Direct analysis of aberrant glycosylation on haptoglobin in patients with gastric cancer

MS-Based Glycome Characterization of Biotherapeutics With N- and O-Glycosylation

With the increasing FDA approvals of glycoprotein-based biotherapeutics including monoclonal antibodies, cytokines, and enzyme treatments, the significance of glycosylation in modulating drug efficacy and safety becomes central. This review highlights the crucial role of mass spectrometry (MS) in elucidating the glycome of biotherapeutics that feature N- and O-glycosylation, directly addressing the challenges posed by glycosylation complexity and heterogeneity. We have detailed the advancements and application of MS technologies including MALDI-TOF MS, LC-MS, and tandem MS in the precise characterization of glycoprotein therapeutics. Emphasizing MS-based strategies for detecting immunogenic glycans and ensuring batch-to-batch consistency, this review highlights targeted approaches for glycoprotein, glycopeptide, and glycan analysis tailored to meet the stringent analytical and regulatory demands of biopharmaceutical development.

Circulating Proteins as Diagnostic Markers in Gastric Cancer

Gastric cancer (GC) is a highly malignant disease affecting humans worldwide and has a poor prognosis. Most GC cases are detected at advanced stages due to the cancer lacking early detectable symptoms. Therefore, there is great interest in improving early diagnosis by implementing targeted prevention strategies. Markers are necessary for early detection and to guide clinicians to the best personalized treatment. The current semi-invasive endoscopic methods to detect GC are invasive, costly, and time-consuming. Recent advances in proteomics technologies have enabled the screening of many samples and the detection of novel biomarkers and disease-related signature signaling networks. These biomarkers include circulating proteins from different fluids (e.g., plasma, serum, urine, and saliva) and extracellular vesicles. We review relevant published studies on circulating protein biomarkers in GC and detail their application as potential biomarkers for GC diagnosis. Identifying highly sensitive and highly specific diagnostic markers for GC may improve patient survival rates and contribute to advancing precision/personalized medicine.

Equivalence assessment of biotherapeutics with N- and O-glycosylation sites by sequential intact glycoform mass spectrometry (IGMS)

Glycosylation is a crucial attribute for biotherapeutics with significant impacts on quality, stability, safety, immunogenicity, pharmacokinetics, and efficacy. Therefore, to ensure consistent glycosylation, a systematic review of biotherapeutics is absolutely required including the variable glycan structure (micro-heterogeneity) and different occupancy at individual site (macro-heterogeneity) from drug design to upstream and downstream bioprocesses. Various methods have been used for glyco-characterization of biotherapeutics at the glycan, glycopeptide, and intact protein levels. In particular, intact protein analysis is considered a facile and rapid glycoform monitoring approach used throughout the product development lifecycle to determine suitable glycosylation lead candidates and reproducible product quality. However, intact glycoform characterization of diverse and complex biotherapeutics with multiple N- and O-glycosylation sites can be very challenging. To address this, a robust analytical platform that enables rapid and accurate characterization of a biotherapeutics with highly complex multiple glycosylation using two-step intact glycoform mass spectrometry has been developed. We used darbepoetin alfa, a second-generation EPO bearing multiple N- and O-glycosylation sites, as a model biotherapeutics to obtain integrated information on glycan heterogeneity and site occupancy through step-by-step MS of intact protein and enzyme-treated protein. In addition, we performed a comparative assessment of the heterogeneity from different products, confirming that our new method can efficiently evaluate glycosylation equivalence. This new strategy provides rapid and accurate information on the degree of glycosylation of a therapeutic glycoprotein with multiple glycosylation, which can be used to assess glycosylation similarity between batches and between biosimilar and reference during development and production.

In-depth investigation of altered glycosylation in human haptoglobin associated cancer by mass spectrometry

Serum haptoglobin (Hp), a highly sialylated biomolecule with four N-glycosylation sites, is a positive acute-phase response glycoprotein that acts as an immunomodulator. Hp has gained considerable attention due to its potential as a signature molecule that exhibits aberrant glycosylation in inflammatory disorders and malignancies. Its glycosylation can be analyzed qualitatively and quantitatively by various methods using mass spectrometry. In this review, we have provided a brief overview of Hp structure and biological function and described mass spectrometry-based techniques for analyzing glycosylation ranging from macroheterogeneity to microheterogeneity of Hp in diseases and cancer. The sugars on haptoglobin can be a sweet bridge to link the potential of cancer-specific biomarkers to clinically relevant applications.

First bioelectronic immunoplatform for quantitative secretomic analysis of total and metastasis-driven glycosylated haptoglobin

The glycosylation status of proteins is increasingly used as biomarker to improve the reliability in the diagnosis and prognosis of diseases as relevant as cancer. This feeds the need for tools that allow its simple and reliable analysis and are compatible with applicability in the clinic. With this objective in mind, this work reports the first bioelectronic immunoplatforms described to date for the determination of glycosylated haptoglobin (Hp) and the simultaneous determination of total and glycosylated Hp. The bioelectronic immunoplatform is based on the implementation of non-competitive bioassays using two different antibodies or an antibody and a lectin on the surface of commercial magnetic microcarriers. The resulting bioconjugates are labeled with the horseradish peroxidase (HRP) enzyme, and after their magnetic capture on disposable electroplatforms, the amperometric transduction using the H2O2/hydroquinone (HQ) system allows the single or multiple detection. The developed immunoplatform achieves limits of detection (LODs) of 0.07 and 0.46 ng mL−1 for total and glycosylated Hp in buffer solution, respectively. The immunoplatform allows accurate determination using simple and relatively short protocols (approx. 75 min) of total and glycosylated Hp in the secretomes of in vitro–cultured colorectal cancer (CRC) cells with different metastatic potentials, which is not feasible, due to lack of sensitivity, by means of some commercial ELISA kits and Western blot methodology.

Graphical abstract

Rapid Evaluation of the Extent of Haptoglobin Glycosylation Using Orthogonal Intact-Mass MS Approaches and Multivariate Analysis

Intact-mass measurements are becoming increasingly popular in mass spectrometry (MS) based protein characterization, as they allow the entire complement of proteoforms to be evaluated within a relatively short time. However, applications of this approach are currently limited to systems exhibiting relatively modest degrees of structural diversity, as the high extent of heterogeneity frequently prevents straightforward MS measurements. Incorporation of limited charge reduction into electrospray ionization (ESI) MS is an elegant way to obtain meaningful information on most heterogeneous systems, yielding not only the average mass of the protein but also the mass range populated by the entire complement of proteoforms. Application of this approach to characterization of two different phenotypes of haptoglobin (1-1 and 2-1) provides evidence of a significant difference in their extent of glycosylation (with the glycan load of phenotype 2-1 being notably lighter) despite a significant overlap of their ionic signals. More detailed characterization of their glycosylation patterns is enabled by the recently introduced technique of cross-path reactive chromatography (XP-RC) with online MS detection, which combines chromatographic separation with in-line reduction of disulfide bonds to generate metastable haptoglobin subunits. Application of XP-RC to both haptoglobin phenotypes confirms that no modifications are present within their light chains and provides a wealth of information on glycosylation patterns of the heavy chains. N-Glycosylation patterns of both haptoglobin phenotypes were found to be consistent with bi- and triantennary structures of complex type that exhibit significant level of fucosylation and sialylation. However, multivariate analysis of haptoglobin 1-1 reveals higher number of the triantennary structures, in comparison to haptoglobin 2-1, as well as a higher extent of fucosylation. The glycosylation patterns deduced from the XP-RC/MS measurements are in agreement with the conclusions of the intact-mass analysis supplemented by limited charge reduction, suggesting that the latter technique can be employed in situations when fast assessment of protein heterogeneity is needed (e.g., process analytical technology applications).

Identification and characterization of non-small cell lung cancer associated sialoglycoproteins

Aberrantly sialylated cellular glycoconjugates were found to be involved in different processes during tumorigenesis. Such alteration was also noted in case of lung cancer, an important cause of cancer-related death throughout the world. Thus, study on lung cancer associated sialoglycoproteins is of paramount relevance to have a deeper insight into the mechanism of the disease pathogenesis. In the present study, sialic acid specific lectin (Maackia amurensis agglutinin and Sambcus nigra agglutinin)-based affinity chromatography followed by 2D-PAGE and MALDI-TOF/TOF mass spectrometric analysis were done to explore the disease-associated serum proteins of squamous cell carcinoma and adenocarcinoma [the major two subtypes of NSCLC (non-small cell lung carcinoma)] patients. Among seven identified proteins, α1-antitrypsin and haptoglobin-β were preferred for further studies. These two proteins were characterized as the disease associated serum-sialoglycoproteins of NSCLC-patients by western immunoblotting using each lectin specific inhibitor. The presence of these sialoglycoproteins was found on NSCLC cell lines (NCI-H520 & A549) by confocal microscopy. Both these proteins were also present in tissue samples of NSCLC origin and involved in proliferation, invasion and migration of NSCLC cells. Our findings suggest that α1-antitrypsin and haptoglobin-β may be the disease-associated sialoglycoproteins in NSCLC, which seem to be involved in disease progression. SIGNIFICANCE: Our contribution regarding the identification of the NSCLC associated sialoglycoproteins may provide a new vision towards the development of clinically useful newer strategies for the treatment of this disease.

Haptoglobin as a Biomarker

Haptoglobin (Hp) is a glycoprotein that binds free hemoglobin (Hb) in plasma and plays a critical role in tissue protection and prevention of oxidative damage. Besides, it has some regulatory functions. Haptoglobin is an acute-phase protein, its concentration in plasma changes in pathology, and the test for its concentration is part of normal clinical practice. Haptoglobin is a conservative protein synthesized mainly in the liver and lungs and is the subject of research as a potential biomarker of many diseases, including various forms of malignant neoplasms. Haptoglobin has several unique biophysical characteristics. The human Нр gene is polymorphic, has three structural alleles that control the synthesis of three major phenotypes of haptoglobin: homozygous Нр1-1 and Нр2-2, and heterozygous Нр2-1, determined by a combination of allelic variants that are inherited. Numerous studies indicate that the phenotype of haptoglobin can be used to judge the individual predisposition of a person to various diseases. In addition, Hp undergoes various post-translational modifications (PTMs). These are structural transformations (removal of the signal peptide, cutting off the Pre-Hp precursor molecule into two subunits, α and β, limited proteolysis of α-chains, formation of disulfide bonds, multimerization), as well as chemical modifications of α-chains and glycosylation of the β-chain. Glycosylation of the β-chain of haptoglobin at four Asn sites is the most important variable PTM that regulates the structure and function of the glycoprotein. The study of modified oligosaccharides of the β-chain of Hp has become the main direction in the study of pathological processes, including malignant neoplasms. These characteristics indicate the possibility of the existence of Hp in the form of a multitude of proteoforms, probably performing different functions. This review is devoted to the description of the structural and functional diversity and the potential use of Hp as a biomarker of various pathologies.

Detection of Aberrant Glycosylation of Serum Haptoglobin for Gastric Cancer Diagnosis Using a Middle-Up-Down Glycoproteome Platform

Gastric cancer is a frequently occurring cancer and is the leading cause of cancer-related deaths. Recent studies have shown that aberrant glycosylation of serum haptoglobin is closely related to gastric cancer and has enormous potential for use in diagnosis. However, there is no platform with high reliability and high reproducibility to comprehensively analyze haptoglobin glycosylation covering microheterogeneity to macroheterogeneity for clinical applications. In this study, we developed a middle-up-down glycoproteome platform for fast and accurate monitoring of haptoglobin glycosylation. This platform utilizes an online purification of LC for sample desalting, and an in silico haptoglobin glycopeptide library constructed by combining peptides and N-glycans to readily identify glycopeptides. In addition, site-specific glycosylation with glycan heterogeneity can be obtained through only a single MS analysis. Haptoglobin glycosylation in clinical samples consisting of healthy controls (n = 47) and gastric cancer patients (n = 43) was extensively investigated using three groups of tryptic glycopeptides: GP1 (including Asn184), GP2 (including Asn207 and Asn211), and GP3 (including Asn241). A total of 23 individual glycopeptides were determined as potential biomarkers (p < 0.00001). In addition, to improve diagnostic efficacy, we derived representative group biomarkers with high AUC values (0.929 to 0.977) through logistic regression analysis for each GP group. It has been found that glycosylation of haptoglobin is highly associated with gastric cancer, especially the glycosite Asn241. Our assay not only allows to quickly and easily obtain information on glycosylation heterogeneity of a target glycoprotein but also makes it an efficient tool for biomarker discovery and clinical diagnosis.

Screening and diagnosis of colorectal cancer and advanced adenoma by Bionic Glycome method and machine learning

Colorectal cancer (CRC), one of the major health problems worldwide, mostly develops from colorectal adenomas. Advanced adenomas are generally considered as precancerous lesions and patients are recommended to remove the adenomas. Screening for colorectal cancer is usually performed by fecal tests (FOBT or FIT) and colonoscopy, however, their benefits are limited by uptake and adherence. Most CRC develops from colorectal advanced adenomas, but there is currently a lack of effective noninvasive screening method for advanced adenomas. N-glycans in human serum hold the great potentials as biomarker for diagnosis of human cancers. Our aim was to discover blood-based markers for screening and diagnosis of advanced adenomas and CRC, and to ascertain their efficiency in classifying healthy controls, patients with advanced adenomas and CRC by incorporating machine learning techniques with reliable and simple quantitative method with "Bionic Glycome" as internal standard based on the high-throughput Matrix-assisted Laser Desorption/Ionization Mass Spectrometry (MALDI-MS). The quantitative results showed that there is a positive correlation between multi-antennary, sialylated N-glycans and CRC progress, while bi-antennary core-fucosylated N-glycans are negatively correlated with CRC progress. Machine learning is a powerful classification tool, suitable for mining big data, especially the large amount of data generated by high-throughput technologies. Using the predictive model constructed by machine learning, we obtained the classification accuracy of 75% for classification of 189 samples including CRC, advanced adenomas and healthy controls, and the accuracy of 87% for detection of the disease group that required treatment, including CRC and advanced adenomas. To our delight, the model successfully applied to the prediction of 176 samples collected a few months later, and five samples were wrongly predicted in the disease group. Overall, this diagnostic model we constructed here has valuable potential in the clinical application of detecting advanced adenomas and colorectal cancer and could compensate for the limitations of the current screening methods for detection of CRC and advanced adenomas.

Novel lamprey antibody recognizes terminal sulfated galactose epitopes on mammalian glycoproteins

The terminal galactose residues of N- and O-glycans in animal glycoproteins are often sialylated and/or fucosylated, but sulfation, such as 3-O-sulfated galactose (3-O-SGal), represents an additional, but poorly understood modification. To this end, we have developed a novel sea lamprey variable lymphocyte receptor (VLR) termed O6 to explore 3-O-SGal expression. O6 was engineered as a recombinant murine IgG chimera and its specificity and affinity to the 3-O-SGal epitope was defined using a variety of approaches, including glycan and glycoprotein microarray analyses, isothermal calorimetry, ligand-bound crystal structure, FACS, and immunohistochemistry of human tissue macroarrays. 3-O-SGal is expressed on N-glycans of many plasma and tissue glycoproteins, but recognition by O6 is often masked by sialic acid and thus exposed by treatment with neuraminidase. O6 recognizes many human tissues, consistent with expression of the cognate sulfotransferases (GAL3ST-2 and GAL3ST-3). The availability of O6 for exploring 3-O-SGal expression could lead to new biomarkers for disease and aid in understanding the functional roles of terminal modifications of glycans and relationships between terminal sulfation, sialylation and fucosylation.

[Haptoglobin as a biomarker]

Haptoglobin (Hp) is a blood plasma glycoprotein that binds free hemoglobin (Hb) and plays a critical role in tissue protection and the prevention of oxidative damage. In addition, it has a number of regulatory functions. Haptoglobin is an acute phase protein, its concentration in plasma changes in pathology, and the test for its concentration is part of normal clinical practice. Haptoglobin is a conservative protein synthesized mainly in the liver and lungs and is the subject of research as a potential biomarker of many diseases, including various forms of malignant neoplasms. Haptoglobin has several unique biophysical characteristics. Only in humans, the Hp gene is polymorphic, has three structural alleles that control the synthesis of three major phenotypes of Hp, homozygous Hp1-1 and Hp2-2, and heterozygous Hp2-1, determined by a combination of allelic variants that are inherited. Numerous studies indicate that the phenotype of haptoglobin can be used to judge the individual's predisposition to various diseases. In addition, Hp undergoes various post-translational modifications (PTMs). These are structural transformations (removal of the signal peptide, cutting of the Pre-Hp precursor molecule into two subunits, α and β, limited proteolysis of α-chains, formation of disulfide bonds, multimerization), as well as chemical modifications of α-chains and glycosylation of the β-chain. Glycosylation of the β-chain of haptoglobin at four Asn sites is the most important variable PTM that regulates the structure and function of the glycoprotein. The study of modified oligosaccharides of the Hp β-chain has become the main direction in the study of pathological processes, including malignant neoplasms. Many studies are focused on the identification of PTM and changes in the level of the α2-chain of this protein in pathology. These characteristics of Hp indicate the possibility of the existence of this protein as different proteoforms, probably with different functions. This review is devoted to the description of the structural and functional diversity of Hp and its potential use as a biomarker of various pathologies.

Glycoproteomic Analysis Reveals Aberrant Expression of Complement C9 and Fibronectin in the Plasma of Patients with Colorectal Cancer

Colorectal cancer (CRC) is a major cause of cancer mortality. Currently used CRC biomarkers provide insufficient sensitivity and specificity; therefore, novel biomarkers are needed to improve the CRC detection. Label-free quantitative proteomics were used to identify and compare glycoproteins, enriched by wheat germ agglutinin, from plasma of CRC patients and age-matched healthy controls. Among 189 identified glycoproteins, the levels of 7 and 15 glycoproteins were significantly altered in the non-metastatic and metastatic CRC groups, respectively. Protein-protein interaction analysis revealed that they were predominantly involved in immune responses, complement pathways, wound healing and coagulation. Of these, the levels of complement C9 (C9) was increased and fibronectin (FN1) was decreased in both CRC states in comparison to those of the healthy controls. Moreover, their levels detected by immunoblotting were validated in another independent cohort and the results were consistent with in the study cohort. Combination of CEA, a commercial CRC biomarker, with C9 and FN1 showed better diagnostic performance. Interestingly, predominant glycoforms associated with acetylneuraminic acid were obviously detected in alpha-2 macroglobulin, haptoglobin, alpha-1-acid glycoprotein 1, and complement C4-A of CRC patient groups. This glycoproteomic approach provides invaluable information of plasma proteome profiles of CRC patients and identification of CRC biomarker candidates.

Esophageal, gastric and colorectal cancers: Looking beyond classical serological biomarkers towards glycoproteomics-assisted precision oncology

Esophageal (OC), gastric (GC) and colorectal (CRC) cancers are amongst the digestive track tumors with higher incidence and mortality due to significant molecular heterogeneity. This constitutes a major challenge for patients' management at different levels, including non-invasive detection of the disease, prognostication, therapy selection, patient's follow-up and the introduction of improved and safer therapeutics. Nevertheless, important milestones have been accomplished pursuing the goal of molecular-based precision oncology. Over the past five years, high-throughput technologies have been used to interrogate tumors of distinct clinicopathological natures, generating large-scale biological datasets (e.g. genomics, transcriptomics, and proteomics). As a result, GC and CRC molecular subtypes have been established to assist patient stratification in the clinical settings. However, such molecular panels still require refinement and are yet to provide targetable biomarkers. In parallel, outstanding advances have been made regarding targeted therapeutics and immunotherapy, paving the way for improved patient care; nevertheless, important milestones towards treatment personalization and reduced off-target effects are also to be accomplished. Exploiting the cancer glycoproteome for unique molecular fingerprints generated by dramatic alterations in protein glycosylation may provide the necessary molecular rationale towards this end. Therefore, this review presents functional and clinical evidences supporting a reinvestigation of classical serological glycan biomarkers such as sialyl-Tn (STn) and sialyl-Lewis A (SLe^A) antigens from a tumor glycoproteomics perspective. We anticipate that these glycobiomarkers that have so far been employed in non-invasive cancer prognostication may hold unexplored value for patients' management in precision oncology settings.

Mass spectrometry-based qualitative and quantitative N-glycomics: An update of 2017-2018

N-glycosylation is one of the most frequently occurring protein post-translational modifications (PTMs) with broad cellular, physiological and pathological relevance. Mass spectrometry-based N-glycomics has become the state-of-the-art instrumental analytical pipeline for sensitive, high-throughput and comprehensive characterization of N-glycans and N-glycomes. Improvement and new development of methods in N-glycan release, enrichment, derivatization, isotopic labeling, separation, ionization, MS, tandem MS and informatics accompany side-by-side wider and deeper application. This review provides a comprehensive update of mass spectrometry-based qualitative and quantitative N-glycomics in the years of 2017-2018.

Probing N-glycoprotein microheterogeneity by lectin affinity purification-mass spectrometry analysis

A lectin affinity purification-mass spectrometry approach to characterize lectin-reactive glycoproteoforms and elucidate lectin specificities at the intact protein level.

Lectins are carbohydrate binding proteins that recognize specific epitopes present on target glycoproteins. Changes in lectin-reactive carbohydrate repertoires are related to many biological signaling pathways and recognized as hallmarks of several pathological processes. Consequently, lectins are valuable probes, commonly used for examining glycoprotein structural and functional microheterogeneity. However, the molecular interactions between a given lectin and its preferred glycoproteoforms are largely unknown due to the inherent complexity and limitations of methods used to investigate intact glycoproteins. Here, we apply a lectin-affinity purification procedure coupled with native mass spectrometry to characterize lectin-reactive glycoproteoforms at the intact protein level. We investigate the interactions between the highly fucosylated and highly branched glycoproteoforms of haptoglobin and α1-acid glycoprotein using two different lectins Aleuria aurantia lectin (AAL) and Phaseolus vulgaris leucoagglutinin (PHA-L), respectively. Firstly we show a co-occurrence of fucosylation and N-glycan branching on haptoglobin, particularly among highly fucosylated glycoproteoforms. Secondly, we analyze the global heterogeneity of highly branched glycoproteoforms of haptoglobin and α1-acid glycoprotein and reveal that while multi-fucosylation attenuates the lectin PHA-L binding to haptoglobin, it has no impact on AGP. Taken together, our lectin affinity purification native MS approach elucidates lectin specificities between intact glycoproteins, not achievable by other methods. Moreover, since aberrant glycosylation of Hp and AGP are potential markers for many diseases, including pancreatic, hepatic and ovarian cancers, understanding their interactions with lectins will help the development of carbohydrate-centric monitoring methods to understand their pathophysiological implications.

The Function of Fucosylation in Progression of Lung Cancer

Lung cancer is a disease that influences human health and has become a leading cause of cancer mortality worldwide. However, it is frequently diagnosed at the advanced stage. It is necessary by means of biology to identify specific lung tumor biomarkers with high sensitivity. Glycosylation is one of the most important post-translational modifications and is related to many different diseases. It is involved in numerous essential biological processes, such as cell proliferation, differentiation, migration, cell-cell integrity and recognition, and immune modulation. However, little was known about deregulation of glycosylation in lung cancer and contribution to tumor–microenvironment interactions. Among the numerous glycosylations, fucosylation is the most common modification of glycoproteins and glycosylated oligosaccharides. Increased levels of fucosylation have been detected in various pathological conditions, as well as in lung cancer. In this article, we reviewed the role of fucosylation in lung cancer. We highlighted some of the fucosylation alterations currently being pursued in sera or tissues of lung cancer patients. Moreover, we elaborated on the regulation mechanism of fucosylation in proliferative invasion and metastasis of lung tumor cells. In summary, alterations in fucosylation provide potential biomarkers and therapeutic targets in lung cancer.

Intact transferrin and total plasma glycoprofiling for diagnosis and therapy monitoring in phosphoglucomutase-I deficiency

Phosphoglucomutase 1 (PGM1) deficiency results in a mixed phenotype of a Glycogen Storage Disorder and a Congenital Disorder of Glycosylation (CDG). Screening for abnormal glycosylation has identified more than 40 patients, manifesting with a broad clinical and biochemical spectrum which complicates diagnosis. Together with the availability of D-galactose as dietary therapy, there is an urgent need for specific glycomarkers for early diagnosis and treatment monitoring. We performed glycomics profiling by high-resolution QTOF mass spectrometry in a series of 19 PGM1-CDG patients, covering a broad range of biochemical and clinical severity. Bioinformatics and statistical analysis were used to select glycomarkers for diagnostics and define glycan-indexes for treatment monitoring. Using 3 transferrin glycobiomarkers, all PGM1-CDG patients were diagnosed with 100% specificity and sensitivity. Total plasma glycoprofiling showed an increase in high mannose glycans and fucosylation, while global galactosylation and sialylation were severely decreased. For treatment monitoring, we defined 3 glycan-indexes, reflecting normal glycosylation, a lack of complete glycans (LOCGI) and of galactose residues (LOGI). These indexes showed improved glycosylation upon D-galactose treatment with a fast and near-normalization of the galactose index (LOGI) in 6 out of 8 patients and a slower normalization of the LOCGI in all patients. Total plasma glycoprofiling showed improvement of the global high mannose glycans, fucosylation, sialylation, and galactosylation status on D-galactose treatment. Our study indicates specific glycomarkers for diagnosis of mildly and severely affected PGM1-CDG patients, and to monitor the glycan-specific effects of D-galactose therapy.

Designation of fingerprint glycopeptides for targeted glycoproteomic analysis of serum haptoglobin: insights into gastric cancer biomarker discovery

Gastric cancer (GC) is one of the leading causes of cancer-related death worldwide, largely because of difficulties in early diagnosis. Despite accumulating evidence indicating that aberrant glycosylation is associated with GC, site-specific localization of the glycosylation to increase specificity and sensitivity for clinical use is still an analytical challenge. Here, we created an analytical platform with a targeted glycoproteomic approach for GC biomarker discovery. Unlike the conventional glycomic approach with untargeted mass spectrometric profiling of released glycan, our platform is characterized by three key features: it is a target-protein-specific, glycosylation-site-specific, and structure-specific platform with a one-shot enzyme reaction. Serum haptoglobin enriched by immunoaffinity chromatography was subjected to multispecific proteolysis to generate site-specific glycopeptides and to investigate the macroheterogeneity and microheterogeneity. Glycopeptides were identified and quantified by nano liquid chromatography-mass spectrometry and nano liquid chromatography-tandem mass spectrometry. Ninety-six glycopeptides, each corresponding to a unique glycan/glycosite pairing, were tracked across all cancer and control samples. Differences in abundance between the two groups were marked by particularly high magnitudes. Three glycopeptides exhibited exceptionally high control-to-cancer fold changes along with receiver operating characteristic curve areas of 1.0, indicating perfect discrimination between the two groups. From the results taken together, our platform, which provides biological information as well as high sensitivity and reproducibility, may be useful for GC biomarker discovery. Graphical abstract ᅟ.