INCREASED STABILIZING EFFECTS OF AMPHIPHILIC EXCIPIENTS ON FREEZE-DRYING OF LACTATE-DEHYDROGENASE (LDH) BY DISPERSION INTO SUGAR MATRICES

Purpose. The stabilizing effect of amphiphilic excipients and sugars a gainst protein inactivation during freeze-drying was studied in relati on to their physical states in freeze-dried cakes. Methods. Physical s tates of amphiphilic excipients were studied by powder X-ray diffracto metry and differential scanning calorimetry (DSC). Stabilizing effects of excipients were studied using lactate dehydrogenase (LDH) as a mod el protein. Results. Although poly(ethylene glycols) (PEGs) 1000 to 20 000 crystallized when freeze-dried alone, the addition of sugars decre ased their crystallinity by dispersing PEG into sugar-dominant matrice s. Sugars species, molecular weight of PEGs, and buffer concentration also affected the crystallinity of PEGs. Sugars also dispersed some of other amphiphilic excipients, which tended to crystallize or become ' 'microscopically liquid'' when freeze-dried without sugar. Only the am phiphilic excipients that remained amorphous solid state protected the enzyme during freeze-drying in the absence of sugars. However, combin ations of sucrose and all the amphiphilic excipients studied increased the stabilizing effects markedly. The remaining activities were great er than the sum of their individual ones. Conclusions. Various amphiph ilic excipients are good stabilizers for freeze-drying of proteins whe n dispersed into sugar-dominant matrices.