ABSTRACT
Satoshi Ohtake, Carolina Schebor, Sean P. Palecek, and Juan J. de Pablo
CONTENTS
Introduction ........................................................................................................ 551
Materials and Methods ..................................................................................... 552
Sample Preparation ................................................................................... 552
Differential Scanning Calorimetry........................................................... 552
Water Content Analysis ............................................................................ 552
Calcein Retention Analysis....................................................................... 552
Results.................................................................................................................. 553
References ........................................................................................................... 556
The desiccation of lipid vesicles has been studied in efforts to understand the
behavior of biological membranes under low water content conditions
(Crowe and Crowe, 1988) and to enhance the stability of liposomes used for
drug-delivery applications (Van Winden et al., 1998). Upon the addition of
sugars, phospholipid liposomes can be protected against the stresses caused
by dehydration through the formation of a glassy matrix (Levine and Slade,
1992). The desiccation of phospholipid liposomes increases their phase
transition temperature (T
) (Crowe and Crowe, 1988; Koster et al., 1994). In
the presence of sugars, however, the transition temperature can be depressed
(Crowe and Crowe, 1993). This T
depression has been ascribed to
hydrogen-bond formation between the sugar molecules and the phospho-
lipid headgroups (Crowe and Crowe, 1993; Sum et al., 2003). With regard to
cholesterol, the majority of previous studies have focused on the physical
properties of cholesterol-containing membranes in aqueous dispersions. It
has been shown that cholesterol incorporation to phospholipid bilayers
modulates the physical properties of the membrane (McMullen et al., 1993).
Given that one of our objectives is to better understand how cell membranes
respond to desiccation, in this study we examine in detail the effects of
membrane composition on the phase transitions and stability of freeze-dried
DPPC-and DPPE-cholesterol liposomes in the presence of trehalose.
