Isoelectric Focusing Research Articles

A new paradigm for optimized experimental design in cIEF platforms aimed at an accurate robust and reliable mAbs charge-variant assessment.

The success of therapeutic monoclonal antibodies (mAbs) and their biosimilars, highlights the challenge to control their purity, identity, and stability. For this purpose, among several orthogonal methodologies, imaged capillary Iso Electric Focusing (icIEF) is one of the leading techniques. Despite the isoelectric point (pI) being a univocal parameter relying on the protein's primary sequence and its post-translational modifications (PTMs), the current Charge Variants Profile Assessment (CVPA) carried out by cIEF relies on relative comparisons with corresponding reference standards, this is because the inconsistent outputs for the same sample across different instruments preclude the uniqueness of the measured parameters. We demonstrate that refining the current calibration approach in the iciEF method allows for obtaining more reliable and objective pIs, and a deeper understanding of the pH gradients along the capillaries. We are confident our advancements will enhance CVPA, by exploring the concept of univocal charge identity. This is crucial for constructing biobanks and developing algorithms to quickly identify divergences from the originators, thus ensuring drug quality, efficacy, and safety. Moreover, our method allows an experimental design optimized to minimize bias ("Unbiased" Experimental Design-UED) to study resolution as a multivariate function of different input variables. This endeavor aims to develop optimal methods tailored to specific pH ranges.

Development of imaged capillary isoelectric focusing as a platform mispairing byproduct testing method for asymmetric WuXiBody-based bispecific antibodies

This study explores the application of imaged capillary isoelectric focusing (icIEF) to distinguish and quantify mispairing byproducts in asymmetric WuXiBody-based bispecific antibodies (AsWXbsAbs). Bispecific antibody (BsAb), developed using Knobs-into-Holes (KiH) technology, often result in byproducts such as knob-knob (KK) and hole-hole (HH) homodimers, which share similar sizes with the target BsAb, complicating their separation by traditional methods like size exclusion chromatography-high performance liquid chromatography (SEC-HPLC). Our approach leverages the unique pI differences introduced by substituting the CH1/CL domain with the T cell receptor (TCR) constant domain in AsWXbsAbs. This modification enables icIEF to effectively differentiate between the KK and HH homodimers and the target BsAb. Through the construction and expression of heavy and light chain variants, we validated that the experimental pI values aligned with theoretical predictions, confirming icIEF’s capability in distinguishing these entities. Enrichment of in-process K-related and H-related species was achieved, allowing for high-purity samples necessary for icIEF method development. The method was qualified and showed good specificity and linearity, with a quantitation limit of 4 % for K-related species (R2 = 0.9919) and 1 % for H-related species (R2 = 0.9805). This method was used effectively as an in-process test and release assay, proving its simple and quick utility in multiple AsWXbsAbs projects.

Development of the SupersonicIEF Method for High-Throughput Charge Variant Analysis.

The analysis of biopharmaceuticals for charge variants occurs from early-stage samples through formulation and process-development optimization. Higher throughput methods allow increased analysis of these samples to facilitate greater understanding of the samples and to better optimize their production and formulation. To enable higher throughput charge variant analysis, a new, rapid platform imaged capillary isoelectric focusing (icIEF) method was optimized to be two to three times faster than standard methods.

Enrichment of low-abundance osteopontin in bovine milk via reciprocating free-flow isoelectric focusing.

Osteopontin (OPN) in milk plays an important role in intestinal and brain development in early infancy, and great attention has been focused on OPN isolation to add extra OPN in infant formula. However, large-scale OPN isolation is limited by the low efficiency of sample pretreatment. Herein, we utilized preparative reciprocating free-flow isoelectric focusing (RFFIEF) to showcase the enrichment of low-abundance OPN in bovine milk, which contained an extremely high concentration of unwanted proteins. The reciprocating IEF format and the design of the multi-channel collector allowed us to enrich OPN in 1 L milk within 6h. We removed 97.5% of unwanted proteins and obtained an enrichment factor of 11. Thus, our RFFIEF method can be applied to the preparative pretreatment of the large-scale milk sample and potentially improve the efficiency of downstream OPN purification.

B-079 Characterization of an isoelectric focusing method for detection of IgG oligoclonal banding in paired cerebrospinal fluid and serum specimens

Abstract Background Qualitative assessment of IgG-specific oligoclonal banding (OCB) in paired serum and cerebrospinal fluid (CSF) samples is useful for evaluating inflammatory conditions of the central nervous system such as multiple sclerosis. Here we characterized the performance of an IgG-specific method using isoelectric focusing on agarose gel matrix for the detection of OCB in paired serum and CSF samples. Methods Specimens of 20 paired, simultaneously collected CSF and serum patient samples were tested on Sebia (Hydrasys 2 System) provided by the National Institutes of Health (NIH) Diagnostic Laboratories. We tested these paired samples using the Helena IgG IFE-20 kit (SPIFE® Touch) method and the results were read by two independent individuals blinded to each other’s assessments. The results were compared to the NIH results for agreement. Positive Percent Agreement (PPA) and Negative Percent Agreement (NPA) were calculated. Analytical sensitivity of the Helena assay was assessed via serial dilutions of a CSF OCB positive sample (total IgG 4.5 mg/dL). Results Figure 1 shows serum and CSF pairs for the control (A), two example positive OCB patients (B & D) and a negative OCB patient (C). The Helena assay was concordant with Sebia for 11/12 positive OCB patients (PPA 91.6%) and 8/8 negative subjects (NPA 100%). 20-fold was the highest dilution that remained positive. Conclusions OCB detection using paired serum and CSF samples and isoelectric focusing electrophoresis is considered the preferred method. The Helena IgG IFE-20 assay is such a method and showed high PPA and NPA concordance with the Sebia System. Thus, the Helena OCB assay can be considered an accurate and analytically sensitive method for assessing OCB in serum and CSF.

B-101 Assessing the Performance of Cerebrospinal Fluid Kappa Immunoglobulin Free Light Chain as a Diagnostic Marker for Multiple Sclerosis Using Automated Chart Review

Abstract Background Multiple sclerosis (MS) is an immune-mediated central nervous system (CNS) demyelinating disease which is diagnosed based on CNS lesions' spatial and temporal dissemination. The 2017 revised McDonald Criteria include cerebrospinal fluid (CSF) specific oligoclonal bands (OCBs) to indicate dissemination in time, but their assessment is labor-intensive and requires a paired serum sample. Kappa immunoglobulin free light chain in CSF (KCSF) has emerged as a more sensitive but less specific MS biomarker, measured from a single CSF sample. Our institution's MS testing panel uses KCSF initially to rule out MS, with reflex to OCB for positive confirmation if KCSF is borderline positive (≥0.06 mg/dL). However, manual correlation of laboratory and clinical data hinders the direct comparison of the diagnostic performance between these markers. Herein we report a retrospective assessment of KCSF and OCB diagnostic performance using automated chart review. Methods Between January 1st, 2021 and December 31st, 2022, there were 1,237 patients with simultaneously measured OCB and KCSF. CSF-specific OCBs were measured by separating CSF and serum proteins using an agarose isoelectric focusing gel with a pH gradient from 3-10 (Sebia). After transfer to nitrocellulose paper, antisera were applied to visualize IgG specific bands and quantify CSF-specific OCBs. KCSF was quantitated using nephelometry by applying free light chain antisera (Binding Site) to CSF samples using a Siemens BNII analyzer. An automated chart review process utilizing keyword matching was implemented to identify patients with MS. An initial filter phase required presence of the term “multiple sclerosis”, while a second required the presence of any of the following terms: “primary progressive,” “secondary progressive,” “relapsing remitting,” “progressive relapsing,” or “tumefactive” to identify patients with diagnosed MS. The automated method’s performance was then compared to a manual chart review of 200 randomly selected patients. Subsequently, the automated process was used to determine the MS diagnosis status of all 1,237 patients. Results Of the 200 manually reviewed patients, 44 MS diagnoses were found. The automated process correctly identified 41 of these with a resulting sensitivity and specificity of 93.18% and 95.51%, respectively. Applied to the entire cohort, the automated review identified 275 MS diagnoses. For the entire cohort, the area under the curve (AUC) for the receiver operating characteristic (ROC) curves for OCB and KCSF were 0.824 (95% confidence interval: 0.794, 0.854) and 0.808 (0.777, 0.839) respectively. Our institution’s diagnostic cutoff of ≥2 for OCB yielded a sensitivity and specificity of 74.2% (68.3%, 79.1%) and 84.9% (73.8%, 89.5%), respectively. The best combination for sensitivity and specificity for KCSF with the Youden index yielded a cutoff ≥0.0654 mg/dL (sensitivity of 79.6% [73.1%, 84.0%] and specificity of 72.4% [62.8%, 76.8%]), which is similar to previous publications. This supports the use of automated chart review and suggests the KCSF cutoff has been stable over time. Conclusions KCSF exhibits comparable MS diagnostic performance to OCB yet only requires one CSF sample and can be measured rapidly. When validated, mining unstructured data allows for test performance characterization in large patient cohorts without the need for manual chart review.

Microcolumn and coelution hydration of oil seal blood spot for efficient screening of newborn α-thalassemia via chip isoelectric focusing

BackgroundThe global prevalence of α-thalassemia necessitates effective newborn screening strategies due to its severe clinical consequences. Traditional methods such as liquid chromatography (LC), capillary electrophoresis (CE), and isoelectric focusing (IEF) face limitations, including low separation efficiency, poor sensitivity for detecting Hb Bart’s, and time-intensive operations, particularly with dried blood spots (DBS). These limitations hinder timely and accurate screening. This study addresses the need for a more efficient, sensitive, and rapid method for detecting Hb Bart’s in newborns. ResultsWe enhanced IEF separation and sensitivity by designing a microfluidic IEF (mIEF) system with shortened columns and employing a coelution sample loading technique using oil-sealed blood spots for rapid sample pretreatment. Our experiments demonstrated significant improvements: the total analysis time was reduced from 1110 minutes (IPG IEF) and 46 minutes (LC) per batch to 36 minutes per batch. For individual samples, the focusing time decreased from 6 minutes (previous mIEF) to 3 minutes, with the microcolumn length shortened by 50%, from 30 mm to 15 mm. The developed method showed excellent consistency with clinical Bart’s detection and PCR diagnosis, achieving 100% sensitivity and 98% specificity for α-thalassemia screening. Significance and NoveltyOur novel mIEF method provides an efficient, sensitive, and rapid tool for screening newborns for α-thalassemia. This advancement addresses the limitations of traditional techniques, improving early diagnosis and intervention strategies and ultimately enhancing health outcomes for at-risk newborns.

Pilot Study for Deciphering Post-Translational Modifications and Proteoforms of Tau Protein by Capillary Electrophoresis-Mass Spectrometry.

Abnormal accumulation of tau protein in the brain is one pathological hallmark of Alzheimer's disease (AD). Many tau protein post-translational modifications (PTMs) are associated with the development of AD, such as phosphorylation, acetylation, and methylation. Therefore, a complete picture of the PTM landscape of tau is critical for understanding the molecular mechanisms of AD progression. Here, we offered a pilot study of combining two complementary analytical techniques, capillary zone electrophoresis (CZE)-tandem mass spectrometry (MS/MS) and reversed-phase liquid chromatography (RPLC)-MS/MS, for bottom-up proteomics of recombinant human tau-0N3R. We identified 50 phosphorylation sites of tau-0N3R in total, which is about 25% higher than that from RPLC-MS/MS alone. CZE-MS/MS provided more PTM sites (i.e., phosphorylation) and modified peptides of tau-0N3R than RPLC-MS/MS, and its predicted electrophoretic mobility helped improve the confidence of the identified modified peptides. We developed a highly efficient capillary isoelectric focusing (cIEF)-MS technique to offer a bird's-eye view of tau-0N3R proteoforms, with 11 putative tau-0N3R proteoforms carrying up to nine phosphorylation sites and lower pI values from more phosphorylated proteoforms detected. Interestingly, under native-like cIEF-MS conditions, we observed three putative tau-0N3R dimers carrying phosphate groups. The findings demonstrate that CE-MS is a valuable analytical technique for the characterization of tau PTMs, proteoforms, and even oligomerization.

Characteristics of lectin receptors on erythrocyte membranes of patients with glioblastoma

Aim. This work is devoted to the search the abnormalities of the receptor-lectin reactions associated with glioblastoma for diagnostic purposes. Methods. Red blood cell (RBC) specimens were taken from 22 persons distributed into the two cohorts: donors without an oncological diagnosis; patients with glioblastoma (GB). Panel of 9 commercial lectins (LECTINOTEST, Lviv, Ukraine) was used: ConA, WGA, PHA-P; PHA-E; PHA-L, SNA, VAA, STA, and LABA. Also the original lectin from persimmon sepals (named PSL) was used. It was obtained by isoelectric focusing and ammonium sulfate fractionation. Intensity of lectin-receptor interactions was determined in reaction of hemagglutination. Results. Тwo lectins showed some directed divergence in patients from donors. For wheat germ agglutinin (WGA) сhanges in the intensity of lectin-receptor binding were downward. In the case of persimmon L (PSL) the alternative result was observed: the intensity of hemagglutination showed a trend to exceed the level of control. Conclusions. Some individual features in the reaction of erythrocytes with a set of lectins are observed in all examined persons. For two studied lectins, namely WGA and PSL, unidirectional deviations were observed in the reaction of erythrocytes of patients with GB compared to individuals without an oncological diagnosis.

Tissue-specific accumulation of PIP aquaporins of a particular heteromeric composition is part of the maize response to mycorrhiza and drought

The systemic coordination of accumulation of plasma membrane aquaporins (PIP) was investigated in this study in relation to mycorrhized maize response to a rapid development of severe drought followed by rewatering. In non-mycorrhizal roots, drought led to a drop in PIP abundance, followed by a transient increase under rewatering, whereas leaves showed an opposite pattern. In contrast, mycorrhiza contributed to maintenance of high and stable levels of PIPs in both plant organs after an initial increase, prolonged over the irrigation period. Isoelectric focusing electrophoresis resolved up to 13 aquaporin complexes with highly reproducible pl positions across leaf and root samples, symbiotic and non-symbiotic, stressed or not. Mass spectrometry recognized in leaves and roots a different ratio of PIP1 and PIP2 subunits within 2D spots that accumulated the most. Regardless of symbiotic status, drought regulation of aquaporins in roots was manifested as the prevalence of complexes that comprise almost exclusively PIP2 monomers. In contrast, the leaf response involved enrichment in PIP1s. PIP1s are thought to enhance water transport, facilitate CO2 diffusion but also affect stomatal movements. These features, together with elevated aquaporin levels, might explain a stress tolerance mechanism observed in mycorrhizal plants, resulting in faster recovery of stomatal water conductance and CO2 assimilation rate after drought.

Semi-quantitative analysis of serum and cerebrospinal fluid transferrin glycoforms by top-down liquid chromatography mass spectrometry

Detection of β-2 transferrin in body fluid could help identify cerebrospinal fluid (CSF) leakage. The most common method, isoelectric focusing, was qualitative and could not provide detailed N-glycan structural information. We presented an alternative method using top-down liquid chromatography-time of flight mass spectrometry (LC-TOF MS). After immunoaffinity enrichment, fluid transferrin glycoforms were analyzed by a high-resolution LC-TOF MS, and the N-glycan structure predicted by accurate mass. The performance was validated with imprecision at 15%, with a cut-off of 0.04 for β-2 transferrin to tetrasialotransferrin ratio to confirm the presence of CSF in fluid samples.

In-depth characterization of a cysteine-linked ADC disitamab vedotin by multiple LC-MS analysis methods and cutting-edge imaged capillary isoelectric focusing coupled with native mass spectrometry

The characterization of cysteine-linked antibody‒drug conjugates (ADCs) can be more challenging than that of monoclonal antibodies (mAbs) and lysine-linked ADCs because the interchain disulfide bonds are reduced for payload conjugation, and the chains are noncovalently bonded to each other. Furthermore, payload conjugation and disulfide bond reduction/scrambling may introduce additional charge heterogeneity to biomolecules. This study illustrates an innovative workflow employing multiple separation techniques and tandem high-resolution mass spectrometry for comprehensive and in-depth characterization of disitamab vedotin, a recent-generation cysteine-linked ADC, including reversed-phase liquid chromatography (RPLC), ion exchange chromatography (IEX) and image capillary isoelectric focusing (icIEF). RPLC was employed for reduced chains analysis, subunit analysis and peptide mapping. IEX and icIEF were used for charge heterogeneity analysis. The innovation of the integrated methodology emphasizes the importance of cutting-edge icIEF-MS online coupling under near-native conditions to reveal the heterogeneity of disitamab vedotin.

Characterization of a GDS(L)-like hydrolase from Pleurotus sapidus with an unusual SGNH motif

The GDS(L)-like lipase from the Basidiomycota Pleurotus sapidus (PSA_Lip) was heterologously expressed using Trichoderma reesei with an activity of 350 U L−1. The isoelectric point of 5.0 was determined by isoelectric focusing. The novel PSA_Lip showed only 23.8–25.1%, 25.5%, 26.6% and 28.4% identity to the previously characterized GDSL-like enzymes phospholipase, plant lipase, acetylcholinesterase and acetylxylan esterase, from the carbohydrate esterase family 16, respectively. Therefore, the enzyme was purified from the culture supernatant and the catalytic properties and the substrate specificity of the enzyme were investigated using different assays to reveal its potential function. While no phospholipase, acetylcholinesterase and acetylxylan esterase activities were detected, studies on the hydrolysis of ferulic acid methyl ester (~ 8.3%) and feruloylated carbohydrate 5-O-transferuloyl-arabino-furanose (~ 0.8%) showed low conversions of these substrates. By investigating the hydrolytic activity towards p-nitrophenyl-(pNP)-esters with various chain-lengths, the highest activity was determined for medium chain-length pNP-octanoate at 65 °C and a pH value of 8, while almost no activity was detected for pNP-hexanoate. The enzyme is highly stable when stored at pH 10 and 4 °C for at least 7 days. Moreover, using consensus sequence analysis and homology modeling, we could demonstrate that the PSA_Lip does not contain the usual SGNH residues in the actives site, which are usually present in GDS(L)-like enzymes.

Identification of snake venom toxins and their biological activities through capillary isoelectric focusing (cIEF) with post-separation high throughput venomics and bioassaying

Identification of snake venom toxins and their biological activities through capillary isoelectric focusing (cIEF) with post-separation high throughput venomics and bioassaying

Assessing carnosinase 1 activity for diagnosing congenital disorders of glycosylation

Diagnosing Congenital Disorders of Glycosylation (CDG) is challenging due to clinical heterogeneity and the limited sensitivity of the classic serum transferrin isoelectric focusing (IEF) or capillary zone electrophoresis test. This study investigates the potential of using the glycoprotein carnosinase 1 (CN1) activity as a diagnostic marker for CDG patients. CN1 activity was measured photometrically in serum from 81 genetically confirmed CDG patients and healthy individuals. While the IEF transferrin method detected 77 patients, four remained undetected.In healthy individuals, serum CN1 activity ranged from 0.1 to 6.4 μmol/ml/h depending on age, with mean CN1 activities up to four-fold higher than in CDG patients. CDG patients´ CN1 activities never exceeded 2,04 μmol/ml/h. Using the 25th percentile to differentiate between groups, the test performance varied by age. For children over 10 years old, the sensitivity and specificity were 96 % and 83 %, respectively. For those under 10, sensitivity and specificity dropped to 71 % and to 64 %. However, CN1 activity successfully identified three of four patients with normal IEF patterns.Although mean CN1 activity in CDG patients is significantly lower than in healthy controls, the test's reliability for classic CDG diagnosis is limited, as the diagnosis is usually made at a young age. Nevertheless, it is a simple, cost-effective assay that can complement classic tests, especially in settings with limited access to complex methods or for patients with normal transferrin patterns but suspicious for CDG.

Overview of Analytical Methods for Characterizing the Charge Heterogeneity of Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are ideal candidates for selective therapy. ADCs display considerable heterogeneity resulting from various modifications. One of the molecular characteristics of ADCs is charge heterogeneity. Several analytical methods could be used to characterize the charge heterogeneity of ADC including ion exchange chromatography (IEC), isoelectric focusing (IEF), and capillary electrophoresis (CE). This work aimed to give insights into the different analytical techniques used to determine pI and the charge distribution profile of ADCs.

Large TRAPPC11 gene deletions as a cause of muscular dystrophy and their estimated genesis

BackgroundTransport protein particle (TRAPP) is a multiprotein complex that functions in localising proteins to the Golgi compartment. The TRAPPC11 subunit has been implicated in diseases affecting muscle, brain, eye and...

Imaged capillary isoelectric focusing method development for charge variants of high DAR ADCs

BackgroundCharge heterogeneity is a critical quality attribute for therapeutic biologics including antibody-drug conjugates (ADCs). Developing an ion exchange chromatography (IEX) or an imaged capillary isoelectric focusing (icIEF) method for ADCs with high drug-to-antibody ratio (DAR) is challenging because of the increased hydrophobicity from the payload-linker, DAR heterogeneity, and payload-linker instability. A sub-optimal method can be poorly stability-indicating due to the inability to discern contributions from charge and size variants conjugated with different number of drugs/payloads. Systematic strategy and guidance on charge variant method development is highly desired for high DAR ADCs with various complex structures. ResultsThis work encompasses the development and optimization of icIEF methods for high DAR ADCs of various DAR values (4–8) and payload linker chemistry. Method optimization focuses on improving resolution and stability indicating capabilities and differentiating contributions from the protein and payload-linker. Types, proportion, and combination of solubilizers and carrier ampholytes, as well as focusing parameters were interrogated. Our findings show that the structural units of the linker, the DAR, and the payload chemistry prescribe the selection of buffer, solubilizer, and ampholyte. We demonstrate that a stronger denaturant or solubilizer is needed for high DAR ADCs with polyethylene glycol (PEG)-containing linker structure compared to peptide linker. For unstable payload-linker, buffer system enhances sample stability which is vital to method robustness. In addition, a longer isoelectric focusing time is necessary for an ADC than its corresponding antibody to reach optimal focusing. SignificanceTo the best of our knowledge, this is the first comprehensive study on icIEF method development for charge variant determination of high DAR ADCs with unique physicochemical properties.

Simple Analysis of Gel Images With IOCBIO Gel Software.

Gel image analyses are often difficult to reproduce, as the most commonly used software, the ImageJ Gels plugin, does not automatically record any steps in the analysis process. This protocol provides detailed steps for image analysis using IOCBIO Gel software with western blot as an example; however, the protocol is applicable to all images obtained by electrophoresis, such as Southern blotting, northern blotting, and isoelectric focusing. IOCBIO Gel allows multiple sample analyses, linking the original image to all the operations performed on it, which can be stored in a central database or on a PC, ensuring ease of access and the possibility to perform corrections at each analysis stage. In addition, IOCBIO Gel is lightweight, with only minimal computer requirements. Key features • Free and open-source software for analyzing gel images. • Reproducibility. • Can be used with images obtained by electrophoresis, such as western blotting, Southern blotting, isoelectric focusing, and more.

Analysis of therapeutic monoclonal antibodies by imaged capillary isoelectric focusing (icIEF).

Imaged capillary isoelectric focusing (icIEF) is a preferred analytical method for determining isoelectric points (pIs) and charge heterogeneity profiles in biotherapeutic proteins. In this study, we optimized the icIEF method for an in-house IgG1κ monoclonal antibody (mAb-1) and assessed its reproducibility, robustness, and autosampler stability. The optimized method was used to evaluate batch-to-batch consistency in pIs for multiple lots of mAb-1 and determine the relative percentages of charge variants. We also tested the method's performance using multiple lots of another IgG1 mAb, commercially available as Herceptin (trastuzumab). Additionally, we designed and assessed native and denaturing platform icIEF methods for 11 other marketed mAbs, with pIs ranging from 6.0 (eculizumab) to 9.22 (tocilizumab).