Analysis of recombinant human follicle-stimulating hormone (FSH) by mass spectrometric approaches

Recombinant human follicle stimulating hormone is an important drug in reproductive medicine. Thorough analysis of the heterodimeric heavily glycosylated protein is a prerequisite for the evaluation of production batches as well as for the determination of essential similarity of new biosimilars. The concerted application of different liquid chromatography-mass spectrometry methods enabled the complete depiction of the primary structure of this pituitary hormone. Sequence coverage of 100% for the alpha- as well as the beta-chain was achieved with tryptic peptides. Most of these peptides could be verified by tandem mass spectrometry. Site-specific analysis of all four glycosylation sites was, however, not possible with tryptic but with chymotryptic peptides. Quantification of the glycoforms of each glycopeptide was accomplished with the software MassMapA (R). Both protein subunits gave interpretable mass spectra upon S-alkylation and separation on a C5 reversed-phase column. Glycan isomer patterns were depicted by separation on porous graphitic carbon, using mass spectrometric detection for the evaluation of the glycopeptide liquid chromatography-electrospray ionization data. The currently marketed product Gonal-f (TM) and a potential biosimilar were compared with the help of these procedures.