title: Protein quantity on the air-solid interface determines degradation rates of human growth hormone in lyophilized samples.
abstract: Recombinant human growth hormone (rhGH) was lyophilized with various glass-forming stabilizers, employing cycles that incorporated various freezing and annealing procedures to manipulate glass formation kinetics, associated relaxation processes, and glass-specific surface areas (SSAs). The secondary structure in the cake was monitored by infrared and in reconstituted samples by circular dichroism. The rhGH concentrations on the surface of lyophilized powders were determined from electron spectroscopy for chemical analysis. Glass transition temperature (Tg ), SSAs, and water contents were determined immediately after lyophilization. Lyophilized samples were incubated at 323 K for 16 weeks, and the resulting extents of rhGH aggregation, oxidation, and deamidation were determined after rehydration. Water contents and Tg were independent of lyophilization process parameters. Compared with samples lyophilized after rapid freezing, rhGH in samples that had been annealed in frozen solids prior to drying, or annealed in glassy solids after secondary drying retained more native-like protein secondary structure, had a smaller fraction of the protein on the surface of the cake, and exhibited lower levels of degradation during incubation. A simple kinetic model suggested that the differences in the extent of rhGH degradation during storage in the dried state between different formulations and processing methods could largely be ascribed to the associated levels of rhGH at the solid-air interface after lyophilization.
authors.affiliation: Center for Pharmaceutical Biotechnology, Department of Biochemistry, University of Colorado, Boulder, Colorado, 80309.
authors.forename: Yemin
authors.initials: Y
authors.lastname: Xu
authors.forename: Pawel
authors.initials: P
authors.lastname: Grobelny
authors.forename: Alexander
authors.initials: A
authors.lastname: Von Allmen
authors.forename: Korben
authors.initials: K
authors.lastname: Knudson
authors.forename: Michael
authors.initials: M
authors.lastname: Pikal
authors.forename: John F
authors.initials: JF
authors.lastname: Carpenter
authors.forename: Theodore W
authors.initials: TW
authors.lastname: Randolph
mesh_terms: D002626:Chemistry, Pharmaceutical / Q000379:methods; D002942:Circular Dichroism / Q000379:methods; D004355:Drug Stability; D005612:Freeze Drying / Q000379:methods; D005898:Glass / Q000737:chemistry; D019382:Human Growth Hormone / Q000737:chemistry*; D006801:Humans; D011208:Powders / Q000737:chemistry; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry*; D044366:Transition Temperature; D014867:Water / Q000737:chemistry
chemical_list: D011208:Powders; D011994:Recombinant Proteins; D014867:Water; D019382:Human Growth Hormone
keywords: annealing; growth hormone; lyophilization; mobility; protein formulation; protein structure; specific surface area; stability; surface degradation