Effects of free fatty acids and transition temperature on the stability of dry liposomes.
Previous studies have shown that liposomes composed of phospholipids with low phase-transition temperatures can be stabilized in the absence of water, provided that fusion is inhibited between the vesicles during drying, and that during rehydration the phospholipids do not pass through the gel to liquid crystalline phase transition. These conditions are met by adding certain disaccharides to the vesicles before drying, which inhibit fusion and depress the transition temperature in the dry lipids. The present study shows that preservation can also be achieved with vesicles made from dipalmitoylphosphatidylcholine (DPPC), but that the retention of trapped solute by such vesicles is much less than in vesicles composed of more fluid phospholipids. Addition of free fatty acids to the vesicles before drying destabilizes them; DPPC vesicles containing 15 mol% or more of palmitic acid leaked all their contents during drying, regardless of how much of the stabilizing sugar was added. Unlike the case for more liquid phospholipids, the leakage in DPPC vesicles is due solely to fusion and not to hydration-dependent phase transitions. Addition of free fatty acids results in increased fusion, leading to leakage.
Crowe
J H
JH
Department of Zoology, University of California, Davis 95616.
McKersie
B D
BD
Crowe
L M
LM
D003890:Desiccation; D005230:Fatty Acids, Nonesterified; D008081:Liposomes; D008561:Membrane Fusion; D008563:Membrane Lipids; D010539:Permeability; D012995:Solubility; D013696:Temperature; D013816:Thermodynamics
D005230:Fatty Acids, Nonesterified; D008081:Liposomes; D008563:Membrane Lipids