The Stabilization and Encapsulation of Human Growth Hormone into Biodegradable Microspheres
Purpose. To produce and evaluate sustained-acting formulations of recombinant human growth hormone (rhGH) made by a novel microencapsulation process.
Methods. The protein was stabilized by forming an insoluble complex with zinc and encapsulated into microspheres of poly (D,L-lactide co-glycolide) (PLGA) which differed in polymer molecular weight (8−3 1kD), polymer end group, and zinc content. The encapsulation procedure was cryogenic, non-aqueous, and did not utilize surfactants or emulsification. The rhGH extracted from each of these microsphere formulations was analyzed by size-exclusion, ion-exchange and reversed-phase chromatography, SDS-polyacrylamide gel electrophoresis, peptide mapping, and cell proliferation of a cell line expressing the hGH receptor. In addition, the in vivorelease profile was determined after subcutaneous administration of the microspheres to rats and juvenile rhesus monkeys.
Results. Protein and bioactivity analyses of the rhGH extracted from three different microsphere formulations showed that the encapsulated protein was unaltered relative to the protein before encapsulation. In vivo, microsphere administration to rats or monkeys induced elevated levels of serum rhGH for up to one month, more than 20-fold longer than was induced by the same amount of protein injected subcutaneously as a solution. The rate of protein release differed between the three microsphere formulations and was determined by the molecular weight and hydrophobicity of the PLGA. The serum rhGH profile, after three sequential monthly doses of the one formulation examined, was reproducible and showed no dose accumulation.
Conclusions. Using a novel process, rhGH can be stabilized and encapsulated in a solid state into PLGA microspheres and released with unaltered properties at different rates.
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