Stability of BSA encapsulated into PLGA microspheres using PAGE and capillary electrophoresis

Bovine serum albumin (BSA, M-w 66200 Da) has been encapsulated as a model protein drug within poly(D,L-lactide-co-glycolide) (PLGA 50:50) microspheres using a w/o/w double emulsion method. The microspheres prepared were smooth and spherical with a mean particle size of 1.32 mu m. The total protein loading and surface-associated protein were 8.61 and 16.60%, respectively. The microspheres showed a triphasic in vitro release profile with an initial burst effect due to the release of the protein adsorbed on the microsphere surface, a second sustained release phase due to protein diffusion through the pores or channels formed in the polymer matrix, and a third phase due to polymer bioerosion. The purpose of this paper was to evaluate the effect of the microencapsulation process on the integrity of the entrapped protein using polyacrylamide gel electrophoresis and capillary electrophoresis. The stability of the protein released during in vitro assays was also assessed. The results obtained showed that there was no apparent effect of the drastic encapsulation conditions (contact with dichloromethane (DCM), probe sonication, and vigorous shaking) on the structural integrity of the protein. On the other hand, it was found that after 1 week of incubation the protein released from the microspheres starts to hydrolyze to smaller fragments, probably due to a significant decrease in the medium pH as a result of the accumulation of the polymer degradation products. (C) 1998 Elsevier Science B.V. All rights reserved.