Influence of PEGylation on the release of low and high molecular-weight proteins from PVA matrices

Model proteins of therapeutic interest, ribonuclease, superoxide dismutase, catalase and albumin, extensively PEGylated with linear 5,000 Mw PEG, were entrapped in PVA hydrogels (31,000-50,000 Mw) by means of a cryogel procedure and the rate of release was evaluated. All of the PEGylated proteins were released from the gel, but at a lower rate than the unmodified proteins. The rate for both native and PEGylated species decreases as the molecular weight of the protein increased. Moreover, for both native and PEGylated proteins, the release rate was reduced when the gel was lyophilized before the release evaluation. Release was also dependent on the PVA Mw, in fact, for Mw's of 124,000-186,000, permanent entrapment was achieved. This behaviour was verified with PEGylated glucose oxidase and coline oxidase which were permanently retained in high Mw PVA. This study indicates the potential for the combination of PEGylation and cryogel entrapment of enzymes for the biotechnological and therapeutic applications.