title: Microencapsulation of human growth hormone within biodegradable polyester microspheres: protein aggregation stability and incomplete release mechanism.
abstract: Recombinant human growth hormone (rhGH) was encapsulated within poly(D,L-lactic-co-glycolic acid) microspheres by a double emulsion solvent evaporation method. A mixture of methylene chloride and ethyl acetate in varying volume ratios was used for the microsphere preparation. Protein release profiles from three different microsphere formulations demonstrated initial burst effects ranging from 28.2% to 54.7% after a 1-day incubation and exhibited no further significant releases up to 19 days. This was because the encapsulated rhGH with the microspheres was largely aggregated in a noncovalent fashion during the formulation. Nonaggregated water soluble rhGH species within the microspheres are likely to be responsible for the rapid release upon incubation. The initially released rhGH in the incubation medium, however, was composed of mostly monomer species with a small amount of dimer as probed by size-exclusion chromatography. Circular dichroism spectra of the initially released rhGH in the medium revealed that the conformation of the released rhGH was correctly folded relative to that of native rhGH, with little variation in alpha-helix contents depending on the formulations. The "nonrelease" mechanism after the initial burst release was attributed to nonspontaneously dissociable noncovalent protein aggregation and surface adsorption of rhGH present within the microspheres.
authors.affiliation: Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Taejon, 305-701, South Korea.
authors.forename: H K
authors.initials: HK
authors.lastname: Kim
authors.forename: T G
authors.initials: TG
authors.lastname: Park
mesh_terms: D000085:Acetates / Q000378:metabolism; D000327:Adsorption / Q000187:drug effects; D001672:Biocompatible Materials / Q000737:chemistry / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D003692:Delayed-Action Preparations; D019281:Dimerization; D004337:Drug Carriers / Q000737:chemistry / Q000378:metabolism; D004339:Drug Compounding; D005612:Freeze Drying; D019791:Guanidine / Q000494:pharmacology; D019382:Human Growth Hormone / Q000008:administration & dosage* / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D019344:Lactic Acid / Q000737:chemistry / Q000378:metabolism; D008752:Methylene Chloride / Q000378:metabolism; D008863:Microspheres; D011091:Polyesters / Q000737:chemistry / Q000378:metabolism; D011100:Polyglycolic Acid / Q000737:chemistry / Q000378:metabolism; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D012995:Solubility / Q000187:drug effects
chemical_list: D000085:Acetates; D001672:Biocompatible Materials; D003692:Delayed-Action Preparations; D004337:Drug Carriers; D011091:Polyesters; D011108:Polymers; D019382:Human Growth Hormone; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D019344:Lactic Acid; D012967:Sodium Dodecyl Sulfate; D008752:Methylene Chloride; C007650:ethyl acetate; D019791:Guanidine