Elucidating the Complexities of the Human Milk Glycomewith Ion Chromatography-Mass Spectrometry (IC-MS)

Significance of the Topic

Glycans in human milk are vital for infant health, influencing immune function, gut microbiota, and nutrition. Their structural diversity—encompassing free oligosaccharides and N-/O-linked glycans on proteins—presents analytical challenges. A high-resolution, derivatization-free method enhances our ability to characterize these molecules and understand their biological roles.

Objectives and Overview of the Study

This work establishes a novel ion chromatography–mass spectrometry (IC-MS) workflow for comprehensive, derivatization-free analysis of the human milk glycome. Key aims include:

• Profiling free human milk oligosaccharides (HMOs)
• Characterizing N-linked and O-linked glycan structures
• Resolving isomeric, neutral, fucosylated, and sialylated species

Methodology

Sample Preparation:
Milk from three donors was centrifuged to separate aqueous (HMOs) and protein fractions. N-glycans were released by PNGase F digestion; O-glycans by beta-elimination. All glycans were purified via HyperSep Hypercarb filter plates and reconstituted in water.

Chromatography and MS Analysis:
Anion exchange separation on a CarboPac PA300-4 µm column was performed using a Dionex ICS-6000 HPIC system. The effluent passed through a pulsed amperometric detector (PAD), an electrolytic desalter (Dionex ERD 500) for salt removal, and into a Q Exactive HF-X Orbitrap MS with HESI-II in negative mode. Full scans (400–2000 m/z) and MS² (data-dependent) provided high-accuracy mass and fragment data for structural elucidation.

Used Instrumentation

• Thermo Scientific Dionex ICS-6000 HPIC system
• CarboPac PA300-4 µm anion exchange column
• Pulsed amperometric detector (PAD)
• Dionex ERD 500 electrolytically regenerated desalter
• Q Exactive HF-X Hybrid Quadrupole-Orbitrap mass spectrometer with HESI-II source
• Software: Chromeleon CDS, Xcalibur, SimGlycan, UniCarb-DB, GlycoWorkbench

Main Results and Discussion

The platform detected 75 free HMOs, with neutral and fucosylated species eluting early, monosialylated later, and disialylated last. Chromatographic resolution enabled differentiation of isomers such as Lacto-N-neotetraose and Lacto-N-tetraose through diagnostic MS² fragments. N-glycan profiling identified 20 structures, covering neutral, fucosylated, sialylated, and hybrid types with distinct elution patterns. O-glycan analysis, without derivatization, revealed six structures with clear extracted ion chromatograms.

Benefits and Practical Applications

The derivatization-free IC-MS workflow provides:

• High-resolution separation of compositionally similar glycans
• Sequential electrochemical and mass detection for comprehensive profiling
• Isomer discrimination without enrichment or labeling steps

This approach supports glycomics research in infant nutrition, quality control in dairy products, and biomarker discovery.

Future Trends and Potential Applications

Future enhancements may integrate ion mobility to further resolve isomers, automate sample preparation for higher throughput, and extend analysis to clinical diagnostics. The method could be applied to monitor glycan changes across lactation stages and in other biological fluids.

Conclusion

A robust, derivatization-free IC-MS platform has been demonstrated for detailed structural analysis of human milk glycans. Coupling high-resolution anion exchange chromatography with sequential PAD-MS detection enables comprehensive characterization of free oligosaccharides and protein-linked glycans, advancing our understanding of milk glycosylation and its biological impact.

References

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2. Lu Y., et al. Mass spectrometry analysis of changes in human milk N/O-glycopatterns at different lactation stages. Journal of Agricultural and Food Chemistry. 67(38):10702–10712 (2019).
3. Ceroni A., et al. GlycoWorkbench: A tool for the computer-assisted annotation of mass spectra of glycans. Journal of Proteome Research. 7:1650–1659 (2008).
4. Domon B., Costello C.E. A systematic nomenclature for carbohydrate fragmentations in FAB-MS/MS spectra of glycoconjugates. Glycoconjugate Journal. 5:397–409 (1988).