Autoimmune hepatitis displays distinctively high multi-antennary sialylation on plasma N-glycans compared to other liver diseases.

BACKGROUND: Changes in plasma protein glycosylation are known to functionally affect proteins and to associate with liver diseases, including cirrhosis and hepatocellular carcinoma. Autoimmune hepatitis (AIH) is a liver disease characterized by liver inflammation and raised serum levels of IgG, and is difficult to distinguish from other liver diseases. The aim of this study was to examine plasma and IgG-specific N-glycosylation in AIH and compare it with healthy controls and other liver diseases. METHODS: In this cross-sectional cohort study, total plasma N-glycosylation and IgG Fc glycosylation analysis was performed by mass spectrometry for 66 AIH patients, 60 age- and sex-matched healthy controls, 31 primary biliary cholangitis patients, 10 primary sclerosing cholangitis patients, 30 non-alcoholic fatty liver disease patients and 74 patients with viral or alcoholic hepatitis. A total of 121 glycans were quantified per individual. Associations between glycosylation traits and AIH were investigated as compared to healthy controls and other liver diseases. RESULTS: Glycan traits bisection (OR: 3.78 [1.88-9.35], p-value: 5.88 × 10- 3), tetraantennary sialylation per galactose (A4GS) (OR: 2.88 [1.75-5.16], p-value: 1.63 × 10- 3), IgG1 galactosylation (OR: 0.35 [0.2-0.58], p-value: 3.47 × 10- 5) and hybrid type glycans (OR: 2.73 [1.67-4.89], p-value: 2.31 × 10- 3) were found as discriminators between AIH and healthy controls. High A4GS differentiated AIH from other liver diseases, while bisection associated with cirrhosis severity. CONCLUSIONS: Compared to other liver diseases, AIH shows distinctively high A4GS levels in plasma, with potential implications on glycoprotein function and clearance. Plasma-derived glycosylation has potential to be used as a diagnostic marker for AIH in the future. This may alleviate the need for a liver biopsy at diagnosis. Glycosidic changes should be investigated further in longitudinal studies and may be used for diagnostic and monitoring purposes in the future.

Native N-glycome profiling of single cells and ng-level blood isolates using label-free capillary electrophoresis-mass spectrometry.

The development of reliable single-cell dispensers and substantial sensitivity improvement in mass spectrometry made proteomic profiling of individual cells achievable. Yet, there are no established methods for single-cell glycome analysis due to the inability to amplify glycans and sample losses associated with sample processing and glycan labeling. In this work, we present an integrated platform coupling online in-capillary sample processing with high-sensitivity label-free capillary electrophoresis-mass spectrometry for N-glycan profiling of single mammalian cells. Direct and unbiased quantitative characterization of single-cell surface N-glycomes are demonstrated for HeLa and U87 cells, with the detection of up to 100 N-glycans per single cell. Interestingly, N-glycome alterations are unequivocally detected at the single-cell level in HeLa and U87 cells stimulated with lipopolysaccharide. The developed workflow is also applied to the profiling of ng-level amounts (5-500 ng) of blood-derived protein, extracellular vesicle, and total plasma isolates, resulting in over 170, 220, and 370 quantitated N-glycans, respectively.

GlycoFibroTyper: A Novel Method for the Glycan Analysis of IgG and the Development of a Biomarker Signature of Liver Fibrosis.

Our group has recently developed the GlycoTyper assay which is a streamlined antibody capture slide array approach to directly profile N-glycans of captured serum glycoproteins including immunoglobulin G (IgG). This method needs only a few microliters of serum and utilizes a simplified processing protocol that requires no purification or sugar modifications prior to analysis. In this method, antibody captured glycoproteins are treated with peptide N-glycosidase F (PNGase F) to release N-glycans for detection by MALDI imaging mass spectrometry (IMS). As alterations in N-linked glycans have been reported for IgG from large patient cohorts with fibrosis and cirrhosis, we utilized this novel method to examine the glycosylation of total IgG, as well as IgG1, IgG2, IgG3 and IgG4, which have never been examined before, in a cohort of 106 patients with biopsy confirmed liver fibrosis. Patients were classified as either having no evidence of fibrosis (41 patients with no liver disease or stage 0 fibrosis), early stage fibrosis (10 METAVIR stage 1 and 18 METAVIR stage 2) or late stage fibrosis (6 patients with METAVIR stage 3 fibrosis and 37 patients with METAVIR stage 4 fibrosis (cirrhosis)). Several major alterations in glycosylation were observed that classify patients as having no fibrosis (sensitivity of 92% and a specificity of 90%), early fibrosis (sensitivity of 84% with 90% specificity) or significant fibrosis (sensitivity of 94% with 90% specificity).

N-glycan profiling alterations of serum and immunoglobulin G in immune thrombocytopenia.

BACKGROUND: The glycosylation alterations of serum and IgG are involved in a variety of autoimmune and inflammatory diseases and have shown great potential in biomarker field. The diagnosis of immune thrombocytopenia (ITP) is exclusive. Our study aimed to discover the potential glyco-biomarkers for auxiliary diagnosis of ITP. METHODS: The serum samples were obtained from 61 ITP patients and 35 healthy controls, and IgG samples were purified from 34 out of 61 ITP patients and 35 healthy controls. DNA sequencer-assisted fluorophore-assisted carbohydrate electrophoresis (DSA-FACE) was used to analyze serum and IgG N-glycan profiling. RESULTS: 6 of 12 serum N-glycan peaks, 6 of 7 IgG N-glycan peaks, serum fucosylation, and IgG galactosylation were significantly different between ITP patients and healthy controls (p < 0.05). IgG peak 7 showed good diagnostic efficacy for discriminating ITP patients from healthy individuals (AUC 0.967). ITP patients with severe thrombocytopenia had a significantly lower serum fucosylation than ITP patients with mild and moderate thrombocytopenia (p < 0.05). Serum fucosylation and serum peak 5 were correlated with platelet counts in ITP patients with severe thrombocytopenia, and the absolute values of correlation coefficient were both over 0.5. CONCLUSIONS: The specific N-glycan patterns of serum and IgG were observed in ITP patients. IgG peak 7 was a potential biomarker for auxiliary diagnosis of ITP.

Genetic and functional evidence links a missense variant in B4GALT1 to lower LDL and fibrinogen.

Increased blood levels of low-density lipoprotein cholesterol (LDL-C) and fibrinogen are independent risk factors for cardiovascular disease. We identified associations between an Amish-enriched missense variant (p.Asn352Ser) in a functional domain of beta-1,4-galactosyltransferase 1 (B4GALT1) and 13.9 milligrams per deciliter lower LDL-C (P = 4.1 × 10­19) and 29 milligrams per deciliter lower plasma fibrinogen (P = 1.3 × 10­5). B4GALT1 gene­based analysis in 544,955 subjects showed an association with decreased coronary artery disease (odds ratio = 0.64, P = 0.006). The mutant protein had 50% lower galactosyltransferase activity compared with the wild-type protein. N-linked glycan profiling of human serum found serine 352 allele to be associated with decreased galactosylation and sialylation of apolipoprotein B100, fibrinogen, immunoglobulin G, and transferrin. B4galt1 353Ser knock-in mice showed decreases in LDL-C and fibrinogen. Our findings suggest that targeted modulation of protein galactosylation may represent a therapeutic approach to decreasing cardiovascular disease.

N-Glycosylation Profiling of Human Blood in Type 2 Diabetes by Capillary Electrophoresis: A Preliminary Study.

Currently, diagnosing type 2 diabetes (T2D) is a great challenge. Thus, there is a need to find rapid, simple, and reliable analytical methods that can detect the disease at an early stage. The aim of this work was to shed light on the importance of sample collection options, sample preparation conditions, and the applied capillary electrophoresis bioanalytical technique, for a high-resolution determination of the N-glycan profile in human blood samples of patients with type 2 diabetes (T2D). To achieve the profile information of these complex oligosaccharides, linked by asparagine to hIgG in the blood, the glycoproteins of the samples needed to be cleaved, labelled, and purified with sufficient yield and selectivity. The resulting samples were analyzed by capillary electrophoresis, with laser-induced fluorescence detection. After separation parameter optimization, the capillary electrophoresis technique was implemented for efficient N-glycan profiling of whole blood samples from the diabetic patients. Our results revealed that there were subtle differences between the N-glycan profiles of the diabetic and control samples; in particular, two N-glycan structures were identified as potential glycobiomarkers that could reveal significant changes between the untreated/treated type 2 diabetic and control samples. By analyzing the resulting oligosaccharide profiles, clinically relevant information was obtained, revealing the differences between the untreated and HMG-CoA reductase-inhibitor-treated diabetic patients on changes in the N-glycan profile in the blood. In addition, the information from specific IgG N-glycosylation profiles in T2D could shed light on underlying inflammatory pathophysiological processes and lead to drug targets.

Glycine additive enhances sensitivity for N- and O-glycan analysis with hydrophilic interaction chromatography-electrospray ionization-mass spectrometry.

Glycosylation is critical for many biological processes and biotherapeutic development. One of the most powerful approaches for analyzing released glycans is hydrophilic interaction chromatography coupled with electrospray ionization mass spectrometry (HILIC-ESI-MS). The high sensitivity of MS is crucial for detecting low-abundance glycans and elucidating their structures. In this study, we presented a simple solution to boost MS response of procainamide (ProcA) labeled glycans for 2- to over 60-fold by including 1 mM glycine in ammonium formate mobile phases for HILIC-ESI-MS. The glycine additive increased charge states, enhanced ion intensities and signal-to-noise ratios, and improved tandem MS spectral quality of various N- and O-glycans without affecting chromatographic performance. Furthermore, more homogeneous ionization among different ProcA labeled glycans was achieved by using the glycine additive, resulting in more comparable quantitative results relative to fluorescence-based quantification. We demonstrated that ammonium formate caused ion suppression to ProcA labeled glycans, which were likely mitigated by glycine with enhanced ESI ionization. Overall, simple addition of glycine to mobile phases during HILIC-ESI-MS analysis significantly improves MS detection sensitivity and will facilitate future profiling and quantitation of glycans released from N- and O-glycoproteins.

Circulating platelet count and glycans.

PURPOSE OF THE REVIEW: This review highlights recent advancements in understanding the regulation of platelet numbers, focusing on mechanisms by which carbohydrates (glycans) link platelet removal with platelet production in the bone marrow in health and disease. RECENT FINDINGS: This review is focused on the role of carbohydrates, specifically sialic acid moieties, as a central mediator of platelet clearance. We discuss recently identified novel mechanisms of carbohydrate-mediated platelet removal and carbohydrate-binding receptors that mediate platelet removal. SUMMARY: The platelet production rate by megakaryocytes and removal kinetics controls the circulating platelet count. Alterations in either process can lead to thrombocytopenia (low platelet count) or thrombocytosis (high platelet count) are associated with the risk of bleeding or overt thrombus formation and serious complications. Thus, regulation of a steady-state platelet count is vital in preventing adverse events. There are few mechanisms delineated that shed light on carbohydrates' role in the complex and massive platelet removal process. This review focuses on carbohydrate-related mechanisms that contribute to the control of platelet numbers.

Altered Glycosylation of Human Alpha-1-Acid Glycoprotein as a Biomarker for Malignant Melanoma.

A high-resolution HILIC-MS/MS method was developed to analyze anthranilic acid derivatives of N-glycans released from human serum alpha-1-acid glycoprotein (AGP). The method was applied to samples obtained from 18 patients suffering from high-risk malignant melanoma as well as 19 healthy individuals. It enabled the identification of 102 glycan isomers separating isomers that differ only in sialic acid linkage (α-2,3, α-2,6) or in fucose positions (core, antenna). Comparative assessment of the samples revealed that upregulation of certain fucosylated glycans and downregulation of their nonfucosylated counterparts occurred in cancer patients. An increased ratio of isomers with more α-2,6-linked sialic acids was also observed. Linear discriminant analysis (LDA) combining 10 variables with the highest discriminatory power was employed to categorize the samples based on their glycosylation pattern. The performance of the method was tested by cross-validation, resulting in an overall classification success rate of 96.7%. The approach presented here is significantly superior to serological marker S100B protein in terms of sensitivity and negative predictive power in the population studied. Therefore, it may effectively support the diagnosis of malignant melanoma as a biomarker.

Probing serum N-glycan patterns for rapid and precise detection of Crohn's disease.

Serum N-glycan patterns from 50 Crohn's disease (CD) patients and 50 healthy controls were acquired using a carbon matrix, from which eight N-glycans with significant difference were screened out to reveal remarkale performance for CD diagnosis. This research is expected to help future glycan-based disease detection not limited to CD.

Glycan biomarkers of autoimmunity and bile acid-associated alterations of the human glycome: Primary biliary cirrhosis and primary sclerosing cholangitis-specific glycans.

We have recently introduced multiple reaction monitoring (MRM) mass spectrometry as a novel tool for glycan biomarker research and discovery. Herein, we employ this technique to characterize the site-specific glycan alterations associated with primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC). Glycopeptides associated with disease severity were also identified. Multinomial regression modelling was employed to construct and validate multi-analyte diagnostic models capable of accurately distinguishing PBC, PSC, and healthy controls from one another (AUC = 0.93 ± 0.03). Finally, to investigate how disease-relevant environmental factors can influence glycosylation, we characterized the ability of bile acids known to be differentially expressed in PBC to alter glycosylation. We hypothesize that this could be a mechanism by which altered self-antigens are generated and become targets for immune attack. This work demonstrates the utility of the MRM method to identify diagnostic site-specific glycan classifiers capable of distinguishing even related autoimmune diseases from one another.

Distinguishing Benign and Malignant Thyroid Nodules and Identifying Lymph Node Metastasis in Papillary Thyroid Cancer by Plasma N-Glycomics.

Background: Biomarkers are needed for patient stratification between benign thyroid nodules (BTN) and thyroid cancer (TC) and identifying metastasis in TC. Though plasma N-glycome profiling has shown potential in the discovery of biomarkers and can provide new insight into the mechanisms involved, little is known about it in TC and BTN. Besides, several studies have indicated associations between abnormal glycosylation and TC. Here, we aimed to explore plasma protein N-glycome of a TC cohort with regard to their applicability to serve as biomarkers. Methods: Plasma protein N-glycomes of TC, BTN, and matched healthy controls (HC) were obtained using a robust quantitative strategy based on MALDI-TOF MS and included linkage-specific sialylation information. Results: Plasma N-glycans were found to differ between BTN, TC, and HC in main glycosylation features, namely complexity, galactosylation, fucosylation, and sialylation. Four altered glycan traits, which were consecutively decreased in BTN and TC, and classification models based on them showed high potential as biomarkers for discrimination between BTN and TC ("moderately accurate" to "accurate"). Additionally, strong associations were found between plasma N-glycans and lymph node metastasis in TC, which added the accuracy of predicting metastasis before surgery to the existing method. Conclusions: We comprehensively evaluated the plasma N-glycomic changes in patients with TC or BTN for the first time. We determined several N-glycan biomarkers, some of them have potential in the differential diagnosis of TC, and the others can help to stratify TC patients to low or high risk of lymph node metastasis. The findings enhanced the understanding of TC.

Bi-allelic variants in the ER quality-control mannosidase gene EDEM3 cause a congenital disorder of glycosylation.

EDEM3 encodes a protein that converts Man8GlcNAc2 isomer B to Man7-5GlcNAc2. It is involved in the endoplasmic reticulum-associated degradation pathway, responsible for the recognition of misfolded proteins that will be targeted and translocated to the cytosol and degraded by the proteasome. In this study, through a combination of exome sequencing and gene matching, we have identified seven independent families with 11 individuals with bi-allelic protein-truncating variants and one individual with a compound heterozygous missense variant in EDEM3. The affected individuals present with an inherited congenital disorder of glycosylation (CDG) consisting of neurodevelopmental delay and variable facial dysmorphisms. Experiments in human fibroblast cell lines, human plasma, and mouse plasma and brain tissue demonstrated decreased trimming of Man8GlcNAc2 isomer B to Man7GlcNAc2, consistent with loss of EDEM3 enzymatic activity. In human cells, Man5GlcNAc2 to Man4GlcNAc2 conversion is also diminished with an increase of Glc1Man5GlcNAc2. Furthermore, analysis of the unfolded protein response showed a reduced increase in EIF2AK3 (PERK) expression upon stimulation with tunicamycin as compared to controls, suggesting an impaired unfolded protein response. The aberrant plasma N-glycan profile provides a quick, clinically available test for validating variants of uncertain significance that may be identified by molecular genetic testing. We propose to call this deficiency EDEM3-CDG.

N-glycan structures of Wisteria floribunda agglutinin-positive Mac2 binding protein in the serum of patients with liver fibrosis†.

The extent of liver fibrosis predicts prognosis and is important for determining treatment strategies for chronic hepatitis. During the fibrosis progression, serum levels of Mac2 binding protein (M2BP) increase and the N-glycan structure changes to enable binding to Wisteria floribunda agglutinin (WFA) lectin. As a novel diagnostic marker, glycosylation isomer of M2BP (M2BPGi) has been developed. However, its glycan structures recognized by WFA are unclear. In this study, we analyzed site-specific N-glycan structures of serum M2BP using Glyco-RIDGE (Glycan heterogeneity-based Relational IDentification of Glycopeptide signals on Elution profile) method. We evaluated five sample types: (1) M2BP immunoprecipitated from normal healthy sera (NHS-IP(+)), (2) M2BP immunoprecipitated from sera of patients with liver cirrhosis (stage 4; F4-IP(+)), (3) M2BP captured with WFA from serum of patients with liver cirrhosis (stage 4; F4-WFA(+)), (4) recombinant M2BP produced by HEK293 cells (rM2BP) and (5) WFA-captured rM2BP (rM2BP-WFA(+)). In NHS-IP(+) M2BP, bi-antennary N-glycan was the main structure, and LacNAc extended to its branches. In F4-IP(+) M2BP, many branched structures, including tri-antennary and tetra-antennary N-glycans, were found. F4-WFA(+) showed a remarkable increase in branched structures relative to the quantity before enrichment. In recombinant M2BP, both no sialylated-LacdiNAc and -branched LacNAc structures were emerged. The LacdiNAc structure was not found in serum M2BP. Glycosidase-assisted HISCL assays suggest that reactivity with WFA of both serum and recombinant M2BP depends on unsialylated and branched LacNAc and in part of recombinant depends on LacdiNAc. On M2BPGi, the highly branched LacNAc, probably dense cluster of LacNAc, would be recognized by WFA.

Serum N-glycan profiles differ for various breast cancer subtypes.

Breast cancer is the most prevalent cancer in women. Early detection of this disease improves survival and therefore population screenings, based on mammography, are performed. However, the sensitivity of this screening modality is not optimal and new screening methods, such as blood tests, are being explored. Most of the analyses that aim for early detection focus on proteins in the bloodstream. In this study, the biomarker potential of total serum N-glycosylation analysis was explored with regard to detection of breast cancer. In an age-matched case-control setup serum protein N-glycan profiles from 145 breast cancer patients were compared to those from 171 healthy individuals. N-glycans were enzymatically released, chemically derivatized to preserve linkage-specificity of sialic acids and characterized by high resolution mass spectrometry. Logistic regression analysis was used to evaluate associations of specific N-glycan structures as well as N-glycosylation traits with breast cancer. In a case-control comparison three associations were found, namely a lower level of a two triantennary glycans and a higher level of one tetraantennary glycan in cancer patients. Of note, various other N-glycomic signatures that had previously been reported were not replicated in the current cohort. It was further evaluated whether the lack of replication of breast cancer N-glycomic signatures could be partly explained by the heterogenous character of the disease since the studies performed so far were based on cohorts that included diverging subtypes in different numbers. It was found that serum N-glycan profiles differed for the various cancer subtypes that were analyzed in this study.

High-throughput and high-sensitivity N-Glycan profiling: A platform for biopharmaceutical development and disease biomarker discovery.

Protein glycosylation contributes to critical biological function of glycoproteins. Glycan analysis is essential for the production of biopharmaceuticals as well as for the identification of disease biomarkers. However, glycans are highly heterogeneous, which has considerably hampered the progress of glycomics. Here, we present an improved 96-well plate format platform for streamlined glycan profiling that takes advantage of rapid glycoprotein denaturation, deglycosylation, fluorescent derivatization, and on-matrix glycan clean-up. This approach offers high sensitivity with consistent identification and quantification of diverse N-glycans across multiple samples on a high-throughput scale. We demonstrate its capability for N-glycan profiling of glycoproteins from various sources, including two recombinant monoclonal antibodies produced from Chinese Hamster Ovary cells, EG2-hFc and rituximab, polyclonal antibodies purified from human serum, and total glycoproteins from human serum. Combined with the complementary information obtained by sequential digestion from exoglycosidase arrays, this approach allows the detection and identification of multiple N-glycans in these complex biological samples. The reagents, workflow, and Hydrophilic interaction liquid chromatography with fluorescence detection (HILIC-FLD), are simple enough to be implemented into a straightforward user-friendly setup. This improved technology provides a powerful tool in support of rapid advancement of glycan analysis for biopharmaceutical development and biomarker discovery for clinical disease diagnosis.

N-glycosylation profiling of Type 2 diabetes mellitus from baseline to follow-up: an observational study in a Ghanaian population.

Aim: The study sought to determine the patterns of N-glycan profiles among Type 2 diabetes mellitus (T2DM) patients over a 6-month period. Materials & methods: Biochemical and clinical data were obtained from 253 T2DM patients at baseline and follow-up. Ultra-performance liquid chromatography and statistical methods were applied for N-glycan profiling. Results: The coefficients of variation were 28% and 29% at baseline and follow-up, respectively, whereas the range of N-glycan variability was from 11% to 56%. Apart from GP1 (FA2) and GP29 (FA3G3S [3,3,3]3), the intra-individual variations of N-glycan peaks were not statistically significant. Conclusion: N-glycan profiles were stable over 6-month period in T2DM patients and could be used to monitor biochemical changes in relation with T2DM comorbidities.

Interlaboratory evaluation of plasma N-glycan antennary fucosylation as a clinical biomarker for HNF1A-MODY using liquid chromatography methods.

Antennary fucosylation alterations in plasma glycoproteins have been previously proposed and tested as a biomarker for differentiation of maturity onset diabetes of the young (MODY) patients carrying a functional mutation in the HNF1A gene. Here, we developed a novel LC-based workflow to analyze blood plasma N-glycan fucosylation in 320 diabetes cases with clinical features matching those at risk of HNF1A-MODY. Fucosylation levels measured in two independent research centers by using similar LC-based methods were correlated to evaluate the interlaboratory performance of the biomarker. The interlaboratory study showed good correlation between fucosylation levels measured for the 320 cases in the two centers with the correlation coefficient (r) of up to 0.88 for a single trait A3FG3S2. The improved chromatographic separation allowed the identification of six single glycan traits and a derived antennary fucosylation trait that were able to differentiate individuals carrying pathogenic mutations from benign or no HNF1A mutation cases, as determined by the area under the curve (AUC) of up to 0.94. The excellent (r = 0.88) interlaboratory performance of the glycan biomarker for HNF1A-MODY further supports the development of a clinically relevant diagnostic test measuring antennary fucosylation levels.

Mass spectrometry glycophenotype characterization of ALG2-CDG in Argentinean patients with a new genetic variant in homozygosis.

Human ALG2 encodes an α 1,3mannosyltransferase that catalyzes the first steps in the synthesis of N-glycans in the endoplasmic reticulum. Variants in ALG2cause a congenital disorder of glycosylation (CDG) known as ALG2-CDG. Up to date, nine ALG2-CDG patients have been reported worldwide. ALG2-CDG is a rare autosomal recessive inherited disorder characterized by neurological involvement, convulsive syndrome of unknown origin, axial hypotonia, and mental and motor regression. In this study, we used MALDI-TOF MS to define both total serum protein and transferrin (Tf) N-glycan phenotypes in three ALG2-CDG patients carrying a c.752G > T, p.Arg251Leu ALG2 missense variant in homozygous state, as determined by exome sequencing. Comparing it to control samples, we have observed Tf under-occupancy of glycosylation site(s) typical of a defective N-glycan assembly and the occurrence of oligomannose and hybrid type N-glycans. Moreover, we have observed a slight oligomannose accumulation in total serum glyco-profiles. The increased heterogeneity of serum N-glycome in the studied patients suggests a marginal disarrangement of the glycan processing in ALG2-CDG. Previous studies reported on slightly increased concentrations of abnormal serum N-glycans in CDG-I due to defects in the mannosylation steps of dolichol-linked oligosaccharide biosynthesis. This preliminary work aims at considering serum N-glycan accumulation of high mannosylated glycoforms, such as oligomannose and hybrid type N-glycans, as potential diagnostic signals for ALG2-CDG patients.