Online nanoliquid chromatography-mass spectrometry and nanofluorescence detection for high-resolution quantitative N-glycan analysis

Highly sensitive two-dimensional profiling of N-linked glycans by hydrophilic interaction liquid chromatography and dual stacking capillary gel electrophoresis

BACKGROUND

N-Glycosylation is one of the most important post-translational modifications in proteins. As the N-glycan profiles in biological samples are diverse and change according to the pathological condition, various profiling methods have been developed, such as liquid chromatography (LC), capillary electrophoresis (CE), and mass spectrometry. However, conventional analytical methods have limitations in sensitivity and/or resolution, hindering the discovery of minor but specific N-glycans that are important both in the basic glycobiology research and in the medical application as biomarkers. Therefore, a highly sensitive and high-resolution N-glycan profiling method is required.

RESULTS

In this study, we developed a novel two-dimensional (2D) separation system, which couples hydrophilic interaction liquid chromatography (HILIC) with capillary gel electrophoresis (CGE) via large-volume dual preconcentration by isotachophoresis and stacking (LDIS). Owing to the efficient preconcentration efficiency of LDIS, limit of detection reached 12 pM (60 amol, S/N = 3) with good calibration curve linearity (R2 > 0.999) in the 2D analysis of maltoheptaose. Finally, 2D profiling of N-glycans obtained from standard glycoproteins and cell lysates were demonstrated. High-resolution 2D profiles were successfully obtained by data alignment using triple internal standards. N-glycans were well distributed on the HILIC/CGE 2D plane based on the glycan size, number of sialic acids, linkage type, and so on. As a result, specific minor glycans were successfully identified in HepG2 and HeLa cell lysates.

SIGNIFICANCE AND NOVELTY

In conclusion, the HILIC/CGE 2D analysis method showed sufficient sensitivity and resolution for identifying minor but specific N-glycans from complicated cellular samples, indicating the potential as a next-generation N-glycomics tool. Our novel approach for coupling LC and CE can also dramatically improve the sensitivity in other separation modes, which can be a new standard of 2D bioanalysis applicable not only to glycans, but also to other diverse biomolecules such as metabolites, proteins, and nucleic acids.

Combining Liquid Chromatography and Cryogenic IR Spectroscopy in Real Time for the Analysis of Oligosaccharides

While the combination of liquid chromatography (LC) and mass spectrometry (MS) serves as a robust approach for oligosaccharide analysis, it has difficulty distinguishing the smallest differences between isomers. The integration of infrared (IR) spectroscopy within a mass spectrometer as an additional analytical dimension can effectively address this limitation by providing a molecular fingerprint that is unique to each isomer. However, the direct interfacing of LC-MS with IR spectroscopy presents a technical challenge arising from the mismatch in the operational time scale of each method. In previous studies, this temporal incompatibility was mitigated by employing strategies designed to slow down or broaden the LC elution peaks of interest, but this workaround is applicable only for a few species at a time, necessitating multiple LC runs for comprehensive analysis. In the current work, we directly couple LC with cryogenic IR spectroscopy by acquiring a spectrum in as little as 10 s. This allows us to generate an orthogonal data dimension for molecular identification in the same amount of time that it normally takes for LC analysis. We successfully demonstrate this approach on a commercially available human milk oligosaccharide product, acquiring spectral information on the eluting peaks in real time and using it to identify both the specified constituents and nonspecified product impurities.

Peptide-N-glycosidase F or A treatment and procainamide-labeling for identification and quantification of N-glycans in two types of mammalian glycoproteins using UPLC and LC-MS/MS

BACKGROUND

N-glycans in glycoproteins can affect physicochemical properties of proteins; however, some reported N-glycan structures are inconsistent depending on the type of glycoprotein or the preparation methods.

OBJECTIVE

To obtain consistent results for qualitative and quantitative analyses of N-glycans, N-glycans obtained by different preparation methods were compared for two types of mammalian glycoproteins.

METHODS

N-glycans are released by peptide-N-glycosidase F (PF) or A (PA) from two model mammalian glycoproteins, bovine fetuin (with three glycosylation sites) and human IgG (with a single glycosylation site), and labeled with a fluorescent tag [2-aminobenzamide (AB) or procainamide (ProA)]. The structure and quantity of each N-glycan were determined using UPLC and LC-MS/MS.

RESULTS

The 21 N-glycans in fetuin and another 21 N-glycans in IgG by either PF-ProA or PA-ProA were identified using LC-MS/MS. The N-glycans in fetuin (8-13 N-glycans were previously reported) and in IgG (19 N-glycans were previously reported), which could not be identified by using the widely used PF-AB, were all identified by using PF-ProA or PA-ProA. The quantities (%) of the N-glycans (>0.1 %) relative to the total amount of N-glycans (100 %) obtained by AB- and ProA-labeling using LC-MS/MS had a similar tendency. However, the absolute quantities (pmol) of the N-glycans estimated using UPLC and LC-MS/MS were more efficiently determined with ProA-labeling than with AB-labeling. Thus, PF-ProA or PA-ProA allows for more effective identification and quantification of N-glycans than PF-AB in glycoprotein, particularly bovine fetuin. This study is the first comparative analysis for the identification and relative and absolute quantification of N-glycans in glycoproteins with PF-ProA and PA-ProA using UPLC and LC-MS/MS.

Qualitative and quantitative characterization of sialylated N-glycans using three fluorophores, two columns, and two instrumentations

Sialylation can influence the stability, half-life, and immunogenicity of glycoproteins, but sialylated N-glycans are known to be difficult to analyze. Human alpha1-acid glycoprotein (AGP) is reported to have glycans that consist of sialylated N-glycans. The N-glycan profiling of AGP is qualitatively and quantitatively investigated here by UPLC and LC-ESI-MS/MS. Three fluorescent tags (AB, AA, and ProA) and two separation columns (HILIC and AEX-HILIC) were adopted to confirm and compare each analytical characteristic. The results of AA were comparable to those of the well-established AB. The qualification of ProA was notable due to its superior fluorescence intensity and ionization efficiency, and ProA showed smaller quantitative or larger-sized fragments in LC-ESI-MS/MS compared to AB and AA. However, the MS quantification of ProA was distorted because the increased sialylation level decreased the LC-ESI-MS/MS ionization efficiency. HILIC had better peak separability, AEX-HILIC had an advantage in UPLC sialylation profiling, and each isomeric glycan could be identified by both columns in LC-ESI-MS/MS. In conclusion, ProA is favored for UPLC and LC-ESI-MS/MS detection but not reliable for MS quantification. This study firstly demonstrates the qualification and quantification of sialylated N-glycans by comparing the commonly used analytical conditions with different fluorescent tags, columns, and instruments.

In-depth structural analysis of glycans in the gas phase

Although there have been substantial improvements in glycan analysis over the past decade, the lack of both high-resolution and high-throughput methods hampers progress in glycomics. This perspective article highlights the current developments of liquid chromatography, mass spectrometry, ion-mobility spectrometry and cryogenic IR spectroscopy for glycan analysis and gives a critical insight to their individual strengths and limitations. Moreover, we discuss a novel concept in which ion mobility-mass spectrometry and cryogenic IR spectroscopy is combined in a single instrument such that datasets consisting of m/z, collision cross sections and IR fingerprints can be obtained. This multidimensional data will then be compared to a comprehensive reference library of intact glycans and their fragments to accurately identify unknown glycans on a high-throughput scale with minimal sample requirements. Due to the complementarity of the obtained information, this novel approach is highly diagnostic and also suitable for the identification of larger glycans; however, the workflow and instrumentation is straightforward enough to be implemented into a user-friendly setup.

The sweet spot for biologics: recent advances in characterization of biotherapeutic glycoproteins

INTRODUCTION

Glycosylation is recognized as a Critical Quality Attribute for therapeutic glycoproteins such as monoclonal antibodies, fusion proteins and therapeutic replacement enzymes. Hence, efficient and quantitative glycan analysis techniques have been increasingly important for their discovery, development and quality control. The aim of this review is to highlight relevant and recent advances in analytical technologies for characterization of biotherapeutic glycoproteins. Areas covered: The review gives an overview of the glycosylation trends of biotherapeutics approved in 2016 and 2017 by FDA. It describes current and novel analytical technologies for characterization of therapeutic glycoproteins and is explored in the context of released glycan, glycopeptide or intact glycoprotein analysis. Ultra performance liquid chromatography, mass spectrometry and capillary electrophoresis technologies are explored in this context. Expert commentary: There is a need for the biopharmaceutical industry to incorporate novel state of the art analytical technologies into existing and new therapeutic glycoprotein workflows for safer and more efficient biotherapeutics and for the improvement of future biotherapeutic design. Additionally, at present, there is no 'gold-standard' approach to address all the regulatory requirements and as such this will involve the use of orthogonal glycoanalytical technologies with a view to gain diagnostic information about the therapeutic glycoprotein.

Fasciola hepatica glycoconjugates immuneregulate dendritic cells through the Dendritic Cell-Specific Intercellular adhesion molecule-3-Grabbing Non-integrin inducing T cell anergy

Dendritic cell-specific ICAM-3 grabbing non-integrin (DC-SIGN) expressed on a variety of DCs, is a C-type lectin receptor that recognizes glycans on a diverse range of pathogens, including parasites. The interaction of DC-SIGN with pathogens triggers specific signaling events that modulate DC-maturation and activity and regulate T-cell activation by DCs. In this work we evaluate whether F. hepatica glycans can immune modulate DCs via DC-SIGN. We demonstrate that DC-SIGN interacts with F. hepatica glycoconjugates through mannose and fucose residues. We also show that mannose is present in high-mannose structures, hybrid and trimannosyl N-glycans with terminal GlcNAc. Furthermore, we demonstrate that F. hepatica glycans induce DC-SIGN triggering leading to a strong production of TLR-induced IL-10 and IL-27p28. In addition, parasite glycans induced regulatory DCs via DC-SIGN that decrease allogeneic T cell proliferation, via the induction of anergic/regulatory T cells, highlighting the role of DC-SIGN in the regulation of innate and adaptive immune responses by F. hepatica. Our data confirm the immunomodulatory properties of DC-SIGN triggered by pathogen-derived glycans and contribute to the identification of immunomodulatory glyans of helminths that might eventually be useful for the design of vaccines against fasciolosis.

Quantitative Glycomics: A Combined Analytical and Bioinformatics Approach

Glycosylation is one of the most common and essential protein modifications. Glycans conjugated to biomolecules modulate the function of such molecules through both direct recognition of glycan structures and indirect mechanisms that involve the control of protein turnover rates, stability, and conformation. The biological attributes of glycans in numerous biological processes and implications in a number of diseases highlight the necessity for comprehensive characterization of protein glycosylation. This chapter reviews cutting-edge methods and tools developed to facilitate quantitative glycomics. This chapter highlights the different methods employed for the release and purification of glycans from biological samples. The most effective labeling methods developed for sensitive quantitative glycomics are also described and discussed. The chromatographic approaches that have been used effectively in glycomics are also highlighted.

Application of Porous Materials to Carbohydrate Chemistry and Glycoscience

There is a growing interest in using a range of porous materials to meet research needs in carbohydrate chemistry and glycoscience in general. Among the applications of porous materials reviewed in this chapter, enrichment of glycans from biological samples prior to separation and analysis by mass spectrometry is a major emphasis. Porous materials offer high surface area, adjustable pore sizes, and tunable surface chemistry for interacting with glycans, by boronate affinity, hydrophilic interactions, molecular imprinting, and polar interactions. Among the materials covered in this review are mesoporous silica and related materials, porous graphitic carbon, mesoporous carbon, porous polymers, and nanoporous gold. In some applications, glycans are enzymatically or chemically released from glycoproteins or glycopeptides, and the porous materials have the advantage of size selectivity admitting only the glycans into the pores and excluding proteins. Immobilization of lectins onto porous materials of suitable pore size allows for the use of lectin-carbohydrate interactions in capture or separation of glycoproteins. Porous material surfaces modified with carbohydrates can be used for the selective capture of lectins. Controlled release of therapeutics from porous materials mediated by glycans has been reported, and so has therapeutic targeting using carbohydrate-modified porous particles. Additional applications of porous materials in glycoscience include their use in the supported synthesis of oligosaccharides and in the development of biosensors for glycans.

Glycan modification of antigen alters its intracellular routing in dendritic cells, promoting priming of T cells

Antigen uptake by dendritic cells and intracellular routing of antigens to specific compartments is regulated by C-type lectin receptors that recognize glycan structures. We show that the modification of Ovalbumin (OVA) with the glycan-structure Lewis^X (Le^X) re-directs OVA to the C-type lectin receptor MGL1. Le^X-modification of OVA favored Th1 skewing of CD4⁺ T cells and enhanced cross-priming of CD8⁺ T cells. While cross-presentation of native OVA requires high antigen dose and TLR stimuli, Le^X modification reduces the required amount 100-fold and obviates its dependence on TLR signaling. The OVA-Le^X-induced enhancement of T cell cross-priming is MGL1-dependent as shown by reduced CD8⁺ effector T cell frequencies in MGL1-deficient mice. Moreover, MGL1-mediated cross-presentation of OVA-Le^X neither required TAP-transporters nor Cathepsin-S and was still observed after prolonged intracellular storage of antigen in Rab11⁺LAMP1⁺ compartments. We conclude that controlled neo-glycosylation of antigens can crucially influence intracellular routing of antigens, the nature and strength of immune responses and should be considered for optimizing current vaccination strategies.

DOI:http://dx.doi.org/10.7554/eLife.11765.001

Immune cells called dendritic cells play a crucial role in defending the body against tumor cells and invading viruses. The dendritic cells take up molecules called antigens from these threats and then display them on their surface. This enables the antigens to be identified by other immune cells that are capable of killing the viruses and the tumor cells. The dendritic cells recognize the antigens with the help of receptor proteins called C-type lectin receptors (CLRs). These receptors can bind to sugar molecules that are naturally found on many antigens. For example, a C-type lectin receptor called MGL1 can bind to sugars known as Lewis^X and Lewis^a on tumor and virus proteins. However, it is not clear how important these receptors are in triggering immune responses.

An antigen called Ovalbumin – which is found in chicken egg white – can trigger immune responses in mammals and so researchers often use it to study the immune system. Although this antigen has several sugar molecules attached to it, quite a large amount of Ovalbumin is needed to trigger strong immune responses. Now, Streng-Ouwehand et al. examine whether attaching Lewis^X to Ovalbumin can results in stronger immune responses in mice.

The experiments show that injecting mice with Ovalbumin-Lewis^X triggers a much stronger immune response than normal Ovalbumin does. This enhanced response was not observed in mice that lacked the MGL1 receptor, which suggests that this receptor is involved in detecting Ovalbumin-Lewis^X. Furthermore, the dendritic cells store the altered Ovalbumin for longer than they store normal Ovalbumin, which gives the cells more time to present the altered Ovalbumin to other immune cells.

Vaccines and some other therapies help to boost immune responses to viruses and tumors by exposing the body to antigens. However, these therapies often use antigens that don’t have sugar molecules attached to them, or are missing the sugar molecules they would normally have. Streng-Ouwehand et al.’s findings suggest that adding specific sugars to antigens in immune therapies might help to make these therapies more effective.

DOI:http://dx.doi.org/10.7554/eLife.11765.002

Quantification of plant cell wall monosaccharides by reversed-phase liquid chromatography with 2-aminobenzamide pre-column derivatization and a non-toxic reducing reagent 2-picoline borane

In this report, we described a sensitive method for quantifying plant cell wall monosaccharides using chemical derivatization, reversed-phase high performance liquid chromatography separation with ultraviolet detection (HPLC-UV). Monosaccharides were derivatized with 2-aminobenzamide (2-AB) by reductive amination to increase the hydrophobicity and detected by ultraviolet absorption for HPLC-UV analysis. A non-toxic reductant, 2-picoline borane was utilized to replace the traditionally used sodium cyanoborohydride (NaCNBH3) to avoid the formation of toxic by-products. Experimental conditions were optimized using glucose as a model system to achieve a high reaction yield of 99%. Under the optimized conditions, we demonstrated that the derivatization yields of several saccharides with 2-AB using 2-picoline borane were all slightly higher than those observed using NaCNBH3. In plants, cell wall monosaccharides consist of arabinose, fucose, galactose, galacturonic acid, glucose, glucuronic acid, mannose, rhamnose, and xylose. Using our method, we successfully quantified these monosaccharides from Arabidopsis cell wall by HPLC-UV, and we obtained a good linearity at a wide dynamic range over five orders (1pmol through 10nmol of injection amount), a detection limit of ∼0.1pmole, and a high precision and accuracy.

MicroQuEChERS-nanoliquid chromatography-nanospray-tandem mass spectrometry for the detection and quantification of trace pharmaceuticals in benthic invertebrates

Due to industrialization and the use of chemical products in everyday life, various types of drugs and pesticides are present in our environment, which threaten and cause negative impacts on aquatic ecosystems. The consequences of these pollutants are gradually becoming visible. Recent evidence confirms that long term exposure to environmental pharmaceutical concentrations can induce adverse effects in aquatic vertebrates and invertebrates such as reproductive impairments and collapse wild populations. Consequently, one of the challenges of environmental science is to evaluate the associated risks. In this context, a new methodology has been developed using nano-LC-nano-ESI MS/MS to quantify traces of two pharmaceuticals (a neuropharmaceutical drug, fluoxetine, and an anticonvulsant drug, carbamazepine) in two molluscs, Potamopyrgus antipodarum and Valvata piscinalis, which are both prosobranch gastropods. A simple and quick extraction method was developed based on a modified and miniaturized version of the QuEChERS method. The procedure involves the extraction of approximately 10 mg of wet mollusc tissue by 500 µL of a mixture of acetonitrile/water/hexane (50/20/30) and 100 mg of buffer salt. Thus, the extraction step was carried out on an individual scale. The sensitivity of this method allowed for the detection of levels as low as 18 ng/g and 128 ng/g for carbamazepine and fluoxetine, respectively, with recoveries of greater than 85% for the two targeted compounds. This method was then applied to both gastropod species exposed to fluoxetine under laboratory conditions. The results provide evidence of bioaccumulation in both P. antipodarum and V. piscinalis and reveal the inter-species differences.

CNS myelin induces regulatory functions of DC-SIGN-expressing, antigen-presenting cells via cognate interaction with MOG

Human myelin oligodendrocyte glycoprotein is decorated with fucosylated N-glycans that are recognized by DC-SIGN⁺ DCs and microglia that control immune homeostasis.

Myelin oligodendrocyte glycoprotein (MOG), a constituent of central nervous system myelin, is an important autoantigen in the neuroinflammatory disease multiple sclerosis (MS). However, its function remains unknown. Here, we show that, in healthy human myelin, MOG is decorated with fucosylated N-glycans that support recognition by the C-type lectin receptor (CLR) DC-specific intercellular adhesion molecule-3–grabbing nonintegrin (DC-SIGN) on microglia and DCs. The interaction of MOG with DC-SIGN in the context of simultaneous TLR4 activation resulted in enhanced IL-10 secretion and decreased T cell proliferation in a DC-SIGN-, glycosylation-, and Raf1-dependent manner. Exposure of oligodendrocytes to proinflammatory factors resulted in the down-regulation of fucosyltransferase expression, reflected by altered glycosylation at the MS lesion site. Indeed, removal of fucose on myelin reduced DC-SIGN–dependent homeostatic control, and resulted in inflammasome activation, increased T cell proliferation, and differentiation toward a Th₁₇-prone phenotype. These data demonstrate a new role for myelin glycosylation in the control of immune homeostasis in the healthy human brain through the MOG–DC-SIGN homeostatic regulatory axis, which is comprised by inflammatory insults that affect glycosylation. This phenomenon should be considered as a basis to restore immune tolerance in MS.

Small scale affinity purification and high sensitivity reversed phase nanoLC-MS N-glycan characterization of mAbs and fusion proteins

N-glycosylation is a complex post-translational modification with potential effects on the efficacy and safety of therapeutic proteins and known influence on the effector function of biopharmaceutical monoclonal antibodies (mAbs). Comprehensive characterization of N-glycosylation is therefore important in biopharmaceutical development. In early development, e.g. during pool or clone selection, however, only minute protein amounts of multiple samples are available for analytics. High sensitivity and high throughput methods are thus needed. An approach based on 96-well plate sample preparation and nanoLC-MS of 2- anthranilic acid or 2-aminobenzoic acid (AA) labeled N-glycans for the characterization of biopharmaceuticals in early development is reported here. With this approach, 192 samples can be processed simultaneously from complex matrices (e.g., cell culture supernatant) to purified 2-AA glycans, which are then analyzed by reversed phase nanoLC-MS. Attomolar sensitivity has been achieved by use of nanoelectrospray ionization, resulting in detailed glycan maps of mAbs and fusion proteins that are exemplarily shown in this work. Reproducibility, robustness and linearity of the approach are demonstrated, making use in a routine manner during pool or clone selection possible. Other potential fields of application, such as glycan biomarker discovery from serum samples, are also presented.

Glycosylation-dependent lectin-receptor interactions preserve angiogenesis in anti-VEGF refractory tumors

The clinical benefit conferred by vascular endothelial growth factors (VEGF)-targeted therapies is variable, and tumors from treated patients eventually reinitiate growth. Here, we identify a glycosylation-dependent pathway that compensates for the absence of cognate ligand and preserves angiogenesis in response to VEGF blockade. Remodeling of the endothelial cell (EC) surface glycome selectively regulated binding of galectin-1 (Gal1), which upon recognition of complex N-glycans on VEGFR2, activated VEGF-like signaling. Vessels within anti-VEGF-sensitive tumors exhibited high levels of α2-6-linked sialic acid, which prevented Gal1 binding. In contrast, anti-VEGF refractory tumors secreted increased Gal1 and their associated vasculature displayed glycosylation patterns that facilitated Gal1-EC interactions. Interruption of β1-6GlcNAc branching in ECs or silencing of tumor-derived Gal1 converted refractory into anti-VEGF-sensitive tumors, whereas elimination of α2-6-linked sialic acid conferred resistance to anti-VEGF. Disruption of the Gal1-N-glycan axis promoted vascular remodeling, immune cell influx and tumor growth inhibition. Thus, targeting glycosylation-dependent lectin-receptor interactions may increase the efficacy of anti-VEGF treatment.

Analysis of glycan variation on glycoproteins from serum by the reverse lectin-based ELISA assay

Altered glycosylation in glycoproteins is associated with carcinogenesis, and certain glycan structures and glycoproteins are well-known markers for tumor progression. To identify potential diagnostic candidate markers, we have developed a novel method for analysis of glycosylation changes of glycoproteins from crude serum samples using lectin-based glycoprotein capture followed by detection with biotin/HRP-conjugated antibodies. The amount of lectin coated on the microplate well was optimized to achieve low background and improved S/N compared with current lectin ELISA methods. In the presence of competing sugars of lectin AAL or with sialic acid removed from the glycoproteins, we confirmed that this method specifically detects glycosylation changes of proteins rather than protein abundance variation. Using our reverse lectin-based ELISA assay, increased fucosylated haptoglobin was observed in sera of patients with ovarian cancer, while the protein level of haptoglobin remained the same between cancers and noncases. The combination of fucosylated haptoglobin and CA125 (AUC = 0.88) showed improved performance for distinguishing stage-III ovarian cancer from noncases compared with CA125 alone (AUC = 0.86). In differentiating early-stage ovarian cancer from noncases, fucosylated haptoglobin showed comparable performance to CA125. The combination of CA125 and fucosylated haptoglobin resulted in an AUC of 0.855, which outperforms CA125 to distinguish early-stage cancer from noncases. Our study provides an alternative method to quantify glycosylation changes of proteins from serum samples, which will be essential for biomarker discovery and validation studies.

Analytical tools for the study of cellular glycosylation in the immune system

It is becoming increasingly clear that glycosylation plays important role in intercellular communication within the immune system. Glycosylation-dependent interactions are crucial for the innate and adaptive immune system and regulate immune cell trafficking, synapse formation, activation, and survival. These functions take place by the cis or trans interaction of lectins with glycans. Classical immunological and biochemical methods have been used for the study of lectin function; however, the investigation of their counterparts, glycans, requires very specialized methodologies that have been extensively developed in the past decade within the Glycobiology scientific community. This mini-review intends to summarize the available technology for the study of glycan biosynthesis, its regulation and characterization for their application to the study of glycans in immunology.

Mass spectrometry of glycans

Powerful new strategies based on mass spectrometry are revolutionizing the structural analysis and profiling of glycans and glycoconjugates. We survey here the major biosynthetic pathways that underlie the biological diversity in glycobiology, with emphasis on glycoproteins, and the approaches that can be used to address the resulting heterogeneity. Included among these are derivatizations, on- and off-line chromatography, electrospray and matrix-assisted laser desorption/ionization, and a variety of dissociation methods, the recently introduced electron-based techniques being of particular interest.