Alpha 1-acid glycoprotein (orosomucoid): pathophysiological changes in glycosylation in relation to its function

Anion Exchange Chromatography-Mass Spectrometry to Characterize Proteoforms of Alpha-1-Acid Glycoprotein during and after Pregnancy

Alpha-1-acid glycoprotein (AGP) is a heterogeneous glycoprotein fulfilling key roles in many biological processes, including transport of drugs and hormones and modulation of inflammatory and immune responses. The glycoform profile of AGP is known to change depending on (patho)physiological states such as inflammatory diseases or pregnancy. Besides complexity originating from five N-glycosylation sites, the heterogeneity of the AGP further expands to genetic variants. To allow in-depth characterization of this intriguing protein, we developed a method using anion exchange chromatography (AEX) coupled to mass spectrometry (MS) revealing the presence of over 400 proteoforms differing in their glycosylation or genetic variants. More precisely, we could determine that AGP mainly consists of highly sialylated higher antennary structures with on average 16 sialic acids and 0 or 1 fucose per protein. Interestingly, a slightly higher level of fucosylation was observed for AGP1 variants compared to that of AGP2. Proteoform assignment was supported by integrating data from complementary MS-based approaches, including AEX-MS of an exoglycosidase-treated sample and glycopeptide analysis after tryptic digestion. The developed analytical method was applied to characterize AGP from plasma of women during and after pregnancy, revealing differences in glycosylation profiles, specifically in the number of antennae, HexHexNAc units, and sialic acids.

Susceptibility of Human Plasma N-glycome to Low-Calorie and Different Weight-Maintenance Diets

Aberrant plasma protein glycosylation is associated with a wide range of diseases, including diabetes, cardiovascular, and immunological disorders. To investigate plasma protein glycosylation alterations due to weight loss and successive weight-maintenance diets, 1850 glycomes from participants of the Diogenes study were analyzed using Ultra-High-Performance Liquid Chromatography (UHPLC). The Diogenes study is a large dietary intervention study in which participants were subjected to a low-calorie diet (LCD) followed by one of five different weight-maintenance diets in a period of 6 months. The most notable alterations of the plasma glycome were 8 weeks after the subjects engaged in the LCD; a significant increase in low-branched glycan structures, accompanied by a decrease in high-branched glycan structures. After the LCD period, there was also a significant rise in N-glycan structures with antennary fucose. Interestingly, we did not observe significant changes between different diets, and almost all effects we observed immediately after the LCD period were annulled during the weight-maintenance diets period.

Infant Gut Microbial Metagenome Mining of α-l-Fucosidases with Activity on Fucosylated Human Milk Oligosaccharides and Glycoconjugates

The gastrointestinal microbiota members produce α-l-fucosidases that play key roles in mucosal, human milk, and dietary oligosaccharide assimilation. Here, 36 open reading frames (ORFs) coding for putative α-l-fucosidases belonging to glycosyl hydrolase family 29 (GH29) were identified through metagenome analysis of breast-fed infant fecal microbiome. Twenty-two of those ORFs showed a complete coding sequence with deduced amino acid sequences displaying the highest degree of identity with α-l-fucosidases from Bacteroides thetaiotaomicron, Bacteroides caccae, Phocaeicola vulgatus, Phocaeicola dorei, Ruminococcus gnavus, and Streptococcus parasanguinis. Based on sequence homology, 10 α-l-fucosidase genes were selected for substrate specificity characterization. The α-l-fucosidases Fuc18, Fuc19A, Fuc35B, Fuc39, and Fuc1584 showed hydrolytic activity on α1,3/4-linked fucose present in Lewis blood antigens and the human milk oligosaccharide (HMO) 3-fucosyllactose. In addition, Fuc1584 also hydrolyzed fucosyl-α-1,6-N-acetylglucosamine (6FN), a component of the core fucosylation of N-glycans. Fuc35A and Fuc193 showed activity on α1,2/3/4/6 linkages from H type-2, Lewis blood antigens, HMOs and 6FN. Fuc30 displayed activity only on α1,6-linked l-fucose, and Fuc5372 showed a preference for α1,2 linkages. Fuc2358 exhibited a broad substrate specificity releasing l-fucose from all the tested free histo-blood group antigens, HMOs, and 6FN. This latest enzyme also displayed activity in glycoconjugates carrying lacto-N-fucopentaose II (Lea) and lacto-N-fucopentaose III (Lex) and in the glycoprotein mucin. Fuc18, Fuc19A, and Fuc39 also removed l-fucose from neoglycoproteins and human α-1 acid glycoprotein. These results give insight into the great diversity of α-l-fucosidases from the infant gut microbiota, thus supporting the hypothesis that fucosylated glycans are crucial for shaping the newborn microbiota composition. IMPORTANCE α-l-Fucosyl residues are frequently present in many relevant glycans, such as human milk oligosaccharides (HMOs), histo-blood group antigens (HBGAs), and epitopes on cell surface glycoconjugate receptors. These fucosylated glycans are involved in a number of mammalian physiological processes, including adhesion of pathogens and immune responses. The modulation of l-fucose content in such processes may provide new insights and knowledge regarding molecular interactions and may help to devise new therapeutic strategies. Microbial α-l-fucosidases are exoglycosidases that remove α-l-fucosyl residues from free oligosaccharides and glycoconjugates and can be also used in transglycosylation reactions to synthesize oligosaccharides. In this work, α-l-fucosidases from the GH29 family were identified and characterized from the metagenome of fecal samples of breastfed infants. These enzymes showed different substrate specificities toward HMOs, HBGAs, naturally occurring glycoproteins, and neoglycoproteins. These novel glycosidase enzymes from the breast-fed infant gut microbiota, which resulted in a good source of α-l-fucosidases, have great biotechnological potential.

The malignant potential of pancreatic intraductal papillary mucinous neoplasm is reflected in expression levels of fucosylated glycans in α1 -acid glycoprotein

BACKGROUND

Pancreatic intraductal papillary mucinous neoplasm (IPMN) involves multiple histopathological stages from benign to malignant lesions. Further, a biomarker to diagnose the malignant IPMN (IPMC) is clinically relevant. Recently, we found that serum fucosylated α₁ -acid glycoprotein (fAGP) level markedly elevated along with disease progression in large cohorts of patients with various cancers.

METHODS

The fAGP level was retrospectively analyzed in preoperative sera from 109 patients with IPMN, and the clinical relevance of fAGP was compared with currently available predictors as standard.

RESULTS

The fAGP level in IPMC was found to be significantly higher than in benign IPMN (P=0.0012). At a cutoff value of 27.04 U/μg, its sensitivity, specificity, and accuracy for IPMC were determined to be 83.61, 65.96 and 75.93%, respectively. Multivariate analyses revealed that the fAGP level was the only independent risk factor for predicting IPMC. Additionally, a combination of the fAGP level and ¹⁸ F-fluorodeoxyglucose uptake on the PET/CT imaging in the lesions seemed to offer the best diagnosis of IPMN. Accordingly, 27 of the 28 patients who were positive in both tests had IPMC, while patients who are negative had benign IPMN.

CONCLUSIONS

The fAGP level appeared to be a relevant biomarker for malignant potential of IPMN.

N-acetylglucosaminyltransferase-V requires a specific noncatalytic luminal domain for its activity toward glycoprotein substrates

N-acetylglucosaminyltransferase-V (GnT-V or MGAT5) catalyzes the formation of an N-glycan β1,6-GlcNAc branch on selective target proteins in the Golgi apparatus and is involved in cancer malignancy and autoimmune disease etiology. Several three-dimensional structures of GnT-V were recently solved, and the recognition mechanism of the oligosaccharide substrate was clarified. However, it is still unclear how GnT-V selectively acts on glycoprotein substrates. In this study, we focused on an uncharacterized domain at the N-terminal side of the luminal region (N domain) of GnT-V, which was previously identified in a crystal structure, and aimed to reveal its role in GnT-V action. Using lectin blotting and fluorescence assisted cell sorting analysis, we found that a GnT-VΔN mutant lacking the N domain showed impaired biosynthetic activity in cells, indicating that the N domain is required for efficient glycosylation. To clarify this mechanism, we measured the in vitro activity of purified GnT-VΔN toward various kinds of substrates (oligosaccharide, glycohexapeptide, and glycoprotein) using HPLC and a UDP-Glo assay. Surprisingly, GnT-VΔN showed substantially reduced activity toward the glycoprotein substrates, whereas it almost fully maintained its activity toward the oligosaccharides and the glycopeptide substrates. Finally, docking models of GnT-V with substrate glycoproteins suggested that the N domain could interact with the substrate polypeptide directly. Our findings suggest that the N domain of GnT-V plays a critical role in the recognition of glycoprotein substrates, providing new insights into the mechanism of substrate-selective biosynthesis of N-glycans.

Proteomic Profile of Urinary Extracellular Vesicles Identifies AGP1 as a Potential Biomarker of Primary Aldosteronism

CONTEXT

Primary aldosteronism (PA) represents 6% to 10% of all essential hypertension patients and is diagnosed using the aldosterone-to-renin ratio (ARR) and confirmatory studies. The complexity of PA diagnosis encourages the identification of novel PA biomarkers. Urinary extracellular vesicles (uEVs) are a potential source of biomarkers, considering that their cargo reflects the content of the parent cell.

OBJECTIVE

We aimed to evaluate the proteome of uEVs from PA patients and identify potential biomarker candidates for PA.

METHODS

Second morning spot urine was collected from healthy controls (n = 8) and PA patients (n = 7). The uEVs were isolated by ultracentrifugation and characterized. Proteomic analysis on uEVs was performed using LC-MS Orbitrap.

RESULTS

Isolated uEVs carried extracellular vesicle markers, showed a round shape and sizes between 50 and 150 nm. The concentration of uEVs showed a direct correlation with urinary creatinine (r = 0.6357; P = 0.0128). The uEV size mean (167 ± 6 vs 183 ± 4nm) and mode (137 ± 7 vs 171 ± 11nm) was significantly smaller in PA patients than in control subjects, but similar in concentration. Proteomic analysis of uEVs from PA patients identified an upregulation of alpha-1-acid glycoprotein 1 (AGP1) in PA uEVs, which was confirmed using immunoblot. A receiver operating characteristic curve analysis showed an area under the curve of 0.92 (0.82 to 1; P = 0.0055).

CONCLUSION

Proteomic and further immunoblot analyses of uEVs highlights AGP1 as potential biomarker for PA.

Different glycoforms of alpha-1-acid glycoprotein contribute to its functional alterations in platelets and neutrophils

Alpha-1-acid glycoprotein (AGP-1) is a positive acute phase glycoprotein with uncertain functions. Serum AGP-1 (sAGP-1) is primarily derived from hepatocytes and circulates as 12-20 different glycoforms. We isolated a glycoform secreted from platelet-activating factor (PAF)-stimulated human neutrophils (nAGP-1). Its peptide sequence was identical to hepatocyte-derived sAGP-1, but nAGP-1 differed from sAGP-1 in its chromatographic behavior, electrophoretic mobility, and pattern of glycosylation. The function of these 2 glycoforms also differed. sAGP-1 activated neutrophil adhesion, migration, and neutrophil extracellular traps (NETosis) involving myeloperoxidase, peptidylarginine deiminase 4, and phosphorylation of ERK in a dose-dependent fashion, whereas nAGP-1 was ineffective as an agonist for these events. Furthermore, sAGP-1, but not nAGP-1, inhibited LPS-stimulated NETosis. Interestingly, nAGP-1 inhibited sAGP-1-stimulated neutrophil NETosis. The discordant effect of the differentially glycosylated AGP-1 glycoforms was also observed in platelets where neither of the AGP-1 glycoforms alone stimulated aggregation of washed human platelets, but sAGP-1, and not nAGP-1, inhibited aggregation induced by PAF or ADP, but not by thrombin. These functional effects of sAGP-1 correlated with intracellular cAMP accumulation and phosphorylation of the protein kinase A substrate vasodilator-stimulated phosphoprotein and reduction of Akt, ERK, and p38 phosphorylation. Thus, the sAGP-1 glycoform limits platelet reactivity, whereas nAGP-1 glycoform also limits proinflammatory actions of sAGP-1. These studies identify new functions for this acute phase glycoprotein and demonstrate that the glycosylation of AGP-1 controls its effects on 2 critical cells of acute inflammation.

Functional exploration of the GH29 fucosidase family

The deoxy sugar l-fucose is frequently found as a glycan constituent on and outside living cells, and in mammals it is involved in a wide range of biological processes including leukocyte trafficking, histo-blood group antigenicity and antibody effector functions. The manipulation of fucose levels in those biomedically important systems may provide novel insights and therapeutic leads. However, despite the large established sequence diversity of natural fucosidases, so far, very few enzymes have been characterized. We explored the diversity of the α-l-fucosidase-containing CAZY family GH29 by bio-informatic analysis, and by the recombinant production and exploration for fucosidase activity of a subset of 82 protein sequences that represent the family's large sequence diversity. After establishing that most of the corresponding proteins can be readily expressed in E. coli, more than half of the obtained recombinant proteins (57% of the entire subset) showed activity towards the simple chromogenic fucosylated substrate 4-nitrophenyl α-l-fucopyranoside. Thirty-seven of these active GH29 enzymes (and the GH29 subtaxa that they represent) had not been characterized before. With such a sequence diversity-based collection available, it can easily be used to screen for fucosidase activity towards biomedically relevant fucosylated glycoproteins. As an example, the subset was used to screen GH29 members for activity towards the naturally occurring sialyl-Lewis x-type epitope on glycoproteins, and several such enzymes were identified. Together, the results provide a significant increase in the diversity of characterized GH29 enzymes, and the recombinant enzymes constitute a resource for the further functional exploration of this enzyme family.

Serum N-glycan profiling can predict biopsy-proven graft rejection after living kidney transplantation

BACKGROUND

To evaluate whether serum N-glycan profile can be used as a diagnostic marker of graft rejection after living-donor kidney transplants (KT).

METHODS

We retrospectively examined 174 KT recipients at five medical centers. N-Glycan levels were analyzed in postoperative serum samples using glycoblotting combined with mass spectrometry. We developed an integrated score to predict graft rejection based on a combination of age, gender, immunological risk factors, and serum N-glycan levels at post-KT day D1 and D7. Rejection-free survival rates stratified by the sum of integrated scores (D1 + D7) were evaluated using Kaplan-Meier curves.

RESULTS

Of 174, 52 showed graft rejection (Rejection-pos. group) and 122 recipients did not show graft rejection (Rejection-neg. group). The integrated scores were significantly higher in the Rejection-pos. group than those of the Rejection-neg. group. Area-under-curve (AUC) value of integrated scores at post-KT D1, and D7 were 0.84 and 0.84, respectively. The sum of integrated scores (D1 + D7) ≥ 0.50 identified graft rejection with 81% sensitivity and 80% specificity; with an AUC value of 0.87. Recipients with higher sum of integrated scores (D1 + D7 ≥ 0.5) had significantly shorter rejection-free survival than those with lower scores.

CONCLUSION

Evaluation of serum N-glycosylation profiles can identify recipients who are prone to rejection.

Fucosylated α1-acid glycoprotein as a biomarker to predict prognosis following tumor immunotherapy of patients with lung cancer

Immunotherapy targeting immune checkpoint molecules has provided remarkable clinical benefits in cancer patients but no clinically relevant biomarker for predicting treatment outcomes exists. Recently, we demonstrated that glycan structures of serum α₁-acid glycoprotein (AGP) changed dramatically in cancer patients and that α1,3fucosylated AGP (fAGP) levels increased along with disease progression and decreased responding to chemotherapy treatments. Here, the fAGP was analyzed in sera prospectively obtained from 39 patients with advanced lung cancer who underwent immunotherapy with anti-PD-1 antibody, nivolumab. Twenty-three patients had significantly high fAGP levels above the cut-off value (H-fAGP) at one month after starting the treatment and 20 patients in this group, whose tumor sizes did not decrease, maintained high fAGP levels continuously and subsequently died. However, the other 16 patients, whose fAGP levels decreased or maintained below the cut-off value (L-fAGP), survived during a 2-year observation even though 5 patients in this group had no tumor shrinkage. Accordingly, the overall survival rate was found to significantly correlate with the fAGP level. Multivariate analyses revealed that the H-fAGP was an independent risk factor for cancer progression. Therefore, the fAGP level appeared to be a reliable biomarker for predicting clinical efficacy of immunotherapy with nivolumab.

Acute phase protein, α - 1- acid glycoprotein (AGP-1), has differential effects on TLR-2 and TLR-4 mediated responses

Alpha-1-acid glycoprotein (AGP-1) is a major positive acute phase glycoprotein with unknown functions that likely play a role in inflammation. We tested its involvement in a variety of inflammatory responses using human AGP-1 purified to apparent homogeneity and confirmed its identity by immunoblotting and mass spectrometry. AGP-1 alone upregulated MAPK signaling in murine peritoneal macrophages. However, when given in combination with TLR ligands, AGP-1 selectively augmented MAPK activation induced by ligands of TLR-2 (Braun lipoprotein) but not TLR-4 (lipopolysaccharide). In vivo treatment of AGP-1 in a murine model of sepsis with or without TLR-2 or TLR-4 ligands, selectively potentiated TLR-2-mediated mortality, but was without significant effect on TLR-4-mediated mortality. Furthermore, in vitro, AGP-1 selectively potentiated TLR-2 mediated adhesion of human primary immune cell, neutrophils. Hence, our studies highlight a new role for the acute phase protein AGP-1 in sepsis via its interaction with TLR-2 signaling mechanisms to selectively promote responsiveness to one of the two major gram-negative endotoxins, contributing to the complicated pathobiology of sepsis.

Evaluation of AGP Fucosylation as a Marker for Hepatocellular Carcinoma of Three Different Etiologies

A mass spectrometric analysis platform has been developed to determine whether glycosylation patterns of alpha-1 acid glycoprotein (AGP) could be used as a marker for early detection of hepatocellular carcinoma (HCC) in different etiologies, i.e. non-alcoholic steatohepatitis (NASH), alcoholic liver disease (ALC), and hepatitis C virus (HCV). MALDI-MS profiling of N-glycans of AGP purified from 20 μL of patient serum in HCC (n = 72) and liver cirrhosis (n = 58) showed that a unique trifucosylated tetra-antennary glycan (m/z 3490.76) was predominantly identified in HCCs but was absent in healthy subjects and the majority of cirrhosis patients. Receiver operation characteristic (ROC) curve analysis showed that the trifucosylated N-glycan of AGP (triFc_AGP) could differentiate HCC from cirrhosis with an area under the curve (AUC) of 0.707, 0.726 and 0.751 for NASH, ALC and HCV, respectively. When combining triFc_AGP with INR and AFP, the panel had the greatest benefit in detection of NASH-related HCCs, with a significantly improved AUC of 0.882 for all NASH HCCs and 0.818 for early NASH HCCs compared to AFP alone (0.761 and 0.641, respectively). Moreover, triFc_AGP could serve as a potential marker for monitoring AFP-negative HCC patients.

The Immune Functions of α1 Acid Glycoprotein

α1-acid glycoprotein (orosomucoid, AGP) is an Acute Phase Protein produced by liver and peripheral tissues in response to systemic reaction to inflammation. AGP functions have been studied mostly in human, cattle and fish, although the protein has been also found in many mammalian species and birds. AGP fulfils at least two set of functions, which are apparently different from each other but in fact intimately linked. On one hand, AGP is an immunomodulatory protein. On the other hand, AGP is one of the most important binding proteins in plasma and, beside modulating pharmacokinetics and pharmacodynamics of many drugs, it is also able to bind and transport several endogen ligands related to inflammation. The focus of this review is the immunomodulatory activity of AGP. This protein regulates every single event related to inflammation, including binding of pathogens and modulating white blood cells activity throughout the entire leukocyte attacking sequence. The regulation of AGP activity is complex: the inflammation induces not only an increase in AGP serum concentration, but also a qualitative change in its carbohydrate moiety, generating a multitude of glycoforms, each of them with different, and sometimes opposite and contradictory, activities. We also present the most recent findings about the relationship between AGP and adipose tissue: AGP interacts with leptin receptor and, given its immunomodulatory function, it may be included among the potential players in the field of immunometabolism.

Serum α-1 Acid Glycoprotein is a Biomarker for the Prediction of Targeted Therapy Resistance in Advanced EGFR-positive Lung Adenocarcinoma

OBJECTIVE

To determine the levels of α-1 acid glycoprotein (ORM1) in the sera of advanced lung adenocarcinoma (LUAD) patients with epidermal growth factor receptor (EGFR) mutation before treatment and after acquirement of EGFR tyrosine kinase inhibitor (EGFR-TKI) resistance, and to explore the clinical cut off value of ORM1 for targeted therapy resistance in LUAD.

METHODS

Enzyme-linked immunosorbent assay was used to determine serum ORM1 levels. Receiver operating characteristic curve was applied to evaluate the serum ORM1 level in the resistance of EGFR-TKI and the cut off value of ORM1 for the diagnosis of EGFR-TKI resistance.

RESULTS

The serum ORM1 concentrations in the healthy group, before and after drug resistance were 1.687 ± 0.103, 1.868 ± 0.101, and 1.731 ± 0.088 µg/ml, respectively. The serum ORM1 concentrations before and after drug resistance were higher than that of the healthy group, whereas the serum ORM1 concentrations in the resistant group were lower than those before drug treatment. In comparison to healthy group, the area under curve (AUC) of the serum ORM1 concentration was 0.918 ± 0.029 with sensitivity of 90.5% and specificity of 78.6% in the patient before EGFR-TKI treatment, while the AUC was 0.644 ± 0.062 with sensitivity of 69.0% and specificity of 66.7% in the resistance group. When compared to those before treatment, the AUC of serum ORM1 concentration was 0.880 ± 0.038 with a sensitivity of 92.9% and specificity of 73.8% in the resistance group. The cutoff value of serum ORM1 was 1.778 µg/ml for advanced EGFR-positive LUAD and 1.723 µg/ml after resistance to EGFR-TKI.

CONCLUSION

Serum ORM1 has an important diagnostic value for the diagnosis of EGFR-positive LUAD and EGFR-TKI resistance in patients especially with advanced EGFR-positive LUAD. Our findings suggest that serum ORM1 is a biomarker in the prediction of EGFR-TKI resistance in EGFR-positive LUAD.

Pharmacokinetic and Pharmacodynamic Considerations for Drugs Binding to Alpha-1-Acid Glycoprotein

According to the free drug hypothesis only the unbound drug is available to act at physiological sites of action, and as such the importance of plasma protein binding primarily resides in its impact on pharmacokinetics and pharmacodynamics. Of the major plasma proteins, alpha-1-acid glycoprotein (AAG) represents an intriguing one primarily due to the high affinity, low capacity properties of this protein. In addition, there are marked species and age differences in protein expression, homology and drug binding affinity. As such, a thorough understanding of drug binding to AAG can help aid and improve the translation of pharmacokinetic/pharmacodynamic (PK/PD) relationships from preclinical species to human as well as adults to neonates. This review provides a comprehensive overview of our current understanding of the biochemistry of AAG; endogenous function, impact of disease, utility as a biomarker, and impact on PK/PD. Experimental considerations are discussed as well as recommendations for understanding the potential impact of AAG on PK through drug discovery and early development.

Microchip gel electrophoretic analysis of perchloric acid-soluble serum proteins in systemic inflammatory disorders

Perchloric acid (PCA) precipitation is a well-known method for the separation of heavily glycosylated proteins and for reducing the masking effect of major serum proteins. The aim of this study is to characterize PCA-soluble serum proteins in healthy individuals and in patients with systemic inflammatory diseases, such as Crohn's disease and sepsis. A PCA precipitation protocol was prepared and adapted to the analytical methods. After PCA treatment of the serum, the soluble proteins in the supernatant were analyzed by SDS-PAGE and by microchip gel electrophoresis (MGE). Characteristic changes of the electrophoretic patterns of the PCA-soluble fractions were observed. Four characteristic bands (at ∼11, ∼65, ∼85, and ∼120 kDa) with varying intensity were detected by MGE. The proportion of the ∼65, ∼85, and ∼120 kDa bands were significantly higher in systemic inflammatory conditions than in healthy individuals (p < 0.001), and characteristic patterns were observed in patients with acute inflammation. The marked differences in the acid-soluble protein patterns, which were observed in patients with ongoing systemic inflammation, might be a good indicator of inflammation. The MGE analysis is a fast screening and quantification method for the detection of characteristic changes among acid-soluble serum proteins.

Glycan analysis of colorectal cancer samples reveals stage-dependent changes in CEA glycosylation patterns

Background

Carcinoembryonic antigen (CEA) is a glycoprotein associated with colorectal cancer (CRC). While the functions of its gene and protein have been fully characterized, its post-translational modifications in the context of CRC development remain undefined.

Methods

To show the correlation between the different stages of CRC development and changes in the glycosylation patterns of CEA, we analyzed CEA in tumor tissues (CEA-T) and paired tumor-adjacent normal tissues (CEA-A) from 53 colorectal cancer patients using a high-density lectin microarray containing 56 plant lectins.

Results

We detected higher expression levels of fucose, mannose and Thomsen–Friedenreich antigen, and lower expression levels of N-acetylgalactosamine, N-acetylglucosamine, galactose, branched and bisecting N-glycans on CEA in the tumor tissues relative to the tumor-adjacent normal tissues. Furthermore, a combinatorial assessment of 9 lectins is sufficient to distinguish CRC tumor tissues from tumor-adjacent normal tissues with 83% sensitivity and ~ 90% specificity. Moreover, the levels of N-acetylgalactosamine, mannose, galactose, N-acetylglucosamine on CEA showed a downward trend after first experiencing an increase at Stage II with the stages of CRC.

Conclusions

Our insights into the changing CEA glycosylation patterns and their role in the development of CRC highlight the importance of glycan variants on CEA for early clinical detection and staging of CRC.

Electronic supplementary material

The online version of this article (10.1186/s12014-018-9182-4) contains supplementary material, which is available to authorized users.

Serum Protein N-Glycosylation Changes with Rheumatoid Arthritis Disease Activity during and after Pregnancy

Symptoms of rheumatoid arthritis (RA) improve during pregnancy, a phenomenon that was found to be associated with N-glycosylation changes of immunoglobulin G. Recent advances in high-throughput glycosylation analysis allow the assessment of the N-glycome of human sera as well. The aim of this study was to identify new protein N-glycosylation properties that associate with changes in RA disease activity during and after pregnancy. A longitudinal cohort of serum samples was collected during 285 pregnancies (32 control individuals and 253 RA patients). Per individual one sample was collected before conception, three during pregnancy, and three after delivery. Released serum protein N-glycans were measured by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) after employing chemical modification of the sialic acids to allow discrimination of sialic acid linkage isomers. Serum protein N-glycosylation showed strongly modified during pregnancy, with similar changes visible in control individuals and RA pregnancies. Namely, a decrease in bisection and an increase in galactosylation in diantennary glycans were found, as well as an increase in tri- and tetraantennary species and α2,3-linked sialylation thereof. The change in RA disease activity [DAS28(3)-CRP] proved negatively associated with the galactosylation of diantennary N-glycans, and positively with the sialylation of triantennary fucosylated species (A3FGS). While the protein source of the novel finding A3FGS is thus far unknown, its further study may improve our understanding of the etiology of RA disease severity.

Quantitative N-glycoproteomics of milk fat globule membrane in human colostrum and mature milk reveals changes in protein glycosylation during lactation

The present study profiled the N-glycoproteome and quantified the changes of N-glycosylation site occupancy of MFGM proteins during lactation.

Serum Aberrant N-Glycan Profile as a Marker Associated with Early Antibody-Mediated Rejection in Patients Receiving a Living Donor Kidney Transplant

We determined if the serum N-glycan profile can be used as a diagnostic marker of antibody-mediated rejection (ABMR) in living donor kidney transplant (LKTx) recipients. Glycoblotting, combined with mass spectrometry, was used to retrospectively examine N-glycan levels in the postoperative sera of 197 LKTx recipients of whom 16 recipients had ABMR with or without T-cell-mediated rejection (TCMR), 40 recipients had TCMR, and 141 recipients had no adverse events. Multivariate discriminant analysis for prediction of ABMR was performed by inputting an ABMR event as an explanatory variable and sex, age, and serum N-glycan level as objective variables. The N-glycan score was calculated by multiplying the level of candidate objective variables by objective function values. The ABMR predictive performance of the N-glycan score was assessed by receiver operator characteristic curve and Kaplan-Meier curve analyses. The N-glycan score discriminated ABMR with 81.25% sensitivity, 87.85% specificity, and an area under the curve (AUC) of 0.892 that was far superior to that of preformed donor-specific antibody status (AUC, 0.761). Recipients with N-glycan-positive scores >0.8770 had significantly shorter ABMR survival than that of recipients with N-glycan-negative scores. Although the limitations of our study includ its small sample size and retrospective nature, the serum N-glycan score may contribute to prediction of ABMR.

IgA N- and O-glycosylation profiling reveals no association with the pregnancy-related improvement in rheumatoid arthritis

Background

The Fc glycosylation of immunoglobulin G (IgG) is well known to associate with rheumatoid arthritis (RA) disease activity. The same may be true for other classes of Igs. In the present study, we sought to determine whether the glycosylation of IgA was different between healthy subjects and patients with RA, as well as whether it was associated with RA disease activity, in particular with the pregnancy-associated improvement thereof or the flare after delivery.

Methods

A recently developed high-throughput method for glycoprofiling of IgA1 was applied to affinity-captured IgA from sera of patients with RA (n = 252) and healthy control subjects (n = 32) collected before, during and after pregnancy.

Results

IgA1 O-glycans bore more sialic acids in patients with RA than in control subjects. In addition, levels of bisecting N-acetylglucosamine of the N-glycans at asparagine 144 were higher in the patients with RA. The levels of several N-glycosylation traits were shown to change with pregnancy, similar to what has been shown before for IgG. However, the changes in IgA glycosylation were not associated with improvement or a flare of disease activity.

Conclusions

The glycosylation of IgA differs between patients with RA and healthy control subjects. However, our data suggest only a minor, if any, association of IgA glycosylation with RA disease activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-017-1367-0) contains supplementary material, which is available to authorized users.

Clinical implications of serum N-glycan profiling as a diagnostic and prognostic biomarker in germ-cell tumors

Serum biomarker monitoring is essential for management of germ‐cell tumors (GCT). However, not all GCT are positive for conventional tumor markers. We examined whether serum N‐glycan‐based biomarkers can be applied for detection and prognosis in patients with GCT. We performed a comprehensive N‐glycan structural analysis of sera from 54 untreated GCT patients and 103 age‐adjusted healthy volunteers using glycoblotting methods and mass spectrometry. Candidate N‐glycans were selected from those with the highest association; cutoff concentration values were established, and an N‐glycan score was created based on the number of positive N‐glycans present. The validity of this score for diagnosis and prognosis was analyzed using a receiver operating characteristic (ROC) curve. We identified five candidate N‐glycans significantly associated with GCT patients. The accuracy of the N‐glycan score for GCT was significant with an area‐under‐the‐curve (AUC) value of 0.87. Diagnostically, the N‐glycan score detected 10 of 12 (83%) patients with negative conventional tumor markers. Prognostically, the N‐glycan score comprised four candidate N‐glycans. The predictive value of the prognostic N‐glycan score was significant, with an AUC value of 0.89. A high value prognostic N‐glycan score was significantly associated with poor prognosis. Finally, to identify a potential carrier protein, immunoglobulin (Ig) fractions of sera were subjected to N‐glycan analysis and compared to whole sera. Candidate N‐glycans in Ig‐fractions were significantly decreased; therefore, the carrier protein for candidate N‐glycans is likely not an immunoglobulin. In summary, our newly developed N‐glycan score seems to be a practical diagnostic and prognostic method for GCT.

Changes in total plasma and serum N-glycome composition and patient-controlled analgesia after major abdominal surgery

Systemic inflammation participates to the complex healing process occurring after major surgery, thus directly affecting the surgical outcome and patient recovery. Total plasma N-glycome might be an indicator of inflammation after major surgery, as well as an anti-inflammatory therapy response marker, since protein glycosylation plays an essential role in the inflammatory cascade. Therefore, we assessed the effects of surgery on the total plasma N-glycome and the association with self-administration of postoperative morphine in two cohorts of patients that underwent major abdominal surgery. We found that plasma N-glycome undergoes significant changes one day after surgery and intensifies one day later, thus indicating a systemic physiological response. In particular, we observed the increase of bisialylated biantennary glycan, A2G2S[3,6]2, 12 hours after surgery, which progressively increased until 48 postoperative hours. Most changes occurred 24 hours after surgery with the decrease of most core-fucosylated biantennary structures, as well as the increase in sialylated tetraantennary and FA3G3S[3,3,3]3 structures. Moreover, we observed a progressive increase of sialylated triantennary and tetraantennary structures two days after surgery, with a concomitant decrease of the structures containing bisecting N-acetylglucosamine along with bi- and trisialylated triantennary glycans. We did not find any statistically significant association between morphine consumption and plasma N-glycome.

Fucosylated Glycans in α1-Acid Glycoprotein for Monitoring Treatment Outcomes and Prognosis of Cancer Patients

One standard treatment option for advanced-stage cancer is surgical resection of malignant tumors following by adjuvant chemotherapy and chemoradiotherapy. Additionally, neoadjuvant chemotherapy may be applied if required. During the time course of treatments, patients are generally followed by computed tomography (CT) surveillance, and by tumor marker diagnosis. However, currently, early evidence of recurrence and/or metastasis of tumors with a clinically relevant biomarker remains a major therapeutic challenge. In particular, there has been no validated biomarker for predicting treatment outcomes in therapeutic settings. Recently, we have looked at glycoforms of serum α₁-acid glycoprotein (AGP) by using a crossed affinoimmunoelectrophoresis with two lectins and an anti-AGP antibody. The primary glycan structures of AGP were also analyzed by a mass spectrometer and a novel software in a large number of patients with various cancers. Accordingly, the relative abundance of α1,3fucosylated glycans in AGP (FUCAGP) was found to be significantly high in cancer patients as compared with the healthy controls. Further, strikingly elevated levels of FUCAGP were found in patients with poor prognosis but not in patients with good prognosis. In the current study, levels of FUCAGP in serum samples from various cancer patients were analyzed and 17 patients including 13 who had undergone chemotherapy were followed for several years post operation. FUCAGP level determined diligently by using a mass spectrometer was found to change along with disease prognosis as well as with responses to treatments, in particular, to various chemotherapies. Therefore, FUCAGP levels measured during following-up of the patients after operation appeared to be clinically relevant biomarker of treatment intervention.

Human plasma protein N-glycosylation

Glycosylation is the most abundant and complex protein modification, and can have a profound structural and functional effect on the conjugate. The oligosaccharide fraction is recognized to be involved in multiple biological processes, and to affect proteins physical properties, and has consequentially been labeled a critical quality attribute of biopharmaceuticals. Additionally, due to recent advances in analytical methods and analysis software, glycosylation is targeted in the search for disease biomarkers for early diagnosis and patient stratification. Biofluids such as saliva, serum or plasma are of great use in this regard, as they are easily accessible and can provide relevant glycosylation information. Thus, as the assessment of protein glycosylation is becoming a major element in clinical and biopharmaceutical research, this review aims to convey the current state of knowledge on the N-glycosylation of the major plasma glycoproteins alpha-1-acid glycoprotein, alpha-1-antitrypsin, alpha-1B-glycoprotein, alpha-2-HS-glycoprotein, alpha-2-macroglobulin, antithrombin-III, apolipoprotein B-100, apolipoprotein D, apolipoprotein F, beta-2-glycoprotein 1, ceruloplasmin, fibrinogen, immunoglobulin (Ig) A, IgG, IgM, haptoglobin, hemopexin, histidine-rich glycoprotein, kininogen-1, serotransferrin, vitronectin, and zinc-alpha-2-glycoprotein. In addition, the less abundant immunoglobulins D and E are included because of their major relevance in immunology and biopharmaceutical research. Where available, the glycosylation is described in a site-specific manner. In the discussion, we put the glycosylation of individual proteins into perspective and speculate how the individual proteins may contribute to a total plasma N-glycosylation profile determined at the released glycan level.

High-Performance Affinity Chromatography: Applications in Drug-Protein Binding Studies and Personalized Medicine

The binding of drugs with proteins and other agents in serum is of interest in personalized medicine because this process can affect the dosage and action of drugs. The extent of this binding may also vary with a given disease state. These interactions may involve serum proteins, such as human serum albumin or α1-acid glycoprotein, or other agents, such as lipoproteins. High-performance affinity chromatography (HPAC) is a tool that has received increasing interest as a means for studying these interactions. This review discusses the general principles of HPAC and the various approaches that have been used in this technique to examine drug-protein binding and in work related to personalized medicine. These approaches include frontal analysis and zonal elution, as well as peak decay analysis, ultrafast affinity extraction, and chromatographic immunoassays. The operation of each method is described and examples of applications for these techniques are provided. The type of information that can be obtained by these methods is also discussed, as related to the analysis of drug-protein binding and the study of clinical or pharmaceutical samples.

The detection and discovery of glycan motifs in biological samples using lectins and antibodies: new methods and opportunities

Recent research has uncovered unexpected ways that glycans contribute to biology, as well as new strategies for combatting disease using approaches involving glycans. To make full use of glycans for clinical applications, we need more detailed information on the location, nature, and dynamics of glycan expression in vivo. Such studies require the use of specimens acquired directly from patients. Effective studies of clinical specimens require low-volume assays, high precision measurements, and the ability to process many samples. Assays using affinity reagents-lectins and glycan-binding antibodies-can meet these requirements, but further developments are needed to make the methods routine and effective. Recent advances in the use of glycan-binding proteins involve improved determination of specificity using glycan arrays; the availability of databases for mining and analyzing glycan array data; lectin engineering methods; and the ability to quantitatively interpret lectin measurements. Here, we describe many of the challenges and opportunities involved in the application of these new approaches to the study of biological samples. The new tools hold promise for developing methods to improve the outcomes of patients afflicted with diseases characterized by aberrant glycan expression.

Avian influenza H5 hemagglutinin binds with high avidity to sialic acid on different O-linked core structures on mucin-type fusion proteins

The interaction between P-selectin glycoprotein ligand-1/mouse IgG2b (PSGL-1/mIgG(2b)) fusion protein carrying multiple copies of the influenza hemagglutinin receptor Siaα2-3Gal on different O-glycan chains and recombinant human influenza H5N1 A/Vietnam/1203/04 hemagglutinin was investigated with a Biacore biosensor. The fusion protein was produced by stable cell lines in large scale cultures and purified with affinity- and gel filtration chromatography. TheC-P55 and 293-P cell lines were established by transfecting the Chinese hamster ovary (CHO)-K1 and Human embryonic kidney (HEK)-293 cell lines with plasmids encoding the PSGL-1/mIgG(2b) fusion protein, while the C-PSLex cell line was engineered by transfecting CHO-K1 cells with the plasmids encoding the core 2 β1,6GnT-I and FUT-VII glycosyltransferases. Glycosylation was characterized by lectin Western blotting of the proteins and liquid chromatography - mass spectrometry of released non-derivatized O-glycans. Biacore experiments revealed that PSGL-1/mIgG(2b) is a good binding partner of H5. The binding curves displayed a slow dissociation indicating a multivalent binding. The H5 hemagglutinin binds with similar strength to PSGL-1/mIgG(2b) carrying mostly sialylated core 1 (clone C-P55), a mix of sialylated core 1 and sialylated lactosamine (clone 293-P) or mainly sialylated lactosamine (clone C-PSLex) O-glycans, indicating that this hemagglutinin is unable to discriminate between these structures.The potential use of the large, flexible PSGL-1/mIgG(2b) mucin-type fusion protein carrying Siaα2-3Gal as a multivalent inhibitor of influenza virus is discussed.

Sugars communicate through water: oriented glycans induce water structuring

Cells are coated with a glycocalyx-a layer of carbohydrate-containing biomolecules, such as glycoproteins. Although the structure and orientation of the cell-surface glycans are frequently regarded as being random, we have found, using α-1-acid glycoprotein and antitrypsin as model systems for surface glycans, that this is not the case. A glycoprotein monolayer was adsorbed onto hydrophilic and hydrophobic substrates. Surface-force measurements revealed that the orientation of the glycans with respect to the aqueous solution has a profound effect on the structure of vicinal water. The glycan antennae of the surface-adsorbed glycoproteins apparently impose an ordering on the water, resulting in a strong repulsive force over some tens of nanometers with superposed film-thickness transitions ranging from ≈0.7 to 1.8 nm. When the glycan orientation is modified by chemical means, this long-range repulsion disappears. These results may provide an explanation as to why the multiantennary structure is ubiquitous in glycoproteins. Although direct, specific interactions between glycans and other biomolecules are essential for their functionality, these results indicate that glycans' long-range structuring of water may also influence their ability to interact with biomolecules in their vicinity.

Serum glycan markers for evaluation of disease activity and prediction of clinical course in patients with ulcerative colitis

BACKGROUND

The aims of this study were to determine the change of whole-serum N-glycan profile in ulcerative colitis (UC) patients and to investigate its clinical utility.

METHODS

We collected serum from 75 UC patients at the time of admission and the same number of age/sex-matched healthy volunteers. Serum glycan profile was measured by comprehensive quantitative high-throughput glycome analysis and was compared with disease activity and prognosis.

RESULTS

Out of 61 glycans detected, 24 were differentially expressed in UC patients. Pathway analysis demonstrated that highly sialylated multi-branched glycans and agalactosyl bi-antennary glycans were elevated in UC patients; in addition, the glycan ratio m/z 2378/1914, which also increased in UC, showed the highest Area under Receiver Operating Characteristic curve (0.923) for the diagnosis of UC. Highly sialylated multi-branched glycans and the glycan ratio m/z 2378/1914 were higher in the patients with total colitis, Clinical Activity Index >10, Mayo endoscopic score 3, or a steroid-refractory status. In particular, the glycan ratio m/z 2378/1914 (above median) was an independent prognostic factor for the need for an operation (hazard ratio, 2.67; 95% confidence interval, 1.04-7.84).

CONCLUSIONS

Whole-serum glycan profiles revealed that the glycan ratio m/z 2378/1914 and highly sialylated multi-branched glycans increase in UC patients, and are correlated with disease activity. The glycan ratio m/z 2378/1914 was an independent predictive factor of the prognosis of UC.

Pig α1-acid glycoprotein: characterization and first description in any species as a negative acute phase protein

The serum protein α1-acid glycoprotein (AGP), also known as orosomucoid, is generally described as an archetypical positive acute phase protein. Here, porcine AGP was identified, purified and characterized from pooled pig serum. It was found to circulate as a single chain glycoprotein having an apparent molecular weight of 43 kDa by SDS-PAGE under reducing conditions, of which approximately 17 kDa were accounted for by N-bound oligosaccharides. Those data correspond well with the properties of the protein predicted from the single porcine AGP gene (ORM1, Q29014 (UniProt)), containing 5 putative glycosylation sites. A monoclonal antibody (MAb) was produced and shown to quantitatively and specifically react with all microheterogenous forms of pig AGP as analyzed by 2-D electrophoresis. This MAb was used to develop an immunoassay (ELISA) for quantification of AGP in pig serum samples. The adult serum concentrations of pig AGP were in the range of 1-3 mg/ml in a number of conventional pig breeds while it was lower in Göttingen and Ossabaw minipigs (in the 0.3 to 0.6 mg/ml range) and higher in young (2-5 days old) conventional pigs (mean: 6.6 mg/ml). Surprisingly, pig AGP was found to behave as a negative acute phase protein during a range of experimental infections and aseptic inflammation with significant decreases in serum concentration and in hepatic ORM1 expression during the acute phase response. To our knowledge this is the first description in any species of AGP being a negative acute phase protein.

Development of a novel system for mass spectrometric analysis of cancer-associated fucosylation in plasma α1-acid glycoprotein

Human plasma α₁-acid glycoprotein (AGP) from cancer patients and healthy volunteers was purified by sequential application of ion-exchange columns, and N-linked glycans enzymatically released from AGP were labeled and applied to a mass spectrometer. Additionally, a novel software system for use in combination with a mass spectrometer to determine N-linked glycans in AGP was developed. A database with 607 glycans including 453 different glycan structures that were theoretically predicted to be present in AGP was prepared for designing the software called AGPAS. This AGPAS was applied to determine relative abundance of each glycan in the AGP molecules based on mass spectra. It was found that the relative abundance of fucosylated glycans in tri- and tetra-antennary structures (FUCAGP) was significantly higher in cancer patients as compared with the healthy group (P < 0.001). Furthermore, extremely elevated levels of FUCAGP were found specifically in patients with a poor prognosis but not in patients with a good prognosis. In conclusion, the present software system allowed rapid determination of the primary structures of AGP glycans. The fucosylated glycans as novel tumor markers have clinical relevance in the diagnosis and assessment of cancer progression as well as patient prognosis.

Nanoscale reversed-phase liquid chromatography-mass spectrometry of permethylated N-glycans

Reversed-phase liquid chromatography on the nanoscale coupled to electrospray tandem mass spectrometry was used to analyse a mixture of four commercial glycan standards, and the method was further adapted to N-glycans enzymatically released from alpha-1-acid glycoprotein and immunoglobulin gamma. Glycans were permethylated to enable their separation by reversed-phase chromatography and to facilitate interpretation of fragmentation data. Prior to derivatization of glycans by permethylation, they were reduced to cancel anomerism because, although feasible, it was not desired to separate α- and β-anomers. The effect of supplementing chromatographic solvent with sodium hydroxide to guide adduct formation was investigated. Raising the temperature in which the separation was performed improved chromatographic resolution and affected retention times as expected. It was shown by using the tetrasaccharides sialyl Lewis X and sialyl Lewis A that reversed-phase chromatography could achieve the separation of methylated isobaric glycan analytes. Isobaric glycans were detected among the N-glycans of immunoglobulin gamma and further analysed by tandem mass spectrometry.

Antibody profiling with protein antigen microarrays in early stage cancer

INTRODUCTION

Proteins not present in normal cells, that is, cancer cells, may elicit a host immune response that leads to the generation of antibodies that might react with these tumor-associated proteins. In recent years, a growing number of reports have showed that autoantibody profiling may provide an alternative approach for the detection of cancer. However, most studies of antigen-autoantibody reactivity have relied on recombinant proteins. Recombinant proteins lack the proper post-translational modifications present in native proteins. Because of this limitation, native or natural protein antigen microarrays are gaining popularity for profiling antibody responses.

AREAS COVERED

i) To illustrate some examples of autoantibodies as signatures for early stage cancer; ii) to briefly outline the various protein antigen microarray platforms; iii) to illustrate the use of native or natural protein microarrays in the discovery of potential biomarkers and iv) to discuss the advantages of native protein antigen microarrays over other approaches.

EXPERT OPINION

The nature of protein microarray platforms is conducive to multiplexing, which amplifies the potential for uncovering effective biomarkers for many significant diseases. However, the major challenge will be in integrating microarray platforms into multiplexed clinical diagnostic tools, as the main drawback is the reproducibility and coefficient of variation of the results from array to array, and the transportability of the array platform to a more automatable platform.

Integrated approach toward the discovery of glyco-biomarkers of inflammation-related diseases

Glycobiology has contributed tremendously to the discovery and characterization of cancer-related biomarkers containing glycans (i.e., glyco-biomarkers) and a more detailed understanding of cancer biology. It is now recognized that most chronic diseases involve some elements of chronic inflammation; these include cancer, Alzheimer's disease, and metabolic syndrome (including consequential diabetes mellitus and cardiovascular diseases). By extending the knowledge and experience of the glycobiology community regarding cancer biomarker discovery, we should be able to contribute to the discovery of diagnostic/prognostic glyco-biomarkers of other chronic diseases that involve chronic inflammation. Future integration of large-scale "omics"-type data (e.g., genomics, epigenomics, transcriptomics, proteomics, and glycomics) with computational model building, or a systems glycobiology approach, will facilitate such efforts.

Chiral interactions of the drug propranolol and α1-acid-glycoprotein at a micro liquid-liquid interface

The investigation of chiral interactions of drugs with plasma proteins is of fundamental importance for drug efficacy and toxicity studies. In this paper, we demonstrate a simple liquid-liquid interface procedure for investigating chiral interactions. Chiral discrimination of the enantiomers of a basic drug, propranolol, was achieved at a micro liquid-liquid interface, using α(1)-acid-glycoprotein (AGP) as a chiral acute phase plasma protein. When the protein is added to an aqueous phase containing the enantiomers of propranalol hydrochloride, the binding of (S)- and (R)-propranolol hydrochloride to the protein results in a decrease in the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) current responses corresponding to the decrease in transfer of propranolol at an aqueous-1,2-dichloroethane interface. This decrease is a consequence of the complexation of the drug and the protein. The complex drug-protein does not transfer across the interface nor changes the transfer potential of the uncomplexed form of propranolol enantiomers. The bound concentration of propranolol enantiomers in the presence of AGP was found to be greater for (S)-propranolol than (R)-propranolol for solutions containing constant concentrations of AGP (50 μM). Scatchard analysis yielded association constants of 2.7 and 1.3 × 10(5) M(-1) for (S)- and (R)-propranolol, respectively.

Quantitative evaluation of lectin-reactive glycoforms of α(1)-acid glycoprotein using lectin affinity capillary electrophoresis with fluorescence detection

α(1)-Acid glycoprotein (AGP) was previously shown to be a marker candidate of disease progression and prognosis of patients with malignancies by analysis of its glycoforms via lectins. Herein, affinity capillary electrophoresis of fluorescein-labeled AGP using lectins with the aid of laser-induced fluorescence detection was developed for quantitative evaluation of the fractional ratios of concanavalin A-reactive or Aleuria aurantia lectin-reactive AGP. Labeled AGP was applied at the anodic end of a fused-silica capillary (50 μm id, 360 μm od, 27 cm long) coated with linear polyacryloyl-β-alanyl-β-alanine, and electrophoresis was carried out for about 10 min in 60 mM 3-morpholinopropane-1-sulfonic acid-NaOH buffer (pH 7.35). Addition of the lectins to the anode buffer resulted in the separation of lectin-reactive glycoform peaks from lectin-non-reactive glycoform peaks. Quantification of the peak area of each group revealed that the percent of lectin-reactive AGP is independent of a labeling ratio ranging from 0.4 to 1.5 mol fluorescein/mol AGP, i.e. the standard deviation of 0.5% for an average of 59.9% (n=3). In combination with a facile procedure for micro-purification of AGP from serum, the present procedure, marking the reactivity of AGP with lectins, should be useful in determining the prognosis for a large number of patients with malignancies.

Tandem 18O stable isotope labeling for quantification of N-glycoproteome

A new strategy using tandem (18)O stable isotope labeling (TOSIL) to quantify the N-glycosylation site occupancy is reported. Three heavy oxygen atoms are introduced into N-glycosylated peptides: two (18)O atoms are incorporated into the carboxyl terminal of all peptides during a tryptic digestion, and the third (18)O atom is incorporated into the N-glycosylation site of asparagines-linked sugar chains specifically via a N-glycosidase F (PNGase F)-mediated hydrolysis. Comparing samples treated in H(2)(18)O and samples treated in H(2)(16)O, a unique mass shift of 6 Da can be shown for N-glycosylated peptide with single glycosylation site, which could be easily distinguished from those nonglycosite peptide pairs with a mass difference of 4 Da only. The relative quantities of N-glycosylated and its parent protein-levels were obtained simultaneous by measuring the intensity ratios of (18)O/(16)O for glycosylated (6 Da) and for nonglycosylated (4 Da) peptides, respectively. Thus, a comparison of these two ratios can be utilized to evaluate the changes of occupancy of N-glycosylation at specific sites between healthy and diseased individuals. The TOSIL approach yielded good linearity in quantitative response within 10-fold dynamic range with the correlation coefficient r(2) > 0.99. The standard deviation (SD) ranged from 0.06 to 0.21, for four glycopeptides from two model glycoproteins. Furthermore, serums from a patient with ovarian cancer and healthy individual were used as test examples to validate the novel TOSIL method. A total of 86 N-glycosylation sites were quantified and N-glycosylation levels of 56 glycopeptides showed significant changes. Most changes in N-glycosylation at specific sites have the same trends as those of protein expression levels; however, the occupancies of three N-glycosylation sites were significantly changed with no change in proteins levels.

Enhanced expression of alpha1-acid glycoprotein and fucosylation in hepatitis B patients provides an insight into pathogenesis

Altered glycosylation and concentration of alpha1-acid glycoprotein has been known to be related to the pathogenesis of the hepatic diseases. The present study investigated enhanced fucosylation of AGP in the sera of chronic hepatitis B (HBV-CH) and hepatitis B cirrhosis (HBV-LC) patients by high performance anion exchange chromatography and by ELISA using fucose binding Aleuria aurantia lectin. The concentration of AGP determined by ELISA using monoclonal anti-human AGP (mAb-AGP) showed high level of AGP in HBV-CH and HBV-LC patients. This was further judged by association constant (K (A)) measured by surface plasmon resonance analysis. There was no apparent linkage variation of sialic acid among different patient groups when tested with two sialic acid binding lectins viz., Maackia amurensis agglutinin (MAA, NeuAc alpha2-3-) and Sambucus nigra agglutinin (SNA, NeuAc alpha2-6-) respectively. There was no change of oligosaccharide branching in HBV-CH in comparison to controls whereas a slight change was observed in HBV-LC using ConA. The above results suggest that the changes in concentration of AGP and fucosylation have a prognostic value of hepatitis diseases and it could be possible to use AGP as diagnostic marker besides clinical examination and routine laboratory investigation.

LC/MS analysis of complex multiglycosylated human alpha(1)-acid glycoprotein as a model for developing identification and quantitation methods for intact glycopeptide analysis

The site-specific characterization of the complex glycans in multiglycosylated proteins requires developing methods where the carbohydrates remain covalently bound to the protein. The complexity in the carbohydrate composition of alpha(1)-acid glycoprotein (AAG) makes it an ideal model protein for such development. AAG has five N-asparaginyl-linked glycosylation sites, each varying in its bi-, tri-, and tetraantennary glycan content. We present an on-line liquid chromatography/mass spectrometry (LC/MS) method that uses high-low cone voltage switching for in-source fragmentation to determine the structures of the complex glycans present on each site for the two gene products of AAG. High cone voltage caused carbohydrate fragmentation, leading to the generation of signature carbohydrate ions that we used as markers to identify the glycopeptides. Low cone voltage produced minimal carbohydrate fragmentation and enabled the identification and quantification of the intact oligosaccharide structures on each glycopeptide based on its monoisotopic mass and intensity. Quantitation was accomplished by using the intensities of peaks from deconvoluted and deisotoped mass spectra or from the areas of the extracted ion chromatograms from the tryptic peptide maps. The combined results from the two methods can be used to better characterize and quantitate site heterogeneity in multiglycosylated proteins.

Multiplexed antibody arrays for the discovery and validation of glycosylated protein biomarkers

Protein glycosylation, the enzymatic linkage of mono- and poly-saccharides to proteins, is a critical determinant of protein function; however, there is a lack of tools for studying the glycosylation of specific proteins in complex samples. A new type of antibody–lectin sandwich assay enables the measurement of the glycosylation of specific proteins that have been captured from complex samples using antibody arrays combined with lectin-based detection probes. Antibody–lectin sandwich arrays have the potential to expand our understanding of the role of glycans and protein glycosylation in disease and to identify and investigate new biomarkers for early detection, disease prognosis and therapeutic response prediction. While antibody–lectin sandwich arrays yield less-detailed structural information regarding protein glycosylation than other available methods, they do provide a simple and reproducible method for investigating changes in protein abundance and glycosylation of multiple proteins and can be easily applied to large or small sample sets. By profiling protein and glycan variations, new disease-associated glycan alterations can be identified and validated for use as biomarkers.

Endogenous ligands for C-type lectin receptors: the true regulators of immune homeostasis

C-type lectin receptors (CLRs) have long been known as pattern-recognition receptors implicated in the recognition of pathogens by the innate immune system. However, evidence is accumulating that many CLRs are also able to recognize endogenous 'self' ligands and that this recognition event often plays an important role in immune homeostasis. In the present review, we focus on the human and mouse CLRs for which endogenous ligands have been described. Special attention is given to the signaling events initiated upon recognition of the self ligand and the regulation of glycosylation as a switch modulating CLR recognition, and therefore, immune homeostasis.

Microarrays in glycoproteomics research

Microarrays have been extremely useful for investigating binding interactions among diverse types of molecular species, with the main advantage being the ability to examine many interactions using small amounts of samples and reagents. Microarrays are increasingly being used to advance research in the field of glycobiology. Several types of microarrays are being used in the study of glycans and proteins in glycobiology, including glycan arrays to study the recognition of carbohydrates, lectin arrays to determine carbohydrate expression on purified proteins or on cells, and antibody arrays to examine the variation in particular glycan structures on specific proteins. This article covers the technology and applications of these types of microarrays, and their use for obtaining complementary information on various aspects of glycobiology.

The prevalence and nature of glycan alterations on specific proteins in pancreatic cancer patients revealed using antibody-lectin sandwich arrays

Changes to the glycan structures of proteins secreted by cancer cells are known to be functionally important and to have potential diagnostic value. However, an exploration of the population variation and prevalence of glycan alterations on specific proteins has been lacking because of limitations in conventional glycobiology methods. Here we report the use of a previously developed antibody-lectin sandwich array method to characterize both the protein and glycan levels of specific mucins and carcinoembryonic antigen-related proteins captured from the sera of pancreatic cancer patients (n = 23) and control subjects (n = 23). The MUC16 protein was frequently elevated in the cancer patients (65% of the patients) but showed no glycan alterations, whereas the MUC1 and MUC5AC proteins were less frequently elevated (30 and 35%, respectively) and showed highly prevalent (up to 65%) and distinct glycan alterations. The most frequent glycan elevations involved the Thomsen-Friedenreich antigen, fucose, and Lewis antigens. An unexpected increase in the exposure of alpha-linked mannose also was observed on MUC1 and MUC5ac, indicating possible N-glycan modifications. Because glycan alterations occurred independently from the protein levels, improved identification of the cancer samples was achieved using glycan measurements on specific proteins relative to using the core protein measurements. The most significant elevation was the cancer antigen 19-9 on MUC1, occurring in 19 of 23 (87%) of the cancer patients and one of 23 (4%) of the control subjects. This work gives insight into the prevalence and protein carriers of glycan alterations in pancreatic cancer and points to the potential of using glycan measurements on specific proteins for highly effective biomarkers.

Evaluation of the serum N-linked glycome for the diagnosis of cancer and chronic inflammation

The identification of serum biomarkers has lead to improvements in the detection and diagnosis of cancer, and combinations of these biomarkers have increased further their sensitivity and specificity. Glycosylation is the most common PTM of secreted proteins and the identification of novel serum glyco-biomarkers has become a topic of increasing interest because the glycan processing pathways are frequently disturbed in cancer cells. A future goal is to combine current biomarkers with glyco-biomarkers to yield further improvements. Well characterised N-glycosylation changes in the serum glycome of cancer patients include changes in the levels of tri- and tetra-antennary glycan structures, sialyl Lewis X epitopes and agalactosylated bi-antennary glycans. Several of these glycosylated markers have been linked to chronic inflammatory diseases, promoting questions about the links between inflammation and cancer. In this review, the glycoproteins which display these glycan epitopes, the glycosyl transferases which can generate them, their potential functions and their use as biomarkers are evaluated.