Heparin-derived oligosaccharides: affinity for acidic fibroblast growth factor and effect on its growth-promoting activity for human endothelial cells

The minimal structural requirements for the interaction of heparin with acidic fibroblast growth factor (aFGF) were investigated. Oligosaccharides (tetra- to decasaccharides) obtained by nitrous acid depolymerisation of standard heparin were separated by affinity chromatography on Sepharose-immobilised aFGF. The shortest fragment retained by the affinity column at 0.2 M NaCl and eluted at 1 M NaCl was a "regular" hexasaccharide, a trimer of the most abundant disaccharide sequence in heparin. More complex octa- and decasaccharides were also retained by the column. The oligosaccharides eluted by 1 M NaCl from the affinity column ("high-affinity" oligosaccharides) and those washed from the column at 0.2 M NaCl ("low-affinity" oligosaccharides) were compared for their capacity to protect aFGF from proteolysis and to potentiate its mitogenic activity. At a low ionic strength, all oligosaccharides tested, except the "regular" disaccharide, protected aFGF against trypsin and collagenase digestion. At higher ionic strength (greater than 0.2 M NaCl), only high-affinity oligosaccharides showed a protective effect. The high-affinity oligosaccharides (hexa- to decasaccharides) potentiated the mitogenic activity of aFGF, as measured by [3H]thymidine incorporation into DNA of human fibroblasts. The effect of the oligosaccharides on human endothelial cell proliferation was more complex: inhibition of proliferation was observed in the presence of serum and low concentrations of aFGF (1-5 ng/ml) and potentiation in the presence of higher concentrations of aFGF. The potentiating effect increased as a function of molecular size of the heparin fragments and, for a given size, as a function of the anionic charge of the oligosaccharide. Our results suggest that inhibition of cell proliferation by heparin may result from interference with an autocrine basic FGF-like activity.     

Determination of molecular weight of heparin by size exclusion chromatography with universal calibration

The molecular weight (MW) of heparin can be accurately determined by size exclusion chromatography using "universal calibration." A universal calibration curve was constructed for Superose 12 with standard pullulan samples and verified using characterized ficoll fractions. This calibration yielded the correct MW of heparin as determined by light scattering, when the ionic strength of the mobile phase was maintained over 1.0M. Sodium poly(styrenesulfonate) samples were not suitable standards because of adsorption at high salt concentration and repulsion from the packing material at low ionic strength. The extraordinarily high charge density of heparin leads to the need for high salt concentration to screen such repulsions.     

Conformational prerequisites for formation of amyloid fibrils from histones

We demonstrate that bovine core histones are natively unfolded proteins in solutions with low ionic strength due to their high net positive charge at pH 7.5. Using a variety of biophysical techniques we characterized their conformation as a function of pH and ionic strength, as well as correlating the conformation with aggregation and amyloid fibril formation. Tertiary structure was absent under all conditions except at pH 7.5 and high ionic strength. The addition of trifluoroethanol or high ionic strength induced significant alpha-helical secondary structure at pH 7.5. At low pH and high salt concentration, small-angle X-ray scattering and SEC HPLC indicate the histones are present as a hexadecamer of globular subunits. The secondary structure at low pH was independent of the ionic strength or presence of TFE, as judged by FTIR. The data indicate that histones are able to adopt five different relatively stable conformations; this conformational variability probably reflects, in part, their intrinsically disordered structure. Under most of the conditions studied the histones formed amyloid fibrils with typical morphology as seen by electron microscopy. In contrast to most aggregation/amyloidogenic systems, the kinetics of fibrillation showed an inverse dependence on histone concentration; we attribute this to partitioning to a faster pathway leading to non-fibrillar self-associated aggregates at higher protein concentrations. The rate of fibril formation was maximal at low pH, and decreased to zero by pH 10. The kinetics of fibrillation were very dependent on the ionic strength, increasing with increasing salt concentration, and showing marked dependence on the nature of the ions; interestingly Gdn.HCl increased the rate of fibrillation, although much less than NaCl. Different ions also differentially affected the rate of nucleation and the rate of fibril elongation.     

Structural determinants of heparin's growth inhibitory activity. Interdependence of oligosaccharide size and charge

The glycosaminoglycan heparin inhibits the growth of several cell types in vitro including smooth muscle cells and rat cervical epithelial cells. The commercially available heparin which has antiproliferative activity is a structurally heterogeneous polymer that undergoes extensive modifications during maturation. In this report we have performed structure-function studies on heparin's antiproliferative activity using three different cell types: both rat and calf vascular aortic smooth muscle cells and rat cervical epithelial cells. The minimal oligosaccharide size requirements for antiproliferative activity were determined for the three cell types by using oligosaccharide fragments of defined length prepared by nitrous acid cleavage and gel filtration and a synthetic pentasaccharide. The size requirements are similar but not identical for the different cell types. Hexasaccharide fragments are antiproliferative for all three cell types but the synthetic pentasaccharide inhibits the growth of only the rat and calf vascular aortic smooth muscle cells. The interdependence between size and charge for antiproliferative activity was investigated using chemically modified oligosaccharides as well as oligosaccharides prepared from heparin and separated into fractions of differing charge by ion-exchange chromatography. There is a strong interdependence between size and charge for antiproliferative activity. For example, increasing the charge of inactive tetrasaccharide fragments by O-oversulfation makes them antiproliferative whereas reducing the charge of active larger fragments causes them to loose their antiproliferative activity. Finally the importance of 2-O-sulfate glucuronic acid moieties for antiproliferative activity was investigated using heparin preparations that lack 2-O-sulfate glucuronic acid. These compounds possess antiproliferative activity indicating that 2-O-sulfate glucuronic acid is not required for antiproliferative activity.     

Heparin binding peptides co-purify with glycosaminoglycans from human plasma

Glycosaminoglycans (GAGs) are complexed with plasma proteins and proteolysis of plasma reduced the protein-GAG ratio about 140-fold. After dialysis, analysis by gradient PAGE revealed heparinase-1-sensitive GAGs, thus suggesting that heparin could be among the plasma GAGs. However, after dialysis most of the plasma GAGs were still not 'free'. PAGE of peptides resistant to proteolysis showed high molecular weight bands on the two sides of the dialysis membrane despite the 3.5 kDa molecular weight cut-off. Progressive dilution of the sample allowed passage of peptides appearing as high molecular weight bands in the diffusate. We interpret this phenomenon as the presence of low molecular weight peptides that aggregate when concentrated. Peptides on both sides of the membranes bound heparin.     

Importance of size and sulfation of heparin in release of basic fibroblast growth factor from the vascular endothelium and extracellular matrix.

We have characterized the importance of size, sulfation, and anticoagulant activity of heparin in release of basic fibroblast growth factor (bFGF) from the subendothelial extracellular matrix (ECM) and the luminal surface of the vascular endothelium. For this purpose, 125I-bFGF was first incubated with ECM and confluent endothelial cell cultures, or administered as a bolus into the blood of rats, the immobilized 125I-bFGF was then subjected to release by various chemically modified species of heparin and size-homogeneous oligosaccharides derived from depolymerized heparin. Both totally desulfated and N-desulfated heparin failed to release the ECM-bound bFGF. Likewise, substitution of N-sulfate groups of heparin and low molecular weight heparin (fragmin) by acetyl or hexanoyl residues resulted in an almost complete inhibition of bFGF release by these polysaccharides. The presence of O-sulfate groups in heparin increased but was not critical for release of ECM-bound bFGF. Similar structural requirements were identified for release of 125I-bFGF bound to low-affinity sites on the surface of vascular endothelial cells. Oligosaccharides derived from depolymerized heparin and containing as little as 8-10 sugar units were, on a weight basis, equivalent to whole heparin in their ability to release bFGF from ECM. Low-sulfate oligosaccharides were less effective releasers of bFGF as compared to medium- and high-sulfate fractions of the same size oligosaccharides. Heparin fractions with high and low affinity to antithrombin III exhibited a similar high bFGF-releasing activity despite a 200-fold difference in their anticoagulant activities.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparison of molecular mass determination of hyaluronic acid using SEC/MALLS and sedimentation equilibrium

Hyaluronic acid (HA) is a natural polysaccharide with importance in the pharmaceutical, medical and cosmetic industries. Determining factors in its final applications are its physicochemical properties, particularly molecular mass. A high molecular mass HA was degraded using five different hydroxyl free-radical starting concentrations chemically produced from ascorbic acid and hydrogen peroxide. The aims of the study were to investigate the effect of different hydroxyl free-radical concentrations on the chain length of HA and compare the molecular masses obtained from analytical ultracentrifugation using sedimentation equilibrium experiments and size exclusion chromatography/multi-angle laser light scattering (SEC/MALLS). The results indicated that their molecular masses varied, depending on the degree of hydroxyl free-radical starting concentration. Molecular mass values obtained from sedimentation equilibrium experiments for each sample showed the same trend as those obtained from the SEC/MALLS in the range of molecular masses studied. The molecular masses obtained from sedimentation equilibrium for high molecular mass samples from reciprocal plots of apparent weight average molecular mass against concentration gave values similar to those obtained by SEC/MALLS. In contrast, the molecular mass from conventional plots for high molecular mass samples were much lower than those from SEC/MALLS, even when high ionic strength buffers were used.     

Multiple interactions of HIV-I Tat protein with size-defined heparin oligosaccharides.

Tat protein, a transactivating factor of the human immunodeficiency virus type I, acts also as an extracellular molecule. Heparin affects the bioavailability and biological activity of extracellular Tat (Rusnati, M., Coltrini, D., Oreste, P., Zoppetti, G., Albini, A., Noonan, D., D'Adda di Fagagna, F., Giacca, M., and Presta, M. (1997) J. Biol. Chem. 272, 11313-11320). Here, a series of homogeneously sized, (3)H-labeled heparin fragments were evaluated for their capacity to bind to free glutathione S-transferase (GST)-Tat protein and to immobilized GST-Tat. Hexasaccharides represent the minimum sized heparin fragments able to interact with GST-Tat at physiological ionic strength. Also, the affinity of binding increases with increasing the molecular size of the oligosaccharides, with large fragments (>/=18 saccharides) approaching the affinity of full-size heparin. 6-Mer heparin binds GST-Tat with a dissociation constant (K(d)) equal to 0.7 +/- 0.4 microM and a molar oligosaccharide:GST-Tat ratio of about 1:1. Interaction of GST-Tat with 22-mer or full-size heparin is consistent instead with two-component binding. At subsaturating concentrations, a single molecule of heparin interacts with 4-6 molecules of GST-Tat with high affinity (K(d) values in the nanomolar range of concentration); at saturating concentrations, heparin binds GST-Tat with lower affinity (K(d) values in the micromolar range of concentration) and a molar oligosaccharide:GST-Tat ratio of about 1:1. In agreement with the binding data, a positive correlation exists between the size of heparin oligosaccharides and their capacity to inhibit cell internalization, long terminal repeat-transactivating activity of extracellular Tat in HL3T1 cells, and its mitogenic activity in murine adenocarcinoma T53 Tat-less cells. The data demonstrate that the modality of heparin-Tat interaction is strongly affected by the size of the saccharide chain. The possibility of establishing multiple interactions increases the affinity of large heparin fragments for Tat protein and the capacity of the glycosaminoglycan to modulate the biological activity of extracellular Tat.     

Structural characterisation of oligosaccharides obtained by Fenton-type radical depolymerisation of dermatan sulfate

The contamination of heparin in 2008 brought to the attention of health authorities an urgent need for structural characterisation of low molecular weight heparins and other glycosaminoglycans (GAGs) intended for clinical applications. Potentially harmful compounds can be introduced into these preparations as contaminants of the original material or as by-products of the depolymerisation process. Radical depolymerisation is one of the methods used for fractionations of GAGs. We report here on the results of the Fenton-type radical depolymerisation of dermatan sulfate (DS) by hydrogen peroxide in the presence of Cu²⁺ cations. A low molecular fraction of the reaction mixture was investigated by a combination of 2D ¹H,¹³C HSQC, 2D HSQC-TOCSY and 2D HMBC experiments at 800 MHz. The analysis of the spectra revealed the formation of oligosaccharides with structures corresponding to the native DS sequence and containing almost exclusively GalNAc4S as the reducing end monosaccharide. In addition, oligosaccharides containing a C-4 sulfated N-acetylgalactosaminic acid in place of the reducing end GalNAc4S were identified. This open chain monosaccharide represents a non-native DS structure.     

Binding of human extracellular superoxide dismutase C to sulphated glycosaminoglycans.

The secretory enzyme extracellular superoxide dismutase (EC-SOD) occurs in at least three forms, which differ with regard to heparin affinity: A lacks affinity, B has intermediate affinity, and C has relatively strong affinity. The affinity of EC-SOD C for various sulphated glycosaminoglycans (GAGs) was assessed (a) by determining the concentration of NaCl required to release the enzyme from GAG-substituted Sepharose 4B and (b) by determining the relative potencies of the GAGs to release EC-SOD C from heparan sulphate-Sepharose 4B. Both methods indicated the same order of affinity. Heparin bound EC-SOD C about 10 times as avidly as the studied heparan sulphate preparation, which in turn was 10 and 150 times as efficient as dermatan sulphate and chondroitin sulphate respectively. Chondroitin sulphate showed weak interaction with EC-SOD C at physiological ionic strength. Heparin subfractions with high or low affinity for antithrombin III were equally efficient. The binding of EC-SOD C to heparin-Sepharose was essentially independent of pH in the range 6.5-9; below pH 6.5 the affinity increased, and beyond pH 9.5 there was a precipitous fall in affinity. The inhibitory effect of NaCl on the binding of EC-SOD C to GAGs indicates that the interaction is of electrostatic nature. EC-SOD C carries a negative net charge at neutral pH, and it is suggested that the binding occurs between the negative charges of the GAG sulphate groups and a structure in the C-terminal end of the enzyme that has a cluster of positive charges. These results are compatible with the notion that heparan sulphate proteoglycans on cell surfaces or in the intercellular matrix may serve to bind EC-SOD C in tissues.     

Liquid chromatography/mass spectrometry sequencing approach for highly sulfated heparin-derived oligosaccharides

Liquid chromatography/mass spectrometry (LC/MS) is applied to the analysis of complex mixtures of oligosaccharides obtained through the controlled, heparinase-catalyzed depolymerization of heparin. Reversed-phase ion-pairing chromatography, utilizing a volatile mobile phase, results in the high resolution separation of highly sulfated, heparin-derived oligosaccharides. Simultaneous detection by UV absorbance and electrospray ionization-mass spectrometry (ESI-MS) provides important structural information on the oligosaccharide components of this mixture. Highly sensitive and easily interpretable spectra were obtained through post-column addition of tributylamine in acetonitrile. High resolution mass spectrometry afforded elemental composition of many known and previously unknown heparin-derived oligosaccharides. UV in combination with MS detection led to the identification of oligosaccharides arising from the original non-reducing end (NRE) of the heparin chain. The structural identification of these oligosaccharides provided sequence from a reading frame that begins at the non-reducing terminus of the heparin chain. Interestingly, 16 NRE oligosaccharides are observed, having both an even and an odd number of saccharide residues, most of which are not predicted based on biosynthesis or known pathways of heparin catabolism. Quantification of these NRE oligosaccharides afforded a number-averaged molecular weight consistent with that expected for the pharmaceutical heparin used in this analysis. Molecular ions could be assigned for oligosaccharides as large as a tetradecasaccharide, having a mass of 4625 Da and a net charge of -32. Furthermore, MS detection was demonstrated for oligosaccharides with up to 30 saccharide units having a mass of >10000 Da and a net charge of -60.     

Use of high-performance size-exclusion chromatography to measure protein molecular weight and hydrodynamic radius. An investigation of the properties of the TSK 3000 SW column

We have conducted a study of the TSK 3000 SW high-performance size-exclusion column to define under what conditions proteins would migrate most consistently with their known hydrodynamic properties. Our findings include the following: 1) the residual negative charge of the column does cause charge-exclusion or charge-retention effects at low ionic strengths; with elution in deionized water several anionic proteins elute approximately in the void volume; 2) at mu greater than or equal to 0.5, protein migration is not only independent of ionic strength, but consistent with protein molecular weight and hydrodynamic volume; 3) small hydrophobic peptides are retarded by the column; and 4) very asymmetric proteins and other hydrodynamic particles are likely to be retarded by an "end-on insertion" mechanisms.     

Ionic interactions in nanofiltration of beta casein peptides

Nanofiltration (NF) membrane technology shows interesting potentials for separating organic components on the basis of solute charge and size in the range of 300-1000 g mol-1. Separation properties of two inorganic NF membranes were studied with a set of 10 small peptides (molecular mass range: 300-900 g mol-1; 3 < pI < 10) contained in a well-characterized tryptic beta casein hydrolysate. Peptides transmission strongly depended on ionic interactions in the system. Physicochemical conditions such as ionic strength and especially pH were crucial to the separation, because the membrane and peptides showed amphoteric properties. Thus, the three categories of peptides (acid, basic, neutral) were separated according to their pI because of presumed concentration gradients of charged peptides at the membrane: positive for basic peptides and negative for acid peptides. At optimum pH 8 this led to high transmissions of basic peptides (even over 100%), intermediate transmissions for neutral peptides, and low transmissions for acid peptides. The addition of multicharged cationic and anionic species in the hydrolysate induced a markedly enhanced selectivity when the polyelectrolyte was a membrane coion and a complete reversion of selectivity when it was a membrane counterion. Copyright 1998 John Wiley & Sons, Inc.     

Separation of neutral oligosaccharide alditols from human meconium using high-pH anion-exchange chromatography

Neutral reduced oligosaccharides are in general not sufficiently retained to achieve adequate separation and reproducible chromatography using high-pH anion-exchange chromatography. We describe a method to increase the retention using two columns in series. This method has been applied to the separation of oligosaccharides purified from human meconium glycoproteins, obtained as their alditols after alkaline-borohydride release of oligosaccharides. The neutral oligosaccharide alditols were significantly retained upon two CarboPac PA-100 columns, connected in series, and eluted in 80 mM sodium hydroxide between 4 and 10 min. Three sialylated alditols studied were substantially retained and could be eluted in a gradient of 0–500 mM sodium acetate—80 mM sodium hydroxide between 10 and 45 min. The elution patterns were based on their size, charge and linkage, such that oligosaccharide alditol isomers could be separated.     

Glycosaminoglycans modulate activation, activity, and stability of tripeptidyl-peptidase I in vitro and in vivo

Tripeptidyl-peptidase I (TPP I, CLN2 protein) is a lysosomal exopeptidase that sequentially removes tripeptides from the N termini of polypeptides and shows a minor endoprotease activity. Mutations in TPP I lead to classic late-infantile neuronal ceroid lipofuscinosis, a neurodegenerative lysosomal storage disease. TPP I proenzyme is converted in lysosomes into a mature enzyme with the assistance of another protease and is able to autoactivate in acidic pH in vitro via a unimolecular mechanism. Because autoactivation in vitro at the pH values reported for lysosomes generated inactive enzyme, we intended to determine whether physiologically relevant factors can modify this process to also make it plausible in vivo. Here, we report that high ionic strength and glycosaminoglycans (GAGs) increase yields (ionic strength) or yields and rates (GAGs) of activation, enhance degradation of liberated TPP I prosegment fragments, and switch effective autoactivation of TPP I proenzyme toward less acidic pH values (up to pH 6.0). Although ionic strength and GAGs also inhibited TPP I activity in vitro and in living cells, the degree of inhibition (from 20 to 60%) appears to be of rather limited functional significance. Importantly, binding to GAGs improved thermal stability of TPP I and protected the enzyme against alkaline pH-induced denaturation in vitro (t((1/2)) of mature enzyme at pH 7.4 increased by approximately 8-fold in the presence of heparin) and in vivo ( approximately 2-fold higher loss of TPP I in cells deficient in GAGs than in control cells after bafilomycin A1 treatment). These findings elucidate a potent physiologically relevant mechanism of TPP I regulation by GAGs and suggest that generation of the active enzyme via autoactivation can be accomplished not only in vitro but in vivo as well.     

The potential role of proteoglycans in cationic lipid-mediated gene delivery. Studies of the interaction of cationic lipid-DNA complexes with model glycosaminoglycans.

Recent evidence supports a role for proteoglycans in polycation-mediated gene delivery. Therefore, the interaction of glycosaminoglycans with cationic lipid-DNA complexes (CLDCs) has been characterized using a combination of biophysical approaches. At low ionic strength, CLDCs bind to heparin-derivatized Sepharose particles, with the ratio of cationic lipid to DNA controlling the binding. Incorporation of the helper lipids cholesterol or 1,2-dioleoyl-phosphatidylethanolamine increases the amount of bound CLDC. Heparin also induces the aggregation of CLDCs, with cholesterol reducing this effect. Isothermal titration calorimetry demonstrates an endothermic heat for the binding of heparin to CLDCs at low ionic strength, whereas circular dichroism studies suggest a heparin-stimulated release of DNA from CLDCs at a greater than 20-fold charge excess. Increasing the ionic strength to 0.11 reduces CLDC binding to heparin beads, and greatly enhances the release of DNA from CLDCs by heparin. The ability of the cell surface glycosaminoglycan heparan sulfate to release DNA from CLDCs is more sensitive than heparin to the incorporation of the cholesterol or 1,2-dioleoyl-phosphatidylethanolamine. Titration calorimetry reveals an exothermic heat for the interaction glycosaminoglycans with CLDCs at higher ionic strength. These results are consistent with the direct involvement of proteoglycans in transfection.     

Heterogeneity of depolymerized heparin SEC fractions: to pool or not to pool?

In the structural analysis of heparin and heparan sulfate, it is customary to combine or pool like-sized fractions obtained by size-exclusion chromatography (SEC) of enzymatically derived heparin oligosaccharides. In this study, we examine the heterogeneity of preparative-scale SEC fractions obtained from enzymatic digests of porcine intestinal mucosa heparin. Each fraction was profiled by capillary electrophoresis with UV detection (CE−UV) using a 60 mM formic acid running buffer at pH 3.43. Differences in the composition and relative concentration of components of the SEC fractions were observed for disaccharides and larger oligosaccharides. The heterogeneity of the fractions becomes more pronounced when heparin is digested using a heparin lyase cocktail. The heterogeneity of preparative SEC fractions was further investigated by reversed-phase ion-pairing ultraperformance liquid chromatography coupled with mass spectrometry (RPIP−UPLC−MS) using the ion-pairing reagent, tributylamine (Bu₃N). Our results suggest that preliminary profiling of preparative SEC fractions prior to pooling may simplify efforts to identify and/or isolate rare structures.     

Specificity of glycosaminoglycan suppression of endothelin-1 production by human umbilical vein endothelial cells.

Endothelin-1 (ET-1) is the most potent vasoconstrictor peptide found in nature. Its production is stimulated by thrombin. By inhibiting thrombin we have previously shown that heparin, a highly negatively-charged glycosaminoglycan (GAG), suppresses the production of ET-1 by cultured human umbilical vein endothelial cells (HUVEC). The purpose of our study is to determine the effect of other GAGs and related compounds on ET-1 production. The GAGs and related compounds used in the study were: chondroitin sulfate A, chondroitin sulfate B, chondroitin sulfate C, fucoidin, low molecular weight dextran sulfate, high molecular weight dextran sulfate, and hyaluronan. HUVEC were incubated for 48 hr with media containing these GAGs and related compounds and with media without GAG as control. ET-1 levels were measured by radioimmunoassay. GAGs and related molecules with higher sulfate content, heparin, chondroitin sulfate B, low and high molecular weight dextran sulfates significantly suppressed ET-1 production by HUVEC. Fucoidin also suppressed ET-1 production despite its lower sulfate content, probably because of its structural similarity to heparin. These compounds may be useful for future in vivo studies.     

Mass spectrometric evidence of heparin disaccharides for the catalytic characterization of a novel endolytic heparinase

Heparin like glycosaminoglycans (HLGAGs) are struc-turally complex linear polysaccharides composed of re-peating disaccharide unit of uronic (α-L-iduronic or β-D-glucuronic) acid linked 1→4 to α-D-glucosamine, whichis a highly variable sulfation pattern and ascribes to eachglycosaminoglycan (GAG) chain a unique structuralsignature. This signature dictates specific the GAG-pro-tein interactions underlying critical biological processesrelated to cell and tissue functions [1]. Only in fe…     

Rapid quantitative analysis of monoclonal antibody heavy and light chain charge heterogeneity

An alternative method to traditional 2-dimensional gel electrophoresis (2D-PAGE) and its application in characterizing the inherent charge heterogeneity of chromatographically isolated monoclonal antibody heavy and light chains is described. This method, referred to as ChromiCE, utilizes analytical size-exclusion chromatography (SEC), performed under reducing and denaturing conditions, followed by imaged capillary isoelectric focusing (icIEF) of the chromatographically separated heavy and light chains. Under conditions suitable for the subsequent icIEF analysis, the absolute and relative SEC elution volumes of the heavy and light chains were found to be highly pH dependent, a phenomenon that can be exploited in optimizing chromatographic separation. Compared to 2D-PAGE, the ChromiCE method substantially decreases the time and labor needed to complete the analysis, improves reproducibility, and provides fully quantitative assessment of charge heterogeneity. The ChromiCE methodology was applied to a set of diverse monoclonal antibodies to demonstrate suitability for quantitative charge variant analysis of heavy and light chains. A typical application of ChromiCE in extended characterization and stability studies of a purified antibody is shown.