Stability study of somatropin by capillary zone electrophoresis

Abstract

Human Growth Hormone (hGH) is a monomeric 22 kilo Dalton (kDa), 191 amino acid protein with an isoelectric point (pI) close to pH 5, produced in the anterior pituitary gland. High level production of somatropin (recombinant hGH) is done in Escherichia coli (E. coli) to meet the demand and to avoid possible Creutzfeldt-Jacob disease (CJD).The present study was initiated on the basis of results from post-marketing control of all somatropin preparations on the Norwegian market. The samples consisted of preparations presented as somatropin in solution, and some freeze-dried preparations were also included for comparison.The present study showed a significant degree of degradation of somatropin in solution. Deamidation increased over time for preparations in solution, as well as for freeze-dried preparations after dissolution. Preparations in solution showed high content of deamidated and cleaved forms. Freeze-dried preparations after dissolution and storage showed high content of deamidated forms, but low content of cleaved forms. Also, in one preparation, an unknown peak was detected in the electropherogram from capillary zone electrophoresis (CZE), eluting after the principal peak, in front of the Gln-18 somatropin peak.