Satoshi Ohtake

Effect of pH, Counter Ion, and Phosphate Concentration on the Glass Transition Temperature of Freeze-Dried Sugar-Phosphate Mixtures

AbstractPurpose. The aim of the present work is to study the interaction of phosphate salts with trehalose and sucrose in freeze-dried matrices, particularly the effect of the salts on the glass transition temperature (Tg) of the sugars. Methods. Freeze-dried trehalose and sucrose systems containing different amounts of sodium or potassium phosphate were analyzed by differential scanning calorimetry to determine the Tg and by Fourier-transform infrared spectroscopy (FTIR) analysis to evaluate the strength of the interaction between sugars and phosphate ions. Results. Sucrose-phosphate mixtures show an increase in Tg up to 40°C in a broad pH range (4-9) compared to that of pure sucrose. Sucrose-phosphate mixtures exhibit a higher Tg than pure sucrose while retaining higher water contents. Trehalose-phosphate mixtures (having a Tg of 135°C at a pH of 8.8) are a better option than pure trehalose for preservation of labile materials. The -OH stretching of the sugars in the presence of phosphates decreases with increase in pH, indicating an increase in the sugar-phosphate interaction. Conclusions. Sugar-phosphate mixtures exhibit several interesting features that make them useful for lyophilization of labile molecules; Tg values much higher than those observed for the pure sugars can be obtained upon the addition of phosphate.

Phase Behavior of Phospholipid-Cholesterol Liposomes Stabilized With Trehalose

Achieving long-term stability in biological systems has been a long-standing goal of the food, pharmaceutical, and biomedical industries. Avoiding the need for refrigeration would reduce production and storage costs drastically. The desiccation of phospholipidic vesicles has been studied in an effort to understand biological membranes under low water content conditions (Crowe and Crowe, 1988; Ohtake et al., 2004). Trehalose is effective in protecting biological membranes upon freeze-drying, and it has been widely used to preserve the integrity of phospholipid liposomes (Crowe and Crowe, 1988; Ohtake, et al., 2004; Crowe et al., 1986). Despite the abundance of cholesterol in mammalian plasma membranes (Rouser, et al., 1968), studies examining the effects of dehydration on cholesterol-containing model membranes are scarce (Van Winden and Crommelin, 1999; Harrigan, et al., 1990). Furthermore, the ability of well known lyoprotectants, such as trehalose, to stabilize cholesterol-containing liposomes has not been examined in detail. The aim of this work is to understand how cholesterol containing liposomes behave upon lyophilization.