A Study on a Method for Evaluating Glycans in Biopharmaceuticals - Part 2 – Comparison of various pretreatment methods for N-Glycan Analysis –

Importance of the Topic

Glycan structures attached to therapeutic glycoproteins play a critical role in their stability, activity and immunogenicity. Monitoring N-glycan profiles during biopharmaceutical development and manufacturing ensures consistent product quality and prevents unexpected alterations in efficacy or safety. Robust and standardized pretreatment, labeling and analysis workflows are essential to achieve reliable glycan characterization.

Objectives and Study Overview

This study compared common pretreatment methods for free N-glycan purification, evaluated labeling conditions using two fluorescent tags, and assessed techniques to remove excess derivatization reagents. Three model glycoproteins (human IgG, RNase B and α1-acid glycoprotein) provided representative neutral and sialylated glycan substrates. Key goals included:

• Assessing reverse-phase SPE, graphitized carbon SPE, ultrafiltration, ethanol precipitation and no-purification approaches.
• Comparing 2-aminobenzamide (2-AB) and 2-aminobenzoic acid (2-AA) labeling at different temperatures and durations.
• Evaluating hydrophilic SPE, gel filtration and acetone precipitation to remove excess labeling reagents.
• Characterizing glycan profiles by MALDI-TOF MS and HILIC-LC with fluorescence detection.

Methodology and Instrumentation

• Release of N-glycans: Denaturation with SDS/DTT, nonionic surfactant, overnight PNGase F digestion at 37 °C.
• Free glycan purification: Five workflows including Oasis HLB and Supelclean ENVI-Carb SPE cartridges, ultrafiltration membranes (10 kDa/30 kDa), ethanol precipitation or direct dried samples.
• Fluorescent labeling: 2-AB or 2-AA with sodium cyanoborohydride in DMSO/acetic acid, reactions at 37 °C (18 h), 65 °C (3 h) or 80 °C (1 h).
• Excess reagent removal: HILIC SPE (Oasis HLB), gel filtration (PD MiniTrap G-10) or acetone precipitation.
• Analysis platforms:
  • MALDI-TOF MS: Shimadzu MALDI-8020, DHB matrix, detection of H+ and Na+ adducts.
  • LC-FLR: Shimadzu Nexera X2 UHPLC, TSKgel Amide-80 HILIC column, fluorescence detection (Ex/Em 330/420 nm for 2-AB; 350/425 nm for 2-AA).

Main Results and Discussion

• Free Glycan Purification:
  • Neutral glycans (IgG, RNase B) yielded consistent MALDI and LC profiles across all methods.
  • Sialylated glycans (α1-acid glycoprotein) showed reduced recovery and sodium adduct formation with ultrafiltration; graphitized carbon SPE and ethanol precipitation led to unlabeled species; HLB SPE provided highest fidelity.
  • When pre-desalting glycoprotein (PD-10), direct derivatization without further purification gave acceptable results.
• Glycan Labeling Conditions:
  • 2-AB and 2-AA labeling at high temperatures (65 °C, 80 °C) caused partial sialic acid loss in heavily sialylated glycans.
  • Extended low-temperature reaction (37 °C, 18 h) preserved labile acidic structures while maintaining labeling efficiency.
  • 2-AA labeled glycans exhibited poor separation on HILIC-amide, unlike 2-AB derivatives.
• Excess Reagent Removal:
  • HILIC SPE, gel filtration and acetone precipitation delivered nearly identical glycan distributions by LC.
  • No-purification of 2-AB labeled samples was possible at similar sample density, but purification improved baseline stability.

Benefits and Practical Applications

• Optimized use of HLB SPE streamlines free glycan cleanup, minimizes loss of sialylated species and avoids unlabeled byproducts.
• Low-temperature prolonged labeling ensures accurate profiling of acidic glycans without extended high-heat incubation.
• Selection of cleanup method for derivatized glycans can be tailored to throughput and cost; acetone precipitation offers a simple alternative.
• Combined MALDI-TOF and HILIC-LC-FLR provides complementary mass and quantitative information for QA/QC in biopharma.

Future Trends and Potential Applications

• Automation of SPE and labeling steps to increase throughput and reduce variability in glycan analysis pipelines.
• Development of novel labeling chemistries or tags with improved fluorescence yield and MS response.
• Integration of microfluidic deglycosylation and cleanup modules for online LC-MS glycomics.
• Standardization of pretreatment and labeling protocols across laboratories to enable robust regulatory compliance.

Conclusion

Systematic comparison of pretreatment, labeling and cleanup methods identified HLB SPE and low-temperature extended fluorescent tagging as versatile strategies for accurate N-glycan profiling. These optimized workflows support reliable quality control of glycoprotein therapeutics.