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

Abstract

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-β-cyclodextrin (HP-β-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±0.4 °C and T m2, 66.4±1.0 °C), respectively, and a total calorimetric enthalpy Δ H tot of 599±42 kJ/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 °C. HP-β-CD was able to suppress the occurrence of an additional peak, whereas mannitol failed. SDS increased the thermal stability of BSA dramatically. Furthermore, HP-β-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-β-CD could be a promising excipient for conformational stability of BSA during synthesis of PLGA microspheres.