Quantification of O-acetyl, N-acetyl and phosphate groups and determination of the extent of O-acetylation in bacterial vaccine polysaccharides by high-performance anion-exchange chromatography with conductivity detection (HPAEC-CD)

Advances in Chromatographic and Mass Spectrometric Techniques for Analyzing Reducing Monosaccharides and Their Phosphates in Biological Samples

Reducing monosaccharides and their phosphates are critical metabolites in the central carbon metabolism pathway of living organisms. Variations in their content can indicate abnormalities in metabolic pathways and the onset of certain diseases, necessitating their analysis and detection. Reducing monosaccharides and their phosphates exhibit significant variations in content within biological samples and are present in many isomers, which makes the accurate quantification of reducing monosaccharides and their phosphates in biological samples a challenging task. Various analytical methods such as spectroscopy, fluorescence detection, colorimetry, nuclear magnetic resonance spectroscopy, sensor-based techniques, chromatography, and mass spectrometry are employed to detect monosaccharides and phosphates. In comparison, chromatography and mass spectrometry are highly favored for their ability to simultaneously analyze multiple components and their high sensitivity and selectivity. This review thoroughly evaluates the current chromatographic and mass spectrometric methods used for detecting reducing monosaccharides and their phosphates from 2013 to 2023, highlighting their efficacy and the advancements in these analytical technologies.

High-Performance Anion-Exchange chromatography with conductivity detection method for simultaneous determination of nitrogen and phosphorus in polysaccharides

Capsular polysaccharides of Streptococcus pneumoniae contain a characteristic mix of monosaccharides in their structure resulting in immunologically distinct serotypes. Pneumococcal capsular polysaccharides include sugars such as hexoses, uronic acids, hexosamines, methyl pentoses, other functional groups are attached to the sugars are N and O-acetyl groups, nitrogen and phosphorus. Most of these components can be quantified using different colorimetric methods. However, available methods for quantifying nitrogen and phosphorus are not sensitive enough and laborious. We report a highly sensitive high-performance anion-exchange chromatography-conductivity detector (HPAEC-CD) method for quantifying nitrogen and phosphorus present in pneumococcal capsular polysaccharides. The method is reliable, robust and reproducible with no interference. The LOQ for nitrogen and phosphorus of 3.125 and 62.5 ng/mL, respectively, is highly critical for estimating low levels of total nitrogen and total phosphorus. We have implemented this method to quantify total nitrogen in Typhoid Vi polysaccharide and phosphorus in Haemophilus influenzae type-b polysaccharide. This method has greater application for quantification of nitrogen and phosphorus present in low concentrations in polysaccharide vaccines/biologicals.

Glycoconjugation of Shigella flexneri type 2a O-polysaccharide with CRM197 as a potential vaccine candidate for shigellosis

Shigellosis, a diarrheal disorder caused by an entero-invasive bacterium Shigella, is a major concern among children often leading to mortality. As most of these strains have developed universal antibiotic resistance, the development of a vaccine is crucial in combating the infection. The O-specific polysaccharide (O-PSs) from S. flexneri type 2a is considered to be the major disease-causing antigen in shigellosis. Therefore, the O-PSs conjugated with carrier proteins, can serve as a potential high molecular weight vaccine candidate. Accordingly, in the present study, O-PS extracted from S. flexneri 2a is conjugated with Cross-Reactive Material (CRM₁₉₇), a non-toxic mutant of diphtheria toxin. We derivatized CRM₁₉₇ and O-PS separately with adipic acid dihydrazide (ADH) and reacted with their counterparts to probe the conjugation efficacy. Among the two strategies, the CRM₁₉₇-ADH treated with O-PS has yielded a stable glycoconjugate of 311 kDa. The conjugation efficiency has been probed by estimating the free protein, free O-PS and O-PS:CRM₁₉₇ ratio using slot-blot, size exclusion and high-performance anion exchange chromatography techniques. The conjugate exhibited enhanced shelf-life of three months. The cytotoxicity studies with Vero/MRC-5 cells have confirmed the non-toxicity of the conjugate, which makes the glycoconjugate a potential vaccine candidate for shigellosis.

Glycoconjugate vaccines against Salmonella enterica serovars and Shigella species: existing and emerging methods for their analysis

The global spread of enteric disease, the increasingly limited options for antimicrobial treatment and the need for effective eradication programs have resulted in an increased demand for glycoconjugate enteric vaccines, made with carbohydrate-based membrane components of the pathogen, and their precise characterisation. A set of physico-chemical and immunological tests are employed for complete vaccine characterisation and to ensure their consistency, potency, safety and stability, following the relevant World Health Organization and Pharmacopoeia guidelines. Variable requirements for analytical methods are linked to conjugate structure, carrier protein nature and size and O-acetyl content of polysaccharide. We investigated a key stability-indicating method which measures the percent free saccharide of Salmonella enterica subspecies enterica serovar Typhi capsular polysaccharide, by detergent precipitation, depolymerisation and HPAEC-PAD quantitation. Together with modern computational approaches, a more precise design of glycoconjugates is possible, allowing for improvements in solubility, structural conformation and stability, and immunogenicity of antigens, which may be applicable to a broad spectrum of vaccines. More validation experiments are required to establish the most effective and suitable methods for glycoconjugate analysis to bring uniformity to the existing protocols, although the need for product-specific approaches will apply, especially for the more complex vaccines. An overview of current and emerging analytical approaches for the characterisation of vaccines against Salmonella Typhi and Shigella species is described in this paper. This study should aid the development and licensing of new glycoconjugate vaccines aimed at the prevention of enteric diseases.

2-Phenoxyethanol: A novel reagent for improved sensitivity of carbohydrate quantification

Anthrone is a routinely used reagent for estimating carbohydrates (Polysaccharides) in research, development and pharmaceutical applications. In presence of sulphuric acid, the polysaccharide gets hydrolyzed to monosaccharides in the form of hydroxymethyl furfural or furfural. The furfural then reacts with anthrone to form a green color complex with a maximum absorbance at 625 nm. Though anthrone reacts well with polysaccharides containing hexoses (such as glucose and galactose) and rhamnose, it is less reactive with uronic acids (such as glucuronic acid and galacturonic acid) and hexosamines (such as fucosamine, glucosamine, galactosamine, mannosamine, pneumosamine). Here, we report a novel reagent, 2-Phenoxyethanol, which reacts with furfural or hydroxymethyl furfural resulting in higher absorptivity. This method is rapid, sensitive, simple and direct, and can be used for quantitative determination of any type of carbohydrate that contains neutral sugars and uronic acids. For these saccharides, the sensitivity of the assay using 2-Phenoxyethanol (2-PE) is twice over anthrone method. Uronic acids show improved sensitivity using 2-PE over Phenol and it is more than twice with glucuronic acid. 2-PE reagent method has greater application for quantification of carbohydrates when present in low concentration in vaccines/biologicals.

Monoclonal Antibodies Against the Capsular Polysaccharides A, C, Y, W, and X of Neisseria meningitidis: A Platform for the Quality Control of Meningococcal Vaccines

Vaccination has reduced morbidity and mortality of many diseases that previously caused devastating epidemics and deaths globally. Vaccines as a biological product may contain microorganisms or their derivatives. This aspect together with the fact that they are administered to healthy individuals (mainly children) means that approximately 70% of vaccines development time is dedicated to quality control. Monoclonal antibodies (MAbs) have become essential analytical tools for application in ELISAs, Western and Dot blotting, immunoprecipitation, and flow cytometric assays that ensure the quality control of vaccines. The aim of this work is to present a review of the methods used to obtain a platform of MAbs against Neisseria meningitidis polysaccharide antigens to use as an analytical tool for quality control of anti-meningococcal polysaccharide (Ps) vaccines. The MAbs obtained are used in five sandwich ELISAs developed for Ps quantification. The assays showed good reproducibility and repeatability, with quantitation and detection limits below 1 ng/mL. Dot Blot, as the Identity test of the Ps vaccine, was carried out to positively identify licensed and experimental vaccines. All assays described are suitable for the screening of multiple vaccine samples and could be useful for monitoring lot-to-lot consistency and stability.

Role of O-Acetylation in the Immunogenicity of Bacterial Polysaccharide Vaccines

The incidence of infectious diseases caused by several bacterial pathogens such as Haemophilus influenzae type b, Streptococcus pneumoniae, and Neisseria meningitidis, has been dramatically reduced over the last 25 years through the use of glycoconjugate vaccines. The structures of the bacterial capsular polysaccharide (CPS) antigens, extracted and purified from microbial cultures and obtained with very high purity, show that many of them are decorated by O-acetyl groups. While these groups are often considered important for the structural identity of the polysaccharides, they play a major role in the functional immune response to some vaccines such as meningococcal serogroup A and Salmonella typhi Vi, but do not seem to be important for many others, such as meningococcal serogroups C, W, Y, and type III Group B Streptococcus. This review discusses the O-acetylation status of CPSs and its role in the immunological responses of these antigens.

Synthesis and immunochemical evaluation of a novel Neisseria meningitidis serogroup A tetrasaccharide and its conjugate

A tetrameric repeating unit of capsular polysaccharide of Neisseria meningitidis serogroup A was synthesized which mimicked natural polysaccharide in immunochemical analysis.

Simple alternative to sialic acid determination in meningococcal polysaccharides W or Y

Physicochemical methods are the primary tests used to ensure that batches of meningococcal polysaccharide (PS) antigens are manufactured consistently to those shown to be safe and effective in clinical trials. Although modern physicochemical methods of analysis providing structural information about the antigens have been developed and used, simpler assays, which can be readily validated, are still in use for polysaccharide batch release. The simple and cheap method for Neisseria meningitidis serogroup W or Y polysaccharide (MenW or MenY PS) content quantification has been developed. This colorimetric method is based on the galactose or glucose quantification in MenW or MenY PS hydrolysate, respectively. Intra- and inter-assay precision and accuracy of the novel method have been demonstrated, in comparison to the same properties of the current regulatory approved method for the same purpose - sialic acid quantification. We provided the calculation of the possible future regulatory requirement for the galactose or glucose content in MenW or MenY PS, respectively, and revealed in detail the stoichiometric calculation behind it.

Deciphering Antigenic Determinants of Streptococcus pneumoniae Serotype 4 Capsular Polysaccharide using Synthetic Oligosaccharides

Streptococcus pneumoniae is a major cause of mortality and morbidity worldwide. More than 90 S. pneumoniae serotypes are distinguished based on the structure of their primary targets to the human immune system, the capsular polysaccharides (CPSs). The CPS of the prevalent serotype 4 (ST4) is composed of tetrasaccharide repeating units and is included in existing pneumococcal vaccines. Still, the structural antigenic determinants that are essential for protective immunity, including the role of the rare and labile cyclic trans-(2,3) pyruvate ketal modification, remain largely unknown. Molecular insights will support the design of synthetic subunit oligosaccharide vaccines. Here, we identified the key antigenic determinants of ST4 CPS with the help of pyruvated and nonpyruvated synthetic repeating unit glycans. Glycan arrays revealed oligosaccharide antigens recognized by antibodies in the human reference serum. Selected depyruvated ST4 oligosaccharides were used to formulate neoglycoconjugates and immunologically evaluated in mice. These oligosaccharides were highly immunogenic, but the resulting antiglycan antibodies showed only limited binding to the natural CPS present on the bacterial surface. Glycan array and surface plasmon resonance analysis of murine polyclonal serum antibodies as well as monoclonal antibodies revealed that terminal sugars are important in directing the immune responses. The pyruvate modification on the oligosaccharide is needed for cross-reactivity with the native CPS. These findings are an important step toward the design of oligosaccharide-based vaccines against S. pneumoniae ST4.

Bioanalysis of meningococcal vaccines

Meningococcal meningitis is feared because of the rapid onset of severe disease from mild symptoms and, therefore, is an important target for vaccine research. Five serogroups, defined by the structures of their capsular polysaccharides, are responsible for the vast majority of disease. Protection against four of these five serogroups can be obtained with polysaccharide or glycoconjugate vaccines, in which fragments of the capsular polysaccharides attached to a carrier protein generate anticarbohydrate immune responses, whilst protection against group B disease requires protein immunogens, often presented in vesicles containing outer membrane proteins. Glycoconjugate vaccines are now an established technology, but outer-membrane protein vaccines are still under development and present significant challenges. This review discusses physicochemical approaches to the characterization and quality control of these vaccines, as well as highlighting the problems and differences in vaccine design required for protection against different serogroups of the same species of pathogen.

Vi-CRM 197 as a new conjugate vaccine against Salmonella Typhi

An efficacious, low cost vaccine against typhoid fever, especially for young children, would make a major impact on disease burden in developing countries. The virulence capsular polysaccharide of Salmonella Typhi (Vi) coupled to recombinant mutant Pseudomonas aeruginosa exoprotein A (Vi-rEPA) has been shown to be highly efficacious. We investigated the use of carrier proteins included in infant vaccines, standardized the conjugation process and developed key assays required for routine lot release at production scale. Vi from a BSL1 organism, Citrobacter freundii, strain WR7011, was used as an alternative to Vi from S. Typhi. We showed that Vi conjugated to CRM(197), a non-toxic mutant of diphtheria toxin, widely used in commercial vaccines, was produced at high yield. Vi-CRM(197) proved immunogenic in animal studies, even without adjuvant. Thus, Vi-CRM(197) appears to be a suitable candidate for the development of a commercially viable, effective typhoid vaccine for developing countries.

C-reactive protein: A pentraxin with anti-acetylcholine activity

Purified C-reactive protein (CRP) diminished effects of acetylcholine (ACh) on the vascular tone and the heart rate of rats in vivo. In vitro CRP inhibited breakdown of ACh by acetylcholinesterase (AChE) while did not interact with AChE itself. CRP appears to bind ACh. CRP did not modify the cardiovascular effects of adenosine, another vasorelaxant. The data suggest that there is a new line of cross-talk between the inflammation and cholinergic regulation with CRP acting on endothelium via the ACh-dependent pathway.

Monitoring activation sites on polysaccharides by GC–MS

A method has been developed to determine the location and order of activation for potential saccharide antigens used in conjugate vaccine development. Saccharides were monitored for activation by sodium periodate oxidation and subsequent analysis by gas chromatography-mass spectrometry (GC-MS). Pneumococcal serotype polysaccharides 7F and 18C were evaluated as polysaccharides containing multiple potential sites for activation. Sialyllactose was used as a model oligosaccharide compound to evaluate oxidation of terminally linked sialic acids and reducing sugar residues. Oxidized saccharides were analyzed by monosaccharide composition and/or linkage analysis to elucidate specific activation of cis versus trans diols, as well as diols containing primary versus secondary alcohols, at specified levels of periodate. Samples (100-500 microg) were sequentially oxidized, reduced, methanolyzed, and derivatized in a single reaction vial for routine analysis by GC-MS.

Characterization of the antigenic lipopolysaccharide O chain and the capsular polysaccharide produced by Actinobacillus pleuropneumoniae serotype 13

Serotyping of Actinobacillus pleuropneumoniae, the etiologic agent of porcine pleuropneumonia, is important for epidemiological studies and for the development of homologous vaccine cell preparations. The serology is based on the specific chemical structures of capsular polysaccharides (CPSs) and lipopolysaccharide (LPS) antigenic O-polysaccharide moieties (O-PSs), and knowledge of these structures is required for a molecular-level understanding of their serological specificities. The structures of A. pleuropneumoniae serotype 1 to 12 CPSs and O-PSs have been elucidated; however, the structures associated with three newly proposed serotypes (serotypes 13, 14, and 15) have not been reported. Herein we described the structures of the antigenic O-PS and CPS of A. pleuropneumoniae serotype 13. The O-PS of the A. pleuropneumoniae serotype 13 LPS is a polymer of branched tetrasaccharide repeating units composed of l-rhamnose, 2-acetamido-2-deoxy-d-galactose, and d-galactose residues (1:1:2). By use of hydrolysis, methylation, and periodate oxidation chemical methods together with the application of one- and two-dimensional 1H and 13C nuclear magnetic resonance spectroscopy and mass spectrometry, the structures of the O chain and CPS were determined. The CPS of A. pleuropneumoniae serotype 13 was characterized as a teichoic-acid type polymer. The LPS O antigen was identical to the O-PS produced by A. pleuropneumoniae serotype 7. The CPS has the unique structure of a 1,3-poly(glycerol phosphate) teichoic acid type I polymer and constitutes the macromolecule defining the A. pleuropneumoniae serotype 13 antigenic specificity.