Monolithic triglyceride matrices: a controlled-release system for proteins

Matrices made of glyceryl trimyristate as a bioerodible and biocompatible material were manufactured by compression in dimensions that would still allow an application via injection. Pyranine, as a low molecular hydrophilic compound with a low detection limit, and tetramethylrhodamine labeled bovine serum albumin (TAMRA-BSA), as a high molecular weight (66 kDa) protein compound, served as model drugs for release investigations. In vitro studies with pyranine revealed that release depends substantially on the gelatin content of the matrices, which proved to be a useful tool as a release modifier. The duration of the drug release period can be adjusted to a desired time interval ranging from days to weeks by choosing the right gelatin content. Moreover, results illustrated the importance of the molecular weight and the nature of the compound to be incorporated into such matrices, since investigations with TAMRA-BSA showed a more pronounced burst release and altered release profiles and periods. Experiments with hyaluronidase, which served as a model enzyme to assess the problem of protein integrity in such matrices, suggested that proteins may display sufficient stability during the manufacturing procedure of the cylinders or while in contact with the triglyceride matrices. In addition to in vitro investigations, a study in mice revealed that after 15 days of subcutaneous implantation the matrices showed a good in vivo stability. The main conclusion that could be drawn from these results was that triglycerides are a promising alternative to biodegradable polymers for the development of parenteral release systems for protein and peptide drugs.