Conformational stability of a model protein (bovine serum albumin) during primary emulsification process of PLGA microspheres synthesis

The goal of this study was to investigate the conformational stability of a model protein, bovine serum albumin (BSA), during the primary emulsification process of poly(D,L-lactide-co-glycolide) (PLGA) microspheres preparation. Differential scanning calorimeter (DSC) was utilized to assess the conformational structure of BSA during primary emulsification in the presence and absence of PLGA. Three excipients [i.e. mannitol, hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and sodium dodecyl sulfate (SDS)] were investigated for their stabilizing effect on BSA during emulsification process. The DSC profile of intact BSA was best fitted by a non-2-state model with two peaks, which have midpoint temperatures (T-m1, 60.9 +/- 0.4degreesC and T-m2, 66.4 +/- 1.0degreesC), respectively, and a total calorimetric enthalpy DeltaH(tot) of 599 +/- 42kJ/mol. After emulsifying BSA aqueous solution with methylene chloride, an additional apparent peak at a higher temperature was observed. The T-m of this peak was 77.4 +/- 0.8 degreesC. HP-beta-CD was able to suppress the occurrence of an additional peak, whereas mannitol failed. SDS increased the thermal stability of BSA dramatically. Furthermore, HP-beta-CD increased BSA recovery from 72 +/- 8% to 89 +/- 7% after extraction from w/o in the presence of PLGA. These results provided evidence that HP-P-CD could be a promising excipient for conformational stability of BSA during synthesis of PLGA microspheres. (C) 2003 Elsevier Science B.V. All rights reserved.