The effect of water plasticization on the molecular mobility and crystallization tendency of amorphous disaccharides.

PURPOSE: To study how water plasticization affects the molecular mobility and crystallization tendency of freeze-dried trehalose, sucrose, melibiose and cellobiose. METHODS: Freeze-dried disaccharides were subjected to different relative humidity atmospheres and their physical stabilities were evaluated. Lyophilizate water sorption tendencies and glass transition temperatures were modeled using Brunauer-Emmett-Teller (BET) and Gordon-Taylor (GT) equations, respectively. Sucrose and cellobiose crystallization tendencies were compared by using the concept of reduced crystallization temperature (RCT), and the molecular mobilities of trehalose and melibiose were compared by measuring their T(1)H relaxation time constants. RESULTS: Based on the BET and GT models, water sorption tendency and the resulting plasticizing effect were different in sucrose when compared to the other disaccharides. Trehalose and melibiose exhibited generally slower crystallization rates when compared to sucrose and cellobiose. Amorphous melibiose was shown to be particularly stable within the studied water content range, which may have partly been caused by its relatively slow molecular mobility. CONCLUSIONS: Slow amorphous-to-crystalline transition rate is known to be important for lyoprotecting excipients when formulating a robust drug product. The physical stabilities of amorphous trehalose and melibiose even with relatively high water contents might make their use advantageous in this respect compared to sucrose and cellobiose.

The use of disaccharides in inhibiting enzymatic activity loss and secondary structure changes in freeze-dried ß-galactosidase during storage.

PURPOSE: The purpose of this study is to show how disaccharides differ in their ability to protect lyophilized ß-galactosidase from enzymatic activity loss and secondary structure changes during storage. METHODS: ß-galactosidase was lyophilized with trehalose, sucrose, cellobiose or melibiose at 2:1, 20:1 and 40:1 excipient/protein weight ratios, and stored up to 90 days at 45 °C. Protein enzymatic activity was studied using o-nitrophenyl-ß-D-galactopyranoside cleavage test, and its secondary structure in lyophilizates analyzed using Fourier transform infrared spectroscopy. The crystallization tendencies, glass transition temperatures and water contents of lyophilizates were evaluated using x-ray powder diffractometry, differential scanning calorimetry and thermogravimetry, respectively. RESULTS: The enzymatic activity of ß-galactosidase decreased more slowly in lyophilizates containing trehalose or melibiose at 2:1 excipient/protein weight ratio when compared to those containing sucrose or cellobiose. Similar behavior was observed when analyzing the protein's secondary structure in lyophilizates. In 20:1 and 40:1 excipient/protein weight ratio lyophilizates the decrease of enzymatic activity was less dependent on the excipient, but activity was always amongst the highest in melibiose lyophilizates. CONCLUSIONS: Melibiose was shown to be effective in protecting lyophilized ß-galactosidase during storage. The protein secondary structure was shown to change at comparable rate in lyophilizates as its enzymatic activity after rehydration.