Glycosylation of site-specific glycans of alpha1-acid glycoprotein and alterations in acute and chronic inflammation

Variability of human Alpha-1-acid glycoprotein N-glycome in a Caucasian population

AIM

Alpha-1-acid glycoprotein (AGP) is a highly glycosylated protein in human plasma and one of the most abundant acute phase proteins in humans. Glycosylation plays a crucial role in its biological functions, and alterations in AGP N-glycome have been associated with various diseases and inflammatory conditions. However, large-scale studies of AGP N-glycosylation in the general population are lacking.

METHODS

Using recently developed high-throughput glycoproteomic workflow for site-specific AGP N-glycosylation analysis, 803 individuals from the Croatian island of Korcula were analyzed and their AGP N-glycome data associated with biochemical and physiological traits, as well as different environmental factors.

RESULTS

After regression analysis, we found that AGP N-glycosylation is strongly associated with sex, somewhat less with age, along with multiple biochemical and physiological traits (e.g. BMI, triglycerides, uric acid, glucose, smoking status, fibrinogen).

CONCLUSION

For the first time we have extensively explored the inter-individual variability of AGP N-glycome in a general human population, demonstrating its changes with sex, age, biochemical, and physiological status of individuals, providing the baseline for future population and clinical studies.

Conformational dynamics of α-1 acid glycoprotein (AGP) in cancer: A comparative study of glycosylated and unglycosylated AGP

α-1 acid glycoprotein (AGP) is one of the most abundant plasma proteins. It fulfills two important functions: immunomodulation, and binding to various drugs and receptors. These different functions are closely associated and modulated via changes in glycosylation and cancer missense mutations. From a structural point of view, glycans alter the local biophysical properties of the protein leading to a diverse ligand-binding spectrum. However, glycans can typically not be observed in the resolved X-ray crystallography structure of AGP due to their high flexibility and microheterogeneity, so limiting our understanding of AGP's conformational dynamics 70 years after its discovery. We here investigate how mutations and glycosylation interfere with AGP's conformational dynamics changing its biophysical behavior, by using molecular dynamics (MD) simulations and sequence-based dynamics predictions. The MD trajectories show that glycosylation decreases the local backbone flexibility of AGP and increases the flexibility of distant regions through allosteric effects. We observe that mutations near the glycosylation site affect glycan's conformational preferences. Thus, we conclude that mutations control glycan dynamics which modulates the protein's backbone flexibility directly affecting its accessibility. These findings may assist in the drug design targeting AGP's glycosylation and mutations in cancer.

Wheat germ agglutinin affinity chromatography enrichment and glyco-proteomic characterization of tetrodotoxin-binding proteins from the plasma of cultured tiger pufferfish (Takifugu rubripes)

Efficient enrichment of tetrodotoxin (TTX)-binding proteins from the plasma of cultured tiger pufferfish (Takifugu rubripes) was achieved by ammonium sulfate fractionation and wheat germ agglutinin (WGA) affinity chromatography. The enrichment efficiency was validated by ultrafiltration-LC/MS-based TTX-binding assay and proteomics. Major proteins in the WGA-bound fraction were identified as isoform X1 (125 kDa) and X2 variants (88 and 79 kDa) derived from pufferfish saxitoxin and tetrodotoxin-binding protein (PSTBP) 1-like gene (LOC101075943). The 125-kDa X1 protein was found to be a novel member of the lipocalin family, having three tandemly repeated domains. X2 variants, X2α and X2β, were estimated to have two domains, and X2β is structurally related to Takifugu pardalis PSTBP2 in their domain type and arrangement. Among 11 potential N-glycosylation sites in the X2 precursor, 5 N-glycosylated Asn residues (N55, N89, N244, N308, and N449) were empirically determined. Structural relationships among PSTBP homologs and complexity of their proteoforms are discussed.

The Association of the Polymorphisms in the FUT8-Related Locus with the Plasma Glycosylation in Post-Traumatic Stress Disorder

The molecular underpinnings of post-traumatic stress disorder (PTSD) are still unclear due to the complex interactions of genetic, psychological, and environmental factors. Glycosylation is a common post-translational modification of proteins, and different pathophysiological states, such as inflammation, autoimmune diseases, and mental disorders including PTSD, show altered N-glycome. Fucosyltransferase 8 (FUT8) is the enzyme that catalyzes the addition of core fucose on glycoproteins, and mutations in the FUT8 gene are associated with defects in glycosylation and functional abnormalities. This is the first study that investigated the associations of plasma N-glycan levels with FUT8-related rs6573604, rs11621121, rs10483776, and rs4073416 polymorphisms and their haplotypes in 541 PTSD patients and control participants. The results demonstrated that the rs6573604 T allele was more frequent in the PTSD than in the control participants. Significant associations of plasma N-glycan levels with PTSD and FUT8-related polymorphisms were observed. We also detected associations of rs11621121 and rs10483776 polymorphisms and their haplotypes with plasma levels of specific N-glycan species in both the control and PTSD groups. In carriers of different rs6573604 and rs4073416 genotypes and alleles, differences in plasma N-glycan levels were only found in the control group. These molecular findings suggest a possible regulatory role of FUT8-related polymorphisms in glycosylation, the alternations of which could partially explain the development and clinical manifestation of PTSD.

N-glycosylation of serum proteins in adult type 1 diabetes mellitus exposes further changes compared to children at the disease onset

OBJECTIVE

Previously we have shown that plasma protein N-glycosylation is changed in children at the onset of type 1 diabetes. In this study, we aim to identify N-glycan changes in adults with T1DM, compare them to those in children, and investigate their associations with disease duration, complications, glycaemic status, and smoking.

METHODS

Serum protein N-glycans from 200 adults with type 1 diabetes and 298 healthy controls were analysed using ultra-high performance liquid chromatography and divided into 39 directly measured glycan groups from which 16 derived traits were calculated.

RESULTS

Compared to healthy controls, subjects with type 1 diabetes showed differences in 19 glycan groups and a decrease in monogalactosylated, an increase in digalactosylated, monosialylated, and antennary fucosylated derived traits, from which changes in monogalactosylation and seven directly measured traits overlapped with previously reported in children. Changes in four directly measured and two derived traits previously seen in children were not detected in adults. HbA1c was positively associated with sialylated and highly branched structures, whereas N-glycome was not influenced by disease duration or diabetic complications.

CONCLUSIONS

Our results suggest potential N-glycome involvement in different stages of type 1 diabetes, including processes underlying its development, the disease itself, as well as those occurring after disease establishment.

Challenges and opportunities for omics-based precision medicine in chronic low back pain

PURPOSE

Chronic low back pain (cLBP) is a common health condition worldwide and a leading cause of disability with an estimated lifetime prevalence of 80-90% in industrialized countries. However, we have had limited success in treating cLBP likely due to its non-specific heterogeneous nature that goes beyond detectable anatomical changes. We propose that omics technologies as precision medicine tools are well suited to provide insight into its pathophysiology and provide diagnostic markers and therapeutic targets. Therefore, in this review, we explore the current state of omics technologies in the diagnosis and classification of cLBP. We identify factors that may serve as markers to differentiate between acute and chronic cases of low back pain (LBP). Finally, we also discuss some challenges that must be overcome to successfully apply precision medicine to the diagnosis and treatment of cLBP.

METHODS

A literature search for the current applications of omics technologies to chronic low back pain was performed using the following search terms- "back pain," "low back pain," "proteomics," "transcriptomics", "epigenomics," "genomics," "omics." We reviewed molecular markers identified from 35 studies which hold promise in providing information regarding molecular insights into cLBP.

RESULTS

GWAS studies have found evidence for the role of single nucleotide polymorphisms (SNPs) associated with pain pathways in individuals with cLBP. Epigenomic modifications in patients with cLBP have been found to be enriched among genes involved in immune signaling and inflammation. Transcriptomics profiles of patients with cLBP show multiple lines of evidence for the role of inflammation in cLBP. The glycomics profiles of patients with cLBP are similar to those of patients with inflammatory conditions. Proteomics and microbiomics show promise but have limited studies currently.

CONCLUSION

Omics technologies have identified associations between inflammatory and pain pathways in the pathophysiology of cLBP. However, in order to integrate information across the range of studies, it is important for the field to identify and adopt standardized definitions of cLBP and control patients. Additionally, most papers have applied a single omics method to a sampling of cLBP patients which have yielded limited insight into the pathophysiology of cLBP. Therefore, we recommend a multi-omics approach applied to large global consortia for advancing subphenotyping and better management of cLBP, via improved identification of diagnostic markers and therapeutic targets.

N-Glycosylation and Inflammation; the Not-So-Sweet Relation

Chronic inflammation is the main feature of many long-term inflammatory diseases such as autoimmune diseases, metabolic disorders, and cancer. There is a growing number of studies in which alterations of N-glycosylation have been observed in many pathophysiological conditions, yet studies of the underlying mechanisms that precede N-glycome changes are still sparse. Proinflammatory cytokines have been shown to alter the substrate synthesis pathways as well as the expression of glycosyltransferases required for the biosynthesis of N-glycans. The resulting N-glycosylation changes can further contribute to disease pathogenesis through modulation of various aspects of immune cell processes, including those relevant to pathogen recognition and fine-tuning the inflammatory response. This review summarizes our current knowledge of inflammation-induced N-glycosylation changes, with a particular focus on specific subsets of immune cells of innate and adaptive immunity and how these changes affect their effector functions, cell interactions, and signal transduction.

HCC and Tumor Biomarkers: Does One Size Fits All?

Hepatocellular carcinoma (HCC) is a highly malignant disease and early diagnosis rates remain to be unsatisfactory. Owing to this limitation, advances in treatment options including liver transplantation (LT) are limited to improve survival. Recent HCC guidelines no longer recommend alpha-fetoprotein (AFP) as a surveillance and diagnostic tool for HCC. Hence, utilization of novel biomarkers has become imperative to improve disease management strategies. Noninvasive, serum-based biomarkers are potential options to aid early diagnosis as well as prompting treatment. However, further studies are required to find out the accuracy and potential of these approaches and introduce into clinical practice.

Thapsigargin suppresses alpha 1-acid glycoprotein secretion independently of N-glycosylation and ER stress

Alpha-1 acid glycoprotein (AGP) is a major acute-phase protein that is involved in drug/ligand binding and regulation of immune response. In response to inflammation, AGP secretion from the liver increases, resulting in elevated concentration of plasma AGP. AGP exhibits multiple N-glycosylation sites, and thus, is highly glycosylated. Although AGP glycosylation is considered to affect its functions, the significance of AGP glycosylation for its secretion is unclear. In this study, we investigated the effects of AGP glycosylation using glycosylation-deficient mouse AGP mutants lacking one, four, or all five N-glycosylation sites. Furthermore, we examined the effects of endoplasmic reticulum (ER) stress-inducing reagents, including tunicamycin and thapsigargin, which induce ER stress in an N-glycosylation-dependent and -independent manner, respectively. Here, we found that glycosylation deficiency and ER stress induce a little or no effect on AGP secretion. Conversely, thapsigargin significantly suppressed AGP secretion in glycosylation-independent manner. These findings indicate that AGP secretion is regulated via thapsigargin-sensitive pathway that might be further controlled by the intracellular calcium concentrations.

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

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

Glycoproteoform Profiles of Individual Patients' Plasma Alpha-1-Antichymotrypsin are Unique and Extensively Remodeled Following a Septic Episode

Sepsis and septic shock remain the leading causes of death in intensive care units (ICUs), yet the pathogenesis originating from the inflammatory response during sepsis remains ambiguous. Acute-phase proteins are typically highly glycosylated, and the nature of the glycans have been linked to the incidence and severity of such inflammatory responses. To further build upon these findings we here monitored, the longitudinal changes in the plasma proteome and, in molecular detail, glycoproteoform profiles of alpha-1-antichymotrypsin (AACT) extracted from plasma of ten individual septic patients. For each patient we included four different time-points, including post-operative (before sepsis) and following discharge from the ICU. We isolated AACT from plasma depleted for albumin, IgG and serotransferrin and used high-resolution native mass spectrometry to qualitatively and quantitatively monitor the multifaceted glycan microheterogeneity of desialylated AACT, which allowed us to monitor how changes in the glycoproteoform profiles reflected the patient's physiological state. Although we observed a general trend in the remodeling of the AACT glycoproteoform profiles, e.g. increased fucosylation and branching/LacNAc elongation, each patient exhibited unique features and responses, providing a resilient proof-of-concept for the importance of personalized longitudinal glycoproteoform profiling. Importantly, we observed that the AACT glycoproteoform changes induced by sepsis did not readily subside after discharge from ICU.

Chronic exposure to low doses of ionizing radiation impacts the processing of glycoprotein N-linked glycans in Medaka (Oryzias latipes)

PURPOSE

Ionizing radiation is found naturally in the environment. Low doses of IR may have beneficial applications, yet there is also potential for detrimental long-term health effects. Impacts following exposure to low levels of IR have been refractory to identification and quantification. Glycoprotein glycosylation is vital to cell-cell communication and organismal function, and sensitive to changes in an organism's macro- and cellular environment. We investigated whether accumulated low doses of IR (LoDIR) affect the N-linked glycoprotein glycans using Medaka fish (Oryzias latipes).

MATERIALS AND METHODS

State-of-the-art methods in radiation exposure and glycan analysis were applied to study N-glycan changes after 190 day exposure at three different rates of gamma irradiation (2.25, 21.01, and 204.3 mGy/day) in wild-type adult Medaka. Tissue N-glycans were analyzed following enzymatic release from extracted proteins.

RESULTS

N-linked glycan profiles are dominated by complex type N-glycans modified with terminal sialic acid and core fucose. Fucosylation and sialylation of N-linked glycoprotein glycans are affected by LoDIR and a subset of N-glycans are involved in the organismal radio-response.

CONCLUSION

This is the first indication that the glycome can be interrogated for biomarkers that report the impact of chronic exposure to environmental stressors, such as low-level IR.

Serum N-Glycome analysis reveals pancreatic cancer disease signatures

Background &Aims

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer type with loco‐regional spread that makes the tumor surgically unresectable. Novel diagnostic tools are needed to improve detection of PDAC and increase patient survival. In this study we explore serum protein N‐glycan profiles from PDAC patients with regard to their applicability to serve as a disease biomarker panel.

Methods

Total serum N‐glycome analysis was applied to a discovery set (86 PDAC cases/84 controls) followed by independent validation (26 cases/26 controls) using in‐house collected serum specimens. Protein N‐glycan profiles were obtained using ultrahigh resolution mass spectrometry and included linkage‐specific sialic acid information. N‐glycans were relatively quantified and case‐control classification performance was evaluated based on glycosylation traits such as branching, fucosylation, and sialylation.

Results

In PDAC patients a higher level of branching (OR 6.19, P‐value 9.21 × 10⁻¹¹) and (antenna)fucosylation (OR 13.27, P‐value 2.31 × 10⁻⁹) of N‐glycans was found. Furthermore, the ratio of α2,6‐ vs α2,3‐linked sialylation was higher in patients compared to healthy controls. A classification model built with three glycosylation traits was used for discovery (AUC 0.88) and independent validation (AUC 0.81), with sensitivity and specificity values of 0.85 and 0.71 for the discovery set and 0.75 and 0.72 for the validation set.

Conclusion

Serum N‐glycome analysis revealed glycosylation differences that allow classification of PDAC patients from healthy controls. It was demonstrated that glycosylation traits rather than single N‐glycan structures obtained in this clinical glycomics study can serve as a basis for further development of a blood‐based diagnostic test.

Structural and functional diversity of neutrophil glycosylation in innate immunity and related disorders

The granulated neutrophils are abundant innate immune cells that utilize bioactive glycoproteins packed in cytosolic granules to fight pathogenic infections, but the neutrophil glycobiology remains poorly understood. Facilitated by technological advances in glycoimmunology, systems glycobiology and glycoanalytics, a considerable body of literature reporting on novel aspects of neutrophil glycosylation has accumulated. Herein, we summarize the building knowledge of the structural and functional diversity displayed by N- and O-linked glycoproteins spatiotemporally expressed and sequentially brought-into-action across the diverse neutrophil life stages during bone marrow maturation, movements to, from and within the blood circulation and microbicidal processes at the inflammatory sites in peripheral tissues. It transpires that neutrophils abundantly decorate their granule glycoproteins including neutrophil elastase, myeloperoxidase and cathepsin G with peculiar glyco-signatures not commonly reported in other areas of human glycobiology such as hyper-truncated chitobiose core- and paucimannosidic-type N-glycans and monoantennary complex-type N-glycans. Sialyl Lewis^x, Lewis^x, poly-N-acetyllactosamine extensions and core 1-/2-type O-glycans are also common neutrophil glyco-signatures. Granule-specific glycosylation is another fascinating yet not fully understood feature of neutrophils. Recent literature suggests that unconventional biosynthetic pathways and functions underpin these prominent neutrophil-associated glyco-phenotypes. The impact of glycosylation on key neutrophil effector functions including extravasation, degranulation, phagocytosis and formation of neutrophil extracellular traps during normal physiological conditions and in innate immune-related diseases is discussed. We also highlight new technologies that are expected to further advance neutrophil glycobiology and briefly discuss the untapped diagnostic and therapeutic potential of neutrophil glycosylation that could open avenues to combat the increasingly prevalent innate immune disorders.

A Matrix-Assisted Laser Desorption/Ionization-Mass Spectrometry Assay for the Relative Quantitation of Antennary Fucosylated N-Glycans in Human Plasma

Changes in the abundance of antennary fucosylated glycans in human total plasma N-glycome (TPNG) have been associated with several diseases ranging from diabetes to various forms of cancer. However, it is challenging to address this important part of the human glycome. Most commonly, time-consuming chromatographic separations are performed to differentially quantify core and antenna fucosylation. Obtaining sufficient resolution for larger, more complex glycans can be challenging. We introduce a matrix-assisted laser desorption/ionization—mass spectrometry (MALDI-MS) assay for the relative quantitation of antennary fucosylation in TPNG. N-linked glycans are released from plasma by PNGase F and further treated with a core fucosidase before performing a linkage-informative sialic acid derivatization. The core fucosylated glycans are thus depleted while the remaining antennary fucosylated glycans are quantitated. Simultaneous quantitation of α2,3-linked sialic acids and antennary fucosylation allows an estimation of the sialyl-Lewis x motif. The approach is feasible using either ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry or time-of-flight mass spectrometry. The assay was used to investigate changes of antennary fucosylation as clinically relevant marker in 14 colorectal cancer patients. In accordance with a previous report, we found elevated levels of antennary fucosylation pre-surgery which decreased after tumor resection. The assay has the potential for revealing antennary fucosylation signatures in various conditions including diabetes and different types of cancer.

Altered N-glycan profile of IgG-depleted serum proteins in Hashimoto's thyroiditis

BACKGROUND

Hashimoto's thyroiditis (HT) is an autoimmune disease characterized by chronic inflammation of thyroid gland. Although HT is the most common cause of hypothyroidism, the pathogenesis of this disease is not fully understood. Glycosylation of serum proteins was examined in HT only to a limited extent. The study was designed to determine the glycosylation pattern of IgG-depleted sera from HT patients.

METHODS

Serum N-glycans released by N-glycosidase F (PNGase F) digestion were analyzed by normal-phase high-performance liquid chromatography (NP-HPLC). N-glycan structures in each collected HPLC fraction were determined by liquid chromatography-mass spectrometry (LC-MS) and exoglycosidase digestion. Fucosylation and sialylation was also analyzed by lectin blotting.

RESULTS

The results showed an increase of monosialylated tri-antennary structure (A3G3S1) and disialylated diantennary N-glycan with antennary fucose (FA2G2S2). Subsequently, we analyzed the serum N-glycan profile by lectin blotting using lectins specific for fucose and sialic acid. We found a significant decrease of Lens culinaris agglutinin (LCA) staining in HT samples, which resulted from the reduction of α1,6-linked core fucose in HT serum. We also observed an increase of Maackia amurensis II lectin (MAL-II) reaction in HT due to the elevated level of α2,3-sialylation in HT sera.

CONCLUSIONS

The detected alterations of serum protein sialylation might be caused by chronic inflammation in HT. The obtained results complete our previous IgG N-glycosylation analysis in autoimmune thyroid patients and show that the altered N-glycosylation of serum proteins is characteristic for autoimmunity process in HT. General Significance Thyroid autoimmunity is accompanied by changes of serum protein sialylation.

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

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

Age-Dependent Variation in Glycosylation Features of Alpha-2-Macroglobulin

Alpha-2-macroglobulin (A2M) is a glycosylated broad spectrum inhibitor of numerous proteases, including those involved in blood coagulation. Glycosylation characteristics can affect protein structure and function. This study compares glycosylation characteristics of A2M in newborn umbilical cord (NUCP) and adult pooled plasmas. Peptide N-Glycosidase F treatment was used to evaluate the total N-glycan content of the molecules. Neuraminidase treatment, and affinity for Ricinus Communis Agglutinin I were used to examine terminal sialic acid and galactose content, respectively. Two-dimensional (2D) electrophoresis was used to determine charge-related isoform profiles and fluorophore-assisted carbohydrate electrophoresis (FACE) was used to characterize N-glycan profiles. Results revealed no difference in total N-glycan mass, however, a statistically significant difference was shown in the change in charge associated with sialic acid loss in the NUCP A2M population. 2D electrophoresis indicated a lower pI range for NUCP A2M isoforms. In addition, NUCP A2M displayed a trend toward higher terminal galactose quantities than adult A2M. FACE revealed an increased abundance of more branched, higher molecular weight glycans in NUCP A2M. These differences in glycan branching and charged residues may impact A2M receptor-based clearance and thus could be responsible for the increased A2M concentration seen in NUCP, and newborns.

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

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

Characterization of Site-Specific N-Glycosylation

Even if a consensus sequence has been identified for a posttranslational modification, the presence of such a sequence motif only indicates the possibility, not the certainty that the modification actually occurs. Proteins can be glycosylated on certain amino acid side chains, and these modifications are designated as C-, N-, and O-glycosylation. C-mannosylation occurs on Trp residues within a relatively loosely defined consensus motif. N-glycosylated species are modified at Asn residues of Asn-Xxx-Ser/Thr/Cys sequons (where Xxx can be any amino acid except proline). N-linked oligosaccharides share a common core structure of GlcNAc₂Man₃. In addition, an enzyme, peptide N-glycosidase F (PNGase F), removes most of the common N-linked carbohydrates unaltered from proteins while hydrolyzing the originally glycosylated Asn residue to Asp. O-glycosylation occurs at Ser, Thr, and Tyr residues, usually in sequence stretches rich in hydroxy-amino acids. O-glycosylation lacks a common core structure. Mammalian proteins have been reported bearing O-linked N-acetylgalactosamine, fucose, glucose, xylose, mannose, and corresponding elongated structures, as well as N-acetylglucosamine. Chemical methods are used to liberate these oligosaccharides because no enzyme would remove all the different O-linked carbohydrates. Characterization of both N- and O-glycosylation is complicated by the fact that the same positions within a population of protein molecules may feature an array of different carbohydrate structures, or remain unmodified. This site-specific heterogeneity may vary by species and tissue, and may also be affected by physiological changes. For addressing site-specific carbohydrate heterogeneity mass spectrometry has become the method of choice. Reversed-phase HPLC directly coupled with electrospray ionization mass spectrometry (LC/ESI-MS/MS) offers the best solution. Using a mass spectrometer as online detector not only assures the analysis of every component eluting (mass mapping), but also at the same time diagnostic carbohydrate ions can be generated by collisional activation that permits the selective and specific detection of glycopeptides. In addition, ESI-compatible alternative MS/MS techniques, electron-capture and electron-transfer dissociation, aid glycopeptide identification as well as modification site assignments.

Plasma N-glycome composition associates with chronic low back pain

BACKGROUND

Low back pain (LBP) is the symptom of a group of syndromes with heterogeneous underlying mechanisms and molecular pathologies, making treatment selection and patient prognosis very challenging. Moreover, symptoms and prognosis of LBP are influenced by age, gender, occupation, habits, and psychological factors. LBP may be characterized by an underlying inflammatory process. Previous studies indicated a connection between inflammatory response and total plasma N-glycosylation. We wanted to identify potential changes in total plasma N-glycosylation pattern connected with chronic low back pain (CLBP), which could give an insight into the pathogenic mechanisms of the disease.

METHODS

Plasma samples of 1128 CLBP patients and 760 healthy controls were collected in clinical centers in Italy, Belgium and Croatia and used for N-glycosylation profiling by hydrophilic interaction ultra-performance liquid chromatography (HILIC-UPLC) after N-glycans release, fluorescent labeling and clean-up. Observed N-glycosylation profiles have been compared with a cohort of 126 patients with acute inflammation that underwent abdominal surgery.

RESULTS

We have found a statistically significant increase in the relative amount of high-branched (tri-antennary and tetra-antennary) N-glycan structures on CLBP patients' plasma glycoproteins compared to healthy controls. Furthermore, relative amounts of disialylated and trisialylated glycan structures were increased, while high-mannose and glycans containing bisecting N-acetylglucosamine decreased in CLBP.

CONCLUSIONS

Observed changes in CLBP on the plasma N-glycome level are consistent with N-glycosylation changes usually seen in chronic inflammation.

GENERAL SIGNIFICANCE

To our knowledge, this is a first large clinical study on CLBP patients and plasma N-glycome providing a new glycomics perspective on potential disease pathology.

Alterations of the serum N-glycan profile in female patients with Major Depressive Disorder

BACKGROUND

Glycans are short chains of saccharides linked to glycoproteins that are known to be involved in a wide range of inflammatory processes. As depression has been consistently associated with chronic low-grade inflammation, we asked whether patients with Major Depressive Disorder show alterations in the N-glycosylation pattern of serum proteins that might be linked to associated changes in inflammatory processes.

METHODS

In a study cohort of 21 female patients with an acute depressive episode and 21 non-depressed female control subjects aged between 50 and 69 years, we analyzed the serum N-glycan profile by DNA Sequencer Adapted-Fluorophore Assisted Carbohydrate Electrophoresis (DSA-FACE) and assessed the serum levels of interleukin (IL)- 6, tumor necrosis factor (TNF)-α and C-reactive protein (CRP) by chemiluminescence immunoassays and nephelometry.

RESULTS

Compared to controls, MDD patients showed significant differences in the serum levels of several N-glycan structures. Alterations in the serum N-glycan profile were associated with depressive symptom severity and exploratory analyses revealed that they were most pronounced in MDD patients with a history of childhood sexual abuse. Furthermore, MDD patients showed higher levels of IL-6 and a trend for higher CRP levels, which were also associated with similar alterations in the serum N-glycan profile as those characteristic for MDD patients.

LIMITATIONS

The relatively small sample size and the presence of potential confounders (e.g., BMI, smoking, medication).

CONCLUSION

The results offer the first evidence that specific differences in the N-glycosylation pattern of serum proteins constitute a so far unrecognized level of biological alterations that might be involved in the immune changes associated with MDD.

Membrane glycomics reveal heterogeneity and quantitative distribution of cell surface sialylation

Sialic acid distribution was quantified by LC-MS/MS. The number of sialylated glycoforms increases at sites nearest to the transmembrane domain.

Given that unnatural sugar expression is metabolically achieved, the kinetics and disposition of incorporation can lend insight into the temporal and localization preferences of sialylation across the cell surface. However, common detection schemes lack the ability to detail the molecular diversity and distribution of target moieties. Here we employed a mass spectrometric approach to trace the placement of azido sialic acids on membrane glycoconjugates, which revealed substantial variations in incorporation efficiencies between N-/O-glycans, glycosites, and glycosphingolipids. To further explore the propensity for sialylation, we subsequently mapped the native glycome of model epithelial cell surfaces and illustrate that while glycosylation sites span broadly across the extracellular region, a higher number of heterogeneous glycoforms occur on sialylated sites closest to the transmembrane domain. Beyond imaging techniques, this integrative approach provides unprecedented details about the frequency and structure-specific distribution of cell surface sialylation, a critical feature that regulates cellular interactions and homeostatic pathways.

Glycosylation Changes in Brain Cancer

Protein glycosylation is a posttranslational modification that affects more than half of all known proteins. Glycans covalently bound to biomolecules modulate their functions by both direct interactions, such as the recognition of glycan structures by binding partners, and indirect mechanisms that contribute to the control of protein conformation, stability, and turnover. The focus of this Review is the discussion of aberrant glycosylation related to brain cancer. Altered sialylation and fucosylation of N- and O-glycans play a role in the development and progression of brain cancer. Additionally, aberrant O-glycan expression has been implicated in brain cancer. This Review also addresses the clinical potential and applications of aberrant glycosylation for the detection and treatment of brain cancer. The viable roles glycans may play in the development of brain cancer therapeutics are addressed as well as cancer-glycoproteomics and personalized medicine. Glycoprotein alterations are considered as a hallmark of cancer while high expression in body fluids represents an opportunity for cancer assessment.

Astrocytic Orosomucoid-2 Modulates Microglial Activation and Neuroinflammation

Orosomucoid (ORM) is an acute-phase protein that belongs to the immunocalin subfamily, a group of small-molecule-binding proteins with immunomodulatory functions. Little is known about the role of ORM proteins in the CNS. The aim of the present study was to investigate the brain expression of ORM and its role in neuroinflammation. Expression of Orm2, but not Orm1 or Orm3, was highly induced in the mouse brain after systemic injection of lipopolysaccharide (LPS). Plasma levels of ORM2 were also significantly higher in patients with cognitive impairment than in normal subjects. RT-PCR, Western blot, and immunofluorescence analyses revealed that astrocytes are the major cellular sources of ORM2 in the inflamed mouse brain. Recombinant ORM2 protein treatment decreased microglial production of proinflammatory mediators and reduced microglia-mediated neurotoxicity in vitro LPS-induced microglial activation, proinflammatory cytokines in hippocampus, and neuroinflammation-associated cognitive deficits also decreased as a result of intracerebroventricular injection of recombinant ORM2 protein in vivo Moreover, lentiviral shRNA-mediated Orm2 knockdown enhanced LPS-induced proinflammatory cytokine gene expression and microglial activation in the hippocampus. Mechanistically, ORM2 inhibited C-C chemokine ligand 4 (CCL4)-induced microglial migration and activation by blocking the interaction of CCL4 with C-C chemokine receptor type 5. Together, the results from our cultured glial cells, mouse neuroinflammation model, and patient studies suggest that ORM2 is a novel mediator of astrocyte-microglial interaction. We also report that ORM2 exerts anti-inflammatory effects by modulating microglial activation and migration during brain inflammation. ORM2 can be exploited therapeutically for the treatment of neuroinflammatory diseases.SIGNIFICANCE STATEMENT Neural cell interactions are important for brain physiology and pathology. Particularly, the interaction between non-neuronal cells plays a central role in regulating brain inflammation, which is closely linked to many brain disorders. Here, we newly identified orosomucoid-2 (ORM2) as an endogenous protein that mediates such non-neuronal glial cell interactions. Based on the critical role of astrocyte-derived ORM2 in modulating microglia-mediated neuroinflammation, ORM2 can be exploited for the diagnosis, prevention, or treatment of devastating brain disorders that have a strong neuroinflammatory component, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis.

Parallel data acquisition of in-source fragmented glycopeptides to sequence the glycosylation sites of proteins

Glycosylation plays important roles in maintaining protein stability and controlling biological processes. In recent years, the correlation between aberrant glycoproteins and many diseases has been reported. Hence, qualitative and quantitative analyses of glycoproteins are necessary to understand physiological processes. LC-MS/MS analysis of glycopeptides is faced with the low glycopeptide signal intensities and low peptide sequence identification. In our study, in-source fragmentation (ISF) was used in conjunction with LC-MS/MS to facilitate the parallel acquisition of peptide backbone sequence and glycan composition information. In ISF method, the identification of glycosylation sites depended on the detection of Y1 ion (ion of peptide backbone with an N-acetylglucosamine attached). To attain dominant Y1 ions, a range of source fragmentation voltages was studied using fetuin. A 45 V ISF voltage was found to be the most efficient voltage for the analysis of glycoproteins. ISF was employed to study the glycosylation sites of three model glycoproteins, including fetuin, α1-acid glycoprotein and porcine thyroglobulin. The approach was then used to analyze blood serum samples. Y1 ions of glycopeptides in tryptic digests of samples were detected. Y1 ions of glycopeptides with different sialic acid groups are observed at different retention times, representing the various numbers of sialic acid moieties associated with the same peptide backbone sequence. With ISF facilitating the peptide backbone sequencing of glycopeptides, identified peptide sequence coverage was increased. For example, identified fetuin sequence percentage was improved from 39 to 80% in MASCOT database searching compared to conventional CID method. The formation of Y1 ions and oxonium ions in ISF facilitates glycopeptide sequencing and glycan composition identification.

Tandem mass spectrometry of isomeric aniline-labeled N-glycans separated on porous graphitic carbon: Revealing the attachment position of terminal sialic acids and structures of neutral glycans

RATIONALE

Quantitative monitoring of changes in the N-glycome upon disease has gained significance in the context of biomarker discovery. Separation and quantification of isobaric glycan isomers can be attained by using high-performance liquid chromatography/electrospray ionization mass spectrometry (HPLC/ESI-MS). Collision-induced dissociation (CID)-based fragmentation of separated isobaric glycans is evaluated in respect to its potential of providing fragment ions specific for the linkage positions of terminal sialic acids and the presence of intersecting GlcNAc moieties, respectively.

METHODS

N-Glycans were labeled via reductive amination using (12)C6-aniline and (13)C6-aniline as isotope-coded labeling reagents. The differently labeled glycans were merged and separated into various species using a porous graphitic carbon (PGC) stationary phase. Identification of structural features of separated isobaric isomers was performed by CID-based tandem mass spectrometry (MS/MS) carried out in a quadrupole time-of-flight (QqTOF) or a quadrupole ion-trap (IT) mass spectrometer.

RESULTS

Working in the negative ion mode, new diagnostic CID fragment ions could be found that are indicative for the α2,6-type linkage of sialic acids. Other diagnostic ions, identified before as being indicative for the substitution of the 6-antenna, could be confirmed as being of relevance also in the case of aniline labeling. In the positive ion mode, CID fragment ions indicative for the structure of short neutral N-glycans were identified.

CONCLUSIONS

One new diagnostic ion specific for the linkage position of the terminal sialic acids and one for the presence of bisecting GlcNAc in N-glycans were identified. The aniline label introduced for improved relative quantitation in MS(1) was found not to significantly alter the CID fragmentation patterns that were reported previously by other authors for unlabeled/reduced glycans or for glycans with more polar labels.

The analysis of the human plasma N-glycome in endometriosis patients

OBJECTIVE

Analysis of the plasma N-glycome in endometriosis patients compared with controls.

STUDY DESIGN

In a case-control study, blood samples were collected from patients who underwent either diagnostic or operative laparoscopy between 2008 and 2011 in the Semmelweis University, Budapest, I. Department of Obstetrics and Gynaecology. From these patients, 92 with endometriosis (30 stage I-II and 62 stage III-IV, including altogether 18 deep infiltrating cases) and 62 controls were selected for glycan analysis. After release, plasma N-glycans were subjected to hydrophilic interaction high performance liquid chromatography, which resulted in 19 chromatographic glycan peaks (GP). The abundances of the GPs were compared between the study groups. For statistical analysis a non-parametric test, the Mann-Whitney-U test, was used.

RESULTS

We found a statistically significant decrease of GP1 and increase of GP14, GP17 and GP18 in endometriosis patients. The latter peaks consist of glycans which play a role in inflammatory processes and malignancy. We also found significant differences in GP2, GP4, GP6, and GP9 between controls and the different endometriosis stage groups. The observed alterations in GP2, GP4 and GP6 may be related to altered glycosylation and remodelling of the glycan branches of the IgG molecule. The alterations of GP9 are presumably associated with changes of transferrin glycosylation. Furthermore we detected a highly significant decrease of GP1 in patients with deep infiltrating endometriosis compared with controls.

CONCLUSIONS

This is the first analysis of the plasma N-glycome in endometriosis. The observed changes in GP14, GP17 and GP18 and in GP2, GP4, GP6 and GP9 provide new aspects to the pathophysiology of the disease and the alterations of the GP1 may serve as a new potential marker in the future.

The glycosylation of AGP and its associations with the binding to methadone

Methadone remains the most common form of pharmacological therapy for opioid dependence; however, there is a lack of explanation for the reports of its relatively low success rate in achieving complete abstinence. One hypothesis is that in vivo binding of methadone to the plasma glycoprotein alpha-1-acid glycoprotein (AGP), to a degree dependent on the molecular structure, may render the drug inactive. This study sought to determine whether alterations present in the glycosylation pattern of AGP in patients undergoing various stages of methadone therapy (titration < two weeks, harm reduction < one year, long-term > one and a half years) could affect the affinity of the glycoprotein to bind methadone. The composition of AGP glycosylation was determined using high pH anion exchange chromatography (HPAEC) and intrinsic fluorescence analysed to determine the extent of binding to methadone. The monosaccharides galactose and N-acetyl-glucosamine were elevated in all methadone treatment groups indicating alterations in AGP glycosylation. AGP from all patients receiving methadone therapy exhibited a greater degree of binding than the normal population. This suggests that analysing the glycosylation of AGP in patients receiving methadone may aid in determining whether the therapy is likely to be effective.

[Glycan ligand specificity of killer lectin receptors]

Sialyl Lewis X (sLeX) antigen, Neu5Acα2,3Galβ1,4(Fucα1,3)GlcNAc-R, is expressed on the glycoproteins in sera or the surface of the cells and the expression of sLeX is enhanced in various conditions such as the inflammation and cancer. SLeX in the serum is utilized as a tumor marker. To clarify the roles of sLeX on secreted glycoproteins in vivo, we investigate the regulation of natural killer (NK) cell-dependent cytotoxicity through sLeX. NK cells express many receptors to kill the target cells such as cancerous cells and non-self, and their protein ligands have been elucidated. Of the killer lectin-like receptors (KLRs) on NK cells, several have been reported to recognize glycans. Using recombinant extracellular domains of KLRs (rKLRs: rNKG2A, C, D and rCD94), we evaluated their glycan ligand specificity and binding affinities using EIA methods. We clarified that all of these rKLRs can bind to high sLeX-expressing glycoprotein and heparin, heparan sulfate and highly sulfated polysaccharides and that glycan binding sites on NKG2D are mostly overlapped with those of protein ligands. In this review, we show the recent findings concerning the glycan ligands of these KLRs.

Endothelial heterogeneity and adhesion molecules N-glycosylation: implications in leukocyte trafficking in inflammation

Inflammation is a major contributing element to a host of diseases with the interaction between leukocytes and the endothelium being key in this process. Much is understood about the nature of the adhesion molecule proteins expressed on any given leukocyte and endothelial cell that modulates adhesive interactions. Although it is appreciated that these proteins are heavily glycosylated, relatively little is known about the roles of these posttranslational modifications and whether they are regulated, and if so how during inflammation. Herein, we suggest that a paucity in this understanding is one major reason for the lack of successful therapies to date for modulating leukocyte-endothelial interactions in human inflammatory disease and discuss developing paradigms of (i) how endothelial adhesion molecule glycosylation (with a focus on N-glycosylation) maybe a critical element in understanding endothelial heterogeneity between different vascular beds and species, (ii) how adhesion molecule N-glycosylation may be under distinct, and as yet, unknown modes of regulation during inflammatory stress to affect the inflammatory response in a vascular bed- and disease-specific manner (analogous to a "zip code" for inflammation) and finally (iii) to underscore the concept that a fuller appreciation of the role of adhesion molecule glycoforms is needed to provide foundations for disease and tissue-specific targeting of inflammation.

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

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

Sub 2-μm macroporous silica particles derivatized for enhanced lectin affinity enrichment of glycoproteins

A new, mechanically stable silica microparticle with macrosized internal pores (1.6 μm particles with 100 nm pores) has been developed for chromatography. The particles are characterized by an extensive network of interconnected macropores with a high intraparticle void volume, as observed by transmission electron microscopy (TEM). They are synthesized by an aerosol assembly technique called ultrasonic spray pyrolysis (USP). The particles have a high surface area for a macroporous material, ∼200 m(2)/g, making them suitable for large biomolecular separations. To demonstrate their potential for bioseparations, they have been functionalized with lectins for affinity enrichment of glycoproteins. The material was derivatized with two lectins, Concanavalin A (Con A) and Aleuria aurantia lectin (AAL), and binding properties were tested with standard glycoproteins. The columns exhibited excellent binding capacities for microaffinity enrichment: Con A was able to bind 75 μg of a standard glycoprotein in a 50 × 1 mm column. Following initial tests, the lectin microcolumns were utilized for enrichment of glycoproteins from 1 μL volumes of blood serum samples, performed in triplicate for each lectin. The enriched serum fractions were subjected to side-by-side glycomic and glycoproteomic profiling analyses with mass spectrometry to show that the new particles offer excellent sensitivity for microscale analyses of precious biological sample materials. The unique combination of the macroporous architecture and small particle diameter suggests the material may have advantages for conventional modes of chromatographic separation of macromolecules in an ultra-high-pressure liquid chromatography (UHPLC) format.

Jacalin bound plasma O-glycoproteome and reduced sialylation of alpha 2-HS glycoprotein (A2HSG) in rheumatoid arthritis patients

Glycosylation studies of plasma proteins can reveal information about the onset and progression of diseases, where in the glycan biosynthetic pathways are disturbed as in rheumatoid arthritis (RA). The present study was focused on analysis of O-linked glycoproteins of plasma in RA patients. Two dimensional gel electrophoresis of jacalin bound plasma of RA patients revealed a number of differentially expressed protein spots as compared to healthy controls. Eighteen protein spots were found to have statistically significant (p<0.05) difference in their expression level from four sets of gels and were identified by MALDI-TOF MS. Most of the identified proteins were predicted to be O-glycosylated proteins by Net-O-Gly 3.1 algorithm. Among these the alpha 2HS glycoprotein (A2HSG) was found to be down regulated whereas inter alpha trypsin inhibitor H4 (ITIH4) was up regulated and this was validated by Western blotting. The glycosylation studies showed the reduced N-linked sialylation of A2HSG in RA patients. Altered glycoprotein expression and functional as well as structural studies of glycans might help in the diagnosis of RA and understanding the disease pathogenesis.

Higher energy collision dissociation (HCD) product ion-triggered electron transfer dissociation (ETD) mass spectrometry for the analysis of N-linked glycoproteins

Large scale mass spectrometry analysis of N-linked glycopeptides is complicated by the inherent complexity of the glycan structures. Here, we evaluate a mass spectrometry approach for the targeted analysis of N-linked glycopeptides in complex mixtures that does not require prior knowledge of the glycan structures or pre-enrichment of the glycopeptides. Despite the complexity of N-glycans, the core of the glycan remains constant, comprising two N-acetylglucosamine and three mannose units. Collision-induced dissociation (CID) mass spectrometry of N-glycopeptides results in the formation of the N-acetylglucosamine (GlcNAc) oxonium ion and a [mannose+GlcNAc] fragment (in addition to other fragments resulting from cleavage within the glycan). In ion-trap CID, those ions are not detected due to the low m/z cutoff; however, they are detected following the beam-type CID known as higher energy collision dissociation (HCD) on the orbitrap mass spectrometer. The presence of these product ions following HCD can be used as triggers for subsequent electron transfer dissociation (ETD) mass spectrometry analysis of the precursor ion. The ETD mass spectrum provides peptide sequence information, which is unobtainable from HCD. A Lys-C digest of ribonuclease B and trypsin digest of immunoglobulin G were separated by ZIC-HILIC liquid chromatography and analyzed by HCD product ion-triggered ETD. The data were analyzed both manually and by search against protein databases by commonly used algorithms. The results show that the product ion-triggered approach shows promise for the field of glycoproteomics and highlight the requirement for more sophisticated data mining tools.

Vitamin D binding protein isoforms as candidate predictors of disease extension in childhood arthritis

INTRODUCTION

Juvenile idiopathic arthritis (JIA) comprises a poorly understood group of chronic autoimmune diseases with variable clinical outcomes. We investigated whether the synovial fluid (SF) proteome could distinguish a subset of patients in whom disease extends to affect a large number of joints.

METHODS

SF samples from 57 patients were obtained around time of initial diagnosis of JIA, labeled with Cy dyes and separated by two-dimensional electrophoresis. Multivariate analyses were used to isolate a panel of proteins which distinguish patient subgroups. Proteins were identified using MALDI-TOF mass spectrometry with expression verified by immunochemical methods. Protein glycosylation status was confirmed by hydrophilic interaction liquid chromatography.

RESULTS

A truncated isoform of vitamin D binding protein (VDBP) is present at significantly reduced levels in the SF of oligoarticular patients at risk of disease extension, relative to other subgroups (p<0.05). Furthermore, sialylated forms of immunopurified synovial VDBP were significantly reduced in extended oligoarticular patients (p<0.005).

CONCLUSION

Reduced conversion of VDBP to a macrophage activation factor may be used to stratify patients to determine risk of disease extension in JIA patients.

Ion mobility mass spectrometry for extracting spectra of N-glycans directly from incubation mixtures following glycan release: application to glycans from engineered glycoforms of intact, folded HIV gp120

The analysis of glycosylation from native biological sources is often frustrated by the low abundances of available material. Here, ion mobility combined with electrospray ionization mass spectrometry have been used to extract the spectra of N-glycans released with PNGase F from a serial titration of recombinantly expressed envelope glycoprotein, gp120, from the human immunodeficiency virus (HIV). Analysis was also performed on gp120 expressed in the α-mannosidase inhibitor, and in a matched mammalian cell line deficient in GlcNAc transferase I. Without ion mobility separation, ESI spectra frequently contained no observable ions from the glycans whereas ions from other compounds such as detergents and residual buffer salts were abundant. After ion mobility separation on a Waters T-wave ion mobility mass spectrometer, the N-glycans fell into a unique region of the ion mobility/m/z plot allowing their profiles to be extracted with good signal:noise ratios. This method allowed N-glycan profiles to be extracted from crude incubation mixtures with no clean-up even in the presence of surfactants such as NP40. Furthermore, this technique allowed clear profiles to be obtained from sub-microgram amounts of glycoprotein. Glycan profiles were similar to those generated by MALDI-TOF MS although they were more susceptible to double charging and fragmentation. Structural analysis could be accomplished by MS/MS experiments in either positive or negative ion mode but negative ion mode gave the most informative spectra and provided a reliable approach to the analysis of glycans from small amounts of glycoprotein.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for the period 2005-2006

This review is the fourth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2006. The review covers fundamental studies, fragmentation of carbohydrate ions, method developments, and applications of the technique to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, glycated proteins, glycolipids from bacteria, glycosides, and various other natural products. There is a short section on the use of MALDI-TOF mass spectrometry for the study of enzymes involved in glycan processing, a section on industrial processes, particularly the development of biopharmaceuticals and a section on the use of MALDI-MS to monitor products of chemical synthesis of carbohydrates. Large carbohydrate-protein complexes and glycodendrimers are highlighted in this final section.

Comparative glycomics using a tetraplex stable-isotope coded tag

This study illustrates the utility of tetraplex stable isotope coded tags in mass spectrometric glycomics using three carbohydrate classes. The teteraplex tags allow for the direct comparison of glycan compositions within four samples using capillary scale hydrophilic interaction chromatography with online mass spectrometry. In addition, the ability to discern glycan structural isomers is shown based on the tandem mass spectra of each composition using nanospray ionization. Results are shown for chondroitin sulfate proteoglycans, low molecular weight heparins, full length heparins, and N-glycans from alpha-1-acid glycoproteins from four mammalian species. The data demonstrate the value of the tetraplex stable isotope tagging approach for producing high-quality glycomics compositional profiling and fine structural analysis.

Glycosylation of liver acute-phase proteins in pancreatic cancer and chronic pancreatitis

PURPOSE

Glycosylation of acute-phase proteins (APP), which is partially regulated by cytokines, may be distinct in disease and provide useful tumour markers. Thus, we have examined the glycosylation of major serum APP in pancreatic cancer (PaC), chronic pancreatitis (CP) and control patients.

EXPERIMENTAL DESIGN

Using a specific anti-sialyl Lewis X antibody and N-glycan sequencing, we have determined glycosylation changes on α-1-acid glycoprotein (AGP), haptoglobin (HPT), fetuin (FET), α-1-antitrypsin (AT) and transferrin (TRF).

RESULTS

Increased levels of sialyl Lewis X (SLe(x) ) were detected on AGP in advanced PaC and CP and on HPT, FET, AT and TRF in CP. An increase in N-glycan branching was detected on AGP and HPT in the advanced stage of PaC and CP and on FET and TRF in the CP. A core fucosylated structure was increased on AGP and HPT only in the advanced PaC patients.

CONCLUSIONS AND CLINICAL RELEVANCE

Changes in APP SLe(x) and branching are probably associated with an inflammatory response because they were detected in both advanced PaC and CP patients and these conditions give rise to inflammation. On the contrary, the increase in APP core fucosylation could be cancer associated and the presence of this glycoform may give an advantage to the tumour.