Simplified quantitative glycomics using the stable isotope label Girard's reagent p by electrospray ionization mass spectrometry.

Fast, sensitive, and simple methods for quantitative analysis of disparities in glycan expression between different biological samples are essential for studies of protein glycosylation patterns (glycomics) and the search for disease glycan biomarkers. Relative quantitation of glycans based on stable isotope labeling combined with mass spectrometric detection represents an emerging and promising technique. However, this technique is undermined by the complexity of mass spectra of isotope-labeled glycans caused by the presence of multiple metal ion adduct signals, which result in a decrease of detection sensitivity and an increase of difficulties in data interpretation. Herein we report a simplified quantitative glycomics strategy, which features nonreductive isotopic labeling of reducing glycans with either nondeuterated (d0-) or deuterated (d5-) Girard's reagent P (GP) without salts introduced and simplified mass spectrometric profiles of d0- and d5-GP derivatives of neutral glycans as molecular ions without complex metal ion adducts, allowing rapid and sensitive quantitative comparison between different glycan samples. We have obtained optimized GP-labeling conditions and good quantitation linearity, reproducibility, and accuracy of data by the method. Its excellent applicability was validated by comparatively quantitative analysis of the neutral N-glycans released from bovine and porcine immunoglobulin G as well as of those from mouse and rat sera. Additionally, we have revealed the potential of this strategy for the high-sensitivity analysis of sialylated glycans as GP derivatives, which involves neutralization of the carboxyl group of sialic acid by chemical derivatization.