Transferrin microheterogeneity in rheumatoid arthritis. Relation with disease activity and anemia of chronic disease

Susceptibility of Human Plasma N-glycome to Low-Calorie and Different Weight-Maintenance Diets

Aberrant plasma protein glycosylation is associated with a wide range of diseases, including diabetes, cardiovascular, and immunological disorders. To investigate plasma protein glycosylation alterations due to weight loss and successive weight-maintenance diets, 1850 glycomes from participants of the Diogenes study were analyzed using Ultra-High-Performance Liquid Chromatography (UHPLC). The Diogenes study is a large dietary intervention study in which participants were subjected to a low-calorie diet (LCD) followed by one of five different weight-maintenance diets in a period of 6 months. The most notable alterations of the plasma glycome were 8 weeks after the subjects engaged in the LCD; a significant increase in low-branched glycan structures, accompanied by a decrease in high-branched glycan structures. After the LCD period, there was also a significant rise in N-glycan structures with antennary fucose. Interestingly, we did not observe significant changes between different diets, and almost all effects we observed immediately after the LCD period were annulled during the weight-maintenance diets period.

GlycA Levels during the Earliest Stages of Rheumatoid Arthritis: Potential Use as a Biomarker of Subclinical Cardiovascular Disease

This study aimed at evaluating the clinical relevance of glycoprotein profiles during the earliest phases of rheumatoid arthritis (RA) as biomarkers of cardiovascular (CV) risk and treatment response. Then, GlycA and GlycB serum levels were measured using 1H-nuclear magnetic resonance in 82 early RA patients, 14 clinically-suspect arthralgia (CSA), and 28 controls. Serum glycosyltransferase activity was assessed by a colorimetric assay. Subclinical CV disease was assessed by Doppler-ultrasound. We found that GlycA and GlycB serum levels were increased in RA (both p < 0.001), but not in CSA, independently of cardiometabolic risk factors. Increased serum glycosyltransferase activity paralleled GlycA (r = 0.405, p < 0.001) and GlycB levels (r = 0.327, p = 0.005) in RA. GlycA, but not GlycB, was associated with atherosclerosis occurrence (p = 0.012) and severity (p = 0.001). Adding GlycA to the mSCORE improved the identification of patients with atherosclerosis over mSCORE alone, increasing sensitivity (29.7 vs. 68.0%) and accuracy (55.8 vs. 76.6%) and allowing reclassification into more appropriate risk categories. GlycA-reclassification identified patients with impaired lipoprotein metabolism. Finally, baseline GlycA levels predicted poor clinical response upon anti-rheumatic treatment at 6 and 12 months in univariate and multivariate analysis. In sum, increased GlycA levels during the earliest stage of RA can be considered a powerful biomarker for CV risk stratification and treatment response.

Alterations in the Glycan Profile of Mouse Transferrin: New Insights in Collagen-Induced Arthritis

Transferrin purification from mice serum samples by immunoaffinity chromatography (IAC) was optimized in order to study the possible modifications occurring in its glycans in collagen-induced arthritis (CIA) samples. SDS-PAGE and nanoLC-MS/MS were used to monitor the IAC purification performance. Afterward, a relative quantification of mouse transferrin (mTf) glycan isomers using [¹²C₆]/[¹³C₆]-aniline was used to unequivocally detect alterations in the glycan profile of CIA mice. In addition, multivariate data analysis was applied to identify the most meaningful glycan isomers for the discrimination between control and pathological samples. Partial least-squares discriminant analysis (PLS-DA) revealed that five out of fifteen mTf glycan isomers could be potential biomarkers of CIA, most of them corresponding to highly sialylated structures (H6N5S3_2, H6N5S3_3, and H5N4S3_2). Moreover, some of these glycan isomers also seemed to be related with the progression of CIA, especially H6N5S2 and H6N5S3_2, as their overexpression increased with the clinical score of the pathology. Hence, the established methodology not only provides valuable information to find glycan-based biomarkers of CIA, but also leaves the door open to evaluate, in the future, glycosylation changes of many other inflammatory diseases, in which transferrin has been described to be altered.

The Profile of Serum Transferrin Isoforms in Rheumatoid Arthritis

INTRODUCTION

Transferrin, a microheterogeneous iron-transporting N-glycoprotein, is an optimal model for the analysis of the glycosylation profile in rheumatoid arthritis (RA). The aim of this study was to assess the transferrin isoforms profile in RA patients at the time of diagnosis and then look into their associations with disease activity.

METHODS

Serum samples were collected from 48 patients with RA. The patients were males (6) and females (42) (age range: 33-85 years). Control group consisted of 30 healthy volunteers. Transferrin isoforms were analysed by capillary electrophoresis on MINICAP electrophoretic system.

RESULTS

There was a significant decrease in the relative concentrations of trisialo- (mean ± SD; 2.130 ± 1.112) and pentasialotransferrin (13.562 ± 3.088), and significant increase in tetrasialotransferrin (83.640 ± 3.165) in RA patients when compared to the control group (3.615 ± 1.156; 76.840 ± 5.621; 18.610 ± 6.027, respectively) (U Mann-Whitney test: p < 0.001 for all comparisons). There were no significant changes in the disialotransferrin concentrations in RA patients. Trisialotransferrin concentration correlated with RA activity expressed as DAS 28 in RA patients (p < 0.001). The low trisialotransferrin concentration was also associated with high platelet count and high ESR (p < 0.001 for both). Disialo-, tetrasialo- and pentasialotransferrin concentrations did not correlate with DAS 28.

CONCLUSIONS

In patients with RA the serum profile of transferrin isoforms is altered. We predict that the levels of trisialylated isoforms of transferrin will serve as a useful biochemical marker of the RA activity.

Serum profile of transferrin isoforms in rheumatoid arthritis treated with biological drugs

BACKGROUND

In the chronic inflammation process in the course of rheumatoid arthritis (RA), many alterations in the expression of plasma proteins, as well as their posttranslational modifications (including glycosylation) can occur. Taking into account the disturbances in protein glycosylation and the emerging new treatment regimens, the aim of this study was to assess the serum profile of transferrin isoforms in RA patients treated with biological drugs.

METHODS

The study included 20 patients (16 females and 4 males; mean age: 53.4 years; range: 24-67) with rheumatoid arthritis treated with rituximab. Serum samples were taken 3 times: before and 3 and 6 months during treatment. The isoforms of transferrin were separated by capillary electrophoresis (MINICAP electrophoretic system, Sebia, France) into five major fractions: asialo-, disialo-, trisialo-, tetrasialo- and pentasialotransferrin. The results were calculated as relative concentrations of each fraction.

RESULTS

The median trisialotransferrin relative concentrations after 3 and 6 months treatment (4.40% and 4.10%, respectively) were significantly higher (p = 0.013, p = 0.009, respectively) than before treatment (3.50%). The levels of serum pentasialotransferrin were also increased 3 and 6 months following treatment (16.5% and 17.7%, p = 0.005 and p = 0.006, respectively) as compared to those before therapy (14.5%), while tetrasialotransferrin concentrations were lower (80.3% and 78.4%, p = 0.009 and p = 0.008, respectively) than before treatment (81.5%). Trisialotransferrin relative concentration correlated with Hb (p = 0.019), whereas pentasialotransferrin with PLT (p = 0.036) after treatment.

CONCLUSIONS

This study indicates that treatment with rituximab of RA patients alters the serum profile of transferrin isoforms. Tri-, tetra- and pentasialotransferrin relative concentrations measurements can be a useful tool to monitor therapy.

Serum profile of transferrin isoforms in juvenile idiopathic arthritis: a preliminary study

It is reported that alterations in protein glycosylation are present in adult rheumatic diseases; however, the data related to pediatric rheumatic conditions are very scarce. The aim of this study was to assess the effect of juvenile idiopathic arthritis (JIA) on the serum glycosylation profile of transferrin isoforms. Twenty-five patients with different clinical forms of an active JIA and 22 healthy controls were studied. Serum samples were analyzed by capillary electrophoresis on MINICAP electrophoretic system (Sebia, France) to determine the levels of transferrin isoforms. In patients with JIA, tetrasialotransferrin (median 82.6%; range 68.8–99.5) concentration was lower (P = 0.032), and pentasialotransferrin (median 14%; range 0.5–31.2) was higher (P = 0.020) in comparison to controls (median 84.45; range 79.8–87.4; median 11.55; range 9.7–16.1, respectively). No significant correlations between concentration of transferrin isoforms and disease activity score (JADAS 27) or the degree of disability (VAS and CHAQ) were found. Erythrocyte sedimentation rate and CRP levels correlated positively with disialotransferrin (R = 0.493, P = 0.017; R = 0.850, P < 0.001, respectively) and pentasialotransferrin (R = 0.533, P = 0.006; R = 0.491, P = 0.045, respectively), and negatively with trisialotransferrin (R = − 0.546, P = 0.007; R = − 0.515, P = 0.049, respectively) and tetrasialotransferrin (R = − 0.436, P = 0.029; R = − 0.504, P = 0.039, respectively). This preliminary study shows the shifts in transferrin isoforms profile among patients with JIA. Our data indicate a potential clinical utility of the transferrin isoforms measurement, especially tetrasialotransferrin and pentasialotransferrin. Further prospective studies on larger groups of patients should be conducted to validate the results.

Serum Protein N-Glycosylation Changes with Rheumatoid Arthritis Disease Activity during and after Pregnancy

Symptoms of rheumatoid arthritis (RA) improve during pregnancy, a phenomenon that was found to be associated with N-glycosylation changes of immunoglobulin G. Recent advances in high-throughput glycosylation analysis allow the assessment of the N-glycome of human sera as well. The aim of this study was to identify new protein N-glycosylation properties that associate with changes in RA disease activity during and after pregnancy. A longitudinal cohort of serum samples was collected during 285 pregnancies (32 control individuals and 253 RA patients). Per individual one sample was collected before conception, three during pregnancy, and three after delivery. Released serum protein N-glycans were measured by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) after employing chemical modification of the sialic acids to allow discrimination of sialic acid linkage isomers. Serum protein N-glycosylation showed strongly modified during pregnancy, with similar changes visible in control individuals and RA pregnancies. Namely, a decrease in bisection and an increase in galactosylation in diantennary glycans were found, as well as an increase in tri- and tetraantennary species and α2,3-linked sialylation thereof. The change in RA disease activity [DAS28(3)-CRP] proved negatively associated with the galactosylation of diantennary N-glycans, and positively with the sialylation of triantennary fucosylated species (A3FGS). While the protein source of the novel finding A3FGS is thus far unknown, its further study may improve our understanding of the etiology of RA disease severity.

Evaluation of ion mobility for the separation of glycoconjugate isomers due to different types of sialic acid linkage, at the intact glycoprotein, glycopeptide and glycan level

The study of protein glycosylation can be regarded as an intricate but very important task, making glycomics one of the most challenging and interesting, albeit under-researched, type of "omics" science. Complexity escalates remarkably when considering that carbohydrates can form severely branched structures with many different constituents, which often leads to the formation of multiple isomers. In this regard, ion mobility (IM) spectrometry has recently demonstrated its power for the separation of isomeric compounds. In the present work, the potential of traveling wave IM (TWIMS) for the separation of isomeric glycoconjugates was evaluated, using mouse transferrin (mTf) as model glycoprotein. Particularly, we aim to assess the performance of this platform for the separation of isomeric glycoconjugates due to the type of sialic acid linkage, at the intact glycoprotein, glycopeptide and glycan level. Straightforward separation of isomers was achieved with the analysis of released glycans, as opposed to the glycopeptides which showed a more complex pattern. Finally, the developed methodology was applied to serum samples of mice, to investigate its robustness when analyzing real complex samples.

BIOLOGICAL SIGNIFICANCE

Ion mobility mass spectrometry is a promising analytical technique for the separation of glycoconjugate isomers due to type of sialic acid linkage. The impact of such a small modification in the glycan structure is more evident in smaller analytes, reason why the analysis of free glycans was easier compared to the intact protein or the glycopeptides. The established methodology could be regarded as starting point in the separation of highly decorated glycoconjugates. This is an important topic nowadays, as differences in the abundance of some glycan isomers could be the key for the early diagnosis, control or differentiation of certain diseases, such as inflammation or cancer.

Acute phase proteins as promising biomarkers: Perspectives and limitations for human and veterinary medicine

Acute phase proteins (APPs) are highly conserved plasma proteins that are increasingly secreted by the liver in response to a variety of injuries, independently of their location and cause. APPs favor the systemic regulation of defense, coagulation, proteolysis, and tissue repair. Various APPs have been applied as general diagnostic parameters for a long time. Through proteomic techniques, more and more APPs have been discovered to be differentially altered. Since they are not consistently explainable by a stereotypic hepatic expression of sets of APPs, most of these results have unfortunately been neglected or attributed to the nonspecificity of the acute phase reaction. Moreover, it appears that various extrahepatic tissues are also able to express APPs. These extrahepatic APPs show focally specific roles in tissue homeostasis and repair and are released primarily into interstitial and distal fluids. Since these focal proteins might leak into the circulatory system, mixtures of hepatic and extrahepatic APP species can be expected in blood. Hence, a selective alteration of parts of APPs might be expected. There are several hints on multiple molecular forms and fragments of tissue-derived APPs. These differences offer the chance for multiple selective determinations. Thus, specific proteoforms might indeed serve as tissue-specific disease indicators.

Transferrin Sialylation in Smoking and Non-Smoking Pregnant Women with Intrauterine Growth Restriction

Transferrin (Tf) is a glycosylated protein responsible for transporting iron. Various sialylation levels of Tf are observed during physiological and pathological processes. We studied if the changes in iron stores as well as tobacco smoke may have an impact on foetal development and in consequence lead to intrauterine growth restriction (IUGR). In the third trimester of pregnancy, lower levels of 4-sialoTf isoform and higher levels of 5-sialoTf were observed in the serum of non-smoking women with IUGR in comparison to the control group. On the day of labour, level of 2-sialoTf was significantly lower and level of 3-sialo was Tf higher in the serum of non-smoking women. Level of 4-sialo was found lower in the serum of smoking women with IUGR than in the control group. The observed changes may suggest a connection between iron stores, transport of iron to the foetus and foetal development.

Sialic acid level reflects the disturbances of glycosylation and acute-phase reaction in rheumatic diseases

In the rheumatic diseases, the changes in the carbohydrate part of serum glycoproteins occur and these abnormalities can be monitored by serum level of total and free sialic acid. The aim of this study was to evaluate the total and free sialic acid level as a marker of inflammation activity (TSA) and the changes in glycosylation of blood glycoproteins (FSA) in rheumatoid arthritis (RA), systemic sclerosis (SSc) and systemic lupus erythematosus (SLE). Studies were carried out in 50 patients with RA, 24 with SLE and 32 with SSc. TSA concentration was measured with an enzymatic, colorimetric method and FSA with a thiobarbituric method. The serum levels of TSA in RA and SLE patients were significantly increased compared to controls and in RA patients were higher than that in SSc patients. The mean serum level of FSA in RA patients was significantly higher, but in SSc patients significantly lower than that in the controls, and in RA patients was significantly higher than in SLE and in SSc patients. All acute-phase proteins were changed: Positive acute-phase proteins were elevated, and the negative protein was decreased. The positive acute-phase proteins positively correlated with the levels of TSA and FSA in RA and SSc patients. In SLE patients, TSA positively correlated with haptoglobin and α1-antitrypsin. In RA patients, there was the positive correlation of TSA and FSA with DAS 28. The changes in the serum levels of TSA and FSA in the course of rheumatic diseases could reflect the abnormalities in glycosylation/sialylation patterns of glycoproteins induced by acute-phase response.

Glycosylation status of serum in inflammatory arthritis in response to anti-TNF treatment

OBJECTIVE

Glycosylation is the most common post-translational modification and is altered in disease. The typical glycosylation change in patients with inflammatory arthritis (IA) is a decrease in galactosylation levels on IgG. The aim of this study is to evaluate the effect of anti-TNF therapy on whole serum glycosylation from IA patients and determine whether these alterations in the glycome change upon treatment of the disease.

METHODS

Serum samples were collected from 54 IA patients before treatment and at 1 and 12 months after commencing anti-TNF therapy. N-linked glycans from whole serum samples were analysed using a high-throughput hydrophilic interaction liquid chromatography-based method.

RESULTS

Glycosylation on the serum proteins of IA patients changed significantly with anti-TNF treatment. We observed an increase in galactosylated glycans from IgG, also an increase in core-fucosylated biantennary galactosylated glycans and a decrease in sialylated triantennary glycans with and without outer arm fucose. This increase in galactosylated IgG glycans suggests a reversing of the N-glycome towards normal healthy profiles. These changes are strongly correlated with decreasing CRP, suggesting a link between glycosylation changes and decreases in inflammatory processes.

CONCLUSION

Glycosylation changes in the serum of IA patients on anti-TNF therapy are strongly associated with a decrease in inflammatory processes and reflect the effect of anti-TNF on the immune system.

High performance liquid chromatography evaluation of serum carbohydrate-deficient transferrin and more sialylated transferrin glycoforms in children

OBJECTIVES

The evaluation of the age-specific distribution of transferrin glycoforms in paediatric patients may help in defining reference intervals which are critical for an improved and earlier diagnosis.

DESIGN AND METHODS

Serum samples from 224 children (age: 2 months-14 years) were analyzed by HPLC (Bio-Rad CDT/HPLC kit) and glycoforms expressed as percentage of the total area of transferrin (Tf).

RESULTS

Asialo- and Monosialo-Tf were not detectable in any patient. Medians (IQR) were respectively 0.92% (0.80-1.04%) for Disialo-Tf; 3.47% (2.69-4.18%) for Trisialo-Tf; 82.54% (81.32-83.53%) for Tetrasialo-Tf; 12.73% (11.91-14.09%) for Pentasialo-Tf. Statistically significant differences in Trisialo-Tf (p < 0.0005), Tetrasialo-Tf (p = 0.001), Pentasialo-Tf (p < 0.0005), but not in Disialo-Tf, were observed between the age groups.

CONCLUSIONS

Age-specific Disialo-Tf cut-offs are not necessary. In children 1.3% and 6.4% may be suggested as upper limits of normal range to detect increases of Disialo- and Trisialo-Tf. The presence of Asialo- and Monosialo-Tf should be considered an abnormal finding and prompt further investigations.

Transferrin and HFE genes interact in Alzheimer's disease risk: the Epistasis Project

Iron overload may contribute to the risk of Alzheimer's disease (AD). In the Epistasis Project, with 1757 cases of AD and 6295 controls, we studied 4 variants in 2 genes of iron metabolism: hemochromatosis (HFE) C282Y and H63D, and transferrin (TF) C2 and -2G/A. We replicated the reported interaction between HFE 282Y and TF C2 in the risk of AD: synergy factor, 1.75 (95% confidence interval, 1.1-2.8, p = 0.02) in Northern Europeans. The synergy factor was 3.1 (1.4-6.9; 0.007) in subjects with the APOEε4 allele. We found another interaction, between HFE 63HH and TF -2AA, markedly modified by age. Both interactions were found mainly or only in Northern Europeans. The interaction between HFE 282Y and TF C2 has now been replicated twice, in altogether 2313 cases of AD and 7065 controls, and has also been associated with increased iron load. We therefore suggest that iron overload may be a causative factor in the development of AD. Treatment for iron overload might thus be protective in some cases.

Relationship between serum acute-phase proteins and high disease activity in patients with rheumatoid arthritis

PURPOSE

The aim of this study was to assess the relationship between serum acute-phase proteins and high disease activity evaluated by activity score (DAS28) in patients with rheumatoid arthritis.

MATERIAL/METHODS

Studies were carried out on 27 females with RA and 32 control women. Acute-phase proteins were divided into 4 fractions as follows: alpha1-globulins represented by alpha1-acid glycoprotein (AGP) and alpha1-antitrypsin (AAT); alpha2-globulins - haptoglobin (Hp); beta-globulins - complement C3 (C3) and total transferrin (Tf); gamma-globulins - C reactive protein (CRP), rheumatoid factor (RF) and immunoglobulin G (IgG), and determined by immunoturbidimetric methods.

RESULTS

The serum levels of acute-phase proteins changed in RA patients. On account of the alterations of concentration, acute-phase proteins are placed in the downgrade scale as follows: CRP, Hp, AGP, C3, AAT and Tf. None of the acute-phase proteins correlated with the RF and the majority of them were closely related to ESR. Almost all of the acute-phase proteins (without C3) were closely related to RA activity (based on DAS28) and their places in the downgrade scale were as follows: CRP, Tf, AGP, Hp and AAT. The degree of disability evaluated by Health Assessment Questionnaire has affected on the concentrations of AGP, Tf and CRP. Serum AGP, AAT and RF levels significantly correlated with the patient's age. No correlations were observed between IgG, TP levels, and clinical data.

CONCLUSIONS

Among the entire panel, the CRP and AGP appeared to be the most useful biochemical markers for evaluation of the disease activity of patients with RA.

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

PURPOSE

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

EXPERIMENTAL DESIGN

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

RESULTS

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

CONCLUSIONS AND CLINICAL RELEVANCE

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

Detection of altered N-glycan profiles in whole serum from rheumatoid arthritis patients

Altered N-glycosylation occurs in many diseases. In rheumatoid arthritis (RA), for example, reduction in galactose residues in IgG and an increase in fucose residues in alpha1-acid glycoprotein have been observed. To further analyse N-glycans in disease, we show N-glycan profiling from whole serum employing reversed phase high performance liquid chromatography/negative-ion mode by sonic spray ionization ion trap mass spectrometry with pyridylamination. Profiles from female 15 RA patients and 18 aged-matched healthy women were compared. The most significant change seen in RA was decreased levels of mono-galactosyl bi-antennary N-glycans, in agreement with the previous reports regarding IgG. We also show previously unreported differences between isomers and increased tri-antennary oligosaccharides. These results indicate that LC-MS analysis of whole serum N-glycans can identify N-glycan alterations in RA and that this is a promising method both for studies of RA mechanisms and diagnosis.

Transferrin microheterogeneity in pregnancies with preeclampsia

BACKGROUND

It has been reported that concentrations of serum transferrin (Tf) and its highly sialylated subfraction increase in normal pregnancy. This study investigated changes in the concentrations of serum transferrin and its subfractions in preeclampsia.

METHODS

The serum concentration of transferrin was determined by a standard turbidimetric assay and microheterogeneous transferrin subgroups (low sialylated, 4-sialo and highly sialylated transferrins) were assessed by crossed immuno-isoelectric focusing.

RESULTS

Compared to normal pregnancy, the concentrations of total, 4-sialo and highly sialylated transferrins decreased by 27%, 16% and 38%, respectively, in severe preeclampsia, while these values did not significantly decrease in mild preeclampsia. The concentration of low sialylated transferrin involving 2-sialo- and 3-sialo-transferrins significantly decreased both in mild and severe preeclampsia, the value in severe preeclampsia was even significantly lower than that in nonpregnant women. The serum concentrations of total and highly sialylated transferrins in preeclampsia were correlated positively with infant birth weights (r=0.587 and r=0.645, respectively).

CONCLUSIONS

The serum concentrations of total and highly sialylated transferrins in severe preeclampsia decrease significantly. This might have a negative impact on intrauterine growth. Additionally, the serum low sialylated transferrin decreases more sensitively in preeclampsia, although the concentration is low even in normal pregnancy.

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.

Changed transferrin sialylation in Parkinson's disease

Variation in the sialylation pattern of transferrin was studied in serum and cerebrospinal fluid (CSF) of 90 patients with Parkinson's disease (PD), dementing and non-dementing, de novo and treated, and was compared with the variation observed in a group of 21 age-matched healthy controls. In serum and CSF of PD patients the proportional contribution of the different sialo-transferrins was independent of sex or dementia. However, a significant shift was found towards the more sialylated fractions for serum transferrin in both de novo and treated PD patients. This shift was not observed for CSF transferrin. The contribution of the tau-transferrin fraction, reduced in de novo PD patients, returns on treatment to the level observed for healthy controls. These observations may be important, as the degree of sialylation of transferrin in serum and CSF plays a role in the homeostasis of iron, and suggest that alterations in transferrin sialylation may play a role in the pathophysiology of PD.