A Simple Strategy to Eliminate Hexosylation Bias in the Relative Quantification of N-Glycosylation in Biopharmaceuticals.

N-glycosylation may affect the safety and efficacy of biopharmaceuticals and is thus monitored during manufacturing. Mass spectrometry of the intact protein is increasingly used to reveal co-existing glycosylation variants. However, quantification of N-glycoforms via this approach may be biased by single hexose residues as introduced by glycation or O-glycosylation. Herein, we describe a simple strategy to reveal actual N-glycoform abundances of therapeutic antibodies, involving experimental determination of glycation levels followed by computational elimination of the "hexosylation bias". We show that actual N-glycoform abundances may significantly deviate from initially determined values. Indeed, glycation may even obscure considerable differences in N-glycosylation patterns of drug product batches. Our observations may thus have implications for biopharmaceutical quality control. Moreover, we solve an instance of the problem of isobaricity, which is fundamental to mass spectrometry.