Lipid microparticles as a parenteral controlled release device for peptides.

To investigate the potential of physiological lipids as an alternative to synthetic polymeric materials such as poly(lactide-co-glycolide), peptide-containing glyceryl tripalmitate microparticles were prepared. A modified solvent evaporation method and a melt dispersion technique without the use of organic solvent were employed. Thymocartin (TP-4), an immunomodulating tetrapeptide and insulin were chosen as model peptides and incorporated as a solid or dissolved in 100 microl aqueous solution. The resulting microparticles were characterized with respect to particle size and morphology, biocompatibility, drug content (encapsulation efficiency) and in vitro release behavior. Electron spectroscopy for chemical analysis was used to investigate the adsorption of the model peptides to the lipid matrix material. The modified solvent evaporation as well as the melt dispersion method were suitable for the preparation of microparticles in the size range of 20-150 microm with an acceptable yield. The biocompatibility of the glyceryl tripalmitate microparticles after implantation into NMRI-mice was comparable to poly(lactide-co-glycolide) microparticles. The encapsulation efficiency for both model peptides was high (>80%) even at high theoretical loadings when the peptide was incorporated as a solution with the melt dispersion technique. The in vitro release behavior was substantially influenced by the physicochemical properties of the model peptides used in this study.