The effect of carbohydrate additives in the freeze-drying of alkaline phosphatase

Alkaline phosphatase was used as a model in studies to assess the effects of lyophilization on biological activity and molecular integrity in the presence or absence of added carbohydrate. The stability of the activity of alkaline phosphatase, lyophilized in Tris buffer alone or in the presence of the carbohydrates mannitol, lactose or trehalose was examined. Enzyme activity in formulations with Tris buffer alone or with mannitol was considerably reduced by freeze-drying and further storage at elevated temperatures; freeze-drying with mannitol failed to maintain activity at a temperature of 37 degrees C over 21 days, whilst the loss of activity was more gradual when freeze-dried in buffer alone and stored at higher temperatures. Lactose and trehalose maintained the alkaline phosphatase activity after freeze-drying and, furthermore, preparations containing trehalose retained activity even when the material was subjected to temperatures of up to 45 degrees C for up to 84 days. At 56 degrees C the alkaline phosphatase activity did not show a significant drop until 14 days with the lactose formulation or until 21 days with trehalose. After 84 days at 56 degrees C, 30% of the activity still remained in the formulation containing trehalose. In addition to the changes in the enzyme activity, FPLC chromatographic traces and SDS-PAGE gels demonstrated compositional differences between each formulation after storage.