Separation of mucin oligosaccharide-alditols by high performance liquid chromatography on alkylamine-bonded silica columns. Effects of structural parameters

Physicochemical properties of mucus and their impact on transmucosal drug delivery

Mucus is a selective barrier to particles and molecules, preventing penetration to the epithelial surface of mucosal tissues. Significant advances in transmucosal drug delivery have recently been made and have emphasized that an understanding of the basic structure, viscoelastic properties, and interactions of mucus is of great value in the design of efficient drug delivery systems. Mucins, the primary non-aqueous component of mucus, are polymers carrying a complex and heterogeneous structure with domains that undergo a variety of molecular interactions, such as hydrophilic/hydrophobic, hydrogen bonds and electrostatic interactions. These properties are directly relevant to the numerous mucin-associated diseases, as well as delivering drugs across the mucus barrier. Therefore, in this review we discuss regional differences in mucus composition, mucus physicochemical properties, such as pore size, viscoelasticity, pH, and ionic strength. These factors are also discussed with respect to changes in mucus properties as a function of disease state. Collectively, the review seeks to provide a state of the art roadmap for researchers who must contend with this critical barrier to drug delivery.

Carbohydrate analysis throughout the development of a protein therapeutic

This review discusses the challenges involved in the characterization of the glycosylation of therapeutic glycoproteins. The focus is on methods that are most commonly used in regulatory filings and lot release testing of therapeutic glycoproteins. The different types of assays for carbohydrate analysis are reviewed, including the distinction between assays appropriate for lot release or better suited to testing during early drug development or in-depth characterization of the glycosylation. Characteristics of the glycoprotein and production process that should be considered when determining the amount of testing, the number of different methods to employ and when the testing should be performed during development of protein therapeutics is also discussed.

Respiratory tract mucin genes and mucin glycoproteins in health and disease

This review focuses on the role and regulation of mucin glycoproteins (mucins) in airway health and disease. Mucins are highly glycosylated macromolecules (> or =50% carbohydrate, wt/wt). MUC protein backbones are characterized by numerous tandem repeats that contain proline and are high in serine and/or threonine residues, the sites of O-glycosylation. Secretory and membrane-tethered mucins contribute to mucociliary defense, an innate immune defense system that protects the airways against pathogens and environmental toxins. Inflammatory/immune response mediators and the overproduction of mucus characterize chronic airway diseases: asthma, chronic obstructive pulmonary diseases (COPD), or cystic fibrosis (CF). Specific inflammatory/immune response mediators can activate mucin gene regulation and airway remodeling, including goblet cell hyperplasia (GCH). These processes sustain airway mucin overproduction and contribute to airway obstruction by mucus and therefore to the high morbidity and mortality associated with these diseases. Importantly, mucin overproduction and GCH, although linked, are not synonymous and may follow from different signaling and gene regulatory pathways. In section i, structure, expression, and localization of the 18 human MUC genes and MUC gene products having tandem repeat domains and the specificity and application of MUC-specific antibodies that identify mucin gene products in airway tissues, cells, and secretions are overviewed. Mucin overproduction in chronic airway diseases and secretory cell metaplasia in animal model systems are reviewed in section ii and addressed in disease-specific subsections on asthma, COPD, and CF. Information on regulation of mucin genes by inflammatory/immune response mediators is summarized in section iii. In section iv, deficiencies in understanding the functional roles of mucins at the molecular level are identified as areas for further investigations that will impact on airway health and disease. The underlying premise is that understanding the pathways and processes that lead to mucus overproduction in specific airway diseases will allow circumvention or amelioration of these processes.

Separation and characterization of underivatized oligosaccharides using liquid chromatography and liquid chromatography–electrospray ionization mass spectrometry

Native cyclodextrin-based columns are particularly useful for the analysis of oligosaccharides because the retention of these carbohydrates is based mainly on the hydrogen bonding interactions of oligosaccharide hydroxyl groups with the stationary phase. Thus, the retention time predictably increases with the number of analyte hydroxyl groups, which corresponds to the elongation of the oligosaccharide chain. High-performance liquid chromatography (HPLC) coupled to electrospray ionization (ESI) mass spectrometry (MS) was used for the separation and characterization of underivatized oligosaccharide mixtures. With the limits of detection as low as 50 pg, all individual components of oligosaccharide mixtures (up to 11 glucose units long) were baseline resolved on a Cyclobond I 2000 column and detected using ESI-MS. Low flow rates and narrow I.D. columns increase the ESI-MS sensitivity significantly. The method showed potential usefulness for the sensitive and quick analysis of hydrolysis products of polysaccharides, and for trace levels of individual oligosaccharide or oligosaccharide isomers from biological systems.

HPLC of oligosaccharides in glycobiology

Carbohydrate chains of glycoproteins are extremely varied and are a wide variety of different biological processes. Determination of their structures is therefore of great interest in both research and clinical fields. HPLC has proved to be the ideal tool for mono- and oligosaccharide purification and analysis. A wide range of adsorbent and solvent systems are available and we describe in this mini-review the main methods used for the separation and detection of oligosaccharides.

HPLC analysis of carbohydrates on POLYSPHER®CH OH columns using pulsed amperometric detection (PAD) with sodium hydroxide as post column detection reagent

Carbohydrates have been separated on POLYSPHER(R)CH OH columns using pulsed amperometric detection (PAD) and UV detection (lambda =196 nm) in series and pure water as mobile phase. Nearly baseline separations have been obtained for the glycoprotein carbohydrates of sialic acid ( N-acetylneuraminic acid, NANA), N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc). As carbohydrates dissolved and eluted with pure water are present in the neutral form they are not detectable with PAD in contrast to carbohydrate anions formed at high pH values. Therefore an additional NaOH post column reagent has been continuously pumped through a mixing chamber into the mobile phase to form carbohydrate anions resulting in improved detection limits. Monosaccharides as well as glycoprotein carbohydrates could be detected in the microg/ml-range. This method has been applied successfully to the analysis of sugars in fruit juice. With only 2 microl of juice per 50 ml water, the determination of the main constituents, sucrose, glucose and fructose, was possible in a few minutes without sample preparation.

O-linked protein glycosylation structure and function

There has been a recent resurgence of interest in the post-translational modification of serine and threonine hydroxyl groups by glycosylation, because the resulting O-linked oligosaccharide chains tend to be clustered over short stretches of peptide and hence they can present multivalent carbohydrate antigenic or functional determinants for antibody recognition, mammalian cell adhesion and microorganism binding. Co-operativity can greatly increase the affinity of interactions with antibodies or carbohydrate binding proteins. Thus, in addition to their known importance in bearing tumour associated antigens in the gastrointestinal and respiratory tracts, glycoproteins with O-linked chains have been implicated as ligands or co-receptors for selectins (mammalian carbohydrate binding proteins). Microorganisms may have adopted similar mechanisms for interactions with mammalian cells in infection, by having relatively low affinity ligands (adhesins) for carbohydrate binding, which may bind with higher affinity due to the multivalency of the host ligand and which are complemented by other virulence factors such as interactions with integrin-type molecules. In addition to specific adhesion signals from O-linked carbohydrate chains, multivalent O-glycosylation is involved in determining protein conformation and forming conjugate oligosaccharide-protein antigenic, and possible functional determinants.

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.

Use of a porous graphitised carbon column for the high-performance liquid chromatography of oligosaccharides, alditols and glycopeptides with subsequent mass spectrometry analysis

HPLC using a porous graphitised carbon (PGC) column eluted in acetonitrile-aqueous trifluoroacetic acid has been shown to give complementary chromatography to reversed-phase (ODS) HPLC for separation of peptides and glycopeptides. The PGC column can also be used for separation of oligosaccharides and oligosaccharide alditols released from protein by enzymes (N-linked chains) or base-borohydride degradation (O-linked chains). The advantages are that peptides, glycopeptides, reducing oligosaccharides, sialylated oligosaccharides and oligosaccharide alditols can be chromatographed under the same conditions. The samples can be readily recovered by evaporation for sensitive liquid secondary ion mass spectrometric (LSI-MS) analysis and there is no contamination or deterioration of chromatography from column leakage. LSI-MS analysis revealed that complete peak separation of all of the possible oligosaccharide components of the standard glycoproteins fetuin and bovine submaxillary mucin was not achieved. However, PGC remains as a useful adjunct to other HPLC profiling and separation techniques in particular where subsequent MS analysis is desired.