Determination of sialic acids by liquid chromatography–mass spectrometry

Sialic acid on avian erythrocytes

Understanding variation in physiological traits across taxa is a central question in evolutionary biology that has wide-ranging implications in biomedicine, disease ecology, and environmental protection. Sialic acid (Sia), and in particular, 5-N-acetylneuraminic acid (Neu5Ac), is chemically bound to galactose and the underlying glycan via α2-3 or α2-6 glycosidic linkage (i.e., Siaα2-3Galactose or Siaα2-6Galactose), conferring two different cell surface structures that affects cell to cell communication and interactions with foreign agents including microparasites and toxins. As an initial step towards understanding variation of Sia across the class Aves, we collected red blood cells (RBCs or erythrocytes) and measured Sia quantity in 76 species and 340 individuals using HPLC-MS/MS and glycosidic linkage type in 24 species and 105 individuals using hemagglutination assay. Although Sia quantity did not, α2-6 glycosidic linkage did exhibit a discernable phylogenetic pattern as evaluated by a phylogenetic signal (λ) value of 0.7. Sia quantity appeared to be higher in after hatch year birds than hatch year birds (P < 0.05); moreover, ~80% of the measured Sia across all individuals or species was expressed by ~20% of the individuals or species. Lastly, as expected, we detected a minimal presence of 5-N-glycolylneuraminic acid in the avian RBCs tested. These data provide novel insights and a large baseline dataset for further study on the variability of Sia in the class Aves which might be useful for understanding Sia dependent processes in birds.

Quantification of Influenza Neuraminidase Activity by Ultra-High Performance Liquid Chromatography and Isotope Dilution Mass Spectrometry

Mounting evidence suggests that neuraminidase's functionality extends beyond its classical role in influenza virus infection and that antineuraminidase antibodies offer protective immunity. Therefore, a renewed interest in the development of neuraminidase (NA)-specific methods to characterize the glycoprotein and evaluate potential advantages for NA standardization in influenza vaccines has emerged. NA displays sialidase activity by cleaving off the terminal N-acetylneuraminic acid on α-2,3 or α-2,6 sialic acid containing receptors of host cells. The type and distribution of these sialic acid containing receptors is considered to be an important factor in transmission efficiency of influenza viruses between and among host species. Changes in hemagglutinin (HA) binding and NA specificity in reassortant viruses may be related to the emergence of new and potentially dangerous strains of influenza. Current methods to investigate neuraminidase activity use small derivatized sugars that are poor models for natural glycoprotein receptors and do not provide information on the linkage specificity. Here, a novel approach for rapid and accurate quantification of influenza neuraminidase activity is achieved utilizing ultra-high performance liquid chromatography (UPLC) and isotope dilution mass spectrometry (IDMS). Direct LC-MS/MS quantification of NA-released sialic acid provides precise measurement of influenza neuraminidase activity over a range of substrates. The method provides exceptional sensitivity and specificity with a limit of detection of 0.38 μM for sialic acid and the capacity to obtain accurate measurements of specific enzyme activity preference toward α-2,3-sialyllactose linkages, α-2,6-sialyllactose linkages, or whole glycosylated proteins such as fetuin.

Quantitative determination and confirmatory analysis of N-acetylneuraminic and N-glycolylneuraminic acids in serum and urine by solid-phase extraction on-line coupled to liquid chromatography-tandem mass spectrometry

N-acetylneuraminic acid (Neu5Ac) and N-acetylglycolylneuraminic acid (Neu5Gc), two acylated derivatives of 9-C carboxylated monosaccharides, are involved in a number of biological processes as modulators of glycoconjugates. A partially automated method is here presented for determination of these sialic acids in the two most important biofluids for clinical analysis: serum and urine. For this purpose, a solid-phase extraction (SPE) workstation was on-line connected to an LC-MS/MS triple quadrupole mass detector. Hydrolysis to release sialic acids bound to glycoconjugates and derivatization were the two steps implemented as sample preparation prior to SPE-LC-MS/MS analysis. Following thorough optimization of the SPE and LC-MS/MS conditions, the analytical method was validated using the standard addition approach to assess the presence of matrix effects. The proposed method affords detection limits of 0.03ng/mL and 0.04ng/mL for Neu5Ac and Neu5Gc, respectively. The precision (expressed as relative standard deviation) was 1.7 and 4.6% for within-day variability, and 4.8 and 7.2% for between-days variability. Accuracy, estimated using spiked (between 1 and 50ng/mL) and non-spiked samples of both biofluids, ranged from 95.2 to 99.6%. The method was applied to human serum and urine of healthy volunteers, thus showing its suitability for application in both clinical and research laboratories.

Systematic investigation of quinoxaline derivatization of sialic acids and their quantitation applicability using high performance liquid chromatography

Quinoxaline derivatization has been the most commonly used approach for sialic acid quantitation of biological samples and glycoproteins by either HPLC or LC-MS/MS.

Quantification of free sialic acid in human plasma through a robust quinoxalinone derivatization and LC-MS/MS using isotope-labeled standard calibration

We report an accurate quantification of free sialic acid (SA) in human plasma using LC-MS/MS method with isotope-labeled standard calibration (ILSC) and robust derivatization. Specifically, derivatization of SA with a stable and inexpensive 3,4-diaminotoluene (DAT) provides a stable product of SA with high MS response, proving a convenient and cost-effective LC-MS/MS analysis of free SA. In addition, the use of (13)C3-SA as calibration standard ensured the accuracy for the measurement. This assay used ultra high performance liquid chromatography (UHPLC) for separation of native/labeled SA and IS from matrix interference, and employed mass spectrometry in multiple reaction monitoring (MRM) mode for sensitive and selective detection. We have achieved a lower limit of quantification (LLOQ) of 20ng/mL and a total running time of 4.2min, which is the most sensitive and quick measurement for free SA in biomatrices.

Fluorous derivatization combined with liquid chromatography/tandem mass spectrometry: a method for the selective and sensitive determination of sialic acids in biological samples

We have developed a novel method for selective and sensitive analysis of sialic acids (N-acetylneuraminic, N-glycolylneuraminic, and 2-keto-3-deoxy-D-glycero-D-galactonononic acid) utilizing liquid chromatography/tandem mass spectrometry (LC/MS/MS) combined with a fluorous derivatization technique. In this method, the carboxylic groups in the sialic acids are derivatized via amidation with heptadecafluoroundecylamine, a commercially available perfluoroalkylamine reagent. This reaction proceeds rapidly and readily at room temperature in the presence of a condensation reagent. Subsequently, the derivatives are retained specifically on an LC column with a perfluoroalkyl stationary phase by means of a fluorophilic or 'fluorous' interaction, and detected by positive electrospray ionization MS/MS. The detection limits of the examined sialic acids are in the range of 60-750 amol on column. We show that the proposed method can be used to analyze trace amounts of sialic acids in biological samples.

Quantification of monosaccharides through multiple-reaction monitoring liquid chromatography/mass spectrometry using an aminopropyl column

A simple, sensitive, and reproducible quantitative liquid chromatography/tandem mass spectrometry (LC/MS/MS) method was designed for the simultaneous quantification of monosaccharides derived from glycoprotein and blood serum using a multiple-reaction monitoring (MRM) approach. Sialic acids and neutral monosaccharides were efficiently separated using an amino-bonded silica phase column. Neutral monosaccharide molecules were detected as their aldol acetate anion adducts [M + CH(3)CO(2)](-) using electrospray ionization in negative ion MRM mode, while sialic acids were detected as deprotonated ions [M-H](-). The new method did not require a reduction step, and exhibited very high sensitivity to carbohydrates with limits of detection of 1 pg for the sugars studied. The linearity of the described approach spanned over three orders of magnitude (pg to ng). The method was validated for monosaccharides originating from N-linked glycans attached to glycoproteins and glycoproteins found in human blood serum. The method effectively quantified monosaccharides originating from as little as 1 microg of glycoprotein and 5 microL of blood serum. The method was robust, reproducible, and highly sensitive. It did not require reduction, derivatization or postcolumn addition of reagents.

Determination of sialic acids in milks and milk-based products

Sialic acids are becoming recognized as important components of milk-based products for infants and young children. As such, many companies now label the sialic acid content of their products. To control the labeling, suitable methods are required for this analysis. The objective of this work was to set up a rapid and sensitive method for the determination of the two most commonly occurring sialic acids, N-acetylneuraminic acid (Neu5Ac) and N-glycolylneuraminic acid (Neu5Gc), using high-performance liquid chromatography (HPLC). The sialic acids were released from their parent oligosaccharides, glycoproteins, or glycolipids by mild acid hydrolysis using formic acid. They were then derivatized using 1,2-diamino-4,5-methylenedioxybenzene (DMB) and subsequently separated on a Zorbax SB-Aq Rapid Resolution column in less than 2 min. The method developed was validated on various milk-based products and ingredients containing sialic acid at levels from 0.3 to 900 mg/100 g. Spiking experiments indicate that the sialic acid recoveries ranged from 87% to 108%. The expanded measurement uncertainty was typically below 15% for Neu5Gc and typically below 10% for Neu5Ac or the sum of the sialic acids, with a few exceptions. The proposed method is fast, specific, and easy to set up for compliance analysis in a routine laboratory.

Multiple-reaction monitoring liquid chromatography mass spectrometry for monosaccharide compositional analysis of glycoproteins

A simple, sensitive, and rapid quantitative LC-MS/MS assay was designed for the simultaneous quantification of free and glycoprotein bound monosaccharides using a multiple reaction monitoring (MRM) approach. This study represents the first example of using LC-MS/MS methods to simultaneously quantify all common glycoprotein monosaccharides, including neutral and acidic monosaccharides. Sialic acids and reduced forms of neutral monosaccharides are efficiently separated using a porous graphitized carbon column. Neutral monosaccharide molecules are detected as their alditol acetate anion adducts [M + CH(3)CO(2)](-) using electrospray ionization in negative ion MRM mode, while sialic acids are detected as deprotonated ions [M - H](-). The new method exhibits very high sensitivity to carbohydrates with limits of detection as low as 1 pg for glucose, galactose, and mannose, and below 10 pg for other monosaccharides. The linearity of the described approach spans over three orders of magnitudes (pg to ng). The method effectively quantified monosaccharides originating from as little as 1 microg of fetuin, ribonuclease B, peroxidase, and alpha(1)-acid glycoprotein human (AGP) with results consistent with literature values and with independent CE-LIF measurements. The method is robust, rapid, and highly sensitive. It does not require derivatization or postcolumn addition of reagents.

Separation methods for sialic acids and critical evaluation of their biologic relevance

Sialic acids are biosynthesized by almost all organisms as a 9-carbon carboxylated monosaccharide and are integral components of glycoconjugates. More than 40 naturally occurring sialic acid derivatives of the three main forms of sialic acids, the N-acetyl- and N-glycolylneuraminic acid and 2-keto-3-deoxy-nonulosonic acid have been identified. Due to the great importance of sialic acids as key mediators in a plethora of cellular events, including cell-cell recognition and cell-matrix interactions, their analysis in biologic samples is useful for a deeper understanding of the various (patho)physiological processes and of value in disease diagnosis and monitoring. In this review we summarize the methodology developed to isolate and liberate sialic acids from biologic samples as well as the chromatographic, electromigration and hyphenated techniques available for their separation and analysis. A critical evaluation of the biological relevance of the results obtained by analyzing sialic acids in biologic samples is also presented.