Determination of lectin-sugar dissociation constants by agarose affinity electrophoresis

The Acute Phase Proteins Reaction in Children Suffering from Pseudocroup

The aim of the study was to evaluate the inflammatory reaction in children with pseudocroup and compare it with other laryngological diseases according to the available literature data. The study group included 51 children hospitalized because of pseudocroup. The measurements of the acute phase proteins (APP), such as C-reactive protein (CRP), alpha-1-antitrypsin (AT), alpha-1-antichymotrypsin (ACT), alpha-1-acid glycoprotein (AGP), ceruloplasmin (Cp), transferrin (Tf), alpha-2-macroglobulin (A2M), and haptoglobin (Hp) were obtained at 3 time points. The glycosylation profiles of AGP, ACT, and Tf were completed. An increased AGP level was observed in girls. The AGP glycosylation revealed the advantage of the W0 variant over the W1 variant. W1 and W2 were decreased in boys. W3 emerged in boys. The Tf concentration and T4 variant were lower compared to the control group. The A2M level was lower after treatment. The Hp and AT levels were decreased a few weeks later. The ACT glycosylation revealed a decrease of the A4 variant in boys. In conclusion, the inflammatory reaction during pseudocroup was of low intensity. The APP glycosylation suggested a chronic process. In a follow-up investigation, no normalization of the parameters was noted, but signs of persistent inflammation were observed.

Global analysis of the glycoproteome in Saccharomyces cerevisiae reveals new roles for protein glycosylation in eukaryotes

To further understand the roles of protein glycosylation in eukaryotes, we globally identified glycan-containing proteins in yeast. A fluorescent lectin binding assay was developed and used to screen protein microarrays containing over 5000 proteins purified from yeast. A total of 534 yeast proteins were identified that bound either Concanavalin A (ConA) or Wheat-Germ Agglutinin (WGA); 406 of them were novel. Among the novel glycoproteins, 45 were validated by mobility shift upon treatment with EndoH and PNGase F, thereby extending the number of validated yeast glycoproteins to 350. In addition to many components of the secretory pathway, we identified other types of proteins, such as transcription factors and mitochondrial proteins. To further explore the role of glycosylation in mitochondrial function, the localization of four mitochondrial proteins was examined in the presence and absence of tunicamycin, an inhibitor of N-linked protein glycosylation. For two proteins, localization to the mitochondria is diminished upon tunicamycin treatment, indicating that protein glycosylation is important for protein function. Overall, our studies greatly extend our understanding of protein glycosylation in eukaryotes through the cataloguing of glycoproteins, and describe a novel role for protein glycosylation in mitochondrial protein function and localization.

Resolution of glycoproteins by a lectin gel-shift assay

Gel-shift assays previously described in the literature are based on protein-protein or protein-DNA interactions. We show that carbohydrate-lectin interactions can be successfully used to alter the electrophoretic mobility of glycosylated, but not nonglycosylated, protein species in SDS-polyacrylamide gels. We were able to separate the two closely migrating mono- (95 kDa) and nonglycosylated (92 kDa) forms of a polytopic membrane protein, anion exchanger 1 (AE1), synthesized by cell-free translation or in transfected HEK293 cells. Concanavalin A was selected as the lectin due to the high mannose content of the oligosaccharide chain on AE1. Concanavalin A was either added to the samples prior to loading or copolymerized in a top layer of the separating gel, the latter being the method of choice. The presence of concanavalin A resulted in slower mobility of the monoglycosylated protein while the mobility of the nonglycosylated form was not altered. The shift in mobility was dependent on concentration of concanavalin A and the length of separating gel containing copolymerized concanavalin A. When a diglycosylated mutant of AE1 was tested, good separation was achieved at lower concentrations of concanavalin A. This lectin gel-shift assay allows the separation of N-glycosylated and nonglycosylated forms of the protein.

Biosynthesis of alpha1-proteinase inhibitor by human lung-derived epithelial cells

Destruction of components of the extracellular matrix of the lung by neutrophil elastase is believed to be a critical event in the development of obstructive lung disease. The local synthesis of alpha1-proteinase inhibitor, the controlling inhibitor of this enzyme, may provide a partial mechanism for neutrophil elastase regulation, especially during inflammation, when proteolytic enzymes are released from phagocytes. In this study, we show that lung-derived epithelial cells not only have the capacity to synthesize functional alpha1-PI but also to increase the rate of its production when stimulated by specific inflammatory mediators, including oncostatin M, interleukin-1, and the glucocorticoid analogue, dexamethasone.

Acute phase proteins and transformed cells

Acute phase proteins (APP) are plasma proteins whose concentration and glycosylation alters in response to tissue injury, inflammation, or tumor growth. Significant interspecies and sex differences in APP response exist. APP are produced mainly by hepatocytes, and their synthesis and glycosylation are controlled by a network consisting of cytokines, their soluble receptors, and glucocorticoids. The major cytokines involved in these processes belong to a group of interleukin-6-type cytokines that act through the hematopoietin receptor complex on hepatocytes and JAK-STAT signal transduction pathway. Transformed cells (hepatoma) display significant differences in synthesis of APP, cytokine responsiveness, expression of cytokine-receptor subunits and signal-transduction machinery. The most striking variability relates to the glycosylation alterations induced by cytokines. However, transformed cells (hepatoma) form a basic model for studying and understanding mechanisms controlling the synthesis and glycosylation of APP. Furthermore, APP may be secreted by transformed (tumor) cells of various origins and may display a growth factor-like function in certain cancer types.

Glycoforms of serum alpha 1-acid glycoprotein as markers of inflammation and cancer

alpha 1-acid glycoprotein (AGP) is a serum acute phase glycoprotein which possesses five N-linked complex type heteroglycan side chains which may be present as bi-, tri- and tetraantennary structures. Depending upon the content of biantennary structure on AGP, up to four glycoforms of AGP are present in serum. These glycoforms can be easily estimated in body fluids by means of crossed affinity-immunoelectrophoresis (CAIE) with the lectin, Concanavalin A (Con A). Con A selectively binds biantennary structures; the more biantennary structures on AGP, the stronger the binding. In acute inflammation, a relative increase of AGP glycoforms with biantennary units is observed-a type I glycosylation change. In some chronic inflammatory states there is an relative decrease of AGP glycoforms with biantennary heteroglycans-a type II glycosylation change. Moreover, in certain other states such as pregnancy, estrogen administration or liver damage, type II glycosylation changes are also seen. A detailed analysis of the clinical applications of the assessment of AGP glycoforms in sera of patients with rheumatic diseases, AIDS and various types of cancers is presented. Accumulated data shows that AGP glycoforms may be very useful in the detection of intercurrent infections in the course of rheumatoid arthritis, systemic lupus erythematosus, or myeloblastic leukaemia, and in the detection of secondary infections in human immunodeficiency virus infected individuals. AGP glycoforms are also very useful in differentiation between various forms of trophoblastic disease and are helpful in monitoring the treatment of these patients. Finally, AGP glycoforms provide valuable information for differentiation between primary and secondary liver cancer.

Lectin affinity electrophoresis

Lectin affinity electrophoresis is a powerful technique to investigate the interaction between a lectin and its ligand. Affinity electrophoresis results from the reduced mobility of a charged species owing to its interaction with an immobile species. In this protocol, a two-dimensional lectin affinity electrophoresis experiment is described that affords separation of oligosaccharides. The first-dimension is composed of a weak, polyacrylamide, capillary tube gel containing a lectin. The example described involves a mixture of fluorescently labeled disaccharides. The mobility of only the lectin-binding disaccharide is reduced affording a separation in the first-dimension. The tube gel is then extruded and placed onto the second-dimension gradient polyacrylamide gel and subjected to electrophoresis. Mobility in the second-dimension is dependent on molecular size and visualization si by fluorescence under transillumination. This method is also applicable, with appropriate modifications, for the separation and analysis of glycopeptides and glycoproteins.

Changes of acute phase proteins glycosylation profile as a possible prognostic marker in myocardial infarction

In 24 consecutive patients with myocardial infarction, the concentrations of C-reactive protein, alpha 1-acid glycoprotein and alpha 1-antichymotrypsin, as well as acid alpha 1-glycoprotein and alpha 1-antichymotrypsin glycosylation profiles were estimated. Blood samples were taken at admission, after 4, 8, 12 and 24 h, on 2, 3, 6, 9, and 12 days of hospitalization. All studied patients were divided into 2 groups: 12 patients without clinical or radiological symptoms of acute heart failure and 12 patients with acute heart failure. The results of all investigations were tested statistically to appraise significance of differences between the two investigated groups. At admission, as well as after 6 and 12 h, C-reactive protein concentration was significantly higher in patients who developed heart failure. Similarly, the glycosylation profile of alpha 1-antichymotrypsin, reported as reactivity coefficient, was of good prognostic value from the first time-point on. Development of acute cardiac failure seemed to correlate more with the magnitude of inflammatory reaction (measured by changes in acute phase proteins) than with enzymatically estimated infarct size.

Different capabilities of monocytes from patients with systemic lupus erythematosus and rheumatoid arthritis to induce glycosylation alterations of acute phase proteins in vitro

The effect of conditioned medium on the biosynthesis and glycosylation profile of acute phase proteins secreted by the human hepatoma cell line Hep G2 was studied. Conditioned medium was prepared from nonactivated [CM-LPS(-)] and ex vivo lipopolysaccharide activated [CM-LPS(+)] monocytes from eight patients with active rheumatoid arthritis (RA), five patients with active systemic lupus erythematosus (SLE), and seven healthy subjects. The biosynthesis of albumin, alpha 1-antichymotrypsin and alpha 1-proteinase inhibitor and the profile of glycosylation of proteinase inhibitor were analysed. CM-LPS(-) from patients with SLE had a similar effect to CM-LPS(-) from healthy subjects. In contrast, CM-LPS(-) from patients with RA had the same effect as CM-LPS(+) from healthy donors. A similar effect to that of CM-LPS(+) of healthy subjects was seen with CM-LPS(+) from patients with SLE and with CM-LPS(+) from patients with RA. The treatment of CM-LPS(+) with antibodies against interleukin 6 neutralised most of its ability to induce changes in the biosynthesis and glycosylation of acute phase proteins. Antibodies to interleukin 1 and tumour necrosis factor alpha had only a limited effect on the ability of CM-LPS(+) to induce changes of albumin and alpha 1-antichymotrypsin syntheses, whereas they had no effect on the biosynthesis and glycosylation of proteinase inhibitor. These results indicate that: (a) monocytes isolated from patients with active SLE and active RA have different capabilities of inducing alterations of acute phase proteins in vitro; (b) ex vivo activation of monocytes from patients with SLE leads to the full induction of its capabilities to change acute phase proteins, whereas the activation of monocytes from patients with RA has no additive effects; and (c) interleukin 6 seems to be a major cytokine involved in the regulation of the glycosylation pattern of acute phase proteins.

Clinical applications of lectin affinity electrophoresis

Principles and several modifications of lectin affinity electrophoresis are described. The results obtained using these newly developed techniques are reviewed for individual glycoproteins, the altered lectin reactivities of which have some clinical implications, showing different lectin reactivities, which occur not only on malignant transformation but also in association with inflammatory process and hormonal action.

Transforming growth factor beta 1 influences glycosylation of alpha 1-protease inhibitor in human hepatoma cell lines

We have previously shown that changes in acute-phase protein glycosylation result from alterations occurring within hepatocytes as a result of regulation by cytokines, that the glycosylation patterns of proteins secreted by Hep 3B and Hep G2 cells respond differently to the crude mixtures of cytokines found in conditioned medium from LPS-stimulated monocytes, and that interleukin-6 (IL-6) causes increased concanavalin A (Con A) binding of alpha 1 protease inhibitor in Hep 3B cells and decreased Con A binding of this protein in Hep G2 cells. In the present study we found that transforming growth factor beta 1 (TGF-beta), like IL-6, led to secretion of forms of alpha 1-protease inhibitor with increased Con A binding in Hep 3B cells, and that IL-6 and TGF-beta in combination were additive. In contrast, in Hep G2 cells, TGF-beta had an effect opposite to that produced by IL-6, leading to secretion of forms of alpha 1-protease inhibitor with increased Con A binding. When employed in combination with IL-6. TGF-beta abolished the effect of that cytokine. These studies indicate that TGF-beta influences glycosylation of alpha 1-protease inhibitor in two human hepatoma cell lines in a manner that can be differentiated from that of IL-6. The identification of TGF-beta as a second defined cytokine capable of influencing glycoprotein glycosylation and the demonstration that the effect of one cytokine can be modulated by another cytokine support the view that changes in glycosylation of plasma proteins are mediated by combinations of cytokines.

Affinity electrophoresis for studies of mechanisms regulating glycosylation of plasma proteins

A model system for studies of mechanisms governing the alterations of glycosylation of plasma glycoproteins was developed. The system employs two human hepatoma cell lines, Hep 3B and Hep G2, as target cells and agarose affinity electrophoresis with lectins for studies of microheterogeneity of alpha 1-protease inhibitor (PI), a model glycoprotein synthesized by hepatocytes. As an example for the application of the system, the effect of cytokines on major microheterogeneity of plasma proteins is demonstrated. The results indicate that interleukin 6, transforming growth factor beta 1 and, to some extent, tumor necrosis factor alpha are directly involved in regulating the pattern of glycosylation of plasma proteins in vitro, but the major effect is obtained by using combinations of interleukin 6, transforming growth factor beta 1, tumor necrosis factor alpha and interleukin 1. In addition, the results underline the dissociation between alteration of gene expression and the changes in the pattern of plasma protein glycosylation.

Microheterogeneity of orosomucoid in pathological conditions

Studies of orosomucoid (alpha 1-acid glycoprotein) in human serum have revealed that orosomucoid is a mixture of molecules with differences in the glycan chains. This microheterogeneity has been studied using crossed affinoimmuno-electrophoresis with the lectin concanavalin A which binds to biantennary glycans. The relative proportions of the three orosomucoid subtypes are altered in various pathological conditions independently of the total serum orosomucoid concentration. There are reproducible differences in microheterogeneity patterns between some pathological conditions: Acute tissue injury or inflammation results in a high proportion of orosomucoid with biantennary glycans. Conditions with increased estrogen levels are associated with a high proportion of orosomucoid with tri- or tetraantennary glycans and a low total serum orosomucoid concentration. Chronic inflammation also seems to be associated with a high proportion of orosomucoid with tri- or tetraantennary glycans but with a high total serum concentration of orosomucoid. Other diseases, such as cancer, can not be associated with any specific microheterogeneity pattern. The microheterogeneity pattern in these conditions seems to be determined by disease activity and unspecific inflammation in surrounding tissues.

Affinity electrophoresis for diagnosis of cancer and inflammatory conditions

Affinity electrophoresis, with concanavalin A and Lens culinaris agglutinin as ligands, was applied to study the microheterogeneity of serum proteins, with special emphasis on alpha 1-fetoprotein and alpha 1-acid glycoprotein, two proteins of potential clinical value. A total of 602 samples of serum from patients with various neoplastic and inflammatory conditions were evaluated. Affinity electrophoresis provided useful information for differential diagnosis of cancers of various origins including hepatomas, metastatic liver cancers and yolk sac tumors. The method also proved indispensable for the detection of intercurrent infection in patients with rheumatoid arthritis, systemic lupus erythematosus and scaled burns.

Microheterogeneity of alpha 1-acid glycoprotein in the detection of intercurrent infection in patients with rheumatoid arthritis

We evaluated the clinical usefulness of determinations of alpha 1-acid glycoprotein (AGP) microheterogeneity in distinguishing patients who have active rheumatoid arthritis (RA) from those who have RA and an intercurrent infection. AGP microheterogeneity was studied by affinity electrophoresis with concanavalin A as the ligand, and the results were expressed as reactivity coefficients (RC). Significant differences were found between the mean RC (+/- SD) in healthy individuals (1.27 +/- 0.16) and the mean RC in RA patients with intercurrent infection (1.74 +/- 0.90), as well as with the mean RC in RA patients with grades III and IV disease activity (0.92 +/- 0.18 and 0.81 +/- 0.25, respectively). Moreover, an additional microheterogeneous form of AGP, similar to that observed in non-RA patients with infections, was noted in RA patients with infections (sensitivity 100%, specificity 100%). The results show that an increase in AGP reactivity with concanavalin A is a sensitive indicator of intercurrent infection in patients with RA.

Interferon beta 2/B-cell stimulating factor 2/interleukin 6 affects glycosylation of acute phase proteins in human hepatoma cell lines

Undefined monocyte-derived cytokines have previously been shown to affect glycan processing in glycoproteins secreted by human hepatoma cell lines. Hep 3B cells, when incubated with the cytokine interferon beta 2/B-cell stimulating factor 2/interleukin 6, secreted forms of alpha 1-protease inhibitor, ceruloplasmin, and alpha-fetoprotein with increased reactivity with concanavalin A (Con A) while incubation of Hep G2 cells with this cytokine led to secretion of forms of these proteins with decreased reactivity with Con A, reflecting changes in their oligosaccharide chains. The difference in response of these two transformed cell lines to this cytokine undoubtedly reflects differences in their intracellular glycan processing mechanisms. Changes in glycosylation patterns were dissociated from changes in rate of synthesis: this cytokine caused increased synthesis of alpha 1-protease inhibitor and ceruloplasmin, and decreased synthesis of alpha-fetoprotein in both cell lines.

Serum IgA, acute phase proteins, and glycosylation of alpha 1-acid glycoprotein in ankylosing spondylitis

Several investigators have suggested that gastrointestinal inflammation has a role in the pathogenesis of ankylosing spondylitis. To test this hypothesis markers of gastrointestinal immunostimulation, as manifested by serum IgA concentrations, were compared with serum markers of inflammation, as manifested by acute phase proteins. Serum samples from 45 unrelated Caucasian patients with ankylosing spondylitis (AS) were tested for correlation of serum IgA and six acute phase proteins: C reactive protein (CRP), alpha 1-antitrypsin, alpha 1-antichymotrypsin, caeruloplasmin, alpha 1-acid glycoprotein (AGP), and haptoglobin. Serum IgA was shown to be significantly positively correlated with four of these six acute phase proteins: CRP (r = 0.58, p less than 0.001), alpha 1-antitrypsin (r = 0.29, p less than 0.05), AGP (r = 0.61, p less than 0.01), and haptoglobin (r = 0.58, p less than 0.001), suggesting that gastrointestinal immunostimulation does have a role in the pathogenesis of inflammation in AS. In addition, the microheterogeneity of the pattern of glycosylation of AGP, expressed as reactivity coefficients, was examined. The AGP reactivity coefficient has been shown to increase in infection, remain the same in systemic lupus erythematosus, and decrease in rheumatoid arthritis. It was found that the AGP reactivity coefficient was significantly decreased in patients with AS as compared with healthy controls (p less than 0.006). As recent studies have indicated that patterns of glycosylation reflect intrahepatocellular biosynthetic processes induced by cytokines our data suggest that cytokine-hepatocellular mechanisms in AS may be similar to those occurring in rheumatoid arthritis, but different from those in systemic lupus erythematosus or infection.

Monokines regulate glycosylation of acute-phase proteins

The acute-phase response to inflammatory stimuli, characterized by increased synthesis of acute-phase proteins (APP), is often accompanied by changes in the glycosylation patterns of some of these proteins. While expression of APP genes in hepatocytes is regulated by monokines, mechanisms governing changes in glycosylation are not known. Exposure of human hepatoma cell line Hep 3B to conditioned medium from LPS-activated human monocytes and to medium from the keratocarcinoma cell line COLO-16 led to increased synthesis of alpha 1 proteinase-inhibitor and ceruloplasmin and to alterations of their glycosylation patterns similar to those seen in human serum in various inflammatory states. IL-1, tumor necrosis factor, and hepatocyte stimulating factor I increased synthesis of ceruloplasmin without alterations in the pattern of its glycosylation. These findings demonstrate that altered glycosylation seen in plasma in some inflammatory states can be explained by the effects of monokines on glycosylation in hepatocytes and that gene expression and glycosylation of some APP during the acute-phase response may be regulated by different mechanisms.

Microheterogeneity of alpha 1-acid glycoprotein in the detection of intercurrent infection in systemic lupus erythematosus

We evaluated the clinical usefulness of determinations of alpha 1-acid glycoprotein microheterogeneity patterns in distinguishing patients who have active systemic lupus erythematosus (SLE) from those who have SLE with intercurrent infection. We used agarose affinity electrophoresis with concanavalin A (Con A) as a ligand. Results were expressed as reactivity coefficients (RC), which are the ratios of variants reactive with Con A to the variants not reactive with Con A. No significant differences were found between the mean RC (+/- SD) in healthy individuals (1.35 +/- 0.26) and that in patients with various degrees of SLE activity. In contrast, a significantly higher mean RC was found in sera from patients with intercurrent infection (2.70 +/- 0.76) compared with each of the other groups studied (P less than 0.001). An RC greater than 2.25 was found in none of 42 sera from patients without infection and in 15 of 18 sera from patients with infection (sensitivity 83%, specificity 100%). C-reactive protein (CRP) levels were also significantly higher in SLE patients with intercurrent infection than in patients with very active disease (P less than 0.05). Levels of CRP greater than 60 mg/liter were found in 3 of 42 SLE patients without infection and in 8 of 18 patients with infection (sensitivity 39%, specificity 93%). The results show that in SLE patients, the finding of a relative increase in Con A-bound serum alpha 1-acid glycoprotein is a more sensitive indicator of intercurrent infection than is the finding of increased levels of CRP.