Development and evaluation of silica-based lectin microcolumns for glycoform analysis of alpha1-acid glycoprotein

Silica-based lectin microcolumns were developed and optimized for the separation and analysis of glycoform fractions in alpha1-acid glycoprotein (AGP) based on both the degree of branching and level of fucosylation. Concanavalin A (Con A) and Aleuria Aurantia lectin (AAL) were immobilized onto HPLC-grade silica by reductive amination and packed into 2.1 mm i.d. × 5.0 cm microcolumns. Factors examined for these microcolumns include their protein content, binding capacity, binding strength and band-broadening under isocratic conditions (Con A) or step elution conditions (AAL) and in the presence of various flow rates or temperatures. These factors were examined by using experiments based on frontal analysis, zonal elution, peak profiling and peak decay analysis. Up to 200 μg AGP could be loaded onto a Con A microcolumn and provide linear elution conditions, and 100 μg AGP could be applied to an AAL microcolumn. The final conditions for separating retained and non-retained AGP glycoform fractions on a Con A microcolumn used a flow rate of 50 μL min-1 and a temperature of 50 °C, which gave a separation of these fractions within 20 min or less. The final conditions for an AAL microcolumn included a flow rate of 0.75 mL min-1, a temperature of 50 °C, and the use of 2.0 mM l-fucose as a competing agent for elution, giving a separation of non-retained and retained AGP glycoforms in 6 min or less. The inter-day precisions were ±0.7-4.0% or less for the retention times of the AGP glycoforms and ±2.2-3.0% or less for their peak areas.

Glycosylation and liver cancer

Liver cancer is the fifth most common cancer, but the second leading cause of cancer death, in the world, with more than 700,000 fatalities annually. The major etiology of liver cancer is infection with an hepatotropic virus such as hepatitis B virus or hepatitis C virus infection. While chronic viral infection remains the main cause of liver disease and risk of hepatocellular carcinoma (HCC), rates of nonviral-associated HCC are occurring at an alarmingly increasing rate. Like many cancers, survival rates are closely associated with time of detection. If HCC is caught early, survival rates can be as high as 50%. Regrettably, most cases of HCC are caught late where survival rates can be as low as 2-7%. Thus, there has been great interest in discovering serum biomarkers that could be used to identify those with HCC. To this end, many groups have examined the N-linked glycans to identify changes that occur with HCC. As the liver secretes the vast majority of proteins into the serum, this has often been a starting point for study. In serum, alterations in core fucosylation, outer-arm fucosylation, increased sialylation, and glycan branching have been observed in patients with HCC. Similar findings have been found directly in HCC tissue suggesting that these glycan changes may play a role in tumor formation and development.

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

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

Detection of a high affinity binding site in recombinant Aleuria aurantia lectin

Lectins are carbohydrate binding proteins that are involved in many recognition events at molecular and cellular levels. Lectin-oligosaccharide interactions are generally considered to be of weak affinity, however some mushroom lectins have unusually high binding affinity towards oligosaccharides with K (d) values in the micromolar range. This would make mushroom lectins ideal candidates to study protein-carbohydrate interactions. In the present study we investigated the properties of a recombinant form of the mushroom lectin Aleuria aurantia (AAL). AAL is a fucose-binding lectin composed of two identical 312-amino acid subunits. Each subunit contains five binding sites for fucose. We found that one of the binding sites in rAAL had unusually high affinities towards fucose and fucose-containing oligosaccharides with K (d) values in the nanomolar range. This site could bind to oligosaccharides with fucose linked alpha1-2, alpha1-3 or alpha1-4, but in contrast to the other binding sites in AAL it could not bind oligosaccharides with alpha1-6 linked fucose. This binding site is not detected in native AAL (nAAL) one possible explanation may be that this site is blocked with free fucose in nAAL. Recombinant AAL was produced in E. coli as a His-tagged protein, and purified in a one-step procedure. The resulting protein was analyzed by electrophoresis, enzyme-linked lectin assay and circular dichroism spectroscopy, and compared to nAAL. Binding properties were measured using tryptophan fluorescence and surface plasmon resonance. Removal of the His-tag did not alter the binding properties of recombinant AAL in the enzyme-linked lectin assay. Our study forms a basis for understanding the AAL-oligosaccharide interaction and for using molecular techniques to design lectins with novel specificities and high binding affinities towards oligosaccharides.

Transiently binding antibody fragments against Lewis x and sialyl-Lewis x

Biomolecular recognition is often characterised by low affinity where many weak interactions work either alone or in concert, resulting in an inherent dynamic situation. For example the well-studied weak binding of cell-cell interactions is predominantly based on a range of carbohydrates that interact with numerous (protein) ligands. Finding appropriate binders to these carbohydrate structures may pave the way for new analytical strategies based on low affinity, and recombinant antibody technology is a promising approach to the development of such reagents. We have in the present study characterised two low affinity human single chain antibody fragments (scFv) by surface plasmon resonance for use in such applications. The two clones, LeX1 and sLeX10, had been selected from a naive phage display library against Lewis x (Le(x)) and sialyl Le(x) (sLe(x)), respectively. Both LeX1 and sLeX10 showed low affinity, with K(D) values of 3.5+/-0.7 x 10(-5) M for Le(x) and 2.6+/-0.7 x 10(-5) M for sLe(x), respectively. Kinetic studies revealed the scFvs to be associated with fast dissociation rates, with Kd values higher than 0.1 s(-1) for both LeX1 and sLeX10. Apart from the Lewis structures Le(x) and sLe(x), we investigated the conformational isomers Lewis a and sialyl-Lewis a together with the monosaccharide units of the Lewis structures, and both scFvs showed high specificity for their respective carbohydrate. Taking these observations together we have demonstrated that scFv with fast reaction kinetics and low affinity have the necessary characteristics for further development as specific tools in analytical strategies, e.g. differentiation of cells based on the various configurations of carbohydrate epitopes.

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

BACKGROUND

alpha(1)-Acid glycoprotein (AGP), an acute phase reactant, is extensively glycosylated at five Asn-linked glycosylation sites. In a number of pathophysiological states, including inflammation, rheumatoid arthritis, and cancer, alterations of Asn-linked glycans (N-glycans) have been reported. We investigated alteration of N-glycans at each of glycosylation sites of AGP in the sera of patients with acute and chronic inflammation.

METHODS

AGP purified from sera was digested with Glu-C and the liberated glycopeptides were isolated by reverse phase HPLC. N-glycans released with peptide N-glycosidase F and followed by neuraminidase treatment were analyzed by matrix-assisted laser desorption ionization-time of flight mass spectrometry.

RESULTS

Site-specific differences in branching structures were observed among N-glycosylation sites 1, 3, 4 and 5. Within the sera of patients with acute inflammation, increases in bi-antennary and decreases in tri- and tetra-antennary structures were observed, as well as increases in alpha1,3-fucosylation, at most glycosylation sites. In the sera of patients with chronic inflammation, increased rates of tri-antennary alpha1,3-fucosylation at sites 3 and 4 and tetra-antennary alpha1,3-fucosylation at sites 3, 4 and 5 were detected. Although there were no significant differences between acute and chronic sera in site directed branching structures, significant differences of alpha1,3-fucosylation were detected in tri-antennary at sites 2, 4 and 5 and in tetra-antennary at sites 3 and 4.

CONCLUSION

Little variation in the N-glycan composition of the glycosylation sites of AGP was observed among healthy individuals, while the sera of patients with acute inflammation demonstrated increased numbers of bi-antennary and alpha1,3-fucosylated N-glycan structures at each glycosylation site.

Fucosylation of serum glycoproteins in lung cancer patients

Increased expression of sialyl Lewis X or A antigens on metastatic cancer cells leads to their selectin-mediated extravasation. Profound fucosylation of the serum microenvironment may be a factor that interrupts adhesion and influences the formation of metastases. In this study we quantitatively analyzed fucosylation of serum glycoproteins in small-cell and non-small-cell lung cancer patients. Fucosylation of four chosen glycoprotein bands was measured as the reactivity with

?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.

Diagnostic Accuracy of α1-Acid Glycoprotein Fucosylation for Liver Cirrhosis in Patients Undergoing Hepatic Biopsy

Background: Increased fucosylation of serum glycoproteins has previously been reported in patients with liver disease. We analyzed α1-acid glycoprotein (AGP) fucosylation in serum samples from patients investigated for suspected liver disease to evaluate its value as a biochemical marker for liver cirrhosis.

Methods: We used a novel lectin immunoassay adapted to the AutoDELFIA system to analyze AGP fucosylation in 261 consecutive patients admitted for liver biopsy at Malmö University Hospital in Southern Sweden. The results were compared with histopathologic findings. In addition, AGP fucosylation was compared with other biochemical markers described as useful in the diagnosis of liver cirrhosis. The biochemical markers were compared by ROC curve analysis.

Results: AGP fucosylation was significantly (P &lt;0.05) higher in patients with liver cirrhosis (n = 65) than in healthy controls (n = 72), patients with normal histology (n = 29), patients with steatosis only (n = 38), patients with viral or chronic hepatitis without cirrhosis (n = 71), and patients with other liver diseases without histologic signs of cirrhosis (n = 58). By calculating the AGP fucosylation index (AGP-FI = AGP fucosylation/AGP serum concentration), we obtained a high diagnostic accuracy. The areas under the ROC curves for AGP-FI were 0.83 and 0.74 for men and women, respectively, compared with 0.82 for hyaluronic acid and 0.77 for the aspartate aminotransferase/alanine aminotransferase ratio in both men and women.

Conclusions: AGP fucosylation appears to be useful in identifying patients with liver cirrhosis among patients investigated for liver disease. The lectin immunoassay showed satisfactory reproducibility and is suitable for routine use in a clinical laboratory.

Quantitative determination of dietary lectin activities by enzyme-linked immunosorbent assay using specific glycoproteins immobilized on microtiter plates

An immunoenzymatic method for the quantitative determination of dietary lectin activities employing immobilized glycoproteins was studied. Lectins from wheat germ (WGA), peanut (PNA), and jack bean (ConA) were added to microtiter plates coated with ovalbumin or asialofetuin and quantified by enzyme-linked immunosorbent assay (ELISA) with lectin-specific antibodies. ELISA responses for lectin activity were dose-dependent in the concentration range 30-1000 ng/mL for WGA and 80-1000 ng/mL for both PNA and ConA. Inhibition assays carried out with different saccharides confirmed that the binding of lectins to immobilized glycoproteins was specific. The proposed method is specific and sensitive, allowing the quantitative determination of lectin activities on raw samples by simple dilution of the extracts. Examples of application to wheat germ and roasted peanut extracts are reported.

Quantification and Utility of Monosialylated α-Fetoprotein in the Diagnosis of Hepatocellular Carcinoma with Nondiagnostic Serum Total α-Fetoprotein

Background: At concentrations &lt;500 μg/L, serum α-fetoprotein (AFP) has low specificity in the diagnosis of hepatocellular carcinoma (HCC), but monosialylated AFP (msAFP) is more specific for HCC. We describe two strategies for quantitative analysis of msAFP and explore their diagnostic accuracy in cases of HCC with nondiagnostic serum total AFP concentrations.

Methods: We first used isoelectric focusing, Western blot, and densitometry (IEF-Western blot assay). We then developed a second assay, a novel glycosylation immunosorbent assay (GISA), based on the specificity of sialyltransferase and immunosorbent technology. Both assays were used to measure msAFP and msAFP percentage relative to total AFP in sera with nondiagnostic AFP concentrations from 36 patients with newly diagnosed HCC and from 18 patients with liver cirrhosis.

Results: The msAFP percentages and concentrations were significantly higher in the HCC patient group regardless of the quantification methods. The msAFP concentrations and msAFP percentages obtained by the two assays were highly correlated (r = 0.70 and 0.49, respectively). For discrimination of HCC with nondiagnostic serum total AFP from liver cirrhosis, the areas under the ROC curves were 0.81 (95% confidence interval, 0.70–0.92) for msAFP by IEF-Western blot assay, 0.73 (0.58–0.87) for msAFP by GISA, 0.89 (0.80–0.97) for msAFP percentage by IEF-Western blot assay, and 0.74 (0.59–0.89) for msAFP percentage by GISA.

Conclusions: Both the serum concentration and percentage of msAFP are potential diagnostic markers for HCC with nondiagnostic AFP. GISA can quantify a specific glycoform of a serologic marker.

Fucosylation of alpha1-acid glycoprotein (orosomucoid) compared with traditional biochemical markers of inflammation in recent onset rheumatoid arthritis

BACKGROUND

Fucosylation of alpha1-acid glycoprotein (AGP, orosomucoid) has previously been found to be increased in patients with rheumatoid arthritis. Furthermore, the degree of fucosylation has been suggested to reflect disease activity. Therefore, we investigated the fucosylation of AGP in 131 patients (96 women and 35 men) with recent onset rheumatoid arthritis (RA). We compared the results with traditional biochemical markers of inflammation, i.e. plasma concentrations of AGP (P-AGP), and C-reactive protein (P-CRP).

METHODS

AGP fucosylation measured with a novel lectin enzyme-linked immunosorbent assay (ELISA) was compared with a disease activity score (DAS28) and its components, and with P-AGP, and P-CRP at the time of diagnosis, and at a follow-up visit 1 year later.

RESULTS

Both men and women with RA had increased AGP fucosylation compared to healthy individuals. We found a weak correlation between AGP fucosylation and DAS28 only in men. In men with initially increased AGP fucosylation, the level of fucosylation correlated with the change in DAS28 during the first year following diagnosis.

CONCLUSION

We conclude that AGP fucosylation is not superior to traditional markers of disease activity in RA. However, AGP fucosylation may give some additional information to traditional biochemical markers on the disease progression in men.

A lectin immunosensor technique for determination of alpha(1)-acid glycoprotein fucosylation

The fucosylation of alpha(1)-acid glycoprotein (AGP), an acute-phase protein, is known to change in association with inflammatory diseases. Thus, fucosylation of AGP could be a potential diagnostic or prognostic marker. The change in fucosylation has previously been investigated using crossed affinoimmunoelectrophoresis, high-pH anion-exchange chromatography, and lectin ELISA. This study describes a surface plasmon resonance-based affinity biosensor assay for quantification of the fucosylation of AGP. Diluted EDTA plasma or serum was injected directly in a BIACORE 2000 biosensor. AGP was captured on the sensor surface using immobilized antibodies and a fucose-binding lectin from Aleuria aurentia was then used for the detection of fucosylation. The feature of the biosensor makes it possible to determine both the amount of bound AGP and the amount of bound lectin. Using a calibration curve it was possible to obtain a fucosylation ratio that was independent of AGP concentration. The assay was validated against a lectin ELISA and used to follow inflammation in patients with severe burns.