α1-3/4 fucosylation at Asn 241 of β-haptoglobin is a novel marker for colon cancer: a combinatorial approach for development of glycan biomarkers

Advancing rare cancer research by MALDI mass spectrometry imaging: Applications, challenges, and future perspectives in sarcoma

MALDI mass spectrometry imaging (MALDI imaging) uniquely advances cancer research, by measuring spatial distribution of endogenous and exogenous molecules directly from tissue sections. These molecular maps provide valuable insights into basic and translational cancer research, including tumor biology, tumor microenvironment, biomarker identification, drug treatment, and patient stratification. Despite its advantages, MALDI imaging is underutilized in studying rare cancers. Sarcomas, a group of malignant mesenchymal tumors, pose unique challenges in medical research due to their complex heterogeneity and low incidence, resulting in understudied subtypes with suboptimal management and outcomes. In this review, we explore the applicability of MALDI imaging in sarcoma research, showcasing its value in understanding this highly heterogeneous and challenging rare cancer. We summarize all MALDI imaging studies in sarcoma to date, highlight their impact on key research fields, including molecular signatures, cancer heterogeneity, and drug studies. We address specific challenges encountered when employing MALDI imaging for sarcomas, and propose solutions, such as using formalin-fixed paraffin-embedded tissues, and multiplexed experiments, and considerations for multi-site studies and digital data sharing practices. Through this review, we aim to spark collaboration between MALDI imaging researchers and clinical colleagues, to deploy the unique capabilities of MALDI imaging in the context of sarcoma.

Development and validation of a model and nomogram for breast cancer diagnosis based on quantitative analysis of serum disease-specific haptoglobin N-glycosylation

BACKGROUND

A better diagnostic marker is in need to distinguish breast cancer from suspicious breast lesions. The abnormal glycosylation of haptoglobin has been documented to assist cancer diagnosis. This study aims to evaluate disease-specific haptoglobin (DSHp)-β N-glycosylation as a potential biomarker for breast cancer diagnosis.

METHODS

DSHp-β chains of 497 patients with suspicious breast lesions who underwent breast surgery were separated from serum immunoinflammatory-related protein complexes. DSHp-β N-glycosylation was quantified by mass spectrometric analysis. After missing data imputation and propensity score matching, patients were randomly assigned to the training set (n = 269) and validation set (n = 113). Logistic regression analysis was employed in model and nomogram construction. The diagnostic performance was analyzed with receiver operating characteristic and calibration curves.

RESULTS

95 N-glycopeptides at glycosylation sites N207/N211, N241, and N184 were identified in 235 patients with benign breast diseases and 262 patients with breast cancer. DSHp-β N-tetrafucosyl and hexafucosyl were significantly increased in breast cancer compared with benign diseases (p < 0.001 and p = 0.001, respectively). The new diagnostic model and nomogram included GN2F2, G6N3F6, GN2FS at N184, G-N&G2S2, G2&G3NFS, G2N3F, GN3 at N207/N211, CEA, CA153, and could reliably distinguish breast cancer from benign diseases. For the training set, validation set, and training and validation sets, the area under the curves (AUCs) were 0.80 (95% CI: 0.75-0.86, specificity: 87%, sensitivity: 62%), 0.77 (95% CI:0.69-0.86, specificity: 75%, sensitivity: 69%), and 0.80 (95% CI:0.76-0.84, specificity: 77%, sensitivity: 68%), respectively. CEA, CA153, and their combination yielded AUCs of 0.62 (95% CI: 0.56-0.67, specificity: 29%, sensitivity: 90%), 0.65 (95% CI: 0.60-0.71, specificity: 74%, sensitivity: 51%), and 0.67 (95% CI: 0.62-0.73, specificity: 60%, sensitivity: 68%), respectively.

CONCLUSIONS

The combination of DSHp-β N-glycopeptides, CEA, and CA153 might be a better serologic marker to differentiate between breast cancer and benign breast diseases. The dysregulated N-glycosylation of serum DSHp-β could provide insights into breast tumorigenesis.

The hidden potential of glycomarkers: Glycosylation studies in the service of cancer diagnosis and treatment

Changes in the glycosylation process appear early in carcinogenesis and evolve with the growth and spread of cancer. The correlation of the characteristic glycosylation signature with the tumor stage and the appropriate therapy choice is an important issue in translational medicine. Oncologists also pay attention to extracellular vesicles as reservoirs of new cancer glycomarkers that can be potent for cancer diagnosis/prognosis. In this review, we recall glycomarkers used in oncology and show their new glycoforms of improved clinical relevance. We summarize current knowledge on the biological functions of glycoepitopes in cancer-derived extracellular vesicles and their potential use in clinical practice. Is glycomics a future of cancer diagnosis? It may be, but in combination with other omics analyses than alone.

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

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

Terminal fucosylation of haptoglobin in cancer-derived exosomes during cholangiocarcinoma progression

Background

Cholangiocarcinoma (CCA) is a silent tumor with a high mortality rate due to the difficulty of early diagnosis and prediction of recurrence even after timely surgery. Serologic cancer biomarkers have been used in clinical practice, but their low specificity and sensitivity have been problematic. In this study, we aimed to identify CCA-specific glycan epitopes that can be used for diagnosis and to elucidate the mechanisms by which glycosylation is altered with tumor progression.

Methods

The serum of patients with various cancers was fractioned into membrane-bound and soluble components using serial ultracentrifugation. Lectin blotting was conducted to evaluate glycosylation. Proteins having altered glycosylation were identified using proteomic analysis and further confirmed using immunoblotting analysis. We performed HPLC, gene analysis, real-time cargo tracking, and immunohistochemistry to determine the origin of CCA glycosylation and its underlying mechanisms. Extracellular vesicles (EV) were isolated from the sera of 62 patients with CCA at different clinical stages and inflammatory conditions and used for glycan analysis to assess their clinical significance.

Results

The results reveal that glycosylation patterns between soluble and membrane-bound fractions differ significantly even when obtained from the same donor. Notably, glycans with α1-3/4 fucose and β1-6GlcNAc branched structures increase specifically in membrane-bound fractions of CCA. Mechanically, it is primarily due to β-haptoglobin (β-Hp) originating from CCA expressing fucosyltransferase-3/4 (FUT 3/4) and N-acetylglucosaminyltransferase-V (MGAT5). Newly synthesized β-Hp is loaded into EVs in early endosomes via a KFERQ-like motif and then secreted from CCA cells to induce tumor progression. In contrast, β-Hp expressed by hepatocytes is secreted in a soluble form that does not affect CCA progression. Moreover, evaluation of EV glycosylation in CCA patients shows that fucosylation level of EV-Hp gradually increases with tumor progression and decreases markedly when the tumors are eliminated by surgery.

Conclusion

This study suggests that terminal fucosylation of Hp in cancer-derived exosomes can be a novel glycan marker for diagnosis and prognosis of CCA. These findings highlight the potential of glycan analysis in different fractions of serum for biomarker discover for other diseases. Further research is needed to understand the role of fucosylated EVs on CCA progression.

Haptoglobin polymorphism affects its N-glycosylation pattern in serum

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Polymorphism affects glycosylation pattern of haptoglobin in healthy population.

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Sample phenotype classification was done based on the number and type of α-chains.

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Glycoproteomic analyses of haptoglobin were done using enzyme-assisted LC-MS/MS.

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Significant differences were obseerved in branching, sialylation and fucosylation.

Introduction

Haptoglobin (Hp) is an abundant acute-phase protein secreted mainly by the liver into the bloodstream. There are three Hp protein phenotypes (Hp type 1–1, 2–1, and 2–2), which differ in the number of α- and β-chains, type of α-chain (the β-chain type remains the same in all the Hp phenotypes), and the polymers that they form via disulfide bonds. Hp has four N-glycosylation sites on the β-chain. Glycosylation of Hp has been reported frequently as a potential glycobiomarker for many diseases; however, whether Hp polymorphism affects its glycosylation has not yet been addressed extensively or in depth.

Objectives

This study investigated the differences between the glycosylation patterns of Hp phenotypes using serum from 12 healthy individuals (four for each Hp phenotype).

Method

An efficient method for isolating Hp from serum was established and subsequently the Hp phenotype of each sample was characterized by immunoblotting. Then, LC-MS/MS analysis of isolated Hp after treatment with three exoglycosidases (sialidase, α2-3 neuraminidase, Endo F3) was performed to characterize the glycosylation pattern of Hp for each individual sample.

Results

The data reveal significant differences among the branching, sialylation, and fucosylation of Hp types, documenting the effect of Hp polymorphism on its glycosylation.

Conclusion

Overall, the study suggests that Hp phenotype characterization should be considered during the investigation of Hp glycosylation.

Molecular Imaging of Ulex Europaeus Agglutinin in Colorectal Cancer Using Confocal Laser Endomicroscopy (With Video)

Background and Study Aims

Previous studies have identified that colorectal cancer has different fucosylation levels compared to the normal colon. Ulex europaeus agglutinin-I (UEA-I), which specifically combines with α1-2 fucose glycan, is usually used to detect fucosylation levels. Therefore, we used confocal laser endomicroscopy (CLE) to investigate fluorescently labeled UEA-Fluorescein isothiocyanate (FITC) for detecting colonic cancer.

Patients and Methods

We stained frozen mouse colon tissue sections of normal, adenoma, and adenocarcinoma species with UEA-FITC to detect fucosylation levels in different groups. White light endoscopy and endocytoscopy were first used to detect the lesions. The UEA-FITC was then stained in the mice and human colon tissues in vitro. The CLE was used to detect the UEA-FITC levels of the corresponding lesions, and videos were recorded for quantitation analysis. The diagnostic accuracy of UEA-FITC using CLE was evaluated in terms of sensitivity and specificity.

Results

The UEA expression level in colorectal cancer was lower than that in normal intestinal epithelium. The fluorescence intensity ratio of UEA-FITC in colorectal cancer was significantly lower than that in normal tissue detected by CLE in both mice and humans. The combination of UEA-FITC and CLE presented a good diagnostic accuracy with a sensitivity of 95.6% and a specificity of 97.7% for detecting colorectal cancer. The positive and negative predictive values were 91.6% and 95.6%, respectively. Overall, 95.6% of the sites were correctly classified by CLE.

Conclusions

We developed a new imaging strategy to improve the diagnostic efficacy of CLE by using UEA-FITC.

Anti-Cancer Potential of Afzelin towards AGS Gastric Cancer Cells

Afzelin demonstrates anti-inflammatory and anti-cancer properties. Our purpose was to assess its influence on apoptosis, Bax, caspases, MUC1, cancer-related carbohydrate antigens, enzymes participating in their formation, and galectin-3 in AGS gastric cancer cells. A total of 60 and 120 μM afzelin was used in all experiments. Flow cytometry was applied to determine apoptotic response. Western blotting and RT PCR were used to detect the expression of mentioned factors. Flavonoid at higher concentration revealed slight apoptotic respond. Bax, caspase-3, -8, -9 increased upon afzelin action. Stimulatory effect of the flavonoid on MUC1 cytoplasmic tail and extracellular domain in cell lysates and on MUC1 gene was revealed. MUC1 release into the culture medium was inhibited by the flavonoid. The 60 μM afzelin dose stimulated GalNAcTL5 protein expression and inhibited C1GalT1. ST6GalNAcT mRNA was inhibited by both flavonoid doses. ST3GalT was inhibited by 120 μM afzelin on protein and mRNA level. Lewisa/b protein was reduced by both afzelin concentrations. FUT3 and FUT4 mRNA was inhibited by 120 μM dose of afzelin. Galectin-3 protein increased in cell lysates and decreased in culture supernatant by 60 and 120 μM flavonoid. Galectin-3 gene expression was stimulated by two used concentrations of afzelin in comparison to control. We conclude that afzelin can be considered as the potential anti-cancer agent, supporting conventional cancer treatment.

[Haptoglobin as a biomarker]

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

The Repertoire of Glycan Alterations and Glycoproteins in Human Cancers

Cancer as the leading cause of death worldwide has many issues that still need to be addressed. Since the alterations on the glycan compositions or/and structures (i.e., glycosylation, sialylation, and fucosylation) are common features of tumorigenesis, glycomics becomes an emerging field examining the structure and function of glycans. In the past, cancer studies heavily relied on genomics and transcriptomics with relatively little exploration of the glycan alterations and glycoprotein biomarkers among individuals and populations. Since glycosylation of proteins increases their structural complexity by several orders of magnitude, glycome studies resulted in highly dynamic biomarkers that can be evaluated for cancer diagnosis, prognosis, and therapy. Glycome not only integrates our genetic background with past and present environmental factors but also offers a promise of more efficient patient stratification compared with genetic variations. Therefore, studying glycans holds great potential for better diagnostic markers as well as developing more efficient treatment strategies in human cancers. While recent developments in glycomics and associated technologies now offer new possibilities to achieve a high-throughput profiling of glycan diversity, we aim to give an overview of the current status of glycan research and the potential applications of the glycans in the scope of the personalized medicine strategies for cancer.

Haptoglobin as a Biomarker

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

Haptoglobin: From hemoglobin scavenging to human health

Haptoglobin (Hp) belongs to the family of acute-phase plasma proteins and represents the most important plasma detoxifier of hemoglobin (Hb). The basic Hp molecule is a tetrameric protein built by two α/β dimers. Each Hp α/β dimer is encoded by a single gene and is synthesized as a single polypeptide. Following post-translational protease-dependent cleavage of the Hp polypeptide, the α and β chains are linked by disulfide bridge(s) to generate the mature Hp protein. As human Hp gene is characterized by two common Hp1 and Hp2 alleles, three major genotypes can result (i.e., Hp1-1, Hp2-1, and Hp2-2). Hp regulates Hb clearance from circulation by the macrophage-specific receptor CD163, thus preventing Hb-mediated severe consequences for health. Indeed, the antioxidant and Hb binding properties of Hp as well as its ability to stimulate cells of the monocyte/macrophage lineage and to modulate the helper T-cell type 1 and type 2 balance significantly associate with a variety of pathogenic disorders (e.g., infectious diseases, diabetes, cardiovascular diseases, and cancer). Alternative functions of the variants Hp1 and Hp2 have been reported, particularly in the susceptibility and protection against infectious (e.g., pulmonary tuberculosis, HIV, and malaria) and non-infectious (e.g., diabetes, cardiovascular diseases and obesity) diseases. Both high and low levels of Hp are indicative of clinical conditions: Hp plasma levels increase during infections, inflammation, and various malignant diseases, and decrease during malnutrition, hemolysis, hepatic disease, allergic reactions, and seizure disorders. Of note, the Hp:Hb complexes display heme-based reactivity; in fact, they bind several ferrous and ferric ligands, including O₂, CO, and NO, and display (pseudo-)enzymatic properties (e.g., NO and peroxynitrite detoxification). Here, genetic, biochemical, biomedical, and biotechnological aspects of Hp are reviewed.

Analysis of serum Haptoglobin using glycoproteomics and lectin immunoassay in liver diseases in Hepatitis B virus infection

BACKGROUND

Hepatocellular carcinoma (HCC) due to Hepatitis B viral (HBV) infection is a major cause in Asia-Pacific countries. Its early detection is of paramount importance using a marker having both sensitivity and specificity. The present study promises diagnostic and prognostic markers by the identification of site-specific glycoforms on Haptoglobin (Hp) using LC-MS/MS and lectin ELISA in liver diseased conditions in HBV infection.

METHODS

Three groups of patients: chronic, liver cirrhosis and HCC with HBV infection along with controls were enrolled. Hp was purified using affinity column chromatography and, peptide sequence, N-glycosylation site, glycan composition and glycoforms were identified using mass spectrometry. Quantitative lectin ELISA was used to measure levels of fucosylation on Hp in liver diseases due to HBV.

RESULTS

Hp levels were significantly lower in HCC when compared with Non-HCC cases (p < .05). Fucosylated glycoforms were significantly increased at site Asn184, Asn207 and Asn211 in liver diseased stages versus controls. A significant association was observed between the Fuc-Hp/Hp Elisa index and, advanced liver disease stages and controls using lectin Elisa (p < .001).

CONCLUSION

Quantitation of fucosylation levels on Hp protein using Lectin ELISA may be useful glycobiomarker either alone or in combination (AFP + DCP + FucHp; AUC = 0.94) in HBV HCC diagnosis in clinical practice.

Serum leucine-rich alpha-2-glycoprotein-1 with fucosylated triantennary N-glycan: a novel colorectal cancer marker

BACKGROUND

Carcinoembryonic antigen (CEA) and carbohydrate antigen (CA)19-9 are used in clinical practice as tumor markers to diagnose or monitor colorectal cancer (CRC) patients, However, their specificities and sensitivities are not ideal, and novel alternatives are needed. In this study, mass spectrometry was used to search for screening markers, focusing on glycan alterations of glycoproteins in the sera of CRC patients.

METHODS

Glycopeptides were prepared from serum glycoproteins separated from blood samples of 80 CRC patients and 50 healthy volunteers, and their levels were measured by liquid chromatography time-of flight mass spectrometry (LC-TOF-MS).

RESULTS

Leucine-rich alpha-2-glycoprotein-1 with fucosylated triantennary N-glycan (LRG-FTG) was identified as CRC marker after evaluating 30,000 candidate glycopeptide peaks. The average LRG-FTG level in CRC patients (1.25 ± 0.973 U/mL) was much higher than that in healthy volunteers (0.496 ± 0.433 U/mL, P < 10^- 10), and its sensitivity and specificity exceeded those of CA19-9. The combination of CEA and LRG-FTG showed a complementary effect and had better sensitivity (84%), specificity (90%), and AUC (0.91 by ROC analysis) than each marker alone or any other previously reported marker. LRG-FTG alone or combined with CEA also corresponded well with patient response to treatment.

CONCLUSIONS

We identified LRG-FTG as a new CRC marker, with a sensitivity and specificity exceeding CA19-9. The combination of LRG-FTG and CEA showed much higher sensitivity and specificity than each marker alone. Further validation beyond this initial exploratory cohort is warranted.

Characteristic glycopeptides associated with extreme human longevity identified through plasma glycoproteomics

BACKGROUND

Glycosylation is highly susceptible to changes of the physiological conditions, and accordingly, is a potential biomarker associated with several diseases and/or longevity. Semi-supercentenarians (SSCs; older than 105 years) are thought to be a model of human longevity. Thus, we performed glycoproteomics using plasma samples of SSCs, and identified proteins and conjugated N-glycans that are characteristic of extreme human longevity.

METHODS

Plasma proteins from Japanese semi-supercentenarians (SSCs, 106-109 years), aged controls (70-88 years), and young controls (20-38 years) were analysed by using lectin microarrays and liquid chromatography/mass spectrometry (LC/MS). Peak area ratios of glycopeptides to corresponding normalising peptides were subjected to orthogonal projections to latent structures discriminant analysis (OPLS-DA). Furthermore, plasma levels of clinical biomarkers were measured.

RESULTS

We found two lectins such as Phaseolus vulgaris, and Erythrina cristagalli (ECA), of which protein binding were characteristically increased in SSCs. Peak area ratios of ECA-enriched glycopeptides were successfully discriminated between SSCs and controls using OPLS-DA, and indicated that tri-antennary and sialylated N-glycans of haptoglobin at Asn207 and Asn211 sites were characterized in SSCs. Sialylated glycans of haptoglobin are a potential biomarker of several diseases, such as hepatocellular carcinoma, liver cirrhosis, and IgA-nephritis. However, the SSCs analysed here did not suffer from these diseases.

CONCLUSIONS

Tri-antennary and sialylated N-glycans on haptoglobin at the Asn207 and Asn211 sites were abundant in SSCs and characteristic of extreme human longevity.

GENERAL SIGNIFICANCE

We found abundant glycans in SSCs, which may be associated with human longevity.

Establishment of an antibody specific for cancer-associated haptoglobin: a possible implication of clinical investigation

We previously found that the serum level of fucosylated haptoglobin (Fuc-Hpt) was significantly increased in pancreatic cancer patients. To delineate the mechanism underlying this increase and develop a simple detection method, we set out to generate a monoclonal antibody (mAb) specific for Fuc-Hpt. After multiple screenings by enzyme-linked immunosorbent assay (ELISA), a 10-7G mAb was identified as being highly specific for Fuc-Hpt generated in a cell line as well as for Hpt derived from a pancreatic cancer patient. As a result from affinity chromatography with 10-7G mAb, followed by lectin blot and mass spectrometry analyses, it was found that 10-7G mAb predominantly recognized both Fuc-Hpt and prohaptoglobin (proHpt), which was also fucosylated. In immunohistochemical analyses, hepatocytes surrounding metastasized cancer cells were stained by the 10-7G mAb, but neither the original cancer cells themselves nor normal hepatocytes exhibited positive staining, suggesting that metastasized cancer cells promote Fuc-Hpt production in adjacent hepatocytes. Serum level of Fuc-Hpt determined with newly developed ELISA system using the 10-7G mAb, was increased in patients of pancreatic and colorectal cancer. Interestingly, dramatic increases in Fuc-Hpt levels were observed at the stage IV of colorectal cancer. These results indicate that the 10-7G mAb developed is a promising antibody which recognizes Fuc-Hpt and could be a useful diagnostic tool for detecting liver metastasis of cancer.

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

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

Lectins: an effective tool for screening of potential cancer biomarkers

In recent years, the use of lectins for screening of potential biomarkers has gained increased importance in cancer research, given the development in glycobiology that highlights altered structural changes of glycans in cancer associated processes. Lectins, having the properties of recognizing specific carbohydrate moieties of glycoconjugates, have become an effective tool for detection of new cancer biomarkers in complex bodily fluids and tissues. The specificity of lectins provides an added advantage of selecting peptides that are differently glycosylated and aberrantly expressed in cancer patients, many of which are not possibly detected using conventional methods because of their low abundance in bodily fluids. When coupled with mass spectrometry, research utilizing lectins, which are mainly from plants and fungi, has led to identification of numerous potential cancer biomarkers that may be used in the future. This article reviews lectin-based methods that are commonly adopted in cancer biomarker discovery research.

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

Based on our previous studies, differential analysis of N-glycan expression bound on serum haptoglobin reveals the quantitative variation on gastric cancer patients. In this prospective case-control study, we explore the clinically relevant glycan markers for gastric cancer diagnosis. Serum samples were collected from patients with gastric cancer (n = 44) and healthy control (n = 44). N-glycans alteration was monitored by intact analysis of Hp using liquid chromatography–mass spectrometry followed by immunoaffinity purification with the serum samples. Intensity and frequency markers were defined depending on the mass spectrometry data analysis. Multiple markers were found with high diagnostic efficacy. As intensity markers (I-marker), six markers were discovered with the AUC > 0.8. The high efficiency markers exhibited AUC of 0.93 with a specificity of 86% when the sensitivity was set to 95%. We additionally established frequency marker (f-marker) panels based on the tendency of high N-glycan expression. The AUC to conclude patients and control group were 0.82 and 0.79, respectively. This study suggested that N-glycan variation of serum haptoglobin were associated with patients with gastric cancer and might be a promising marker for the cancer screening.

Glycomic profiling of targeted serum haptoglobin for gastric cancer using nano LC/MS and LC/MS/MS

Gastric cancer has one of the highest cancer mortality rates worldwide, largely because of difficulties in early-stage detection. Aberrant glycosylation in serum proteins is associated with many human diseases including inflammation and various types of cancer. Serum-based global glycan profiling using mass spectrometry has been explored and has already led to several potential glycan markers for several disease states. However, localization of the aberrant glycosylation is desirable in order to improve the specificity and sensitivity for clinical use. Here, we combined protein-specific immunoaffinity purification, glycan release, and MS analysis to examine haptoglobin glycosylation of gastric cancer patients for glyco-markers. Age- and sex-matched 60 serum samples (30 cancer patients and 30 healthy controls) were used to profile and quantify haptoglobin N-glycans. A T-test based statistical analysis was performed to identify potential glyco-markers for gastric cancer. Interestingly, abundances of several tri- and tetra-antennary fucosylated N-glycans were increased in gastric cancer patients. Additionally, structural analysis via LC/MS/MS indicated that the fucosylated complex type N-glycans were primarily decorated with antenna fucose, which can be categorized as sialyl-Le^a or sialyl-Le^x type structures. This platform demonstrates quantitative, structure-specific profiling of haptoglobin glycosylation for the purposes of biomarker discovery for gastric cancer.

Changes in the expression of N- and O-glycopeptides in patients with colorectal cancer and hepatocellular carcinoma quantified by full-MS scan FT-ICR and multiple reaction monitoring

Alternations in the glycosylation of proteins have been described in connection with several cancers, including hepatocellular carcinoma (HCC) and colorectal cancer. Analytical tools, which use combination of liquid chromatography and mass spectrometry, allow precise and sensitive description of these changes. In this study, we use MRM and FT-ICR operating in full-MS scan, to determine ratios of intensities of specific glycopeptides in HCC, colorectal cancer, and liver metastasis of colorectal cancer. Haptoglobin, hemopexin and complement factor H were detected after albumin depletion and the N-linked glycopeptides with fucosylated glycans were compared with their non-fucosylated forms. In addition, sialylated forms of an O-linked glycopeptide of hemopexin were quantified in the same samples. We observe significant increase in fucosylation of all three proteins and increase in bi-sialylated O-glycopeptide of hemopexin in HCC of hepatitis C viral (HCV) etiology by both LC-MS methods. The results of the MRM and full-MS scan FT-ICR analyses provide comparable quantitative readouts in spite of chromatographic, mass spectrometric and data analysis differences. Our results suggest that both workflows allow adequate relative quantification of glycopeptides and suggest that HCC of HCV etiology differs in glycosylation from colorectal cancer and liver metastasis of colorectal cancer.

SIGNIFICANCE

The article compares N- and O-glycosylation of several serum proteins in different diseases by a fast and easy sample preparation procedure in combination with high resolution Fourier transform ion cyclotron resonance mass spectrometry. The results show successful glycopeptides relative quantification in a complex peptide mixture by the high resolution instrument and the detection of glycan differences between the different types of cancer diseases. The presented method is comparable to conventional targeted MRM approach but allows additional curation of the data.

Multifucosylated Alpha-1-acid Glycoprotein as a Novel Marker for Hepatocellular Carcinoma

High-sensitivity and -specificity diagnostic techniques to detect early-stage hepatocellular carcinoma (HCC) are in high demand. Screening with serum HCC markers, such as alpha-fetoprotein, is not practical because they possess poor sensitivity and specificity. As such, we focused on glycan alterations of glycoproteins found in patient sera in an attempt to discover novel HCC markers that are more specific and sensitive than current HCC markers. Sera from 42 HCC patients and 80 controls, composed of 27 chronic hepatitis B patients, 26 chronic hepatitis C patients, and 27 healthy volunteers, were analyzed in this study. Glycopeptides obtained from serum proteins by trypsin digestion were enriched by ultrafiltration and Aleuria aurantia lectin-based affinity chromatography, followed by analysis using liquid chromatography time-of-flight mass spectrometry. The data were analyzed by our newly developed software, which calculates peak intensities and positions (m/z and elution time), aligns all sample peaks, and integrates all data into a single table. HCC markers were extracted from more than 30 000 detected glycopeptide peaks by t test, mean-fold change, and ROC analyses. As a result, we revealed that alpha-1-acid glycoprotein with multifucosylated tetraantennary N-glycans was significantly elevated in HCC patients, whereas the single fucosylated derivative was not.

Multimodal Mass Spectrometry Imaging of N-Glycans and Proteins from the Same Tissue Section

On-tissue digestion matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) can be used to record spatially correlated molecular information from formalin-fixed, paraffin-embedded (FFPE) tissue sections. In this work, we present the in situ multimodal analysis of N-linked glycans and proteins from the same FFPE tissue section. The robustness and applicability of the method are demonstrated for several tumors, including epithelial and mesenchymal tumor types. Major analytical aspects, such as lateral diffusion of the analyte molecules and differences in measurement sensitivity due to the additional sample preparation methods, have been investigated for both N-glycans and proteolytic peptides. By combining the MSI approach with extract analysis, we were also able to assess which mass spectral peaks generated by MALDI-MSI could be assigned to unique N-glycan and peptide identities.

A novel inflammatory biomarker, GlycA, associates with disease activity in rheumatoid arthritis and cardio-metabolic risk in BMI-matched controls

Background

RA and CVD both have inflammation as part of the underlying biology. Our objective was to explore the relationships of GlycA, a measure of glycosylated acute phase proteins, with inflammation and cardiometabolic risk in RA, and explore whether these relationships were similar to those for persons without RA.

Methods

Plasma GlycA was determined for 50 individuals with mild-moderate RA disease activity and 39 controls matched for age, gender, and body mass index (BMI). Regression analyses were performed to assess relationships between GlycA and important markers of traditional inflammation and cardio-metabolic health: inflammatory cytokines, disease activity, measures of adiposity and insulin resistance.

Results

On average, RA activity was low (DAS-28 = 3.0 ± 1.4). Traditional inflammatory markers, ESR, hsCRP, IL-1β, IL-6, IL-18 and TNF-α were greater in RA versus controls (P < 0.05 for all). GlycA concentrations were significantly elevated in RA versus controls (P = 0.036). In RA, greater GlycA associated with disease activity (DAS-28; R_DAS-28 = 0.5) and inflammation (R_ESR = 0.7, R_hsCRP = 0.7, R_IL-6 = 0.3: P < 0.05 for all); in BMI-matched controls, these inflammatory associations were absent or weaker (hsCRP), but GlycA was related to IL-18 (R_hsCRP = 0.3, R_IL-18 = 0.4: P < 0.05). In RA, greater GlycA associated with more total abdominal adiposity and less muscle density (R_{abdominal-adiposity} = 0.3, R_{muscle-density} = −0.3, P < 0.05 for both). In BMI-matched controls, GlycA associated with more cardio-metabolic markers: BMI, waist circumference, adiposity measures and insulin resistance (R = 0.3-0.6, P < 0.05 for all).

Conclusions

GlycA provides an integrated measure of inflammation with contributions from traditional inflammatory markers and cardio-metabolic sources, dominated by inflammatory markers in persons with RA and cardio-metabolic factors in those without.

Insights on N-glycosylation of human haptoglobin and its association with cancers

Protein glycosylation is one of the most significant post-translation modifications and plays a critical role in various biological functions. Haptoglobin (Hp) is one of the acute-phase response proteins secreted by liver. Its glycosylation could be analyzed by many analytical techniques qualitatively and quantitatively. The glycosylation alterations of Hp are reported to be associated with different kinds of diseases. The main glycosylation alterations of Hp in cancer appear to be the presence of aberrantly fucosylated and sialylated structures as well as increased branching. In this mini review, we provided a brief overview of Hp structure and biological function, discussed its glycosylation alterations in different cancers, and described the existing technologies for analyzing glycosylation site and glycan of Hp. Given the importance of Hp glycosylation, its unknown and unclear biological complexity and significances, Hp glycosylation has become a major target in cancer research. Development of sensitive and specific detection of Hp glycosylation including large-scale validation may be significant steps forward to its clinical application.

Site-specific and linkage analyses of fucosylated N-glycans on haptoglobin in sera of patients with various types of cancer: possible implication for the differential diagnosis of cancer

Fucosylation is an important type of glycosylation involved in cancer, and fucosylated proteins could be employed as cancer biomarkers. Previously, we reported that fucosylated N-glycans on haptoglobin in the sera of patients with pancreatic cancer were increased by lectin-ELISA and mass spectrometry analyses. However, an increase in fucosylated haptoglobin has been reported in various types of cancer. To ascertain if characteristic fucosylation is observed in each cancer type, we undertook site-specific analyses of N-glycans on haptoglobin in the sera of patients with five types of operable gastroenterological cancer (esophageal, gastric, colon, gallbladder, pancreatic), a non-gastroenterological cancer (prostate cancer) and normal controls using ODS column LC-ESI MS. Haptoglobin has four potential glycosylation sites (Asn184, Asn207, Asn211, Asn241). In all cancer samples, monofucosylated N-glycans were significantly increased at all glycosylation sites. Moreover, difucosylated N-glycans were detected at Asn 184, Asn207 and Asn241 only in cancer samples. Remarkable differences in N-glycan structure among cancer types were not observed. We next analyzed N-glycan alditols released from haptoglobin using graphitized carbon column LC-ESI MS to identify the linkage of fucosylation. Lewis-type and core-type fucosylated N-glycans were increased in gastroenterological cancer samples, but only core-type fucosylated N-glycan was relatively increased in prostate cancer samples. In metastatic prostate cancer, Lewis-type fucosylated N-glycan was also increased. These data suggest that the original tissue/cell producing fucosylated haptoglobin is different in each cancer type and linkage of fucosylation might be a clue of primary lesion, thereby enabling a differential diagnosis between gastroenterological cancers and non-gastroenterological cancers.

Screening of enzymatic synthesis and expression of Lewis determinants in human colorectal carcinoma

BACKGROUND

Although colorectal carcinogenesis has been intensively studied, the published investigations do not provide a consistent description of how different carbohydrate determinants of colorectal epithelium are modified in colorectal cancer (CRC).

OBJECTIVE

This study is an attempt to characterize the terminal fucosylation steps responsible for the synthesis of mono- Le(a)/Le(x)- and difucosylated -Le(b)/Le(y)- Lewis antigens in healthy and tumour CRC tissue.

METHODS

An immunohistochemical study of Lewis antigens' expression was undertaken, along with screening of the fucosyltransferase (FT) activities involved in their synthesis, on healthy and tumour samples from 18 patients undergoing CRC.

RESULTS

Analysis of alpha(1,2/3/4)FT activities involved in the sequential fucosylation of cores 1 and 2 showed significant increases in tumour tissue. Expressed as microU/mg and control vs. tumour activity (pfrom Wilcoxon's test), the FT activities for Le(a)/Le(b) synthesis were: lacto-N-biose alpha(1,2)/alpha(1,4)FT, 65.4 ± 19.0 vs. 186 ± 35.1 (p< 0.005); lacto-N-fucopentaose 1 alpha(1,4)FT, 64.9 ± 11.9 vs. 125.4 ± 20.7 (p< 0.005); Le(a) alpha(1,2)FT, 56.2 ± 7.2 vs. 130.5 ± 15.6 (p< 0.001). Similarly, for Le(x)/Le(y) synthesis were: N-acetyllactosamine alpha(1,2)-/alpha(1,3)FT, 53.4 ± 12.2 vs. 108.1 ± 18.9 (p< 0.001); 2'-Fucosyl-N-acetyllactosamine alpha(1,3)FT, 61.3 ± 10.7 vs. 126.4 ± 22.9 (p< 0.001); 2'-Fucosyllactose alpha(1,3)FT, 38.9 ± 10.9 vs. 143.6 ± 28.9 (p< 0.001); 2'-Methyllactose alpha(1,3)FT, 30.9 ± 4.8 vs. 66.1 ± 8.1 (p< 0.005); and Le(x) alpha(1,2)FT, 54.3 ± 11.9 vs. 88.2 ± 14.4 (p< 0.001). Immunohistochemical Le(y) expression was increased (p< 0.01 according to Wilcoxon's test) in tumour tissue, with 84.6% of specimens being positive: 7.7% weak, 15.4% moderate and 61.5% high intensity.

CONCLUSIONS

Results suggest the activation of the biosynthesis pathways of mono- and difucosylated Lewis histo-blood antigens in tumour tissue from CRC patients, leading to the overexpression of Le(y), probably at the expense of Le(x).

Overexpression of α2,3sialyl T-antigen in breast cancer determined by miniaturized glycosyltransferase assays and confirmed using tissue microarray immunohistochemical analysis

Glycan structure alterations during cancer regulate disease progression and represent clinical biomarkers. The study determined the degree to which changes in glycosyltransferase activities during cancer can be related to aberrant cell-surface tumor associated carbohydrate structures (TACA). To this end, changes in sialyltransferase (sialylT), fucosyltransferase (fucT) and galactosyltransferase (galT) activity were measured in normal and tumor tissue using a miniaturized enzyme activity assay and synthetic glycoconjugates bearing terminal LacNAc Type-I (Galβ1-3GlcNAc), LacNAc Type-II (Galβ1-4GlcNAc), and mucin core-1/Type-III (Galβ1-3GalNAc) structures. These data were related to TACA using tissue microarrays containing 115 breast and 26 colon cancer specimen. The results show that primary human breast and colon tumors, but not adjacent normal tissue, express elevated β1,3GalT and α2,3SialylT activity that can form α2,3SialylatedType-IIIglycans (Siaα2-3Galβ1-3GalNAc). Prostate tumors did not exhibit such elevated enzymatic activities. α1,3/4FucT activity was higher in breast, but not in colon tissue. The enzymology based prediction of enhanced α2,3sialylated Type-III structures in breast tumors was verified using histochemical analysis of tissue sections and tissue microarrays. Here, the binding of two markers that recognize Galβ1-3GalNAc (peanut lectin and mAb A78-G/A7) was elevated in breast tumor, but not in normal control, only upon sialidase treatment. These antigens were also upregulated in colon tumors though to a lesser extent. α2,3sialylatedType-III expression correlated inversely with patient HER2 expression and breast metastatic potential. Overall, enzymology measurements of glycoT activity predict truncated O-glycan structures in tumors. High expression of the α2,3sialylated T-antigen O-glycans occur in breast tumors. A transformation from linear core-1 glycan to other epitopes may accompany metastasis.

Serum N-glycan profiles in patients with intraductal papillary mucinous neoplasms of the pancreas

BACKGROUND/OBJECTIVES

Diagnosing the invasiveness of intraductal papillary mucinous neoplasms (IPMNs) is difficult, especially by blood test. Alterations in serum glycan profiles have been reported for several cancers, but changes in serum glycan profiles have not been investigated in patients with IPMNs. The objectives of this study were to determine the serum N-glycan profile and to investigate its clinical utility in patients with IPMNs.

METHODS

We measured serum N-glycan profiles in 79 patients with IPMNs, including 13 invasive IPMNs, by performing comprehensive glycome analysis and assessed the relationship between N-glycan changes and clinical parameters.

RESULTS

Seventy glycans were identified and their expression profiles were significantly different depending on the cyst size, the presence of an enhancing solid component, and the histological grade of the IPMN. Nine glycans were highly expressed in patients with invasive IPMNs. The glycan m/z 3195, which is a fucosylated tri-antennary glycan, had the highest diagnostic value for distinguishing invasive IPMNs from non-invasive IPMNs (area under the receiver operating characteristic curve = 0.803). Multivariate analyses revealed high levels of m/z 3195 [odds ratio (OR), 20.5; 95% confidence interval (CI) 2.60-486.4] and the presence of enhancing solid components (OR, 35.8; 95% CI, 5.39-409.6) were significant risk factors for invasive IPMNs.

CONCLUSIONS

We performed a comprehensive evaluation of the changes in serum N-glycan profiles in patients with IPMNs for the first time. We determined that increased expression of fucosylated complex-type glycans, especially m/z 3195, is a potential marker for invasive IPMNs.

Establishment of a novel lectin-antibody ELISA system to determine core-fucosylated haptoglobin

BACKGROUND

Fucosylated haptoglobin (Fuc-Hpt) is a novel cancer biomarker that increases in various pathological conditions. We previously established a Fuc-Hpt lectin-antibody assay using Aleuria aurantia lectin (AAL), and applied this to diagnose several diseases, including various cancers. AAL recognizes both α1-3/1-4 and α1-6 fucosylation on N/O-linked glycans. These fucosylation types differ in biological function, and in regulation by different fucosyltransferases. Recently, we identified a novel lectin, Pholiota squarrosa lectin (PhoSL), which specifically recognizes α1-6 fucosylation (core-fucosylation).

METHODS

We developed a lectin-antibody ELISA kit using PhoSL to determine core-Fuc-Hpt levels in sera from colorectal or pancreatic cancer patients.

RESULTS

Serum levels of AAL-reactive Hpt are higher in pancreatic cancer patients, whereas those of PhoSL-reactive Hpt are higher in colorectal cancer patients. Mass spectrometry analyses of Hpt fucosylation levels were consistent with lectin-antibody ELISA results. Hpt-transfected colorectal cancer cell lines produced significant amounts of core-Fuc-Hpt, suggesting that colorectal cancer tissues produce core-Fuc-Hpt.

CONCLUSIONS

These differences in Fuc-Hpt patterns might depend on cancer cells and the surrounding cells, which produce Hpt.

Differentially expressed glycosylated patterns of α-1-antitrypsin as serum biomarkers for the diagnosis of lung cancer

Lung cancer is the most common malignancy worldwide. Thus, there is a critical need for diagnostic biomarkers with adequate sensitivity and specificity for lung cancer detection. Glycans in glycoproteins are significantly altered in cancer, and may serve as a tool for identifying potential diagnostic biomarkers. Recent studies have reported changes in α-1-antitrypsin (A1AT) glycosylation in lung cancer serum, tissue and cell lines. In this study, a lectin microarray was used to detect glycosylation changes in serum A1AT from patients with lung adenocarcinoma (ADC), squamous cell lung cancer, small-cell lung cancer (SCLC) and benign pulmonary diseases. Differentially expressed glycosylated patterns of A1AT were identified by lectin arrays and were confirmed by lectin-based enzyme-linked immunosorbent assay (ELISA). We found that galactosylated A1AT could distinguish non-small-cell lung cancer (NSCLC) from benign pulmonary diseases (AUC = 0.834); fucosylated A1AT showed exceptional capability in distinguishing ADC from benign diseases (AUC = 0.919) or other lung cancer subtypes (AUC = 0.844), and A1AT containing poly-LacNAc could detect SCLC from benign diseases (AUC = 0.905) or NSCLC (AUC = 0.707). The present study indicates that glycosylated patterns of A1AT may serve as potential biomarkers for detection of lung cancer. Further studies in larger sample sizes are necessary to validate the clinical utility of these markers.

The role of glycosylation in IBD

A number of genetic and immunological studies give impetus for investigating the role of glycosylation in IBD. Experimental mouse models have helped to delineate the role of glycosylation in intestinal mucins and to explore the putative pathogenic role of glycosylation in colitis. These experiments have been extended to human studies investigating the glycosylation patterns of intestinal mucins as well as levels of glycans of serum glycoproteins and expression of glycan receptors. These early human studies have generated interesting hypotheses regarding the pathogenic role of glycans in IBD, but have generally been restricted to fairly small underpowered studies. Decreased glycosylation has been observed in the intestinal mucus of patients with IBD, suggesting that a defective inner mucus layer might lead to increased bacterial contact with the epithelium, potentially triggering inflammation. In sera, decreased galactosylation of IgG has been suggested as a diagnostic marker for IBD. Advances in glycoprofiling technology make it technically feasible and affordable to perform high-throughput glycan pattern analyses and to build on previous work investigating a much wider range of glycan parameters in large numbers of patients.

Pinellia pedatisecta agglutinin-based lectin blot analysis distinguishes between glycosylation patterns in various cancer cell lines

The analysis of altered glycosylation patterns may provide biomarkers for various types of cancer. The present study developed a Pinellia pedatisecta agglutinin (PPA)-based lectin blot analysis technique, which was used to analyze the glycosylation patterns in various types of cancer cells. Results showed that a typical band located between 47 and 85 kDa was obtained in the HL60 leukemia cells, whereas three typical bands located between 20 and 47 kDa were observed in the Kasumi-1 leukemia cells. For the PLC, BEL-7404, Huh7 and H1299 solid tumor cell lines, different band patterns were detected, with bands typically located between 55 and 100 kDa. The findings of the present study show that PPA-based lectin blot analysis is capable of distinguishing between glycosylation patterns in leukemia and solid tumor cell lines. The glycofiles detected using PPA-based lectin blot analysis may provide a ‘glycosylation fingerprint’ for a variety of cancer cells, which may be valuable for cancer prognosis and diagnosis.

Mass spectrometry-based analysis of glycoproteins and its clinical applications in cancer biomarker discovery

Glycosylation is one of the most important posttranslational modifications of proteins and plays essential roles in various biological processes. Aberration in the glycan moieties of glycoproteins is associated with many diseases. It is especially critical to develop the rapid and sensitive methods for analysis of aberrant glycoproteins associated with diseases. Mass spectrometry (MS) has become a powerful tool for glycoprotein analysis. Especially, tandem mass spectrometry can provide highly informative fragments for structural identification of glycoproteins. This review provides an overview of the development of MS technologies and their applications in identification of abnormal glycoproteins and glycans in human serum to screen cancer biomarkers in recent years.

Identification of a specific haptoglobin C-terminal fragment in arthritic synovial fluid and its effect on interleukin-6 expression

Haptoglobin (Hp), a major acute-phase plasma protein, has been found in arthritic synovial fluid (SF). However, the function and structural modifications of Hp in arthritic SF are unknown. To investigate in vivo generation of modified Hp associated with inflammatory disease, we examined a new Hp isoform in SF from patients with rheumatoid arthritis (RA). Specific Hp fragments of 28 000 and 15 000 molecular weight were identified in SF of patients with RA, and the two polypeptides were presumed to be fragments of the Hp β-chain (43 000 MW) produced by cleavage with plasmin. The 15 000 MW fragment, which is a C-terminal region of Hp, was observed at higher frequency and levels in RA than in osteoarthritis. Plasmin activity was also higher in SF of RA patients. A recombinant 15 000 MW Hp fragment up-regulated interlukin-6 expression in monocytic cells. These findings indicate that the C-terminal Hp fragment is generated by plasmin in local inflammatory environments and acts as an inflammatory mediator. They further suggest that a specific Hp fragment might be applied as a novel biomarker for the diagnosis and prognosis of inflammatory diseases such as RA.

Trapping of human hemoglobin by haptoglobin: molecular mechanisms and clinical applications

SIGNIFICANCE

Haptoglobin (Hp) is an abundant plasma protein controlling the fate of hemoglobin (Hb) released from red blood cells after intravascular hemolysis. The complex formed between Hp and Hb is extraordinary strong, and once formed, this protein-protein association can be considered irreversible.

RECENT ADVANCES

A model of the Hp-Hb complex has been generated and the first steps toward understanding the mechanism behind the shielding effects of Hp have been taken. The clinical potential of the complex for modulating inflammatory reactions and for functioning as an Hb-based oxygen carrier have been described.

CRITICAL ISSUES

The three-dimensional structure of the Hp-Hb complex is unknown. Moreover, Hp is not a homogeneous protein. There are two common alleles at the Hp genetic locus denoted Hp1 and Hp2, which when analyzed on the protein levels result in differences between their physiological behavior, particularly in their shielding against Hb-driven oxidative stress. Additional cysteine residues on the α-subunit allow Hp2 to form a variety of native multimers, which influence the biophysical and biological properties of Hp. The multimeric conformations, in turn, also modulate the glycosylation patterns of Hp by steric hindrance.

FUTURE DIRECTIONS

A detailed analysis of the influence of Hp glycosylation will be instrumental to generate a deeper understanding of its biological function. Several pathological conditions also modify the glycan compositions allowing Hp to be potentially used as a marker protein for these disorders.

B4GALT family mediates the multidrug resistance of human leukemia cells by regulating the hedgehog pathway and the expression of p-glycoprotein and multidrug resistance-associated protein 1

β-1, 4-Galactosyltransferase gene (B4GALT) family consists of seven members, which encode corresponding enzymes known as type II membrane-bound glycoproteins. These enzymes catalyze the biosynthesis of different glycoconjugates and saccharide structures, and have been recognized to be involved in various diseases. In this study, we sought to determine the expressional profiles of B4GALT family in four pairs of parental and chemoresistant human leukemia cell lines and in bone marrow mononuclear cells (BMMC) of leukemia patients with multidrug resistance (MDR). The results revealed that B4GALT1 and B4GALT5 were highly expressed in four MDR cells and patients, altered levels of B4GALT1 and B4GALT5 were responsible for changed drug-resistant phenotype of HL60 and HL60/adriamycin-resistant cells. Further data showed that manipulation of these two gene expression led to increased or decreased activity of hedgehog (Hh) signaling and proportionally mutative expression of p-glycoprotein (P-gp) and MDR-associated protein 1 (MRP1) that are both known to be related to MDR. Thus, we propose that B4GALT1 and B4GALT5, two members of B4GALT gene family, are involved in the development of MDR of human leukemia cells, probably by regulating the activity of Hh signaling and the expression of P-gp and MRP1.

Transforming growth factor beta receptor 2 (TGFBR2) changes sialylation in the microsatellite unstable (MSI) Colorectal cancer cell line HCT116

Aberrant glycosylation is a common feature of many malignancies including colorectal cancers (CRCs). About 15% of CRC show the microsatellite instability (MSI) phenotype that is associated with a high frequency of biallelic frameshift mutations in the A10 coding mononucleotide microsatellite of the transforming growth factor beta receptor 2 (TGFBR2) gene. If and how impaired TGFBR2 signaling in MSI CRC cells affects cell surface glycan pattern is largely unexplored. Here, we used the TGFBR2-deficient MSI colon carcinoma cell line HCT116 as a model system. Stable clones conferring doxycycline (dox)-inducible expression of a single copy wildtype TGFBR2 transgene were generated by recombinase-mediated cassette exchange (RMCE). In two independent clones, dox-inducible expression of wildtype TGFBR2 protein and reconstitution of its signaling function was shown. Metabolic labeling experiments using the tritiated sialic acid precursor N-acetyl-D-mannosamine (ManNAc) revealed a significant decline (∼30%) of its incorporation into newly synthesized sialoglycoproteins in a TGFBR2-dependent manner. In particular, we detected a significant decrease of sialylated ß1-integrin upon reconstituted TGFBR2 signaling which did not influence ß1-integrin protein turnover. Notably, TGFBR2 reconstitution did not affect the transcript levels of any of the known human sialyltransferases when examined by real-time RT- PCR analysis. These results suggest that reconstituted TGFBR2 signaling in an isogenic MSI cell line model system can modulate sialylation of cell surface proteins like ß1-integrin. Moreover, our model system will be suitable to uncover the underlying molecular mechanisms of altered MSI tumor glycobiology.

Quantitative liquid chromatography-mass spectrometry-multiple reaction monitoring (LC-MS-MRM) analysis of site-specific glycoforms of haptoglobin in liver disease

Development of liver disease is associated with the appearance of multiply fucosylated glycoforms of haptoglobin. To analyze the disease-related haptoglobin glycoforms in liver cirrhosis and hepatocellular carcinoma, we have optimized an LC-MS-multiple reaction monitoring (MRM) workflow for glycopeptide quantification. The final quantitative analysis included 24 site-specific glycoforms generated by treatment of a tryptic digest of haptoglobin with α(2-3,6,8)-neuraminidase and β(1-4)-galactosidase. The combination of LC-MS-MRM with exoglycosidase digests allowed resolution of isobaric glycoforms of the haptoglobin-T3 glycopeptide for quantification of the multiply fucosylated Lewis Y-containing glycoforms we have identified in the context of liver disease. Fourteen multiply fucosylated glycoforms of the 20 examined increased significantly in the liver disease group compared with healthy controls with an average 5-fold increase in intensity (p < 0.05). At the same time, two tri-antennary glycoforms without fucoses did not increase in the liver disease group, and two tetra-antennary glycoforms without fucoses showed a marginal increase (at most 40%) in intensity. Our analysis of 30 individual patient samples (10 healthy controls, 10 cirrhosis patients, and 10 hepatocellular carcinoma patients) showed that these glycoforms were substantially increased in a small subgroup of liver disease patients but did not significantly differ between the groups of hepatocellular carcinoma and cirrhosis patients. The tri- and tetra-antennary singly fucosylated glycoforms are associated with a MELD score and low platelet counts (p < 0.05). The exoglycosidase-assisted LC-MS-MRM workflow, optimized for the quantification of fucosylated glycoforms of haptoglobin, can be used for quantification of these glycoforms on other glycopeptides with appropriate analytical behavior.

Differences between the glycosylation patterns of haptoglobin isolated from skin scales and plasma of psoriatic patients

Improved diagnosis of psoriasis, by new biomarkers, is required for evaluating the progression rate of the disease and the response to treatment. Haptoglobin (Hpt), a glycoprotein secreted by hepatocytes and other types of cells including keratinocytes, was found with glycan changes in psoriasis and other diseases. We previously reported that Hpt isolated from plasma of psoriatic patients is more fucosylated than Hpt of healthy subjects. The aim of this study was to compare the glycosylation pattern of Hpt isolated from skin scales or plasma of patients with psoriasis with that of Hpt from cornified epidermal layer or plasma of healthy subjects. High performance liquid chromatography analysis of the glycans isolated from the protein backbone revealed that glycan patterns from skin and plasma of patients were similar, and mostly displayed quantitative rather than qualitative differences from normal pattern. Biotin-labeled lectins were used to evaluate quantitative differences in the glycoforms of Hpt from plasma and psoriatic skin scales. Hpt from skin and plasma of patients showed more fucosylated and branched glycans than Hpt from plasma of healthy subjects. Tryptic glycopeptides of Hpt were also analyzed by mass spectrometry, and a decreased amount of sialylated glycan chains was found in glycopeptides of skin Hpt, as compared with Hpt from plasma. High levels of glycans with fucosylated and tetra-antennary chains were detected on the peptide NLFLNHSENATAK from Hpt of psoriatic patients. Our data demonstrate that specific changes in glycan structures of Hpt, such as enhanced glycan branching and fucose content, are associated with psoriasis, and that differences between circulating and skin Hpt do exist. A lower extent of glycan fucosylation and branching was found in Hpt from plasma of patients in disease remission. Altered glycoforms might reflect changes of Hpt function in the skin, and could be used as markers of the disease.

Semi-automated identification of N-Glycopeptides by hydrophilic interaction chromatography, nano-reverse-phase LC-MS/MS, and glycan database search

Glycoproteins fulfill many indispensable biological functions, and changes in protein glycosylation have been observed in various diseases. Improved analytical methods are needed to allow a complete characterization of this complex and common post-translational modification. In this study, we present a workflow for the analysis of the microheterogeneity of N-glycoproteins that couples hydrophilic interaction and nanoreverse-phase C18 chromatography to tandem QTOF mass spectrometric analysis. A glycan database search program, GlycoPeptideSearch, was developed to match N-glycopeptide MS/MS spectra with the glycopeptides comprised of a glycan drawn from the GlycomeDB glycan structure database and a peptide from a user-specified set of potentially glycosylated peptides. Application of the workflow to human haptoglobin and hemopexin, two microheterogeneous N-glycoproteins, identified a total of 57 distinct site-specific glycoforms in the case of haptoglobin and 14 site-specific glycoforms of hemopexin. Using glycan oxonium ions and peptide-characteristic glycopeptide fragment ions and by collapsing topologically redundant glycans, the search software was able to make unique N-glycopeptide assignments for 51% of assigned spectra, with the remaining assignments primarily representing isobaric topological rearrangements. The optimized workflow, coupled with GlycoPeptideSearch, is expected to make high-throughput semiautomated glycopeptide identification feasible for a wide range of users.