Modes of degradation and impurity characterization in rhPTH (1-34) during stability studies

摘要

During storage of recombinant human parathyroid hormone (rhPTH) (amino acid residues 1-34) at 25 ± 2°C, several impurities were obtained, which were detected by the tricine sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and reversed-phase high-performance liquid chromatography (RP-HPLC) methods. To characterize the impurities generated, forceful chemical oxidation and deamidation was done. The oxidized positions were characterized by cyanogen bromide (CNBr) cleavage followed by liquid chromatography/mass spectrometry (LCMS) and further confirmed through N-terminal sequencing. Three oxidized variants were observed: sulfoxide of Met8 and Met18 and a variant comprising sulfoxide forms of both the methionine residues. LCMS results confirmed the presence of deamidated (+1 Da) and succinimide (-17 Da) variants. The low molecular weight impurities observed by tricine SDS-PAGE was confirmed to be peptide fragments by N-terminal sequencing and LCMS, resulting from cleavage at the C-terminal of asparagine (Asn)16, Asn33, and Asp30. Studies showed that rhPTH (1-34) undergoes oxidation, deamidation, and peptide bond cleavage during storage at pH 4.0 in acetate buffer.