the electrolyte were studied in a multifactorial design of experiment. CE-SDS and CZE proved to be suitable for protein mapping and we were able to distinguish different batches of peanut extract and burned peanut extract.

Glycan analysis for protein therapeutics

Glycosylation can be a critical quality attribute for protein therapeutics due to its extensive impact on product safety and efficacy. Glycan characterization is important in the process of protein drug development, from early stage candidate selection to late stage regulatory submission. It is also an indispensable part in the evaluation of biosimilarity. This review discusses the effects of glycosylation on the stability and activity of protein therapeutics, regulatory considerations corresponding to manufacturing and structural characterization of glycosylated protein therapeutics, and focuses on mass spectrometry compatible separation methods for glycan characterization of protein therapeutics. These approaches include hydrophilic interaction liquid chromatography, reversed-phase liquid chromatography, capillary electrophoresis, porous graphitic carbon liquid chromatography and two-dimensional liquid chromatography. Advances and novelties in each separation method, as well as associated challenges and limitations, are discussed at the released glycan, glycopeptide, glycoprotein subunit and intact glycoprotein levels.

Capillary Zone Electrophoresis-Mass Spectrometry of Intact Proteins

Capillary electrophoresis (CE) coupled with mass spectrometry (MS) has proven to be a powerful analytical tool for the characterization of intact proteins. It combines the high separation efficiency, short analysis time, and versatility of CE with the mass selectivity and sensitivity offered by MS detection. This chapter focuses on important practical considerations when applying CE-MS for the analysis of intact proteins. Technological aspects with respect to the use of CE-MS interfaces and application of noncovalent capillary coatings preventing protein adsorption are treated. Critical factors for successful protein analysis are discussed and four typical CE-MS systems are described demonstrating the characterization of different types of intact proteins by CE-MS. These methodologies comprise the use of sheath-liquid and sheathless CE-MS interfaces, and various types of noncovalent capillary coatings allowing efficient and reproducible protein separations. The discussion includes the analysis of lysozyme-drug conjugates and the therapeutic proteins human growth hormone, human interferon-β-1a, and human erythropoietin.

Chemical vapor deposition of aminopropyl silanes in microfluidic channels for highly efficient microchip capillary electrophoresis-electrospray ionization-mass spectrometry

We describe a chemical vapor deposition (CVD) method for the surface modification of glass microfluidic devices designed to perform electrophoretic separations of cationic species. The microfluidic channel surfaces were modified using aminopropyl silane reagents. Coating homogeneity was inferred by precise measurement of the separation efficiency and electroosmotic mobility for multiple microfluidic devices. Devices coated with (3-aminopropyl)di-isopropylethoxysilane (APDIPES) yielded near diffusion-limited separations and exhibited little change in electroosmotic mobility between pH 2.8 and pH 7.5. We further evaluated the temporal stability of both APDIPES and (3-aminopropyl)triethoxysilane (APTES) coatings when stored for a total of 1 week under vacuum at 4 °C or filled with pH 2.8 background electrolyte at room temperature. Measurements of electroosmotic flow (EOF) and separation efficiency during this time confirmed that both coatings were stable under both conditions. Microfluidic devices with a 23 cm long, serpentine electrophoretic separation channel and integrated nanoelectrospray ionization emitter were CVD coated with APDIPES and used for capillary electrophoresis (CE)-electrospray ionization (ESI)-mass spectrometry (MS) of peptides and proteins. Peptide separations were fast and highly efficient, yielding theoretical plate counts over 600,000 and a peak capacity of 64 in less than 90 s. Intact protein separations using these devices yielded Gaussian peak profiles with separation efficiencies between 100,000 and 400,000 theoretical plates.

Capillary electrophoresis-mass spectrometry using noncovalently coated capillaries for the analysis of biopharmaceuticals

In this work, the usefulness of capillary electrophoresis-electrospray ionization time-of-flight-mass spectrometry for the analysis of biopharmaceuticals was studied. Noncovalently bound capillary coatings consisting of Polybrene-poly(vinyl sulfonic acid) or Polybrene-dextran sulfate-Polybrene were used to minimize protein and peptide adsorption, and achieve good separation efficiencies. The potential of the capillary electrophoresis-mass spectrometry (CE-MS) system to characterize degradation products was investigated by analyzing samples of the drugs, recombinant human growth hormone (rhGH) and oxytocin, which had been subjected to prolonged storage, heat exposure, and/or different pH values. Modifications could be assigned based on accurate masses as obtained with time-of-flight-mass spectrometry (TOF-MS) and migration times with respect to the parent compound. For heat-exposed rhGH, oxidations, sulfonate formation, and deamidations were observed. Oxytocin showed strong deamidation (up to 40%) upon heat exposure at low pH, whereas at medium and high pH, mainly dimer (>10%) and trisulfide formation (6-7%) occurred. Recombinant human interferon-β-1a (rhIFN-β) was used to evaluate the capability of the CE-MS method to assess glycan heterogeneity of pharmaceutical proteins. Analysis of this N-glycosylated protein revealed a cluster of resolved peaks which appeared to be caused by at least ten glycoforms differing merely in sialic acid and hexose N-acetylhexosamine composition. Based on the relative peak area (assuming an equimolar response per glycoform), a quantitative profile could be derived with the disialytated biantennary glycoform as most abundant (52%). Such a profile may be useful for in-process and quality control of rhIFN-β batches. It is concluded that the separation power provided by combined capillary electrophoresis and TOF-MS allows discrimination of highly related protein species.

Capillary electrophoresis-mass spectrometry for the analysis of intact proteins 2007-2010

CE coupled to MS has proven to be a powerful analytical tool for the characterization of intact proteins, as it combines the high separation efficiency of CE with the selectivity of MS. This review provides an overview of the development and application of CE-MS methods within the field of intact protein analysis as published between January 2007 and June 2010. Ongoing technological developments with respect to CE-MS interfacing, capillary coatings for CE-MS, coupling of CIEF with MS and chip-based CE-MS are treated. Furthermore, CE-MS of intact proteins involving ESI, MALDI and ICP ionization is outlined and overviews of the use of the various CE-MS methods are provided by tables. Representative examples illustrate the applicability of CE-MS for the characterization of proteins, including glycoproteins, biopharmaceuticals, protein-ligand complexes, biomarkers and dietary proteins. It is concluded that CE-MS is a valuable technique with high potential for intact protein analysis, providing useful information on protein identity and purity, including modifications and degradation products.

Electrophoretic and electrochromatographic separation of proteins in capillaries: an update covering 2007-2009

This review article covers 3-year period from 2007 to 2009 and is a continuation of the review article by V. Dolnik, [Electrophoresis 2008, 29, 143-156]. This article with 125 references describes recent developments in CE and CEC of proteins in capillary format and does not cover the developments of CE and CEC in microchip format, since Tran et al. review the microchip subject in this special issue. The present review article has four major topics including (i) the separation media, (ii) multidimensional separations, (iii) detection, and (iv) applications.

Effectiveness of charged noncovalent polymer coatings against protein adsorption to silica surfaces studied by evanescent-wave cavity ring-down spectroscopy and capillary electrophoresis

Protein adsorption to silica surfaces is a notorious problem in analytical separations. Evanescent-wave cavity ring-down spectroscopy (EW-CRDS) and capillary electrophoresis (CE) were employed to investigate the capability of positively charged polymer coatings to minimize the adsorption of basic proteins. Adsorption of cytochrome c (cyt c) to silica coated with a single layer of polybrene (PB), or a triple layer of PB, dextran sulfate (DS), and PB, was studied and compared to bare silica. Direct analysis of silica surfaces by EW-CRDS revealed that both coatings effectively reduce irreversible protein adsorption. Significant adsorption was observed only for protein concentrations above 400 microM, whereas the PB-DS-PB coating was shown to be most effective and stable. CE analyses of cyt c were performed with and without the respective coatings applied to the fused-silica capillary wall. Monitoring of the electroosmotic flow and protein peak areas indicated a strong reduction of irreversible protein adsorption by the positively charged coatings. Determination of the electrophoretic mobility and peak width of cyt c revealed reversible protein adsorption to the PB coating. It is concluded that the combination of results from EW-CRDS and CE provides highly useful information on the adsorptive characteristics of bare and coated silica surfaces toward basic proteins.