Characterization and in vivo study of sustained-release formulation of human growth hormone using sodium hyaluronate.

Abstract

Aiming at once-a-week injection, a novel sustained release formulation of recombinant human growth hormone (SR-hGH) using sodium hyaluronate was developed for the treatment of children who have growth failure due to the lack of adequate secretion of endogenous growth hormone. SR-hGH was produced in the form of solid microparticle using a Niro spray dryer and characterized by Malvern particle size analysis, scanning electron microscopy (SEM), size exclusion chromatography (SEC), reverse phase-high-performance chromatography (RP-HPLC), and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). After in vitro release test, pharmacokinetic and pharmacodynamic studies were carried out in beagle dogs. SR-hGH was dispersed in medium-chain triglyceride (MCT) and administered at a dose of 1.0 mg hGH/kg subcutaneously. SR-hGH microparticles were successfully produced with a mean particle size of 5.6+/-1.0 microm. Physicochemical analysis with SEC, RP-HPLC, and SDS-PAGE showed that hGH extracted from SR-hGH was intact and comparable to that of hGH bulk standard indicating no structural change in hGH during the formulation processes. Monomeric content of hGH recovered from SR-hGH was 97.4% by SEC analysis, and its purity was 96% by RP-HPLC analysis. In vitro release test showed the sustained-release characteristics of SR-hGH up to 48 h with the complete release of hGH loaded. The continuous and monotonous release profile observed in in vitro release test was supported by pharmacokinetic study in beagle dogs. Delayed absorption of hGH was observed with Cmax of 69.5+/-8.0 ng/ml and Tmax between 10 and 12 h. The administration of SR-hGH induced elevation of serum insulin-like growth factor-I (IGF-I) level for 6 days with a maximum value higher than the predose level by ca. 350 ng/ml. After 6 days, IGF-I level returned to the initial baseline level. Sustained-release formulation of hGH for once-a-week injection was successfully developed using high-molecular-weight sodium hyaluronate. No adverse effect was observed during and after the in vivo test using beagle dogs.