Prevalence of tri- and tetraantennary glycans of human alpha 1-acid glycoprotein in release of macrophage inhibitor of interleukin-1 activity

Identifying glycan motifs using a novel subtree mining approach

Background

Glycans are complex sugar chains, crucial to many biological processes. By participating in binding interactions with proteins, glycans often play key roles in host–pathogen interactions. The specificities of glycan-binding proteins, such as lectins and antibodies, are governed by motifs within larger glycan structures, and improved characterisations of these determinants would aid research into human diseases. Identification of motifs has previously been approached as a frequent subtree mining problem, and we extend these approaches with a glycan notation that allows recognition of terminal motifs.

Results

In this work, we customised a frequent subtree mining approach by altering the glycan notation to include information on terminal connections. This allows specific identification of terminal residues as potential motifs, better capturing the complexity of glycan-binding interactions. We achieved this by including additional nodes in a graph representation of the glycan structure to indicate the presence or absence of a linkage at particular backbone carbon positions. Combining this frequent subtree mining approach with a state-of-the-art feature selection algorithm termed minimum-redundancy, maximum-relevance (mRMR), we have generated a classification pipeline that is trained on data from a glycan microarray. When applied to a set of commonly used lectins, the identified motifs were consistent with known binding determinants. Furthermore, logistic regression classifiers trained using these motifs performed well across most lectins examined, with a median AUC value of 0.89.

Conclusions

We present here a new subtree mining approach for the classification of glycan binding and identification of potential binding motifs. The Carbohydrate Classification Accounting for Restricted Linkages (CCARL) method will assist in the interpretation of glycan microarray experiments and will aid in the discovery of novel binding motifs for further experimental characterisation.

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.

Identification of changes in serum analytes and possible metabolic pathways associated with canine obesity-related metabolic dysfunction

The main objective of this study was to identify analytes that could change and that could help to clarify the metabolic and physiopathological changes related to canine obesity-related metabolic dysfunction (ORMD). For this, serum from 35 overweight/obese dogs, with and without ORMD, was submitted to a comprehensive panel of biochemistry analysis, a gel-free tandem mass tag isobaric label-based proteomic analysis, and, finally, selected proteins were used as a starting point for creating a protein interaction network. Dogs with ORMD showed significantly higher serum concentrations of alanine aminotransferase (ALT), alkaline phosphatase (ALP), Ca, total proteins, albumin, total cholesterol, triglycerides, glucose, and butyrylcholinesterase (BChE) activity in comparison with dogs without ORMD. Proteomic analysis revealed that 23 proteins related to lipid metabolism, the complement factor system, cellular adhesion and functionality, inflammation, and coagulation were altered in dogs with ORMD. Finally, the obtained protein interaction network highlighted that the central term of this network was the negative regulation of the immune response. These data suggest that canine ORMD is associated with changes in analytes that reflect altered lipid metabolism, and liver and immune function impairment and suggests the potential for a prothrombotic state and lung function alterations.

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.

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.

A comparative binding mechanism between human serum albumin and α-1-acid glycoprotein with corilagin: biophysical and computational approach

The interaction between corilagin and serum proteins was studied by biophysical and molecular dynamics techniques which in turn provides valuable information about the interaction of phytochemical corilagin with serum proteins.

An acute-phase protein as a regulator of sperm survival in the bovine oviduct: alpha 1-acid-glycoprotein impairs neutrophil phagocytosis of sperm in vitro

We have previously shown that polymorphonuclear neutrophils (PMNs) are present in bovine oviduct fluid under physiological conditions, and that the oviduct provides a microenvironment that protects sperm from phagocytosis by PMNs. Alpha 1-acid glycoprotein (AGP) is a major acute-phase protein produced mainly in the liver that has immunomodulatory functions. AGP mRNA is expressed in extrahepatic organs, such as the lung, kidney, spleen, lymph node, uterus, and ovary. Therefore, in this study, we investigated, 1) the local production of AGP in the bovine oviduct, 2) the effect of AGP on the phagocytic activity of PMNs for sperm and superoxide production and 3) the impact of AGP desialylation on the PMN phagocytosis of sperm. The AGP gene was expressed in cultured bovine oviduct epithelial cells (BOECs) and AGP protein was detected in oviduct fluid. Preexposure of PMNs to AGP at physiological levels impaired PMN phagocytosis for sperm and superoxide generation. The desialylation of AGP eliminated these suppressive effects of AGP on PMN. Scanning electron microscopy revealed that AGP drastically reduced the formation of DNA-based neutrophil extracellular traps (NETs) for sperm entanglement. Additionally, AGP dose-dependently stimulated BOECs to produce prostaglandin E2 (PGE2) which has been shown to partially contribute to the regulation of sperm phagocytosis in the bovine oviduct. AGP and PGE2 at concentrations detected in the oviducts additively suppressed sperm phagocytosis by PMNs. These results provide evidence that locally produced AGP may be involved in protecting sperm from phagocytosis by PMNs in the bovine oviduct.

RAPID PULMONARY EXPRESSION OF ACUTE-PHASE REACTANTS AFTER LOCAL LIPOPOLYSACCHARIDE EXPOSURE IN MICE IS FOLLOWED BY AN INTERLEUKIN-6 MEDIATED SYSTEMIC ACUTE-PHASE RESPONSE

This study investigated local and systemic innate immune responses in lipopolysaccharide (LPS)-induced lung inflammation in mice. Intratracheal LPS exposure resulted in increased pulmonary mRNA expression for acute-phase reactants (APRs) alpha(1)-antitrypsin (alpha(1)-AT), alpha(1)-acid glycoprotein (AGP), and LPS-binding protein (LBP) from 4 hours post exposure. Although pulmonary serum amyloid P component (SAP) mRNA was not increased, systemic levels of SAP, AGP, and LBP were elevated from 24 hours post exposure. Systemic APRs increase was associated with hepatic mRNA expression. As in vivo neutralization of interleukin (IL)-6, but not tumor necrosis factor (TNF)-alpha, fully ablated hepatic APR mRNA expression, IL-6 may act as signaling molecule between lung and liver. In conclusion, pulmonary LPS exposure induced rapid APR expression in lung, which precedes IL-6-mediated systemic elevation of APRs associated with hepatic APRs expression.

An alpha-1-acid glycoprotein-like protein as a major component of the ovarian cavity fluid of viviparous fish, Neoditrema ransonnetii (Perciformes, Embiotocidae)

Developing fetuses of surfperch (Neoditrema ransonnetii, Perciformes; Embiotocidae) are retained in the ovarian cavity until birth, where they are surrounded by ovarian cavity fluid (OCF). Expecting the OCF to have key roles in maintaining pregnancy, we purified and characterized a major glycoprotein of 51 kDa in the OCF of surfperch. On the basis of the N-terminal amino acid sequence, we cloned and sequenced a full-length cDNA. The deduced sequence comprises 214 amino acids (aa) including a signal peptide of 20 aa and a mature protein of 194 aa. This protein had an extremely low pI (below 2.8) and extraordinarily high glycosylation rate (more than 50%), characteristics being shared with alpha-1-acid glycoprotein (AGP), a member of the lipocalin superfamily. A homology search and phylogenetic analysis indicated that the 51 kDa protein and tributyltin-binding protein found in Japanese flounder are the closest known relatives of AGP. We therefore named the protein nrF-AGP. Messenger RNA of nrF-AGP was expressed intensively in the liver, but not at all in the ovarian tissue. Because nrF-AGP is the most salient component in OCF but not in plasma, we reasoned that it was selectively sequestered from blood to the ovarian cavity in pregnant females, and consequently, plays crucial roles in pregnancy.

Alpha1-acid glycoprotein suppresses rat acute inflammatory paw edema through the inhibition of neutrophils activation and prostaglandin E2 generation

Alpha(1)-acid glycoprotein (AGP) is an acute phase protein. Whereas the expression of AGP in an inflammatory state is enhanced by inflammatory cytokines including interleukin-1, 6 (IL-1 and IL-6), and tumor necrosis factor-alpha (TNF-alpha), the biological significance of AGP remains unclear. In the current study, the anti-inflammatory effect of AGP on the acute inflammatory state was examined in vivo and in vitro. AGP suppressed carrageenan-, dextran- and kaolin-induced paw edema and vascular permeability in rat. These results suggest that both initial inflammatory mediators (serotonin and histamine) and later inflammatory mediators (prostaglandin and bradykinin) are involved in the anti-inflammatory effects of AGP. In fact, prostaglandin E(2) (PGE(2)) generation in plasma was significantly inhibited by AGP. Moreover, AGP inhibited the migration of neutrophils treated with N-formyl-methionyl-leucyl-phenylalanine (fMLP) through membrane filter. In addition, AGP significantly suppressed superoxide generation from neutrophils that has been treated with fMLP or phorbol 12-myristate 13-acetate. These results imply that the anti-inflammatory effect of AGP may involve the inhibition of neutrophils migration. The data obtained in this study support a scenario in which an increase in AGP concentration in pathological conditions suppresses inflammation reactions induced by autacoids and neutrophils activities and that AGP plays an important role in the maintenance in the body.

The acute‐phase protein α1‐acid glycoprotein (AGP) induces rises in cytosolic Ca2+in neutrophil granulocytesviasialic acid binding immunoglobulin‐like lectins (Siglecs)

We studied whether the acute-phase protein alpha1-acid glycoprotein (AGP) induces rises in [Ca2+]i in neutrophils and sought to identify the corresponding AGP receptor (or receptors). We found that AGP elicited a minimal rise in [Ca2+]i in Fura-2-loaded neutrophils, and this response was markedly enhanced by pretreatment with anti-L-selectin antibodies. (The EC50 value of the AGP-induced Ca2+ response was 9 microg/ml.) Activation of phospholipase-C, Src tyrosine kinases, and PI3 kinases proved to be essential for the AGP-mediated increase in [Ca2+]i, whereas the p38 MAPK and SYK signaling pathways were not involved. Furthermore, antibodies against sialic acid binding, immunoglobulin-like lectin 5 (Siglec-5) and oligosaccharide 3'-sialyl-lactose both antagonized the AGP-induced response and caused an immediate increase in [Ca2+]i in anti-L-selectin-treated neutrophils, which indicates a signaling capacity of Siglec-5. We used modified forms of AGP (treated with mild periodate or neuraminidase) to establish the importance of sialic acid residues. The modified forms of AGP caused a much smaller rise in [Ca2+]i than did unaltered AGP. Affinity chromatography confirmed that unchanged AGP, but not neuraminidase-treated AGP, bound to Siglec-5. Our report provides the first evidence for a signaling capacity by AGP through a defined receptor. Pre-engagement of L-selectin significantly enhanced this signaling capacity.

The alterations of mouse plasma proteins during septic development

A fundamental issue for sepsis therapy is to control the development of inflammation at an early stage. With cecal ligation and puncture (CLP) surgery, the mouse model has clearly shown the septic signs triggered by chronic insult. To monitor the plasma proteomic responses to sepsis, the mouse blood was collected at intervals after sham and CLP surgery followed by the sample treatment to remove high abundance serum albumin. The treated mouse plasma proteins were well resolved by two-dimensional electrophoresis (2-DE). The image analysis revealed that these 2-DE spots observed from the sham and the CLP samples 4 h after surgery were comparable, whereas more than 30 different spots appeared on the 2-DE gels between the sham and CLP mouse plasma 24 h after surgery, indicating that some plasma proteins responded to the inflammatory development. These differential spots were verified by MALDI-TOF/TOF MS, resulting in 13 unique sepsis-responsive proteins. More importantly, most of them exhibited multiple spots as difference on the 2-DE gels. Furthermore, these isospots were incubated with PNGase F to eliminate N-linked oligosaccharides on proteins and then evaluated by Western blot as well as mass spectrometry. The results of PNGase F digestion suggested that most sepsis-associated proteins remained in N-glycosylation status but changed their N-glycans during septic development.

Decreased sialylation of the acute phase protein alpha1-acid glycoprotein in feline infectious peritonitis (FIP)

Feline infectious peritonitis (FIP) is an immune-mediated disease of domestic and exotic felides infected with feline coronavirus. FIP is characterized by the overexpression of an acute phase protein, the α1-acid glycoprotein (AGP). In humans, AGP is a heavily glycosylated protein that undergoes several modifications of its glycan moiety during acute and chronic inflammatory pathologies. We studied the changes in AGP glycosylation in the course of FIP. Specifically, we focussed our attention on the degree of sialylation, fucosylation and branching. This study presents a purification method for feline AGP (fAGP) from serum, using an ion exchange chromatography strategy. The glycosylation pattern was analyzed in detail by means of interaction of purified fAGP with specific lectins. In particular, Sambucus nigra agglutinin I and Maackia amurensis agglutinin lectins were used to detect sialic acid residues, Aleuria aurantia lectin was used to detect l-fucose residues and Concanavalin A was used to evaluate the branching degree. By this method we showed that fAGP did not present any l-fucose residues on its surface, and that its branching degree was very low, both in normal and in pathological conditions. In contrast, during FIP disease, fAGP underwent several modifications in the sialic acid content, including decreased expression of both α(2–6)-linked and α(2–3)-linked sialic acid (76 and 44%, respectively when compared to non-pathological feline AGP).

Tissue distribution of a feline AGP related protein (fAGPrP) in cats with feline infectious peritonitis (FIP)

Feline α₁-acid glycoprotein (fAGP) increases during feline infectious peritonitis (FIP). We have recently identified a 29 kDa protein that we named feline AGP-related protein (fAGPrP) due to its cross-reactivity with an anti-human AGP monoclonal antibody. In this work we describe the tissue distribution of fAGPrP during FIP, and its relationship with feline coronavirus (FCoV) and myeloid cells. Tissues from five control cats and from 15 cats with FIP were examined by immunohistochemistry using monoclonal antibodies against human AGP, FCoV and myeloid antigens. Diffuse fAGPrP positivity within the lesions, likely due to vascular plasma leakage, endothelial and epithelial lining were detectable. Compared to controls, fAGPrP-expressing cells often increased in number and were diffusely distributed in lymph nodes, as usually occurs for IgM-producing plasma cells during early immune responses. These findings did not depend on the presence of FCoVs or of myeloid cells, suggesting that fAGPrP is not directly involved in the pathogenesis of FIP.

?1-Acid glycoprotein fucosylation as a marker of carcinoma progression and prognosis

BACKGROUND

Serum alpha1-acid glycoprotein (AGP), an acute-phase protein secreted by the liver, carries alpha(1,3)-fucosylated structures on its 5 highly branched, N-linked sugar chains.

METHODS

Serum AGP levels in patients with various types of malignancies (n=214 patients) were measured using an enzyme-linked immunosorbent assay with anti-AGP antibody. To investigate glycoforms that differed in their degree of branching and extent of fucosylation, serum AGP samples were analyzed by crossed affinoimmunoelectrophoresis (CAIE) with concanavalin A, and Aleuria aurantia lectin (AAL), and anti-AGP antibody.

RESULTS

A significant difference (P <0.001) in serum AGP levels was observed in preoperative patients compared with levels in the healthy control group, but the levels in individual patients did not reflect their clinical status. Conversely, it was found not only that the patterns of AGP glycoforms differed widely in the patient group compared with the healthy control group, but they also changed depending on each patient's clinical status. Furthermore, AGP glycoforms seemed to be appropriate markers of disease progression and prognosis according to follow-up studies of 45 patients during prolonged preoperative and postoperative periods.

CONCLUSIONS

Patients with advanced malignancies who had AGP glycoforms that contained highly fucosylated triantennary and tetraantennary sugar chains for long periods after surgery were likely to have a poor prognosis. However, patients who had AGP glycoforms without such changes were expected to have a good prognosis.

Alpha(1)-acid glycoprotein: an acute phase protein with inflammatory and immunomodulating properties

alpha(1)-Acid glycoprotein (AGP) is a protein with a molecular weight of 41-43 kDa and is heavily glycosylated (45%). Due to the presence of sialic acids, it is negatively charged (pI=2.7-3.2). AGP is an acute phase protein in all mammals investigated to date. The serum concentration of AGP rises several fold during an acute phase response, the systemic answer to a local inflammatory stimulus. Also, its glycosylation pattern can change depending on the type of inflammation. The biological function of this protein is not clear. A number of activities on different type of blood cells have been described. In vivo, AGP clearly has protective effects in several models of inflammation. Here we review the data supporting an anti-inflammatory and immunomodulating role of AGP.

Effects of alpha 1-acid glycoprotein on erythrocyte deformability and membrane stabilization

The effects of alpha(1)-acid glycoprotein (AGP) on human erythrocyte membrane were examined in vitro. Bovine and dog AGP, in addition to human AGP or asialo human AGP were used, and the collected data were compared with that for human serum albumin (HSA). A new technique developed by Kikuchi was used to investigate erythrocyte deformability. The addition of AGPs including human AGP facilitated the passage of human erythrocytes with an average diameter of 7.2 microm suspended in phosphate buffered saline (PBS) through a 5 microm wide microchannel; hemolysis was suppressed after the passage. The stabilizing effects of AGPs on membrane were evaluated. Human AGP prevented hemolysis induced by hypotonic phosphate buffer solution. The effects of human AGP on the oxidative changes in erythrocytes exposed to oxygen radicals were investigated. Human AGP protected erythrocytes from H(2)O(2) and prevented the oxidation of dihydrorhodamine 123 to rhodamine 123 from H(2)O(2). We propose that the antioxidant activity of human AGP is due to the binding of free radicals. In all studies, the effects of human AGP on erythrocytes might not be a function of the negative charge associated with sialyl residues, because the presence of N-acetylneuraminic acid had no effect. However, human AGP may promote microcirculation and antioxidant activity compared with HSA. No species differences in the physiological function of AGP were found. These results suggest that an increase in the AGP content of serum above the normal value found under pathological conditions facilitates the passage of erythrocytes through capillaries, stabilizes erythrocyte membranes and protects against oxidative stress, all of which are favorable for microcirculation.

Up-regulation by clarithromycin of alpha(1)-acid glycoprotein expression in liver and primary cultured hepatocytes

alpha(1)-Acid glycoprotein (AGP) is the major transport protein for cationic drugs, endogenous ligands, and some anionic drugs in plasma. Hepatic synthesis and secretion of AGP are altered during acute inflammation as well as by a number of drugs. This alteration could influence the binding of drugs and its biological function. Macrolide antibiotics are widely used in the treatment of a variety of infectious diseases. The effects of macrolide antibiotics have been studied with respect to rat AGP expression in vivo. After the individual administration of six macrolides to rats, with the exception of oleandomycin, five increased AGP levels in serum. Of these five, clarithromycin (CAM) was the most potent inducer of AGP, which reached a maximum level between 3 to 7 days after administration. CAM increased the steady-state level of AGP mRNA in liver as well as protein level in serum in a dose-dependent manner. In addition, CAM increased AGP mRNA levels in primary cultured hepatocytes. In the luciferase promoter assay, CAM potentiated dexamethasone-increased promoter activity of the AGP gene, which contained the glucocorticoid response element, in cultured rat hepatocytes, although CAM itself had no effect on its activity. The effect of CAM and dexamethasone was diminished by glucocorticoid response element deletion or mutation or by adding the antiglucocorticoid, RU486. Further, in the mouse mammary tumor virus (MMTV) promoter containing functional glucocorticoid response element, CAM potentiated dexamethasone-increased promoter activity. In the adrenalectomized rats, CAM did not increase AGP levels in serum. These findings suggest that CAM may cause transcriptional induction of AGP, at least in part, via a glucocorticoid-mediated mechanism.

FK506 (tacrolimus) increases rat alpha1-acid glycoprotein expression in liver and primary cultured hepatocytes

FK506 (tacrolimus) (10 mg/kg, s.c., 5 days) increased rat alpha1-acid glycoprotein (AGP) in serum and AGP mRNA in liver. FK506 potentiated the dexamethasone-increased AGP expression in primary cultured hepatocytes. In the luciferase promoter assay, FK506 potentiated the dexamethasone-increased promoter activity of the AGP gene in cultured rat hepatocytes, although FK506 alone had no effect on its activity. The combined effect of FK506 and dexamethasone was diminished by glucocorticoid responsive element (GRE) deletion and mutation or by an anti-glucocorticoid. These results indicated that FK506 causes the transcriptional induction of AGP, at least in part, via a glucocorticoid-mediated mechanism.

Alpha-1-acid glycoprotein

Alpha-1-acid glycoprotein (AGP) or orosomucoid (ORM) is a 41-43-kDa glycoprotein with a pI of 2.8-3.8. The peptide moiety is a single chain of 183 amino acids (human) or 187 amino acids (rat) with two and one disulfide bridges in humans and rats,respectively. The carbohydrate content represents 45% of the molecular weight attached in the form of five to six highly sialylated complex-type-N-linked glycans. AGP is one of the major acute phase proteins in humans, rats, mice and other species. As most acute phase proteins, its serum concentration increases in response to systemic tissue injury, inflammation or infection, and these changes in serum protein concentrations have been correlated with increases in hepatic synthesis. Expression of the AGP gene is controlled by a combination of the major regulatory mediators, i.e. glucocorticoids and a cytokine network involving mainly interleukin-1 beta (IL-1 beta), tumour necrosis factor-alpha (TNF alpha), interleukin-6 and IL-6 related cytokines. It is now well established that the acute phase response may take place in extra-hepatic cell types, and may be regulated by inflammatory mediators as observed in hepatocytes. The biological function of AGP remains unknown; however,a number of activities of possible physiological significance, such as various immunomodulating effects, have been described. AGP also has the ability to bind and to carry numerous basic and neutral lipophilic drugs from endogenous (steroid hormones) and exogenous origin; one to seven binding sites have been described. AGP can also bind acidic drugs such as phenobarbital. The immunomodulatory as well as the binding activities of AGP have been shown to be mostly dependent on carbohydrate composition. Finally, the use of AGP transgenic animals enabled to address in vivo, functionality of responsive elements and tissue specificity, as well as the effects of drugs that bind to AGP and will be an useful tool to determine the physiological role of AGP.

Immunocalins: a lipocalin subfamily that modulates immune and inflammatory responses

A subset of the lipocalins, notably alpha(1)-acid glycoprotein, alpha(1)-microglobulin, and glycodelin, exert significant immunomodulatory effects in vitro. Interestingly, all three are encoded from the q32-34 region of human chromosome 9, together with at least four other lipocalins (neutrophil gelatinase-associated lipocalin, complement factor gamma-subunit, tear prealbumin, and prostaglandin D synthase) that also may have anti-inflammatory and/or antimicrobial activity. This review addresses important features of this genetically linked subfamily of lipocalins (involvement with the acute phase response, immunomodulatory and anti-inflammatory properties, the tissue localization, complex formation with other proteins and receptors, etc.). It is likely that these proteins have evolved to be an integrated part of the body's defense system as part of the extended cytokine network. Its members exert a regulatory, dampening influence on the inflammatory cascade, thereby protecting against tissue damage from excessive inflammation. That most major mammalian allergens are lipocalins may reflect this connection of lipocalins with the immune system. We propose that this immunologically active lipocalin subset be named the 'immunocalins', signifying not only the structural homology and close genetic linkage of its members, but also their protective involvement with immunological and inflammatory processes. As immune mediators, immunocalins appear to use at least three interactive sites: the lipocalin 'pocket', binding sites for other plasma proteins, and binding sites for cell surface receptors.

The degree of branching of the glycans of alpha(1)-acid glycoprotein in asthma. A correlation with lung function and inflammatory parameters

Alpha(1)-acid glycoprotein (AGP) is a plasma protein belonging to the group of acute-phase proteins. It contains five N-linked glycans which, depending on pathophysiologic state, differ in their degree of branching (i.e., in the relative proportions of di-, tri-, and tetraantennary glycans). Changes in the degree of branching of these glycans have been shown to affect various immunomodulatory properties of AGP. We wanted to investigate whether changes occur in the branching of AGP glycans in plasma and in bronchoalveolar lavage fluid (BALF) in asthma. For this purpose, we selected three groups of patients for study: patients with atopic asthma (AA), atopic nonasthmatic patients, and a group of patients with various interstitial lung diseases (ILDs). The plasma AGP concentration was normal in both atopic study groups, but was increased in ILD patients. In contrast, the branching of glycans of AGP was altered in subjects with AA, whereas it was normal in the other study groups. The presence of asthma symptoms correlated with the increased glycan branching of AGP in both plasma and BALF. Additionally, the degree of branching of AGP in BALF was related to FEV(1), to the provocative dose of histamine causing a 20% decrease in FEV (PD(20)), and to the number of eosinophils. In conclusion, asthma is accompanied by changes in the branching of AGP glycans that indicate an inflammatory reaction that differs markedly from a normal acute-phase response, in which decreased branching of AGP occurs.

Effect of semisynthetic analog of alpha(1)-acid glycoprotein on immunomodulatory and antiinflammatory activity of natural glycoprotein

Pseudo-alpha(1)-acid glycoprotein with carbohydrate chain ratio typical of native form was synthesized by a previously developed original technique of quantitative transfer of alpha(1)-acid glycoprotein carbohydrate chains to other polymeric carrier. Similarly to native glycoprotein, the semisynthetic analog inhibited lymphocyte proliferation and stimulated the production of antiinflammatory cytokines by peripheral blood mononuclear leukocytes. However, it possessed no antioxidant activity and did not inhibit complement activation by the alternative pathway. The role of carbohydrate and protein components of alpha(1)-acid glycoprotein molecule in the realization of its biological effects is discussed.

Inducible Expression and Regulation of the α1-Acid Glycoprotein Gene by Alveolar Macrophages: Prostaglandin E2 and Cyclic AMP Act as New Positive Stimuli

We have reported that α1-acid glycoprotein (AGP) gene expression was induced in lung tissue and in alveolar type II cells during pulmonary inflammatory processes, suggesting that local production of this immunomodulatory protein might contribute to the modulation of inflammation within the alveolar space. Because AGP may also be secreted by other cell types in the alveolus, we have investigated the expression and the regulation of the AGP gene in human and rat alveolar macrophages. Spontaneous AGP secretion by alveolar macrophages was increased 4-fold in patients with interstitial lung involvement compared with that in controls. In the rat, immunoprecipitation of [35S]methionine-labeled cell lysates showed that alveolar macrophages synthesize and secrete AGP. IL-1β had no effect by itself, but potentiated the dexamethasone-induced increase in AGP production. RNase protection assay demonstrated that AGP mRNA, undetectable in unstimulated cells, was induced by dexamethasone. Conditioned medium from LPS-stimulated macrophages as well as IL-1β had no effect by themselves, but potentiated the dexamethasone-induced increase in AGP mRNA levels. In addition to cytokines, PGE2 as well as dibutyryl cAMP increased AGP mRNA levels in the presence of dexamethasone. When AGP expression in other cells of the monocyte/macrophage lineage was examined, weak and no AGP production by human blood monocytes and by rat peritoneal macrophages, respectively, were observed. Our data showed that 1) AGP expression is inducible specifically in alveolar macrophages in vivo and in vitro; and 2) PGE2 and cAMP act as new positive stimuli for AGP gene expression.

Effect of alpha 1-acidic glycoprotein in the ascitic fluid of cancer patients on human NK cells: selective suppression of interferon-induced NK activation

The in vitro effect of C-AGP (pure alpha1-acid glycoprotein from the ascitic fluid of cancer patients) on NK cell cytotoxicity was tested using normal healthy human PBMC. C-AGP had no inhibitory effect on basal NK cell activity. C-AGP selectively suppressed the augmentation of NK cell activity by rIFNalphaA and rIFNgamma, but C-AGP did not prevent the NK activation by rIL-2. NK cells in PBMC treated with C-AGP for 12 h and then washed just once, to remove the C-AGP, fully recovered the ability to respond to rIFNalphaA. However, after the treatment of PBMC with C-AGP for 5 or 6 days, NK cells failed to respond to rIFNalphaA, in spite of washing to remove C-AGP from the cultures. Monocytes were necessary for the suppressive effect of C-AGP on rIFNalphaA activation of NK cells. Indomethacin restored the ability of NK cells to respond to rIFNalphaA in C-AGP-treated PBMC. These results suggest that monocytes are able to selectively suppress the response of NK cells to IFNs in the presence of, or following treatment with C-AGP.

cDNA cloning and expression of bovine UDP-N-acetylglucosamine: alpha1, 3-D-mannoside beta1,4-N-acetylglucosaminyltransferase IV

UDP-N-acetylglucosamine:alpha1,3-D-mannoside beta1, 4-N-acetylglucosaminyltransferase (GnT-IV) is one of the essential enzymes in the production of tri- and tetra-antennary Asn-linked sugar chains. Recently, we have successfully purified GnT-IV from bovine small intestine. Based on the partial amino acid sequence of the purified bovine GnT-IV enzyme, its cDNA has been cloned from bovine small intestine. The open reading frame is 1,605 base pairs long, and this sequence produced GnT-IV activity on transient expression in COS-7 cells. Although the deduced amino acid sequence does not have any significant homology with other known N-acetylglucosaminyltransferases (GnTs), the hydrophobicity profile showed a typical type II transmembrane protein structure, which is common to many glycosyltransferases. N-terminal amino acid sequencing of the purified GnT-IV revealed that 92 amino acids, including a transmembrane region, were truncated during purification. Of the three potential N-glycosylation sites Asn-458 was actually glycosylated in the purified enzyme, although this N-glycosylation site could be abolished without any reduction in GnT-IV activity. Serial deletions at both the N and C termini proved that the catalytic domain of GnT-IV is located in the central region of the enzyme. The GnT-IV mRNA level correlated with enzymatic activity in the various bovine tissues tested.

Inducible Expression of the α1-Acid Glycoprotein by Rat and Human Type II Alveolar Epithelial Cells

α1-Acid glycoprotein (AGP) is a major acute phase protein in rat and human. AGP has important immunomodulatory functions that are potentially important for pulmonary inflammatory response. The liver is the main tissue for AGP synthesis in the organism, but the expression of AGP in the rat lung has not been investigated. We show that AGP mRNA was induced in the lung of dexamethasone-, turpentine-, or LPS-treated rats, whereas AGP mRNA was not detected in the lung of control rats. In the lung of animals treated intratracheally with LPS, in situ hybridization showed that AGP gene expression was restricted to cells located in the corners of the alveolus, consistent with an alveolar type II (ATII) cell localization. The inducible expression of the AGP gene was confirmed in vitro with SV40 T2 cells and rat ATII cells in primary culture: maximal expression required the presence of dexamethasone. IL-1 and the conditioned medium of alveolar macrophages acted synergistically with dexamethasone. Rat ATII cells secreted immunoreactive AGP in vitro when stimulated with dexamethasone or with a combination of dexamethasone and the conditioned medium of alveolar macrophages. In vivo, in the human lung, we detected immunoreactive AGP in hyperplastic ATII cells, whereas we did not detect AGP in the normal lung. We conclude that AGP is expressed in the lung in cases of inflammation and that ATII cells are the main source of AGP in the lung.

Changes in plasma alpha 1-acid glycoprotein concentration and selected immune response in broiler chickens injected with Escherichia coli lipopolysaccharide

1. Changes in plasma alpha 1-acid glycoprotein (AGP) concentration and immune responses following Escherichia coli lipopolysaccharide (LPS) injection were studied in broiler chickens. 2. Higher plasma AGP concentrations were observed from 12 to 48 h after a single injection of LPS. 3. The highest concentration of plasma AGP was observed on day 2 followed by a gradual decrease in chicks injected with 150 micrograms/kg body weight of LPS every day for 13 d. 4. Plasma AGP concentration in chicks injected daily with LPS at 900 micrograms/kg body weight for 13 d increased on day 2, and decreased on day 4 to the concentration found before the injection. The concentration increased again on day 10. 5. Changes in plasma interleukin-1 (IL-1) like activity were similar to those in plasma AGP concentration when LPS was injected daily at 900 micrograms/kg body weight for 3 d. 6. Responses of blood mononuclear cell (MNC) proliferation to mitogen or concanavalin A, (Con A), and pokeweed mitogen (PWM) were positively correlated with changes in plasma AGP concentration. 7. The results suggest that plasma AGP concentration could be used as a positive indicator of changes in blood MNC proliferation to a mitogen and in plasma IL-1 like activity.

Studies on the interaction between hyaluronan and a rat colon cancer cell line

Binding studies with 125I-Tyr labelled hyaluronan (HA) on a cultured rat colon cancer cell line were performed to characterize the association of HA to tumour cells in vitro. Results show a specific and saturable binding (Kd=1.36 nM) which indicates the presence of an HA binding receptor on the tumour cells. There is a specific constant increase of cell-associated HA over time, which indicates that HA is specifically taken up by the cells through endocytosis. The binding of 125I-Tyr labelled HA was more effectively inhibited by unlabelled HA of high MW in relation to low MW species of the polysaccharide indicating that the receptor binds HA of high MW with greater affinity than low MW species. In competition experiments, the HA-binding could not be inhibited by other polysaccharides such as chondroitin sulphate and heparin. Nor could ligands for scavenger receptors and antibodies directed towards ICAM-1, CD 44 and RHAMM (Receptor for HA Mediated Motility) significantly inhibit the association of HA to tumour cells.

Immunomodulating activities of a natural alpha1-acid glycoprotein and its carbohydrate chains attached to the protein-free polymer

Immunomodulating effects of a neoglycoconjugate created on the basis of alpha1-acid glycoprotein (AGP) carbohydrate chains and synthetic protein-free carrier have been investigated. It was demonstrated that this pseudo-AGP suppressed PHA- or anti-CD3 antibody-induced lymphocyte proliferation in a dose-dependent manner. Pseudo-AGP revealed a similar antiproliferative effect as the natural AGP samples. Stimulation of the LPS-induced proinflammatory cytokine production by mononuclear cells treated with both natural and pseudo-AGP has been also demonstrated. These data show that carbohydrate chains of AGP play a crucial role in the studied biological effect realization.

Do synovial fluid acute phase proteins from patients with rheumatoid arthritis originate from serum?

This study was performed in order to gain insight into the occurrence, glycosylation and the possible origin of the acute-phase proteins alpha1-acid glycoprotein (AGP) and alpha1-protease inhibitor (PI) in sera and synovial fluid from patients with rheumatoid arthritis (RA). Therefore paired sera and synovial fluid samples from patients with RA, and paired synovial fluid samples from right and left knees of patients with varying degrees of arthritis were studied. Crossed affinity immunoelectrophoresis (CAIE) was used with concanavalin A and Aleuria aurantia lectin for the detection of the degree of branching and fucosylation, respectively, and the monoclonal CSLEX-1 for the detection of Sialyl Lewis(X) (SLe(X)) groups on AGP. For PI, not only CAIE, but also high-pressure-anion-exchange chromatography with pulsed amperometric detection was used to study the glycosylation. It was established that the concentrations of AGP and PI were increased in the serum of RA patients compared to normal healthy controls, but that the concentration of both proteins, as well as albumin, was significantly lower in synovial fluid than in serum. Furthermore, the type of glycosylation of both AGP and PI found in RA was significantly different from that found in normals, with increased fucosylation, but there were no major differences in the degree of branching of AGP- or PI-glycans in RA, compared to normals. No differences in glycosylation could be established between serum and synovial fluid in RA. For PI an increased fucosylation was found, both in serum and synovial fluid, using both methods of detection, and it could be established that only the alpha1-->3- and not the alpha1-->6-fucosylation of PI was affected by RA. The increased fucosylation of AGP resulted in an increased expression of SLe(X) on AGP-glycans. Since the alpha1-->3-fucosylation of AGP was significantly increased in both serum and synovial fluid from RA patients, and this correlated with systemic but not with local disease parameters, it can be suggested that acute phase proteins in synovial fluid are most probably of hepatic origin.

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.

Glycosylation of alpha 1-acid glycoprotein in septic shock: changes in degree of branching and in expression of sialyl Lewis(x) groups

The occurrence of differences in acute-phase response, with respect to concentration and glycosylation of alpha 1-acid glycoprotein (AGP) was studied in the sera of patients, surviving or not from septic shock. Crossed affino-immunoelectrophoresis was used with concanavalin A and Aleuria aurantia lectin for the detection of the degree of branching and fucosylation, respectively, and the monoclonal CSLEX-1 for the detection of sialyl Lewisx (SLeX) groups on AGP. Septic shock apparently induced an acute-phase response as indicated by the increased serum levels and changed glycosylation of AGP. In the survivor group a transient increase in diantennary glycan content was accompanied by a gradually increasing fucosylation and SLeX expression, comparable to those observed in the early phase of an acute-inflammatory response. Remarkably, in the non-survivor group a modest increase in diantennary glycan content was accompanied by a strong elevation of the fucosylation of AGP and the expression of SLeX groups on AGP, typical for the late phase of an acute-phase response. Our results suggest that these changes in glycosylation of AGP can have a prognostic value for the outcome of septic shock.

Effect of dietary protein concentration on responses to Escherichia coli endotoxin in broiler chickens

The effect of dietary protein concentration on stress responses against injection of Escherichia coli lipopolysaccharide (LPS) was studied in male broiler chickens. Chickens (7 d of age) were fed on a 100 (low-protein; LP) or 300 g protein/kg (high-protein; HP) diet for 2 weeks. LPS was injected intraperitoneally every 2 d during the final 6 d, or once 16 h before the end of the experiment, at a concentration of 900 micrograms/chick. The LPS injection did not affect body-weight gain, feed intake, gain:intake ratio, or plasma Fe concentration. The single injection of LPS reduced plasma Zn concentration, but the repeated injections did not. Feeding the HP diet increased the response of plasma Zn concentration to the single injection of LPS. Plasma albumin concentration was reduced by LPS injection. Feeding the HP diet resulted in a higher plasma alpha 1-acid glycoprotein (AGP) concentration than feeding the LP diet, in chicks untreated with LPS. An increase in plasma AGP concentration observed after LPS injection in chicks fed on the LP diet was greater than that seen in chicks fed on the HP diet. No significant changes in plasma AGP concentration in response to repeated injections of LPS were observed in chicks fed on the HP diet. Plasma interleukin-1 (IL-1)-like activity was greater in chicks fed on the LP diet than in those fed on the HP diet, when LPS was injected. The response of plasma IL-1-like activity to the single injection of LPS in chicks fed on the LP diet was the greatest among the treatment groups. These results suggest that acute-phase responses to LPS injection are much greater in chicks fed on a LP diet than in those fed on a HP diet, and multiple injection of LPS weakens the responses.

Interleukin-6-type cytokine-induced changes in acute phase protein glycosylation

The plasma levels and the glycosylation of acute-phase proteins (APP) are subject to marked changes during acute and chronic inflammation. The pathophysiological variations in different glycoforms of APP in serum most likely result from changes in the glycosylation process during their biosynthesis in the parenchymal cells of the liver. This is suggested from in vitro studies with isolated hepatocytes and hepatoma cell lines. Inflammatory cytokines appear to regulate the changes in glycosylation independent from the rate of synthesis of the APP. In addition, other humoral factors like corticosteroids and growth factors are involved. The interplay of these factors is determined by the stage of the disease (as in rheumatoid arthritis) or the physiological situation (as in pregnancy). The changes in glycosylation of specific APP might affect the operation of the immune system.

Alpha 1-acid glycoprotein (orosomucoid): pathophysiological changes in glycosylation in relation to its function

The aim of this review is to summarize the research efforts of the last two decades with respect to (i) the determination and characterization of the changes in glycosylation of AGP under various physiological and pathological states; and (ii) the effects of such changes on its possible anti-inflammatory functions. It will become clear that the heterogeneity observed in the glycosylation of AGP in serum, represents various so-called glycoforms of AGP, of which the relative amounts are strictly determined by the (patho) physiological conditions.

alpha 1-Acid glycoprotein binds human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein via N-linked glycans

In the present study, we demonstrate a specific low-affinity interaction between recombinant precursor gp160 (rgp160) or surface unit gp120 (rgp120) of human immunodeficiency virus type 1 (HIV-1) and alpha 1-acid glycoprotein (AGP), a human glycoprotein displaying complex type N-glycans. Binding of rgp160/rgp120 to agarose-coupled AGP was dose-dependent, saturable, calcium-, pH- and temperature-dependent. Binding was inhibited by soluble AGP, asialo-AGP, fetuin, beta-D-GlcNAc47-BSA, alpha-D-Man20-BSA, mannan, complex-type asialo-agalacto-tetraanternary precursor oligosaccharide from human AGP and oligomannose 9 from porcine thyroglobulin; fully deglycosylated AGP was not inhibitory. The three AGP glycoforms separated on immobilized ConA bound rgp160 to the same extent as did unfractionated AGP. These findings extend our previous results on the carbohydrate-binding properties of HIV-1 envelope (Env) glycoprotein in that they demonstrate the involvement of AGP glycan moieties in the binding to rgp160/rgp120. Preincubation of rgp160 with AGP or mannan significantly reduced its binding to monocyte-derived macrophages (MDM), suggesting that AGP may play a role in preventing binding of soluble or virus-bound Env glycoprotein to CD4+ monocytic cells.

Does alpha 1-acid glycoprotein act as a non-functional receptor for alpha 1-adrenergic antagonists?

The ability of a variety of alpha 1-acid glycoproteins (AAG) to affect the intrinsic activity of the alpha 1-adrenergic antagonist prazosin was studied in rabbit aortic strip preparations. From these studies, the activity of AAG appears to be linked to their ability to bind the antagonist. However, a capability to bind prazosin was not the only requirement for this effect. The removal of sialic acid and partial removal of the galactose and mannose residues by periodate oxidation of human AAG all but eliminated the ability of AAG to affect the intrinsic pharmacologic activity of prazosin, although the binding of prazosin was not significantly affected. The presence of bovine AAG, a protein that has a low ability to bind prazosin, reduced the effect of human AAG on prazosin activity. Based upon these results, we propose that AAG is able to bind in the vicinity of the alpha 1-adrenoceptors, therefore extending the binding region for antagonists in such a way as to decrease the ability of the antagonist to interact with the receptor. The carbohydrate side-chains are important for the binding of AAG in the region of the adrenoceptor.

Protection by alpha 1-acid glycoprotein against tumor necrosis factor-induced lethality

We here report that alpha 1-acid glycoprotein, a typical acute phase protein, protects mice from lethal shock induced by tumor necrosis factor (TNF) or endotoxin. The protection is observed both in normal and in galactosamine-sensitized mice. Optimal desensitization requires at least 3 mg alpha 1-acid glycoprotein administered 2 h before the lethal challenge. Under these conditions, complete inhibition of all TNF-induced metabolic changes was observed: fall in body temperature, release of liver transaminases, enhanced clotting time, and mortality. The known platelet aggregation-inhibitory activity of alpha 1-acid glycoprotein provides a possible explanation for this protective capacity.