Stability of human growth hormone in supercritical carbon dioxide.

The instability of human growth hormone (hGH) to temperature and interfaces makes its formulation into injectable, sustained-release drug delivery systems challenging. A novel method of encapsulating hGH in polymeric microparticles has been developed using supercritical CO(2) (scCO(2)) technology, but there is limited understanding of the stability of hGH within this system. The aim of this study was to evaluate the stability of hGH in scCO(2) processing. The integrity of the protein was assessed following exposure to scCO(2) using a range of different analytical techniques. Mass spectrometry showed that no peptide cleavage occurred as a result of processing or exposure to scCO(2). Size-exclusion chromatography detected formation of aggregates at high temperatures, but not as a result of the encapsulation process. Reverse-phase chromatography demonstrated that the production of deamidation products occurred as a function of temperature, but only at temperatures higher than those used for the encapsulation process. Circular dichroism and infrared spectroscopy demonstrated that the use of scCO(2) was not detrimental to the secondary molecular structure of hGH. Together, these results show that the structural integrity of hGH is unaffected by scCO(2) processing and that hGH can be successfully encapsulated in polymer microparticles using this technique.