Shigeyuki Takada

Sustained release of human growth hormone from microcapsules prepared by a solvent evaporation technique.

Biodegradable microcapsules for sustained release of recombinant human growth hormone (rhGH) were prepared by a solid-in-oil-in-water (S/O/W) emulsion solvent evaporation technique using lyophilized protein microparticles. The minimum mean particle size of rhGH in S/O dispersions was 2.8-3.0 microm when ammonium acetate was added at molar ratios of 10-20 times against rhGH. High entrapment of rhGH in microcapsules was achieved by incorporating rhGH powder with a smaller particle size obtained by lyophilizing with ammonium acetate. As the particle size of rhGH decreased, the in vivo initial release decreased, while subsequent serum levels of rhGH in sustained release phase were higher. Addition of zinc oxide to microcapsules resulted in higher serum levels than those prepared without zinc oxide, suggesting a stabilizing effect of zinc oxide after subcutaneous injection into rats. The release profile of rhGH from microcapsules was controllable by selecting the proper copoly(DL-lactic/glycolic)acid (PLGA) with L/G ratio and molecular weight. Utilization of rhGH powder with a smaller particle size obtained by lyophilizing with ammonium acetate is essential for preparation of microcapsules with high entrapment and well-controlled sustained release profile with small initial release.

Utilization of an amorphous form of a water-soluble GPIIb/IIIa antagonist for controlled release from biodegradable microspheres.

AbstractPurpose. We prepared injectable microspheres for controlled release of TAK-029, a water-soluble GPIIb/IIIa antagonist and discussed the characteristics of controlled release from microspheres. Methods. Copoly(dl-lactic/glycolic)acid (PLGA) microspheres were used for controlled release of TAK-029 [4-(4-amidinobenzoylglycyl)-3-methoxycarbonyl-2-oxopiperazine-l-acetic acid]. They were prepared with a solid-in-oil-in-water (S/O/W) emulsion solvent evaporation technique using either a crystalline form or an amorphous form of the drug. Results. An amorphous form of TAK-029 gave more homogeneous S/O dispersion and higher viscosity than its crystalline form when added to dichloromethane solution of PLGA, resulting in a high drug entrapment into microspheres and a well-controlled release of the drug. Additions of sodium chloride into an external aqueous phase and L-arginine into an oil phase also increased entrapment of the drug, and reduced initial burst of the drug from the microspheres. The micro-spheres demonstrated a desirable plasma level profile in therapeutic range (20−100 ng/ml) for 3 weeks in rats after single subcutaneous injection. Conclusions. A well-controlled release of TAK-029, a water-soluble neutral drug, with small initial burst was achieved by utilizing its amorphous form as a result of possible interaction with PLGA and L-arginine.

Preparation of a copoly (dl-lactic/glycolic acid)-zinc oxide complex and its utilization to microcapsules containing recombinant human growth hormone

A procedure to prepare a complex of copoly (dl-lactic/glycolic acid) and zinc oxide (PLGA-zinc oxide complex) was developed. Out of sparingly water-soluble zinc compounds, zinc oxide was most remarkably soluble in a PLGA/dichloromethane solution and the dissolution rates became faster as the water contents in the PLGA/dichloromethane solutions increased. Since the solubility of zinc oxide was saturated at approximately 0.5-fold molar ratio to PLGA and water was generated with dissolution of zinc oxide in the PLGA/dichloromethane solutions, it is suggested that zinc oxide interacts with the terminal carboxyl group of PLGA. In addition, the glass-transition temperature of a solid material obtained by vacuum-drying the PLGA/dichloromethane solution dissolving zinc oxide became higher as the zinc content increased, suggesting that the formation of a PLGA-zinc oxide complex. Microcapsules were prepared with the PLGA-zinc oxide complex using recombinant human growth hormone (rhGH) in order to evaluate an effect of the complex on protein release and stability of protein in the microcapsules. Released rhGH amount from the microcapsules prepared with the PLGA-zinc oxide complex after subcutaneous administration in rats was significantly larger than that from microcapsules prepared with PLGA alone, indicating that rhGH molecules in the microcapsules was stabilized by the PLGA-zinc oxide complex.

Sustained release of a water-soluble GP IIb/IIIa antagonist from copoly(dl-lactic/glycolic)acid microspheres

Sustained release of TAK-029 [4-(4-amidinobenzoylglycyl)-3-methoxycarbonyl-2-oxopiperazine-l-acetic acid], a glycoprotein (GP) IIb/IIIa antagonist, from injectable microspheres was achieved by a W/O/W emulsion solvent evaporation technique using copoly(d-lactic/glycolic)acid (PLGA). Entrapment of the drug into microspheres increased with addition of sodium chloride into an external aqueous polyvinyl alcohol solution. Addition of l-arginine to an internal water phase dose-dependently reduced initial burst of the drug from the microspheres in vitro and in vivo, probably by forming hydrophobic diffusion barriers with rigid inner structure and increased glass transition temperature (Tg). Microspheres obtained using sodium chloride and l-arginine demonstrated sustained plasma levels of TAK-029 for 3 weeks after subcutaneous injection in rats, while causing a slight increase of its plasma levels in 2–3 weeks.

A new animal model for evaluation of long-term growth rate over one month by rhGH/PLGA microcapsule formulations

A new animal model to evaluate the long‐term growth rate produced by a sustained‐release formulation of recombinant human growth hormone (rhGH) over one month was developed and the usefulness of our microcapsule formulations was demonstrated in this model. Long‐term pharmacological effects by subcutaneous injection of microcapsules for sustained release of rhGH were evaluated in hypophysectomized (Hpx) rats treated with immunosuppressive agent along with hormone supplement. Copoly(dl‐lactic/glycolic)acid (PLGA) microcapsules for sustained release of rhGH, a two‐week sustained‐release formulation (rhGH‐SR‐2W) and a one‐month sustained‐release formulation (rhGH‐SR‐1M), were prepared by a solid‐in‐oil‐in‐water emulsion solvent evaporation technique. Body‐weight gain, body‐length gain and serum levels of rat insulin‐like growth factor‐l (rlGF‐l) induced by subcutaneous injection of rhGH‐SR were compared with those by daily injections of rhGH solution in Hpx rats for 35 days. Serum IGF‐l levels in Hpx rats after the injection of rhGH‐SR‐2W microcapsules were higher than those after daily injections of rhGH solution. Body‐length gain, a new parameter, after single injection of rhGH‐SR‐1M microcapsules demonstrated the higher growth rate than that after daily injections of rhGH solution for 35 days. Thus, single injection of rhGH‐SR microcapsules demonstrated long‐term pharmacological effects greater than those by daily injections of rhGH solution in a newly developed model, immunosuppressed Hpx rats.