Simultaneous determination of the association constants of oligosaccharides to a lectin by capillary electrophoresis

Identification of a Novel Oligosaccharide in Maple Syrup as a Potential Alternative Saccharide for Diabetes Mellitus Patients

The incidence of diabetes mellitus (DM) is increasing rapidly and is associated with changes in dietary habits. Although restrictions in the use of sweeteners may prevent the development of DM, this might reduce the quality of life of patients with DM. Therefore, there has been a great deal of research into alternative sweeteners. In the search for such sweeteners, we analyzed the carbohydrate content of maple syrup and identified a novel oligosaccharide composed of fructose and glucose, linked at the C-4 of glucose and the C-6 of fructose. This oligosaccharide inhibited the release of fructose from sucrose by invertase (IC₅₀: 1.17 mmol/L) and the decomposition of maltose by α-(1-4) glucosidase (IC₅₀: 1.72 mmol/L). In addition, when orally administered together with sucrose to rats with DM, the subsequent plasma glucose concentrations were significantly lower than if the rats had been administered sucrose alone, without having any effect on the insulin concentration. These findings suggest that this novel oligosaccharide might represent a useful alternative sweetener for inclusion in the diet of patients with DM and may also have therapeutic benefits.

Clinical and pharmaceutical applications of affinity ligands in capillary electrophoresis: A review

Affinity capillary electrophoresis (ACE) is a separation technique that combines a biologically-related binding agent with the separating power and efficiency of capillary electrophoresis. This review will examine several classes of binding agents that have been used in ACE and applications that have been described for the resulting methods in clinical or pharmaceutical analysis. Binding agents that will be considered are antibodies, aptamers, lectins, serum proteins, carbohydrates, and enzymes. This review will also describe the various formats in which each type of binding agent has been used in CE, including both homogeneous and heterogeneous methods. Specific areas of applications that will be considered are CE-based immunoassays, glycoprotein/glycan separations, chiral separations, and biointeraction studies. The general principles and formats of ACE for each of these applications will be examined, along with the potential advantages or limitations of these methods.

On-column ligand/receptor derivatization coupled to affinity capillary electrophoresis

The coupling of on-column derivatization of small molecules to affinity capillary electrophoresis (ACE) has only been realized during the past 5 yr. In this technique, multiple zones of reagent(s) and ligand or receptor are injected into the capillary column. Upon electrophoresis, zones of sample overlap, yielding product. Continued electrophoresis results in the product overlapping with receptor (or ligand, if the receptor was derivatized), thereby causing a shift in migration time of the compound in question. Subsequent Scatchard analysis using noninteracting standards realizes a binding constant. Herein, we describe the use of on-column-ligand and receptor derivatization coupled to partial-filling ACE (PFACE) to probe the binding of vancomycin (Van) from Streptomyces orientalis and teicoplanin (Teic) from Actinoplanes teicomyceticus to D-Ala-D-Ala terminus peptides.

Separation, identification, and interaction of heparin oligosaccharides with granulocyte-colony stimulating factor using capillary electrophoresis and mass spectrometry

A capillary electrophoresis (CE) method was developed for the separation of heparin oligosaccharides compatible to study the interactions between the oligosaccharides and granulocyte-colony stimulating factor (G-CSF). Unfractionated heparin was eliminitively degraded to heparin oligosaccharides by an endolytic heparinase. The degraded smaller oligosaccharides (M(r) < 1000) were baseline-separated by CE under a 50 mM phosphate buffer (pH 9.0) in 10 min. Standard heparin disaccharides and larger oligosaccharides (1000 < M(r) < 8000) were all separated under optimized separation conditions. Compared with standard heparin disaccharides, smaller oligosaccharides contained one nonsulfated, two monosulfated, and two disulfated disaccharides, but trisulfated disaccharides were not found. The smaller oligosaccharides were also identified and molecular mass was deduced by electrospray ionization-mass spectrometry (ESI-MS). Furthermore, interactions between G-CSF and the oligosaccharides were studied by using capillary zone electrophoresis (CZE) under the above separation conditions. It was found that larger oligosaccharides could interact with G-CSF while smaller oligosaccharides were not observed to bind to G-CSF under the experimental conditions. In conclusion, the purified heparinase could selectively degrade heparin into oligosaccharides and the interaction between G-CSF and heparin was correlated with the chain length of heparin.

Capillary zone electrophoresis characterization of low molecular weight heparin binding to interleukin 2

A method based on capillary zone electrophoresis (CZE) was used to study the interaction between low molecular weight heparin (LMWH) and interleukin 2 (IL-2). The results showed that the increase of the concentration of LMWH led to the decrease of the peak height and the increase of the peak width of IL-2, but the peak areas were kept constant. The binding constant of IL-2 with LMWH was calculated as 1.2 x 10(6)M(-1) by Scatchard analysis, which is in good agreement with the results found in the references using enzyme-linked immunosorbent assay (ELISA). The results demonstrated that the interaction between IL-2 and LMWH is of fast on-and-off kinetic binding reaction. CZE might be used to study not only slow on-and-off rates interactions, but also fast on-and-off rates ones. The binding constant can be calculated easily, and the method can be applied to study a wide range of heparin-protein interactions.

A new fungal lectin recognizing alpha(1-6)-linked fucose in the N-glycan

In this report, we describe a new lectin from the fungus Rhizopus stolonifer that agglutinates rabbit red blood cells. Agglutinating activity was detected in the extract of mycelium-forming spores cultured on agar plates but not in the mycelium-forming no spores from liquid medium. This lectin, which we designated R. stolonifer lectin (RSL), was isolated by affinity chromatography with porcine stomach mucin-Sepharose. SDS-polyacrylamide gel electrophoresis and mass spectral analysis showed that RSL is approximately 4.5 kDa, whereas gel filtration indicated a mass of 28 kDa. This indicates that the lectin is a hexamer of noncovalently associated RSL monomers. RSL activity was very stable, since it was insensitive to heat treatment at 70 degrees C for 10 min. Analysis of RSL binding specificity by both microtiter plate and precipitation assays showed that N-glycans with l-fucose linked to the reducing terminal GlcNAc residues are the most potent inhibitors of RSL binding, whereas N-glycans without alpha(1-6)-linked fucose residues are approximately 100-fold weaker inhibitors of binding. Oligosaccharides with alpha(1-2, -3, and -4) linkages showed no inhibition of binding in these assays. In a mirror resonance biosensor assay, high affinity binding was observed between RSL and the glycopeptide of bovine gamma-globulin, which has N-glycans with alpha(1-6)-linked fucose residues. However, RSL showed only a weak interaction with the glycopeptide of quail ovomucoid, which lacks fucose residues. Finally, capillary affinity electrophoresis studies indicated that RSL binds strongly to N-glycans with alpha(1-6)-linked fucose residues. Together, these results show that RSL recognizes the core structure of N-glycans with alpha(1-6)-linked l-fucose residues. This specificity could make RSL a valuable tool for glycobiological studies.

Analysis of carbohydrates as 1-phenyl-3-methyl-5-pyrazolone derivatives by capillary/microchip electrophoresis and capillary electrochromatography

The 1-phenyl-3-methyl-5-pyrazolone (PMP) method has many advantages over hitherto reported methods based on reductive amination and hydrazone formation. This short review summarizes the various aspects of the PMP method, including the principle of derivatization, the simplicity of derivatization procedure, the high sensitivities to UV monitoring and ESI-MS, and the diversity of separation modes in capillary electrophoresis, and presents a number of application data for carbohydrate analysis in biological samples by this method. It also describes successful automation of carbohydrate analysis by in-capillary derivatization with PMP and miniaturization to microchip electrophoresis with whole channel UV detection allowing rapid (within 1 min) analysis of small amounts of PMP derivatives of carbohydrates. Furthermore, it discusses the possibility of capillary electrochromatography in carbohydrate analysis as PMP derivatives, and proposes an in-capillary modification strategy for improving column efficiency and elution time reproducibility.

Capillary electrophoretic separation of drug enantiomers in human serum

Enantiomers of various solutes including several basic drugs and alpha-amino acids were analyzed by capillary electrophoresis in diluted human serum, and chloroquine and tryptophan were found to be well enantioseparated. In order to specify the protein responsible for enantioseparation, these drug enantiomers were analyzed in the presence of various serum protein fractions. The results indicated that albumin fraction caused enantioseparation but the alpha and beta -globulin mixed fraction, the gamma-globulin fraction and the alpha(1)-acid glycoprotein fraction did not exhibit any enantioseparation. The association constants between these drugs and albumin were roughly estimated based on our method. Approximate values were 1.50 x 10(3) and 1.85 x 10(3) M(-1) for chloroquine enantiomers, and 1.51 x 10(4) and 2.45 x 10(4) M(-1) for tryptophan enantiomers. The difference of the association constant values between the enantiomers was found to be 19% for chloroquine and 38% for tryptophan, when calculated based on the slower moving enantiomers.

Capillary affinity electrophoresis for the screening of post-translational modification of proteins with carbohydrates

Glycosylation is one of the most important post-translational events for proteins, affecting their functions in health and disease, and plays significant roles in various information traffics for intracellular and intercellular biological events (Hancock, W. S. J. Proteome Res. 2002, 1, 297). We have attempted to obtain the information on the numbers and amounts of carbohydrate chains. Interaction between carbohydrate chains and proteins that recognize them is a target to understand the biological roles of glycosylation. To date, there have been a few strategies for simultaneous analysis of the interactions between complex mixtures of carbohydrates and proteins. Here, we report an approach to categorize carbohydrate chains using a few glycoprotein samples as models for the studies on the analysis of post-translational modification of proteins with carbohydrates. A combination of some specific lectins was used as carbohydrate-binding proteins. The method is based on high-resolution separation of fluorescent-labeled carbohydrates by capillary electrophoresis with laser-induced fluorescent detection in the presence of carbohydrate-binding proteins at different concentrations. The present technique affords (1) simultaneous determination of carbohydrate chains, (2) binding specificity of the constituent carbohydrate chains to specific proteins, and (3) kinetic data such as the association constant of each carbohydrate. We found that the lectins employed in the present study could discriminate subtle difference in linkages and resolved the carbohydrate mixtures. The results will be useful, for example, to understand the biological events expressed with carbohydrate changes on the cell surface.

Simultaneous estimation of the association constants of glycoprotein glycoforms to a common protein by capillary electrophoresis

The efficacy of our capillary electrophoresis method for simultaneous estimation of the association constants of glycoprotein glycoforms to a common target protein was demonstrated using ribonuclease and ovalbumin glycoforms as glycoform models and Lens culinaris agglutinin (LCA) as a protein model. The ribonuclease glycoforms were fairly well separated in the absence of LCA at pH 5.8, but the peaks were retarded without any change of separation profile in the presence of LCA, the retardation becoming greater as LCA concentration increased. The estimated values of apparent association constant (K(a)) were at the 10(6)M(-1) level for all the ribonuclease glycoforms, and there was no significant difference among glycoforms. The high-mannose-type N-glycans released from a mixture of ribonuclease glycoforms gave lower values of K(a) at the 10(4)-10(5)M(-1) level to the same protein, and the glycans having a larger number of the mannose residue gave larger K(a) values. These results imply that the glycan moiety in this glycoprotein might contribute to its binding to the protein, but the polypeptide core played the major role. In contrast, ovalbumin glycoforms gave poorly resolved peaks in the absence of LCA, but they were separated into several peaks in the presence of LCA, which were tentatively assigned based on the knowledge of affinity to this lectin, and K(a) values were estimated simultaneously. The estimated K(a) values were smaller than those of the ribonuclease glycoforms, suggesting the major role of the N-glycan moiety. Thus, capillary electrophoresis allowed simultaneous estimation of K(a) values under common conditions using small amounts of glycoform mixtures and proteins without prior isolation and purification. Comparison of the obtained values will provide useful information on the glycan structure-affinity correlation.

Colominic acid: a novel chiral selector for capillary electrophoresis of basic drugs

We introduced colominic acid as a new chiral selector for capillary electrophoresis of basic drugs. Use of a low concentration phosphate buffer containing this polysaccharide and a Polybrene/colominic acid double coated capillary allowed excellent separation of the enantiomers of primaquine, chloroquine and tryptophan. Other drugs giving partial enantioseparation include laudanosine and salbutamol. Capillary coating with Polybrene followed by colominic acid eliminated the problems of peak tailing and low reproducibility of migration time in uncoated capillaries. The optimum pH was in the acidic region but varied among drugs. A low capillary temperature of 16 degrees C and a colominic acid concentration of 9 w/v% are recommended for practical analysis of these drugs. Colominic acid preparations having higher molecular masses gave better enantioseparation, and N-acetylneuraminic acid, the component monosaccharide, did not give any enantioseparation.

Effect of structure modification of chondroitin sulfate C on its enantioselectivity to basic drugs in capillary electrophoresis

The effect of structure modification of chondroitin sulfate C on its enantioselectivity to several representative basic drugs in capillary electrophoresis was investigated. Chemical desulfation showed no remarkable decrease in selectivity, whereas depolymerization with chondroitinase ABC resulted in complete loss of selectivity. Comparison with chondroitin sulfate A indicated considerable decrease in selectivity with this isomer. The great retention of enantioselectivity in the desulfated derivative suggests that the selectivity comes from the difference of the magnitude of an interaction in the multipoint mechanism between a part of the drug molecule and a functional group in chondroitin sulfate C other than the sulfate group. The sulfate group is not considered to play a major role for chiral separation. The complete loss of selectivity by depolymerization is consistent with a general tendency of lower selectivity in smaller saccharides, and the priority of chondroitin sulfate C to chondroitin sulfate A suggests the importance of the hydroxyl group at C4 in the galactosamine residue. During the course of this work we observed heavy tailing of the peaks of basic drugs in some batches of uncoated fused-silica capillaries under acidic conditions and solved this problem by doubly coating capillaries with Polybrene followed by chondroitin sulfate C. On the other hand, we demonstrated the usefulness of a special technique which uses a short, wider bore PTFE tube-attached capillary for the study of the effect of depolymerization, in order to minimize sample amount.

Sugar-lectin interactions investigated through affinity capillary electrophoresis

The affinity interactions of Concanavalin A (Con A) with various saccharide oligomers (dextrins, dextrans, and selected N-linked glycans from various glycoproteins) have been investigated through a capillary electrophoresis approach. Con A has shown a notable binding discrimination between the alpha-1,6-linked dextran and alpha-1,4-linked dextrin oligomers. Both the binding capacity and binding discrimination appear to decrease with an increase in sugar chainlength. While the core structure of N-linked glycans is deemed to be responsible for the overall binding of various glycans to Con A, the presence of mannose units at the non-reducing ends was found to be very beneficial to the affinity interaction with Con A. Finally, a connection between the glycan-lectin interaction and glycoprotein-lectin interaction has also been suggested.

Estimation of receptor-ligand interactions by the use of a two-marker system in affinity capillary electrophoresis

The study of receptor-ligand interactions by affinity capillary electrophoresis (ACE) requires an accurate form of analysis. Here, we examine the use of two noninteracting standards (markers) in the analysis of binding constant data in ACE studies. This concept is demonstrated using two model systems: carbonic anhydrase B (CAB, EC 4.2.1.1) and arylsulfonamides, and vancomycin (Van) from Streptomyces orientalis and the dipeptide N-acetyl-d-Ala-d-Ala. In this procedure a plug of receptor and noninteracting standards is injected, and analysis of the change in the relative migration time ratio of the receptor, relative to the noninteracting standards, as a function of the concentration of the ligand yields a value for the binding constant. The findings described here demonstrate that data from ACE studies can best be analyzed using two noninteracting standards, yielding values comparable to those estimated using other binding and ACE techniques.

Capillary electrophoresis of drugs: current status in the analysis of pharmaceuticals

The current status of capillary electrophoresis (CE) in pharmaceutical analyses is reviewed with about 300 references, mainly from 1996 until 1999. This article covers the use of CE for assay and purity determination of the main component, analysis of natural medicines, antisense DNA, peptides, and proteins. Analysis of hydrophobic and/or electrically neutral drugs by electrokinetic chromatography, capillary electrochromatography and nonaqueous CE is critically evaluated. Detailed techniques for the separation of enantiomers are given in the text with some actual applications. Furthermore, this review includes sensitivity and regulatory aspects for the actual use of CE in new drug applications (NDA). The analytical validation required for CE in NDA is also treated.