Mass Spectrometric N-Glycan Analysis of Haptoglobin from Patient Serum Samples Using a 96-Well Plate Format

High sensitivity profiling of N-glycans from mouse serum using fluorescent imidazolium tags by HILIC electrospray ionisation spectrometry

N-linked glycosylation is a ubiquitous protein post-translational modification in which aberrant glycan biosynthesis has been linked to severe conditions like cancer. Accurate qualitative and quantitative analysis of N-glycans are crucial for investigating their physiological functions. Owing to the intrinsic absence of chromophores and high polarity of the glycans, current detection methods are restricted to liquid chromatography and mass spectrometry. Herein, we describe three new imidazolium-based glycan tags: 2'GITag, 3'GITag, and 4'GITag, that significantly improve both the limit of detection and limit of quantification of derivatized oligosaccharides, in terms of fluorescence intensity and ionisation efficiency. Our top-performing derivatisation agent, 4'GITag, shifted the detection sensitivity range from high femtomole to sub-femtomole levels in ESI-MS compared to traditional glycan label, 2AB, enabling the identification of 24 N-glycans in mouse serum, including those bearing sialic acids. Additionally, 4'GITag stabilized Na-salt forms of sialic acids, simplifying the simultaneous analysis of neutral and negative charged N-glycans significantly, avoiding the need for complex derivatisation procedures typically required for the detection of sialylated species. Overall, the favorable performance of imidazolium tags in the derivatisation and sensitive profiling of glycans has the potential for labeling tissue or live cells to explore disease biomarkers and for developing new targeted therapeutic strategies.

Decoding the glycoproteome: a new frontier for biomarker discovery in cancer

Cancer early detection and treatment response prediction continue to pose significant challenges. Cancer liquid biopsies focusing on detecting circulating tumor cells (CTCs) and DNA (ctDNA) have shown enormous potential due to their non-invasive nature and the implications in precision cancer management. Recently, liquid biopsy has been further expanded to profile glycoproteins, which are the products of post-translational modifications of proteins and play key roles in both normal and pathological processes, including cancers. The advancements in chemical and mass spectrometry-based technologies and artificial intelligence-based platforms have enabled extensive studies of cancer and organ-specific changes in glycans and glycoproteins through glycomics and glycoproteomics. Glycoproteomic analysis has emerged as a promising tool for biomarker discovery and development in early detection of cancers and prediction of treatment efficacy including response to immunotherapies. These biomarkers could play a crucial role in aiding in early intervention and personalized therapy decisions. In this review, we summarize the significant advance in cancer glycoproteomic biomarker studies and the promise and challenges in integration into clinical practice to improve cancer patient care.

Systematic review: Glycomics as diagnostic markers for hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is the most prevalent primary liver cancer with one of the highest cancer-related mortality rates worldwide. Early diagnosis is crucial for improving the therapeutic options and reducing the disease-related mortality.

AIM

To investigate serum N-glycomics as diagnostic markers for HCC.

METHODS

We performed a comprehensive search in PubMed, EMBASE, Web of Science and Scopus through August 17, 2023. Eligible studies assessed the potential use of serum N-glycomics as diagnostic biomarkers for HCC. Study selection, data extraction and quality assessment were performed by two independent reviewers.

RESULTS

Of the 48 articles included, 11 evaluated the utility of N-glycomics for the diagnosis of HCC in whole serum while the remaining articles focused on specific protein glycoforms or protein levels. Of these specific proteins, haptoglobin, alpha-fetoprotein (AFP), kininogen (Kin), α-1-antitrypsin and Golgi protein 73 (GP73) were the most frequently studied. Increased levels of fucosylation and branching presented as the most prevalent post-translational modifications of glycoproteins in patients with HCC compared to controls. Notably, glycomics-based biomarkers may provide a clinical benefit for the diagnosis of early HCC, as several algorithms achieved AUCs between 0.92-0.97. However, these were based on single studies with limited sample sizes and should therefore be validated.

CONCLUSIONS

Alterations in serum N-glycomics, characterised by increased levels of fucosylation and branching, have potential as diagnostic biomarkers for HCC. Optimisation of study design, patient selection and analysing techniques are needed before clinical implementation will be possible.

Discovery of a haptoglobin glycopeptides biomarker panel for early diagnosis of hepatocellular carcinoma

Background

There is a need for new serum biomarkers for early detection of hepatocellular carcinoma (HCC). Haptoglobin (Hp) N-glycosylation is altered in HCC, but the diagnostic value of site-specific Hp glycobiomarkers is rarely reported. We aimed to determine the site-specific glycosylation profile of Hp for early-stage HCC diagnosis.

Method

Hp glycosylation was analyzed in the plasma of patients with liver diseases (n=57; controls), early-stage HCC (n=50) and late-stage HCC (n=32). Hp phenotype was determined by immunoblotting. Hp was immunoisolated and digested into peptides. N-glycopeptides were identified and quantified using liquid chromatography-mass spectrometry. Cohort samples were compared using Wilcoxon rank-sum (Mann-Whitney U) tests. Diagnostic performance was assessed using receiver operating characteristic (ROC) curves and area under curve (AUC).

Results

Significantly higher fucosylation, branching and sialylation of Hp glycans, and expression of high-mannose glycans, was observed as disease progressed from cirrhosis to early- and late-stage HCC. Several glycopeptides demonstrated high values for early diagnosis of HCC, with an AUC of 93% (n=1), >80% (n=3), >75% (n=13) and >70% (n=11), compared with alpha-fetoprotein (AFP; AUC of 79%). The diagnostic performance of the identified biomarkers was only slightly affected by Hp phenotype.

Conclusion

We identified a panel of Hp glycopeptides that are significantly differentially regulated in early- and late-stage HCC. Some glycobiomarkers exceeded the diagnostic value of AFP (the most commonly used biomarker for HCC diagnosis). Our findings provide evidence that glycobiomarkers can be effective in the diagnosis of early HCC - individually, as a panel of glycopeptides or combined with conventional serological biomarkers.

Disease-Specific Haptoglobin N-Glycosylation in Inflammatory Disorders between Cancers and Benign Diseases of 3 Types of Female Internal Genital Organs

BACKGROUND

N-glycosylation of the haptoglobin is closely related to pathological states. This study aims to evaluate the association of glycosylation of disease-specific Hp (DSHp) β chain with different pathological states of the cervix, uterus, and ovary to explore differences in their inflammatory responses and to screen potential biomarkers to distinguish cancer from benign diseases.

METHODS

DSHp-β chains of 1956 patients with cancers and benign diseases located in the cervix, uterus, and ovary organs were separated from serum immunoinflammatory-related protein complexes (IIRPCs). The N-glycopeptides from DSHp-β chains were detected using mass spectrometry, followed by an analysis of machine learning algorithms.

RESULTS

55 N-glycopeptides at N207/N211, 19 at N241, and 21 at N184 glycosylation sites of DSHp for each sample were identified. Fucosylation and sialylation of DSHp in cervix, uterus, and ovary cancer were significantly increased compared to their corresponding benign diseases (p < 0.001). The cervix diagnostic model, a combination of G2N3F, G4NFS, G7N2F2S5, GS-N&GS-N, G2N2&G4N3FS, G7N2F2S5, G2S2&G-N, and GN2F&G2F at N207/N211 sites, G3NFS2 and G3NFS at N241site, G9N2S, G6N3F6, G4N3F5S, G4N3F4S2, and G6N3F4S at N184 site), has shown a good diagnostic capability to distinguish cancer from benign diseases, with the area under curve (AUC) of 0.912. The uterus diagnostic model including G4NFS, G2S2&G2S2, G3N2S2, GG5N2F5, G2&G3NFS, and G5N2F3S3 at N207/N211 sites, and G2NF3S2 at N184 site, with an AUC of 0.731. The ovary diagnostic model including G2N3F, GF2S-N &G2F3S2, G2S&G2, and G2S&G3NS at N207/N211 sites; G2S and G3NFS at N241 site, G6N3F4S at N184 site, with an AUC of 0.747.

CONCLUSIONS

These findings provide insights into differences in organ-specific inflammatory responses of DSHp for different pathological states among the organs of the cervix, uterus, and ovary.

Analysis of N-linked Glycan Alterations in Tissue and Serum Reveals Promising Biomarkers for Intrahepatic Cholangiocarcinoma

There is an urgent need for the identification of reliable prognostic biomarkers for patients with intrahepatic cholangiocarcinoma (iCCA) and alterations in N-glycosylation have demonstrated an immense potential to be used as diagnostic strategies for many cancers, including hepatocellular carcinoma (HCC). N-glycosylation is one of the most common post-translational modifications known to be altered based on the status of the cell. N-glycan structures on glycoproteins can be modified based on the addition or removal of specific N-glycan residues, some of which have been linked to liver diseases. However, little is known concerning the N-glycan alterations that are associated with iCCA. We characterized the N-glycan modifications quantitatively and qualitatively in three cohorts, consisting of two tissue cohorts: a discovery cohort (n = 104 cases) and a validation cohort (n = 75), and one independent serum cohort consisting of patients with iCCA, HCC, or benign chronic liver disease (n = 67). N-glycan analysis in situ was correlated to tumor regions annotated on histopathology and revealed that bisected fucosylated N-glycan structures were specific to iCCA tumor regions. These same N-glycan modifications were significantly upregulated in iCCA tissue and serum relative to HCC and bile duct disease, including primary sclerosing cholangitis (PSC) (P < 0.0001). N-glycan modifications identified in iCCA tissue and serum were used to generate an algorithm that could be used as a biomarker of iCCA. We demonstrate that this biomarker algorithm quadrupled the sensitivity (at 90% specificity) of iCCA detection as compared with carbohydrate antigen 19-9, the current "gold standard" biomarker of CCA.

Significance

This work elucidates the N-glycan alterations that occur directly in iCCA tissue and utilizes this information to discover serum biomarkers that can be used for the noninvasive detection of iCCA.

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.

Glycopeptides with Sialyl Lewis Antigen in Serum Haptoglobin as Candidate Biomarkers for Nonalcoholic Steatohepatitis Hepatocellular Carcinoma Using a Higher-Energy Collision-Induced Dissociation Parallel Reaction Monitoring-Mass Spectrometry Method

Nonalcoholic steatohepatitis (NASH) is the fastest growing cause of hepatocellular carcinoma (HCC) in the United States. Changes in N-glycosylation on specific glycosites of serum proteins have been investigated as potential markers for the early detection of NASH-related HCC. Herein, we report a glycopeptide with a Sialyl Lewis structure derived from serum haptoglobin (Hp) as a potential marker for NASH related HCCs among 95 patients with NASH, including 46 cirrhosis, 32 early-stage HCC, and 17 late-stage HCC. Hp immuno-isolated from patient serum was analyzed using LC-HCD-PRM-MS/MS followed by data analysis via Skyline software. Two glycopeptides involving site N184 and four glycopeptides involving site N241 were significantly changed in patients with HCC vs NASH cirrhosis (P < 0.05). The two-marker panel using N-glycopeptide N241_A4G4F2S4 showed the best performance for HCC detection when combined with α-fetoprotein (AFP), with an improved estimated area under the curve (AUC) = 0.898 (95% CI: 0.835, 0.951), compared to the AUC of 0.790(95% CI, 0.697 0.872) using AFP alone (P = 0.048). At 90% specificity, the combination of N241_A4G4F2S4 + AFP had an improved sensitivity of 63.3%, compared to the sensitivity of 52.3% using AFP alone. When using three markers, the panel of AFP + N241_A2G2F1S2 + N241_A4G4F2S4 yielded an estimated AUC of 0.928 (95% CI: 0.877, 0.970). Our findings indicated that N241_A4G4F2S4 may play an important role in distinguishing HCC from NASH cirrhosis.

Serum Glycoprotein Markers in Nonalcoholic Steatohepatitis and Hepatocellular Carcinoma

Fatty liver disease progresses through stages of fat accumulation and inflammation to nonalcoholic steatohepatitis (NASH), fibrosis and cirrhosis, and eventually hepatocellular carcinoma (HCC). Currently available diagnostic tools for HCC lack sensitivity and specificity. In this study, we investigated the use of circulating serum glycoproteins to identify a panel of potential prognostic markers that may be indicative of progression from the healthy state to NASH and further to HCC. Serum samples were processed and analyzed using a novel high-throughput glycoproteomics platform. Our initial dataset contained healthy, NASH, and HCC serum samples. We analyzed 413 glycopeptides, representing 57 abundant serum proteins, and compared among the three phenotypes. We studied the normalized abundance of common glycoforms and found 40 glycopeptides with statistically significant differences in abundances in NASH and HCC compared to controls. Summary level relative abundances of core-fucosylated, sialylated, and branched glycans containing glycopeptides were higher in NASH and HCC as compared to controls. We replicated some of our findings in an independent set of samples of individuals with benign liver conditions and HCC. Our results may be of value in the management of liver diseases. Data generated in this work can be downloaded from MassIVE (https://massive.ucsd.edu) with identifier MSV000088809.

Column-based Technology for CD9-HPLC Immunoaffinity Isolation of Serum Extracellular Vesicles

Serum-derived extracellular vesicles (EVs) are a promising source of biomarkers; however, major challenges in EV separation and proteomic profiling remain for isolating EVs from a small amount, that is, on the microliter scale, of human serum while minimizing the contamination of blood proteins and lipoprotein particles coeluting in EV preparations. Herein we have developed a column-based CD9-antibody-immobilized high-performance liquid chromatography immunoaffinity chromatography(CD9-HPLC-IAC) technology for EV isolation from a microliter scale of serum for downstream proteomic analysis. The CD9-HPLC-IAC method achieved EV isolation from 40 μL of serum in 30 min with a yield of 8.0 × 10⁹ EVs, where EVs were further processed with a postcolumn cleaning step using the 50 kDa molecular weight cut-off filter for the buffer exchange, concentration, and reduction of potentially coeluting serum proteins. In total, 482 proteins were identified in EVs by using liquid chromatography tandem mass spectrometry, including the common exosomal markers such as CD63, CD81, CD82, Alix, and TSG101. The statistical analysis of EV protein content showed that the top 10 serum proteins in EVs were significantly decreased by using the CD9-HPLC-IAC method compared with the use of ultracentrifugation (p = 0.001) and size exclusion chromatography (p = 0.009), and apolipoproteins were significantly reduced 4.8-fold compared with the SEC method (p < 0.001). The result demonstrates the potential of the CD9-HPLC-IAC method for the efficient isolation and proteomic characterization of EVs from a microscale volume of serum.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Input of serum haptoglobin fucosylation profile in the diagnosis of hepatocellular carcinoma in patients with non-cirrhotic liver disease

BACKGROUND

Haptoglobin bifucosylated tetra-antennary glycan have been identified in patients with early stage hepatocellular carcinoma, but its specificity according to the presence or not of cirrhosis has never been assessed. The aims of this study were to determine if haptoglobin bifucosylated tetra-antennary glycan (1) could be a marker of HCC in patients without cirrhosis; (2) could increase the performance of standard alpha-fetoprotein (AFP) or recent blood tests for HCC detection, i.e., lectin-reactive alpha-fetoprotein (AFP-L3), des-gamma-carboxy prothrombin (DCP) and Liver-Cancer-Risk-test (LCR1-test).

METHODS

We retrospectively selected patients, 102 with HCC (21 without cirrhosis), matched by stages with 140 controls without HCC (81 without cirrhosis). Haptoglobin fucosylation was assessed by MALDI-TOF. LCR-glycan algorithm was constructed combining components of the LCR-1 test (haptoglobin, gammaglutamyl-transpeptidase, apolipoproteinA1, alpha-2-macroglobulin) with AFP, AFP-L3, DCP and haptoglobin bifucosylated tetra-antennary glycan.

RESULTS

In 102 patients without cirrhosis (21 HCC and 81 controls), the intention-to-diagnose analyses showed that haptoglobin bifucosylated tetra-antennary glycan alone had a sensitivity of 71% (15/21;95%CI 50-86), significantly better (P=0.02) than standard AFP (43%;9/21;95%CI 24-63), and a specificity of 96% (78/81;95% 90-99). The sensitivity of LCR-glycan, in patients without cirrhosis, was 86% (18/21; 95%CI 63-95) significantly better (P=0.001) than standard AFP (43%; 9/21; 95%CI 24-63), with an AUROC of 0.943 (95%CI 0.806-0.98) compared to 0.811 (95%CI 0.630-0.908) for AFP (P=0.06).

CONCLUSION

Haptoglobin bifucosylated tetra-antennary glycan is associated with the presence of HCC in patients with chronic liver disease including those without cirrhosis. Its combination with existing HCC biomarkers could improve the performance of standard AFP for HCC detection.

Glycopeptide Biomarkers in Serum Haptoglobin for Hepatocellular Carcinoma Detection in Patients with Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is rising in prevalence in the United States and is a growing cause of hepatocellular carcinomas (HCCs). Site-specific glycan heterogeneity on glycoproteins has been shown as a potential diagnostic biomarker for HCC. Herein, we have performed a comprehensive screening of site-specific N-glycopeptides in serum haptoglobin (Hp), a reporter molecule for aberrant glycosylation in HCC, to characterize glycopeptide markers for NASH-related HCCs. In total, 70 NASH patients (22 early HCC, 15 advanced HCC, and 33 cirrhosis cases) were analyzed, with Hp purified from 20 μL of serum in each patient, and 140 sets of mass spectrometry (MS) data were collected using liquid chromatography coupled with electron-transfer high-energy collisional dissociation tandem MS (LC-EThcD-MS/MS) for quantitative analysis on a novel software platform, Byos. Differential quantitation analysis revealed that five N-glycopeptides at sites N184 and N241 were significantly elevated during the progression from NASH cirrhosis to HCC (p < 0.05). Receiver operating characteristic (ROC) curve analysis demonstrated that the N-glycopeptides at sites N184 and N241 bearing a monofucosylated triantennary glycan A3G3F1S3 had the best diagnostic performance in detection of early NASH HCC, area under the curve (AUC) = 0.733 and 0.775, respectively, whereas α-fetoprotein (AFP) had an AUC of 0.692. When combined with AFP, the two panels improved the sensitivity for early NASH HCC from 59% (AFP alone) to 73% while maintaining a specificity of 70%, based on the optimal cutoff. Two-dimensional (2-D) scatter plots of the AFP value and N-glycopeptides showed that these N-glycopeptide markers detected 58% of AFP-negative HCC patients as distinct from cirrhosis. These site-specific N-glycopeptides could serve as potential markers for early detection of HCC in patients with NASH-related cirrhosis.

Expression of genes that control core fucosylation in hepatocellular carcinoma: Systematic review

BACKGROUND

Changes in N-linked glycosylation have been observed in the circulation of individuals with hepatocellular carcinoma. In particular, an elevation in the level of core fucosylation has been observed. However, the mechanisms through which core fucose is increased are not well understood. We hypothesized that a review of the literature and related bioinformatic review regarding six genes known to be involved in the attachment of core fucosylation, the synthesis of the fucosylation substrate guanosine diphosphate (GDP)-fucose, or the transport of the substrate into the Golgi might offer mechanistic insight into the regulation of core fucose levels.

AIM

To survey the literature to capture the involvement of genes regulating core N-linked fucosylation in hepatocellular carcinoma

METHODS

The PubMed biomedical literature database was searched for the association of hepatocellular carcinoma and each of the core fucose-related genes and their protein products. We also queried The Cancer Genome Atlas Liver hepatocellular carcinoma (LIHC) dataset for genetic, epigenetic and gene expression changes for the set of six genes using the tools at cBioportal.

RESULTS

A total of 27 citations involving one or more of the core fucosylation-related genes (FPGT, FUK, FUT8, GMDS, SLC35C1, TSTA3) and hepatocellular carcinoma were identified. The same set of gene symbols was used to query the 371 patients with liver cancer in the LIHC dataset to identify the frequency of mRNA over or under expression, as well as non-synonymous mutations, copy number variation and methylation level. Although all six genes trended to more samples displaying over expression relative to under-expression, it was noted that a number of tumor samples had undergone amplification of the genes of the de novo synthesis pathway, GMDS (27 samples) and TSTA3 (78 samples). In contrast, the other four genes had undergone amplification in 2 or fewer samples.

CONCLUSION

Amplification of genes involved in the de novo pathway for generation of GDP-fucose, GMDS and TSTA3, likely contributes to the elevated core fucose observed in hepatocellular carcinoma.

Glycoproteomic markers of hepatocellular carcinoma-mass spectrometry based approaches

Hepatocellular carcinoma (HCC) is the third most-common cause of cancer-related death worldwide. Most cases of HCC develop in patients that already have liver cirrhosis and have been recommended for surveillance for an early onset of HCC. Cirrhosis is the final common pathway for several etiologies of liver disease, including hepatitis B and C, alcohol, and increasingly non-alcoholic fatty liver disease. Only 20-30% of patients with HCC are eligible for curative therapy due primarily to inadequate early-detection strategies. Reliable, accurate biomarkers for HCC early detection provide the highest likelihood of curative therapy and survival; however, current early-detection methods that use abdominal ultrasound and serum alpha fetoprotein are inadequate due to poor adherence and limited sensitivity and specificity. There is an urgent need for convenient and highly accurate validated biomarkers for HCC early detection. The theme of this review is the development of new methods to discover glycoprotein-based markers for detection of HCC with mass spectrometry approaches. We outline the non-mass spectrometry based methods that have been used to discover HCC markers including immunoassays, capillary electrophoresis, 2-D gel electrophoresis, and lectin-FLISA assays. We describe the development and results of mass spectrometry-based assays for glycan screening based on either MALDI-MS or ESI analysis. These analyses might be based on the glycan content of serum or on glycan screening for target molecules from serum. We describe some of the specific markers that have been developed as a result, including for proteins such as Haptoglobin, Hemopexin, Kininogen, and others. We discuss the potential role for other technologies, including PGC chromatography and ion mobility, to separate isoforms of glycan markers. Analyses of glycopeptides based on new technologies and innovative softwares are described and also their potential role in discovery of markers of HCC. These technologies include new fragmentation methods such as EThcD and stepped HCD, which can identify large numbers of glycopeptide structures from serum. The key role of lectin extraction in various assays for intact glycopeptides or their truncated versions is also described, where various core-fucosylated and hyperfucosylated glycopeptides have been identified as potential markers of HCC. Finally, we describe the role of LC-MRMs or lectin-FLISA MRMs as a means to validate these glycoprotein markers from patient samples. These technological advancements in mass spectrometry have the potential to lead to novel biomarkers to improve the early detection of HCC.

Glycan-based biomarkers for diagnosis of cancers and other diseases: Past, present, and future

Glycans are essential biomolecules in regulating human physiology and pathology ranging from signal transduction to microbial infections. Developing complex human diseases, such as cancer, diabetes, and cardiovascular diseases, are a combination of genetic and environmental factors. Genetics dominates embryonic development and the passing of genes to the next generation whereas the information in glycans reflects the impact of internal and external environmental factors, such as diseases, lifestyle, and social factors, on a person's health and disease. The reason behind this is that glycans are not directly encoded in a genetic template. Instead, they are assembled dynamically by hundreds of enzymes organized in more than 10 complex biosynthetic pathways. Any environmental changes affecting enzymatic activities or the availability of high-energy monosaccharide donors in a specific location will disturb the final structure of glycans. The glycan structure-dependent biological activities subsequently enable or disable gene expressions, which partially explain that it is difficult to pinpoint specific genetic defects to aging-associated diseases. Glycan-based biomarkers are currently used for diagnosis of diabetes, cancers, and other complex diseases. We will recapitulate the discovery of glucose, glycated proteins, glycan-, and glycoprotein-based biomarkers followed by summarizing clinically used glycan/glycoprotein-based biomarkers. The potential serum/plasma-derived N- and O-linked glycans as biomarkers will also be discussed.

Differential Quantitative Determination of Site-Specific Intact N-Glycopeptides in Serum Haptoglobin between Hepatocellular Carcinoma and Cirrhosis Using LC-EThcD-MS/MS

Intact N-glycopeptide analysis remains challenging due to the complexity of glycopeptide structures, low abundance of glycopeptides in protein digests, and difficulties in data interpretation/quantitation. Herein, we developed a workflow that involved advanced methodologies, the EThcD-MS/MS fragmentation method and data interpretation software, for differential analysis of the microheterogeneity of site-specific intact N-glycopeptides of serum haptoglobin between early hepatocellular carcinoma (HCC) and liver cirrhosis. Haptoglobin was immunopurified from 20 μL of serum in patients with early HCC, liver cirrhosis, and healthy controls, respectively, followed by trypsin/GluC digestion, glycopeptide enrichment, and LC-EThcD-MS/MS analysis. Identification and differential quantitation of site-specific N-glycopeptides were performed using a combination of Byonic and Byologic software. In total, 93, 87, and 68 site-specific N-glycopeptides were identified in early HCC, liver cirrhosis, and healthy controls, respectively, with high confidence. The increased variety of N-glycopeptides in liver diseases compared to healthy controls was due to increased branching with hyper-fucosylation and sialylation. Differential quantitation analysis showed that 5 site-specific N-glycopeptides on sites N184 and N241 were significantly elevated in early HCC compared to cirrhosis ( p < 0.05) and normal controls ( p ≤ 0.001). The result demonstrates that the workflow provides a strategy for detailed profiles of N-glycopeptides of patient samples as well as for relative quantitation to determine the level changes in site-specific N-glycopeptides between disease states.

N-Linked Glycan Branching and Fucosylation Are Increased Directly in Hcc Tissue As Determined through in Situ Glycan Imaging

Hepatocellular carcinoma (HCC) remains as the fifth most common cancer in the world and accounts for more than 700,000 deaths annually. Changes in serum glycosylation have long been associated with this cancer but the source of that material is unknown and direct glycan analysis of HCC tissues has been limited. Our laboratory previously developed a method of in situ tissue based N-linked glycan imaging that bypasses the need for microdissection and solubilization of tissue prior to analysis. We used this methodology in the analysis of 138 HCC tissue samples and compared the N-linked glycans in cancer tissue with either adjacent untransformed or tissue from patients with liver cirrhosis but no cancer. Ten glycans were found significantly elevated in HCC tissues as compared to cirrhotic or adjacent tissue. These glycans fell into two major classes, those with increased levels of fucosylation and those with increased levels of branching with or without any fucose modifications. In addition, increased levels of fucosylated glycoforms were associated with a reduction in survival time. This work supports the hypothesis that the increased levels of fucosylated N-linked glycans in HCC serum are produced directly from the cancer tissue.

LC-MS/MS isomeric profiling of permethylated N-glycans derived from serum haptoglobin of hepatocellular carcinoma (HCC) and cirrhotic patients

Early stage detection and cancer treatment demand the identification of reliable biomarkers. Over the past decades, efforts have been devoted to assess the variation of glycosylation level as well as the glycan structures of proteins in blood or serum, associated with the development and/or progression of several cancers, including liver. Herein, an LC-MS/MS-based analysis was conducted to define the glycosylation patterns of haptoglobin glycoprotein derived from sera collected from cirrhotic and hepatocellular carcinoma (HCC) patients. The haptoglobin samples were extracted from serum using an antibody-immobilized column prior to the release of N-glycans. A comparison of non-isomeric and isomeric permethylated glycan forms was achieved using C18 and porous graphitic carbon (PGC) columns, respectively. In the case of C18-LC-MS/MS analysis, 25 glycan structures were identified of which 10 sialylated structures were found to be statistically significant between the two cohorts. Also, 8 out of 34 glycan structures identified by PGC-LC-MS/MS were found to be statistically significant, suggesting that isomeric distributions of a particular glycan composition were different in abundances between the two cohorts. The glycan isoform patterns distinguished early stage HCC from cirrhotic patients. Both retention times and tandem mass spectra were utilized to determine the specific isomeric glycan structures. All of the glycan isomers, which were statistically significant, were either branch fucosylated or composed of α-2,6 linked sialic acid moieties. The result of this study demonstrates the potential importance of isomeric separation for defining disease prompted aberrant glycan changes. The levels of several glycan isoforms effectively distinguished early stage HCC from cirrhosis.

Recent advances in mass spectrometric analysis of glycoproteins

Glycosylation is one of the most common posttranslational modifications of proteins that plays essential roles in various biological processes, including protein folding, host-pathogen interaction, immune response, and inflammation and aberrant protein glycosylation is a well-known event in various disease states including cancer. As a result, it is critical to develop rapid and sensitive methods for the analysis of abnormal glycoproteins associated with diseases. Mass spectrometry (MS) in conjunction with different separation methods, such as capillary electrophoresis (CE), ion mobility (IM), and high performance liquid chromatography (HPLC) has become a popular tool for glycoprotein analysis, providing highly informative fragments for structural identification of glycoproteins. This review provides an overview of the developments and accomplishments in the field of glycomics and glycoproteomics reported between 2014 and 2016.

Serum glycoprotein-derived N- and O-linked glycans as cancer biomarkers

Early detection of cancer is the key to improving survival. Since most clinically used serum cancer biomarkers are either glycoproteins or glycan structures that can be recognized by specific monoclonal antibodies, developing glycan structure-based biomarkers from human serum/plasma glycoproteins through mass spectrometry (MS) analysis are active research field during the past decades. Numerous studies have shown that changes in serum/plasma glycan structures occur during cancer initiation, progression, and treatment. This review describes N- and O-linked glycan structures identified from serum/plasma glycoprotein (s) by MS analysis with focus on alterations associated with different types of human cancers. The global changes in serum N- and O-linked glycan structures, especially the glycans that are not made by cancer cells such as B lymphocyte-derived IgG and liver-synthesized haptoglobin and α1 acid glycoprotein, suggest that glycans might be the long sought diagnostic biomarkers associated with system malfunction in the blood circulation of cancer patients. Therefore, N- and O-linked glycan structures have great potential to serve as cancer diagnosis, prognosis, and treatment monitoring biomarkers to facilitate personalized medicine.

ESI-LC-MS Method for Haptoglobin Fucosylation Analysis in Hepatocellular Carcinoma and Liver Cirrhosis

A method for the detection of fucosylated glycans from haptoglobin in patient serum has been developed that provides enhanced sensitivity. The workflow involves isolation of the haptoglobin using an HPLC-based affinity column followed by glycan removal, extraction, and desialylation. The fucosylated glycans are then derivatized by Meladrazine, which significantly enhances the detection of the glycans in electrospray ionization. The separation of the derivatized glycans in a HILIC column shows that eight glycans from haptoglobin can be detected using less than 1 μL of a serum sample, with excellent reproducibility and quantitation, where without derivatization the glycans could not be detected. The ratio of the fucosylated peaks to their corresponding nonfucosylated forms shows that the fucosylated glycans are upregulated in the case of hepatocellular carcinoma (HCC) samples versus cirrhosis samples, where the relatively low abundance bifucosylated tetra-antennary form can be detected and may be a particularly good marker for HCC.