Pegylation enhances protein stability during encapsulation in PLGA microspheres

During encapsulation of proteins in biodegradable microspheres. a significa nt amount of the protein reportedly undergoes denaturation to form irrevers ible insoluble aggregates. incomplete in vitro release of proteins from the microspheres is a common observation. An attempt was made to overcome this problem by pegylation of the protein to be encapsulated. Lysozyme, a model protein, was conjugated with methoxy polyethylene glycol (mPEG, MW 5000). The conjugate was characterized by SDS-PAGE. SE-HPLC, and MALDI-TOF mass sp ectroscopy. The pegylated lysozyme (Lys-mPEG) consisted of different isomer s of mono-, di- and tri-pegylated with about 15% as native lysozyme. The sp ecific activity of the protein was retained after pegylation (101.3 +/- 10. 4%). The microsphere encapsulation process was simulated for psgylated and native lysozyme. Pegylated lysozyme exhibited much better stability than na tive lysozyme against exposure to organic solvent (dichloromethane), homoge nization, and showed reduced adsorption onto the surface of blank PLGA micr ospheres. Release profiles of the two proteins from microspheres were very different. For native lysozyme, it was high initial release (about 50%) fol lowed by a nearly no release (about 10% in 50 days). In contrast, Lys-mPEG conjugate showed a triphasic and near complete release over 83 days. This s tudy shows that the pegylation of protein can provide substantial protectio n against the destabilization of protein during encapsulation. (C) 2001 Els evier Science B.V. All rights reserved.