Carbohydrate composition and immunomodulatory activity of different glycoforms of alpha1-acid glycoprotein

Precursor carboxy-silica for functionalization with interactive ligands. III. Carbodiimide assisted preparation of immobilized lectin stationary phases for high performance lectin affinity chromatography of sub-glycoproteomics from cancer and disease free human sera

In this study, a precursor carboxy-silica support was demonstrated in the immobilization of two different lectins, namely concanavalin A (Con A) and wheat germ agglutinin (WGA) for use in high performance lectin affinity chromatography (LAC) for the selective capturing and enrichment of glycoproteins from healthy/disease free and cancer human sera. The lectin columns thus obtained (i.e., Con A- and WGA-columns) showed no nonspecific interactions toward some chosen standard glycoproteins and non-glycoproteins. Both columns were shown in sub-glycoproteomics enrichment from human sera including disease free and adenocarcinoma cancer sera. The collected fractions were subjected to LC-MS/MS for identification of the captured glycoproteins, whereby the total number of identified proteins using Con A column from disease-free and cancer sera were 164 and 188, respectively while 133 and 103 proteins were identified in the fractions captured by the WGA column from disease-free and cancer sera samples, respectively. Differentially expressed proteins (DEPs) between the disease free and cancer sera in both the Con A and WGA column fractions were identified via the plot of the abundance vs. the protein ratio whereby the binary logarithm of average intensities of cancer and disease free sera were plotted against the binary logarithm of cancer/disease free sera ratios. The proteins that exhibit log 2 (cancer/healthy) ratio values greater than +2 and less than -2 in both categories are considered as DEPs. Furthermore, for visualization of the data arrangement, Q-Q scatterplot were also used whereby the binary logarithm of cancer serum was plotted against the binary logarithm of disease-free serum for both Con A and WGA. For Con A column, 28 up-regulated and 10 down regulated proteins were identified with a total of 38 DEPs while only two being non-glycoproteins. Furthermore, the up-regulated, and down regulated proteins recorded for WGA column are 14 and 6, respectively, totaling 20 proteins including 3 non-glycoproteins. Some of the non-specific binding to lectin are most likely due to protein-protein interactions.

Roles of the structural units, glycotopes / mammalian N-glycans for Con A-glycan interactions, their codes, and their recognition factors

The binding property of Con A has been studied intensively and applied widely to glycoconjugates / glycobiology for over 80 years. However, its role and functional relationship of Con A with these mammalian structural units, glycotopes, N-glycan chains, as well as their polyvalent forms in N-glycoproteins involved in the Con A-glycan interactions have not been well defined and organized. In this study, the recognition factors involved in these interactions were analyzed by our well developed method- the enzyme linked lectinosorbent (ELLSA) and inhibition assay. Based on all the data obtained, it is concluded that Con A, as previously reported, has a relatively broad and wide recognition ability of the Manα1 → and Glcα1 → related glycans. It reacted not only strongly with yeast mannan and glycogens, but also bound well with a large number of mammalian N-glycans, including the N-glycans of rat sublingual gp (RSL), human Tamm-Horsfall glycoprotein (THGP), thyroglobulin and lactoferrin. The recognition specificity of Con A towards ligands, expressed by Molar Relative Potency (Molar R.P.), in a decreasing order is as follows: α1 → 3, α1 → 6 Mannopentaose (M5) and Biantennary N-linked core pentasaccharide (MDi) ≥ α1 → 3, α1 → 6 Mannotriose (M3) > Manα1 → 3Man (α1 → 3Mannobiose), Manα1 → 2Man (α1 → 2Mannobiose), Manα1 → 6Man (α1 → 6Mannobiose), Manα1 → 4Man (α1 → 4Mannobiose) > GlcNAcβ1 → 2Man (β1 → 2 N-Acetyl glucosamine-mannose) > Manα1 → /Glcα1 → > Man > Glc, while Gal / GalNAc were inactive. Furthermore, the Man related code system, in this study, is proposed to express by both numbers of Man and GlcNAcβ1 → branches (M3 to M9 / MMono to Penta etc.) and a table of three Manα1 → and Glcα1 → related biomasses of six recognition factors involved in the Con A-glycan interactions has also been demonstrated. These themes should be one of the most valuable advances since 1980s.

Effect of nanocellulose polymorphism on electrochemical analytical performance in hybrid nanocomposites with non-oxidized single-walled carbon nanotubes

Two cellulose nanocrystals/single-walled carbon nanotube (CNC/SW) hybrids, using two cellulose polymorphs, were evaluated as electrochemical transducers: CNC type I (CNC-I/SW) and CNC type II (CNC-II/SW). They were synthesized and fully characterized, and their analytical performance as electrochemical sensors was carefully studied. In comparison with SWCNT-based and screen-printed carbon electrodes, CNC/SW sensors showed superior electroanalytical performance in terms of sensitivity and selectivity, not only in the detection of small metabolites (uric acid, dopamine, and tyrosine) but also in the detection of complex glycoproteins (alpha-1-acid glycoprotein (AGP)). More importantly, CNC-II/SW exhibited 20 times higher sensitivity than CNC-I/SW for AGP determination, yielding a LOD of 7 mg L^-1.These results demonstrate the critical role played by nanocellulose polymorphism in the electrochemical performance of CNC/SW hybrid materials, opening new directions in the electrochemical sensing of these complex molecules. In general, these high-active-surface hybrids smartly exploited the preserved non-oxidized SW conductivity with the high aqueous dispersibility of the CNC, avoiding the use of organic solvents or the incorporation of toxic surfactants during their processing, making the CNC/SW hybrids promising nanomaterials for electrochemical detection following greener approaches.

Isolation of lymphocytes from the human gastric mucosa

Flow cytometry is widely used for lymphocyte immunophenotyping in clinical settings. However, few studies have applied it for analyzing lymphocytes of the gastric mucosa. This review offers an overview of methodologies for isolating lymphocytes from the human stomach. Previously reported articles were reviewed, focusing on procedures for isolating human gastric mucosal lymphocytes. Helicobacter pylori-associated peptic diseases and gastric cancer are two major subjects of research in this field. Enzymatic dissociation, mechanical dissociation, or a combination of the two have been used to isolate lymphocytes from the stomach. Intra-epithelial and lamina propria lymphocytes were separately isolated in several studies. We also summarize the history and present trends in analyzing lymphocytes in patients with gastric disease.

Serum Levels and Glycosylation Changes of Alpha-1-Acid Glycoprotein According to Severity of Breast Cancer in Korean Women

Elevated serum levels of alpha-1-acid glycoprotein (AGP) are known to be associated with several types of cancer. In addition, some reports have indicated that changes in glycosylation of AGP are associated with cancer progression. However, changes in AGP levels of serum and changes in glycosylation of AGPs in breast cancer have not been specifically studied. In the present study, serum AGP levels in benign (BN) cancer and breast cancer stage I (BC I), BC IIA, BC IIB, and BC III in Korean women were measured using an enzyme-linked immunosorbent assay (ELISA). AGP was purified from individual sera by hot phenol extraction and then subjected to AGP glycosylation analysis. Three types of AGP glycosylation (fucosylation, high-mannose-type and sialylation) were detected using enzyme-linked lectin assays (ELLAs). Serum AGP levels were higher in BC I, BC IIA, BC IIB, and BC III, than in the BN group, and the level in BC I and BC IIA was high enough to be distinguished from BN. Meanwhile, terminal fucosylation and high-mannose-type glycans appeared to be lowest in BC I. The glycosylation levels of BC I provide sensitivity and specificity that make BC I clearly distinguishable from BC IIA, BC IIB, and BC III as well as BN. Therefore, determination of serum AGP or AGP glycosylation level could be useful for detecting the early stages of breast cancer.

Profiling tear proteomes of patients with unilateral relapsed Behcet's disease-associated uveitis using data-independent acquisition proteomics

Purpose

To explore whether unilateral relapse of Bechet’s disease-associated uveitis (BDU) causes differences in the tear proteome between the diseased and the contralateral quiescent eye and potential tear biomarkers for uveitis recurrence and disease monitoring.

Method

To minimize interindividual variations, bilateral tear samples were collected from the same patient (n = 15) with unilateral relapse of BDU. A data-independent acquisition (DIA) strategy was used to identify proteins that differed between active and quiescent eyes.

Results

A total of 1,797 confident proteins were identified in the tear samples, of which 381 (21.2%) were also highly expressed in various tissues and organs. Fifty-one (2.8%) proteins differed in terms of expression between tears in active and quiescent eyes, 9 (17.6%) of which were functionally related to immunity or inflammation. Alpha-1-acid glycoprotein 1 (fold change = 3.2, p = 0.007) was increased and Annexin A1 (fold change = −1.7, p < 0.001) was decreased in the tears of the active BDU eye compared to the contralateral quiescent eye.

Conclusions

A substantial amount of confident proteins were detected in the tears of BDU patients, including proteins that were deferentially expressed in the uveitis-relapsed eyes and the contralateral quiescent eyes. Some of these identified tear proteins play important roles in immune and inflammatory processes. Tear proteome might be a good source of biomarkers for uveitis.

The Immune Functions of α1 Acid Glycoprotein

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

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

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

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

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

Human plasma lipocalins and serum albumin: Plasma alternative carriers?

Lipocalins are an evolutionarily conserved family of proteins that bind and transport a variety of exogenous and endogenous ligands. Lipocalins share a conserved eight anti-parallel β-sheet structure. Among the different lipocalins identified in humans, α-1-acid glycoprotein (AGP), apolipoprotein D (apoD), apolipoprotein M (apoM), α1-microglobulin (α1-m) and retinol-binding protein (RBP) are plasma proteins. In particular, AGP is the most important transporter for basic and neutral drugs, apoD, apoM, and RBP mainly bind endogenous molecules such as progesterone, pregnenolone, bilirubin, sphingosine-1-phosphate, and retinol, while α1-m binds the heme. Human serum albumin (HSA) is a monomeric all-α protein that binds endogenous and exogenous molecules like fatty acids, heme, and acidic drugs. Changes in the plasmatic levels of lipocalins and HSA are responsible for the onset of pathological conditions associated with an altered drug transport and delivery. This, however, does not necessary result in potential adverse effects in patients because many drugs can bind both HSA and lipocalins, and therefore mutual compensatory binding mechanisms can be hypothesized. Here, molecular and clinical aspects of ligand transport by plasma lipocalins and HSA are reviewed, with special attention to their role as alterative carriers in health and disease.

O-glycosylation of α-1-acid glycoprotein of human milk is lactation stage related

BACKGROUND

Human milk provides a multitude of glycoproteins, including highly glycosylated α-1-acid glycoprotein (AGP), which elicits anti-inflammatory and immunomodulatory properties. The milk AGP glycoforms may provide the breastfed infant with a wide range of biological benefits. Here, we analyzed the reactivity of O-linked sugar-specific lectins with human milk AGP over the process of lactation and compared the results with those of the lactating mother's plasma.

MATERIALS AND METHODS

Relative amounts of human skim milk AGP O-glycans were analyzed in early colostrum, colostrum, and transitional and mature milk samples of 127 healthy mothers by lectin-AGP enzyme-linked immunosorbent assay using sialyl T (sialyl-α2,3/α2,6 Galβ1,3GalNAc-), asialyl T (Galβ1,3GalNAc-), and Tn (GalNAc-) antigen-specific biotinylated Artocarpus integrifolia (Jacalin), Arachis hypogaea (PNA), and Vicia villosa (VVA) lectins, respectively.

RESULTS

Milk AGP elicited high expression of Jacalin- and PNA-reactive glycotopes and low expression of VVA-reactive glycotopes, which were absent on plasma AGP of lactating mothers and healthy individuals. The expression of sialyl, asialyl T, and Tn glycotopes of human milk AGP was lactation stage related. The relative amount of Jacalin-reactive AGP glycotope was highest in the colostrum samples and then decreased starting from Day 8 of lactation. In contrast, an increase of the relative amount of PNA-reactive glycotope with milk maturation was observed. The relative amount of VVA-reactive glycotope remained almost constant over the development of lactation.

CONCLUSIONS

Milk AGP differs from mother's plasma AGP by the presence of O-linked sialylated and asialylated T as well as Tn antigens. The variation of the expression of sialylated and asialylated T and Tn antigens on AGP is associated with milk maturation.

Lactation stage-related expression of sialylated and fucosylated glycotopes of human milk α-1-acid glycoprotein

BACKGROUND

Because terminal sugars of α-1-acid glycoprotein (AGP) are reported to be involved in anti-inflammatory and immunomodulatory processes, their expressions might have an influence on the proper function of immune system of newborns. Here, relative amounts of sialylated and fucosylated glycotopes on human milk AGP over normal lactation were investigated.

MATERIALS AND METHODS

AGP concentration and relative amounts of its sialylated and fucosylated glycovariants were analyzed in early colostrum, colostrum, and transitional and mature milk samples of 127 healthy mothers by lectin-AGP enzyme-linked immunosorbent assay using α2,3- and α2,6-sialic acid and α1,2-, α1,3-, and α1,6-fucose specific biotinylated Maackia amurensis, Sambucus nigra, Ulex europaeus, Tetragonolobus purpureus, and Lens culinaris lectins, respectively.

RESULTS

AGP concentration in human milk was about 30 times lower than in plasma of lactating mothers and decreased gradually over lactation. Milk AGP showed significantly higher expression of sialylated and fucosylated glycotopes in comparison with those of plasma AGP. Milk AGP glycovariants containing α2,6-sialylated and α1,6- and α1,2-fucosylated glycotopes showed the highest relative amounts in early colostrums. With progression of lactation, the expressions of glycotopes α1,2-fucosylated decreased starting from Day 4 and those of α2,6-sialylated and α1,6-fucosylated from Day 8 of lactation, whereas the level of α2,3-sialyl-glycotope was almost constant over 45 days of lactation. In contrast, the expression of α1,3-linked fucose on AGP was low in colostrums and significantly higher in transitional and mature milk.

CONCLUSIONS

The relative amounts of sialylated and fucosylated glycovariants of human hindmilk AGP significantly varied between Days 2 and 45 of normal lactation.

Effects of desialylation on human α1-acid glycoprotein-ligand interactions

Human α1-acid glycoprotein (AGP), an acute-phase glycoprotein, exists predominantly in blood. With its ability to bind basic, lipophilic, and acidic drugs, AGP has served as a drug carrier. It has been shown that the carbohydrate composition of AGP changes in response to tissue injury, inflammation, or infection and can have a great impact on AGP's drug binding activities. The molecular-level details of the effects of desialylation on the AGP conformation and AGP-ligand interactions, however, are unknown. Here we report the use of hydrogen-deuterium exchange coupled with mass spectrometry (HDX-MS) to reveal the changes in AGP conformational dynamics induced by the removal of terminal sialic acid. HDX-MS also reveals the changes in the conformational dynamics of sialylated and unsialylated AGP upon formation of complexes of holo-AGP with progesterone or propranolol. Our HDX-MS results demonstrate that desialylation stabilizes two loop regions that are exterior to the β-sheet barrel in AGP, and this stabilization minimizes the conformational changes of AGP upon binding with progesterone or propranolol.

Unlike natural killer (NK) p30, natural cytotoxicity receptor NKp44 binds to multimeric α2,3-NeuNAc-containing N-glycans

Natural cytotoxicity receptor 2 (NCR2 or natural killer (NK)p44) and NCR3 (NKp30) bind to heparin and heparin sulfate; however, other natural ligands have yet to be identified. We previously reported that NCR1 (NKp46) can bind to multimeric NeuNAc-containing N-glycans and sulfated glycans. In this study, we investigated whether NKp44 and NKp30 can bind to NeuNAc-containing glycans using their common recombinant extracellular domain tagged with 6×His (NKp44-H6 and NKp30-H6). NKp44-H6, but not NKp30-H6, bound multimeric sialyl Lewis X expressing transferrin secreted by HepG2 cells (HepTF) with a K(d) of 420 nM. Competitive and direct binding assays revealed that NKp44-H6 mainly recognizes α2,3-NeuNAc residues on non-reducing ends of N-glycans on HepTF. Moreover, site-directed mutants of NKp44-H6, such as R47Q, R55Q, R92Q, R95Q, K103Q, and R106Q, had reduced binding to α2,3-sialylated N-glycans. These results suggest that NKp44 binds to α2,3-sialylated N-glycans through ionic interactions, and that these binding sites might have some overlap with heparin binding sites.

Smoking and lung cancer-induced changes in N-glycosylation of blood serum proteins

Glycosylation is a key post-translational protein modification which appears important in malignant transformation and tumor metastasis. Abnormal glycosylation of different proteins can often be measured in the blood serum. In this study, we extend our serum-based structural investigations to samples provided by patients diagnosed with lung cancer, paying particular attention to the effects of smoking on the serum glycomic traces. Following a battery of glycomic tests, we find that several fucosylated tetra-antennary structures with varying degrees of sialylation are increased in their abundances in control samples provided by the former smokers, with further elevations in the lung cancer patients who were former smokers. Further detailed investigations demonstrated that the level of outer-arm fucosylation was elevated in the control samples of the former smokers and again in the lung cancer samples provided by the former smokers. This trend was particularly noticeable for the tri- and tetra-antennary structures. Different ratios of sialylation linkages were also observed that could be correlated with the different states of health and smoking status. Decreases in the abundance levels of isomers with two and three α2,3-linked sialic acids and an increased abundance of an isomer with two α2,6-linked sialic acids were noted for a fucosylated tri-sialylated tri-antennary glycan. These results demonstrate the long-term effects of smoking on glycomic profiles and that this factor needs to be considered in these and other serum-based analyses.

Flow cytometric detection of alpha-1-acid glycoprotein on feline circulating leucocytes

OBJECTIVE

To assess whether alpha-1-acid glycoprotein (AGP) can be detected on the membrane of feline circulating leucocytes.

DESIGN

The presence of AGP on circulating leucocytes was investigated in both clinically healthy cats and cats with different diseases. A group of feline coronavirus (FCoV)-positive cats, comprising cats with feline infectious peritonitis (FIP) and cats not affected by FIP but seropositive for FCoV, were included in this study because the serum concentration of AGP increases during FCoV infection.

PROCEDURE

Flow cytometry (using an anti-feline AGP antibody), serum protein electrophoresis, routine haematology and measurement of the serum AGP concentration were performed using blood samples from 32 healthy cats (19 FCoV-seropositive), 13 cats with FIP and 12 with other diseases (6 FCoV-seropositive). The proportion of cats with AGP-positive leucocytes in the different groups (e.g. controls vs sick; FIP vs other diseases, etc.) or in cats with different intensities of inflammatory response was compared using a Chi-square test.

RESULTS

AGP-positive leucocytes were found in 23% of cats. Compared with controls, the proportion of patients with positive granulocytes and monocytes was higher among sick cats (especially cats with diseases other than FIP) and cats with high serum AGP concentration, but not in cats with leucocytosis or that were FCoV-seropositive.

CONCLUSION

AGP-positive leucocytes can be found in feline blood, especially during inflammation. Conversely, no association between AGP-positive leucocytes and FIP was found. Further studies are needed to elucidate the mechanism responsible for this finding and its diagnostic role in cats with inflammation.

α1-Acid glycoprotein induced effects in rat brain microvessel endothelial cells

α1-Acid glycoprotein (AGP) is a positive acute phase protein which is elevated 1-10 times during inflammation. Whereas AGP has been reported to have immunomodulatory properties, other biological functions of this protein such as its effects on the blood-brain barrier (BBB) endothelium are unknown. Tight junction (TJ) proteins (ZO-1 and occludin) are crucial in maintaining BBB integrity and brain homeostasis. As inflammatory cytokines have been shown to alter BBB integrity and TJ protein expression, we hypothesized that AGP changes BBB function by stimulating inflammatory cytokines and/or directly modulating TJ protein expression. We used primary rat brain microvessel endothelial cells (RBMECs) as an in vitro BBB model to study the direct effects of AGP on the brain microvasculature. No change in cytokine levels was detected in supernatant from AGP-treated RBMECs, despite increased mRNA expression by the cells. Paracellular permeability was decreased up to 20%, across RBMEC monolayers following treatment with AGP, suggesting its role in enhancing BBB integrity. RBMECs showed a biphasic response of increased occludin protein expression following AGP treatment while ZO-1 expression changed in a dose- and time-dependent manner. These changes in TJ proteins suggest that AGP induced changes in occludin related to enhanced barrier properties while the change in ZO-1 may play a secondary role in BBB integrity and/or as an intracellular signaling molecule. AGP significantly changed transcription factor activator protein 1 (AP-1) DNA-binding activity which provides evidence of the potential cell signaling pathways that contribute to the effect of AGP in RBMECs. Together, this supports our hypothesis that AGP has a direct effect in brain microvasculature and may play an important role in altering BBB integrity in inflammatory-related diseases.

Statistical evaluation of CZE-UV and CZE-ESI-MS data of intact α-1-acid glycoprotein isoforms for their use as potential biomarkers in bladder cancer

α-1-acid glycoprotein (AGP) is a highly heterogeneous protein that presents a vast number of isoforms (molecules of the protein differing in its peptidic and/or glycosidic moieties). In the last years, several authors have studied the potential use of AGP as a cancer biomarker. These studies focus on the correlation of different features of AGP structure (i.e. fucosylation, antennarity) with cancer or on the total protein blood concentration. In this study, the potential of CZE-UV and CZE-ESI-MS analysis of intact AGP isoforms to study the correlation of this protein with bladder cancer is shown. Samples from 16 individuals (eight healthy, eight bladder cancer) were analyzed and characterized in great detail including data on intact protein isoforms and on released glycans. The analytical data were evaluated employing different statistical techniques (ANOVA; principal component analysis, PCA; linear discriminant analysis; and partial least squares-discriminant analysis). Statistical differences between the two groups of study were observed. The best results were obtained by linear discriminant analysis of the CZE-ESI-MS data for intact AGP isoforms (93.75% of correct classification). Due to MS characterization, it can be observed that differences between the samples are mainly due to higher abundance of AGP isoforms containing tri- and tetra-antennary fucosylated oligosaccharides in cancer patients. The results show the great potential of CE-MS in combination with advanced data processing for the use of intact protein isoforms as disease biomarkers.

Natural killer group 2A (NKG2A) and natural killer group 2C (NKG2C) bind to sulfated glycans and α2,3-NeuAc-containing glycoproteins

Killer lectin-like receptors on natural killer (NK) cells mediate cytotoxicity through glycans on target cells. We prepared recombinant glutathione S-transferase-fused extracellular lectin-like domains (AA 94-231) of natural killer group 2A (NKG2A) (rGST-NKG2A) and NKG2C (rGST-NKG2C) and determined the binding of these receptors to plates coated with heparin-conjugated bovine serum albumin (heparin-BSA) and glycoproteins. rGST-NKG2A and rGST-NKG2C directly bound to heparin-BSA with K(d) values of 20 and 40 nM, respectively. Binding of rGST-NKG2A and rGST-NKG2C to heparin-BSA was suppressed in the presence of soluble heparin, heparan sulfate, fucoidan, λ-carrageenan, and dextran sulfate. 2-O-Sulfate residues in heparin were essential for the binding of rGST-NKG2A and rGST-NKG2C. Moreover, rGST-NKG2A and rGST-NKG2C bound to multimeric sialyl Lewis X expressing transferrin secreted by HepG2 cells with K(d) values of 80 and 114 nM, respectively. This is the first report showing that NKG2A and NKG2C bind to heparin and α2,3-NeuAc-containing glycoproteins.

Binding of natural cytotoxicity receptor NKp46 to sulfate- and α2,3-NeuAc-containing glycans and its mutagenesis

Natural cytotoxicity receptor 1 (NCR1, NKp46) binds to heparin and heparan sulfate; however, other natural ligands for NKp46 have yet to be elucidated. Using the recombinant extracellular region (coding for AA 22-258) of NKp46 tagged with 6× His (NKp46-H6), and mutants K136Q, R139Q, H142Q, R145Q, and K149Q, we determined their binding affinities to sulfate- and NeuAc-containing glycans-coated plates. NKp46-H6 directly bound to plates coated with heparin- and heparan sulfate-conjugated bovine serum albumin with K(d) values of 770 and 850 nM, respectively. The binding of NKp46-H6 to heparin-BSA was suppressed by soluble heparin, herparan sulfate, fucoidan, λ-carrageenan, and dextran sulfate, but not by 2-O-, 6-O-, and N-desulfated heparin. NKp46-H6 also bound to multimeric sialyl Lewis X expressing transferrin secreted by human hepatoma HepG2 cells (HepTF) with a K(d) value of 530 nM, but not to desialylated HepTF, commercially available TF, or 1-acid glycoprotein. Moreover, mutants R139Q, R145Q, and K149Q had significantly reduced binding to these sulfate-containing glycans, and K136Q and K149Q to HepTF, indicating that NKp46 binds to sulfate- and 2,3-NeuAc-containing glycans mainly via ionic interactions. However, the binding sites of NKp46 were different.

Quantification of monosaccharides through multiple-reaction monitoring liquid chromatography/mass spectrometry using an aminopropyl column

A simple, sensitive, and reproducible quantitative liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was designed for the simultaneous quantification of monosaccharides derived from glycoprotein and blood serum using a multiple-reaction monitoring (MRM) approach. Sialic acids and neutral monosaccharides were efficiently separated using an amino-bonded silica phase column. Neutral monosaccharide molecules were detected as their aldol acetate anion adducts [M + CH(3)CO(2)](-) using electrospray ionization in negative ion MRM mode, while sialic acids were detected as deprotonated ions [M-H](-). The new method did not require a reduction step, and exhibited very high sensitivity to carbohydrates with limits of detection of 1 pg for the sugars studied. The linearity of the described approach spanned over three orders of magnitude (pg to ng). The method was validated for monosaccharides originating from N-linked glycans attached to glycoproteins and glycoproteins found in human blood serum. The method effectively quantified monosaccharides originating from as little as 1 microg of glycoprotein and 5 microL of blood serum. The method was robust, reproducible, and highly sensitive. It did not require reduction, derivatization or postcolumn addition of reagents.

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

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

Development of a fast and simple immunochromatographic method to purify alpha 1-acid glycoprotein from serum for analysis of its isoforms by capillary electrophoresis

Alpha 1-acid glycoprotein (AGP) is a very heterogeneous glycoprotein presenting several isoforms due to variations in its polypeptidic and glycosidic moieties. Differences in AGP isoforms between healthy and diseased individuals have been related to different pathological situations such as cancer or cardiovascular diseases, among others. Capillary electrophoresis study of the role of AGP isoforms as biomarkers requires prior purification of AGP from biological samples. Current AGP purification methods are time- and labour-consuming, and generally they have not been proven to be compatible with capillary electrophoresis analysis. In this work, different methods for AGP purification from human serum are developed and compared. The applicability of acidic precipitation and immunoaffinity chromatographic methods for AGP purification are studied. Two different immunoaffinity approaches are employed; in the first one, interferents present in the AGP sample are captured and removed, and in the second one, AGP is retained in a house-made anti-AGP column, being in this way isolated from the rest of interferents of the sample. Best results in AGP purification from human serum to be analyzed by capillary zone electrophoresis (CZE) were obtained when acidic purification was combined with immunoaffinity chromatography (IAC) employing the house-made anti-AGP column. The method was shown not to alter the proportion of AGP peaks due to isoforms existing in AGP samples. The applicability of this fast and easy purification method developed for analyzing by CZE isoforms of AGP from natural serum samples by CZE is demonstrated.

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

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

Carbamate-linked lactose: design of clusters and evidence for selectivity to block binding of human lectins to (neo)glycoproteins with increasing degree of branching and to tumor cells

Various pathogenic processes are driven by protein(lectin)-glycan interactions, especially involving beta-galactosides at branch ends of cellular glycans. These emerging insights fuel the interest to design potent inhibitors to block lectins. As a step toward this aim, we prepared a series of ten mono- to tetravalent glycocompounds with lactose as a common headgroup. To obtain activated carbonate for ensuing carbamate formation, conditions for the facile synthesis of pure isomers from anomerically unprotected lactose were identified. To probe for the often encountered intrafamily diversity of human lectins, we selected representative members from the three subgroups of adhesion/growth-regulatory galectins as receptors. Diversity of the glycan display was accounted for by using four (neo)glycoproteins with different degrees of glycan branching as matrices in solid-phase assays. Cases of increased inhibitory potency of lactose clusters compared to free lactose were revealed. Extent of relative inhibition was not directly associated with valency in the glycocompound and depended on the lectin type. Of note for screening protocols, efficacy of blocking appeared to decrease with increased degree of glycan branching in matrix glycoproteins. Binding to tumor cells was impaired with selectivity for galectins-3 and -4. Representative compounds did not impair growth of carcinoma cells up to a concentration of 5 mM of lactose moieties (valence-corrected value) per assay. The reported bioactivity and the delineation of its modulation by structural parameters of lectins and glycans set instructive examples for the further design of selective inhibitors and assay procedures.

The expression of fucose isoforms of amniotic and plasma alpha-1-acid glycoprotein derived from 2nd and 3rd trimester normal pregnancies

OBJECTIVES

To analyse modifications in AGP fucosylation in relation to different stages of human pregnancy.

DESIGN AND METHODS

The relative amounts of three fucosyl-glycotopes on AGP were analysed by lectin-ELISA using fucose-specific biotinylated lectins in 169 plasma and 178 amniotic fluid samples from normal pregnancies with gestational ages of 14 to 42 weeks.

RESULTS

The plasma AGPs of all the pregnant women and amniotic AGPs from the 2nd trimester lacked fucoses. In contrast, in the 3rd trimester the amniotic AGPs were highly decorated by the innermost alpha1,6-fucose as well as alpha1,2- and alpha1,3-fucoses of the outer arms, reaching the highest expression around the perinatal period. At delivery the relative amounts of the alpha1,3- and alpha1,2-AGP isoforms, but not the alpha1,6 isoform, significantly decreased.

CONCLUSIONS

The highly fucosylated amniotic AGP isoforms could be implicated in regulatory processes to ensure homeostasis during pregnancy and to protect the fetus. They have the potential of becoming laboratory markers in obstetrics to monitor pregnancy.

NKG2D and CD94 bind to multimeric alpha2,3-linked N-acetylneuraminic acid

Killer lectin-like receptors on natural killer cells mediate cytotoxicity through glycans on target cells including the sialyl Lewis X antigen (sLeX). We investigated whether NK group 2D (NKG2D) and CD94 can bind to sialylated N-linked glycans, using recombinant glutathione S-transferase-fused extracellular lectin-like domains of NKG2D (rNKG2Dlec) and CD94 (rCD94lec). Both rNKG2Dlec and rCD94lec bound to plates coated with high-sLeX-expressing transferrin secreted by HepG2 cells (HepTF). The binding of rNKG2Dlec and rCD94lec to HepTF was markedly suppressed by treatment of HepTF with neuraminidase and in the presence of N-acetylneuraminic acid. Moreover, rNKG2Dlec and rCD94lec bound to alpha2,3-sialylated human alpha(1)-acid glycoprotein (AGP) but not to alpha2,6-sialylated AGP. Mutagenesis revealed that (152)Y of NKG2D and (144)F and (160)N of CD94 were critical for HepTF binding. This is the first report that NKG2D and CD94 bind to alpha2,3-sialylated but not to alpha2,6-sialylated multi-antennary N-glycans.

Effects of differential glycosylation of glycodelins on lymphocyte survival

Glycodelin is a human glycoprotein with four reported glycoforms, namely glycodelin-A (GdA), glycodelin-F (GdF), glycodelin-C (GdC), and glycodelin-S (GdS). These glycoforms have the same protein core and appear to differ in their N-glycosylation. The glycosylation of GdA is completely different from that of GdS. GdA inhibits proliferation and induces cell death of T cells. However, the glycosylation and immunomodulating activities of GdF and GdC are not known. This study aimed to use ultra-high sensitivity mass spectrometry to compare the glycomes of GdA, GdC, and GdF and to study the relationship between the immunological activity and glycosylation pattern among glycodelin glycoforms. Using MALDI-TOF strategies, the glycoforms were shown to contain an enormous diversity of bi-, tri-, and tetra-antennary complex-type glycans carrying Galbeta1-4GlcNAc (lacNAc) and/or GalNAcbeta1-4GlcNAc (lacdiNAc) antennae backbones with varying levels of fucose and sialic acid substitution. Interestingly, they all carried a family of Sda (NeuAcalpha2-3(GalNAcbeta1-4)Gal)-containing glycans, which were not identified in the earlier study because of less sensitive methodologies used. Among the three glycodelins, GdA is the most heavily sialylated. Virtually all the sialic acid on GdC is located on the Sda antennae. With the exception of the Sda epitope, the GdC N-glycome appears to be the asialylated counterpart of the GdA/GdF glycomes. Sialidase activity, which may be responsible for transforming GdA/GdF to GdC, was detected in cumulus cells. Both GdA and GdF inhibited the proliferation, induced cell death, and suppressed interleukin-2 secretion of Jurkat cells and peripheral blood mononuclear cells. In contrast, no immunosuppressive effect was observed for GdS and GdC.

Down-regulatory effect of alpha 1-acid glycoprotein on bovine neutrophil degranulation

In this paper, the possible involvement of the acute phase protein alpha(1)-acid glycoprotein (AGP) in the local immunomodulation of inflammation was investigated. The dose response of bovine neutrophils to AGP as to mobilization of primary and secondary granules was studied. It was found that AGP fulfils a protective role against spontaneous exocytosis of secondary, but not primary, granules. This downregulatory effect is much more evident when degranulation is challenged with Zymosan activated serum (ZAS). AGP activity is dose-dependent, the acute phase concentration being more active than the physiological one. Carbohydrate moiety of AGP was found to be critical, since experimentally desialylated protein does not maintain its exocytosis-modulatory activity. The fact that AGP may modulate the degranulation of neutrophils confirms the hypothesis that AGP is heavily involved in the fine tuning of neutrophil activity in the inflammatory environment.

Diversity in tissue expression, substrate binding, and SCF complex formation for a lectin family of ubiquitin ligases

Post-translational modification of proteins regulates many cellular processes. Some modifications, including N-linked glycosylation, serve multiple functions. For example, the attachment of N-linked glycans to nascent proteins in the endoplasmic reticulum facilitates proper folding, whereas retention of high mannose glycans on misfolded glycoproteins serves as a signal for retrotranslocation and ubiquitin-mediated proteasomal degradation. Here we examine the substrate specificity of the only family of ubiquitin ligase subunits thought to target glycoproteins through their attached glycans. The five proteins comprising this FBA family (FBXO2, FBXO6, FBXO17, FBXO27, and FBXO44) contain a conserved G domain that mediates substrate binding. Using a variety of complementary approaches, including glycan arrays, we show that each family member has differing specificity for glycosylated substrates. Collectively, the F-box proteins in the FBA family bind high mannose and sulfated glycoproteins, with one FBA protein, FBX044, failing to bind any glycans on the tested arrays. Site-directed mutagenesis of two aromatic amino acids in the G domain demonstrated that the hydrophobic pocket created by these amino acids is necessary for high affinity glycan binding. All FBA proteins co-precipitated components of the canonical SCF complex (Skp1, Cullin1, and Rbx1), yet FBXO2 bound very little Cullin1, suggesting that FBXO2 may exist primarily as a heterodimer with Skp1. Using subunit-specific antibodies, we further demonstrate marked divergence in tissue distribution and developmental expression. These differences in substrate recognition, SCF complex formation, and tissue distribution suggest that FBA proteins play diverse roles in glycoprotein quality control.

Serum protein profiling to identify high-risk neuroblastoma: preclinical relevance of blood-based biomarkers

INTRODUCTION

Development of early detection assays for advanced stage neuroblastoma (NB) remains elusive. We have previously shown that serum protein profiling technologies can differentiate healthy from NB children. As various sources of patient related bias exist in serum proteins, we hypothesized a well controlled animal model may provide a better method to identify tumor blood-based markers during NB progression.

METHODS

Tumors were induced in the left kidneys of nude mice by the injection of cultured human NB cells (10(6)). Sera were collected from control and tumor-bearing mice at 2, 4, and 6 wk. Albumin-depleted sera were subjected to comparative proteomic profiling using 2D gel electrophoresis. Paired samples at each time point were analyzed and differentially expressed serum proteins were identified by mass spectrometry. Additionally, sera proteomic analysis from children with Stage IV NB and healthy controls were performed.

RESULTS

Overexpression of five mouse serum proteins [alpha(1)-acid glycoprotein, alpha(1)-antitrypsin, alpha(2)-macroglobulin, serum amyloid P-component, and serum amyloid A) were found only in NB-bearing mice. Changes in protein abundance were found to increase 2.5-fold (P < or = 0.05) between 2-, 4-, and 6-wk old mice. Underexpression of immunoglobulin kappa chain constant region was observed in the sera of tumor bearing mice compared with controls (2.5-fold, P < or = 0.05). Among NB patients, alpha(1)-acid glycoprotein, apolipoprotein A-IV, haptoglobin, and serum amyloid A were found to be up-regulated.

CONCLUSIONS

We identified distinct acute phase proteins that show up-regulation in both an animal tumor model and high-risk NB patients. As these serum proteins have been recognized as markers of tumor progression and prognosis in human malignancies, the validation of these polypeptides may enable serum proteomic profiling to become a valuable tool for identifying high-risk NB.

The feline acute phase reaction

The acute phase reaction (APR) is a response to potentially pathogenic stimuli. It begins with the release of interleukin (IL)-1, IL-6 and tumour necrosis factor (TNF)-α from inflammatory cells. These cytokines induce fever, leucocytosis and release of serum acute phase proteins (APPs). In this review, the characteristics of the feline APR are described. In cats with inflammatory conditions, fever is a common finding, with leucocytosis due to the release of cells from the marginal pool, followed by activation of myelopoiesis. Because excitement frequently causes leucocytosis in cats, a diagnosis of inflammation should therefore be supported by additional findings such as the presence of toxic neutrophils. The major APPs are serum amyloid A and α₁-acid glycoprotein (AGP), which both increase a few hours after the inflammatory stimulus and remain elevated for as long as the inflammation persists. AGP plays an important role in the diagnosis of feline infectious peritonitis (FIP) and may also be useful also in studies of FIP pathogenesis.

Tools for glycomics: relative quantitation of glycans by isotopic permethylation using 13CH3I

Analysis of oligosaccharides by mass spectrometry (MS) has enabled the investigation of the glycan repertoire of organisms with high resolution and sensitivity. It is difficult, however, to correlate the expression of glycosyltransferases with the glycan structures present in a particular cell type or tissue because the use of MS for quantitative purposes has significant limitations. For this reason, in order to develop a technique that would allow relative glycan quantification by MS analysis between two samples, a procedure was developed for the isotopic labeling of oligosaccharides with (13)C-labeled methyl iodide using standard permethylation conditions. Separate aliquots of oligosaccharides from human milk were labeled with (12)C or (13)C methyl iodide; the labeled and non-labeled glycans were mixed in known proportions, and the mixtures analyzed by MS. Results indicated that the isotopic labeling described here was capable of providing relative quantitative data with a dynamic range of at least two orders of magnitude, adequate linearity, and reproducibility with a coefficient of variation that was 13% on average. This procedure was used to analyze N-linked glycans released from various mixtures of glycoproteins, such as alpha-1 acid glycoprotein, human transferrin, and bovine fetuin, using MS techniques that included matrix assisted laser desorption ionization-time of flight MS and electrospray ionization with ion cyclotron resonance-Fourier transformation MS. The measured (12)C:(13)C ratios from mixtures of glycans permethylated with either (12)CH(3)I or (13)CH(3)I were consistent with the theoretical proportions. This technique is an effective procedure for relative quantitative glycan analysis by MS.

Alpha2,3 and alpha2,6 N-linked sialic acids facilitate efficient binding and transduction by adeno-associated virus types 1 and 6

Recombinant adeno-associated viruses (AAVs) are promising vectors in the field of gene therapy. Different AAV serotypes display distinct tissue tropism, believed to be related to the distribution of their receptors on target cells. Of the 11 well-characterized AAV serotypes, heparan sulfate proteoglycan and sialic acid have been suggested to be the attachment receptors for AAV type 2 and types 4 and 5, respectively. In this report, we identify the receptor for the two closely related serotypes, AAV1 and AAV6. First, we demonstrate using coinfection experiments and luciferase reporter analysis that AAV1 and AAV6 compete for similar receptors. Unlike heparin sulfate, enzymatic or genetic removal of sialic acid markedly reduced AAV1 and AAV6 binding and transduction. Further analysis using lectin staining and lectin competition assays identified that AAV1 and AAV6 use either alpha2,3-linked or alpha2,6-linked sialic acid when transducing numerous cell types (HepG2, Pro-5, and Cos-7). Treatment of cells with proteinase K but not glycolipid inhibitor reduced AAV1 and AAV6 infection, supporting the hypothesis that the sialic acid that facilitates infection is associated with glycoproteins rather than glycolipids. In addition, we determined by inhibitor (N-benzyl GalNAc)- and cell line-specific (Lec-1) studies that AAV1 and AAV6 require N-linked and not O-linked sialic acid. Furthermore, a resialylation experiment on a deficient Lec-2 cell line confirmed a 2,3 and 2,6 N-linked sialic acid requirement, while studies of mucin with O-linked sialic acid showed no inhibition effect for AAV1 and AAV6 transduction on Cos-7 cells. Finally, using a glycan array binding assay we determined that AAV1 efficiently binds to NeuAcalpha2-3GalNAcbeta1-4GlcNAc, as well as two glycoproteins with alpha2,3 and alpha2,6 N-linked sialic acids. Taken together, competition, genetic, inhibitor, enzymatic reconstitution, and glycan array experiments support alpha2,3 and alpha2,6 sialic acids that are present on N-linked glycoproteins as primary receptors for efficient AAV1 and AAV6 viral infection.