Melted glyceryl palmitostearate (GPS) pellets for protein delivery

Lysozyme was incorporated into glyceryl palmitostearate (GPS) pellets by compression and melting at loadings of 2, 5 and 10% (w/w). Released lysozyme from both compressed and melted pellets showed good retention of enzymatic activity (>80% active). The percentage lysozyme recovered during in vitro release experiments, over 120 h, was significantly lower from the melted pellets (<15%) compared with compressed pellets (71-85%). Scanning electron microscopy suggested this difference in release was due to differences in porosity of the compressed and melted pellets. Inclusion of hydrophilic components, PEG 4000 and Gelucire 50/13, in the melted matrices increased the percentage of lysozyme released in vitro. Lysozyme released from GPS/PEG 4000 matrices showed good retention of enzymatic activity (>88% active) while that from GPS/Gelucire 50/13 showed reduced activity (68 and 51% active). PEG 4000 was not completely miscible with GPS at the concentrations studied and heterogenous systems resulted. At a loading of 20-35% (w/w) PEG 4000 in GPS greater than 80% of the incorporated lysozyme was released, indicating the likely achievement of interconnecting hydrophilic channels throughout the GPS matrix. In conclusion, melted GPS demonstrated potential as a matrix for the controlled release of proteins and release rates could be modified by inclusion of hydrophilic components.