Influence of process parameters on the protein stability encapsulated in poly-DL-lactide-poly(ethylene glycol) microspheres

Glucose oxidase (GOD) has been encapsulated as a model protein within poly- DL-lactide-poly(ethylene glycol) (PELA) microspheres to evaluate the activi ty retention during microencapsulation process. This paper was aimed to inv estigate the effect of process parameters, such as the preparation method, the used matrix polymer with different compositions, the solvent system and the addition of stabilizer on the structural integrity and activity retent ion of encapsulated protein. The stability of the protein released during i n vitro assay was also assessed. The obtained results showed that the solve nt extraction/evaporation method based on the Formation of double emulsion w(1)/o/w(2) benefited the activity retention compared with the phase separa tion method based on the formation of w/o(1) /o(2). And in the emulsion-eva poration system most of the protein activity was lost during the first emul sification procedure to form primary emulsion w(1)/o (ca. 28%) and the seco nd emulsification procedure to form the double emulsion w(1)/o/w(2) (ca. 20 %), in contrast to other processes occurring during microspheres preparatio n. The matrix polymer and the solvent system in the oil phase had an impres sive impact on the activity retention, while the addition of gelatin in the internal aqueous phase resulted in no major reduction of activity loss. GO D release from PELA microspheres exhibited a triphasic profile, that is, th e initial burst release during the first day, the gradual release over abou t 1 month, and then the second burst release. The encapsulation of GOD in P ELA microspheres was effective in reducing its specific activity loss. Sixt y-seven per cent of the initial specific activity retention was detected fo r the released GOD from microspheres formulation during 1 week of incubatio n, but nearly all the activity was lost for GOD in solution incubated under the same condition. SDS-PAGE results showed that, although the activity lo ss was detected, no rough changes of molecular weight of GOD was observed d uring encapsulation procedure and the initial days of incubation into the i n vitro release medium. (C) 2000 Elsevier Science B.V. All rights reserved.