Biophysical studies and intracellular destabilization of pH-sensitive liposomes.
We examined changes in membrane properties upon acidification of dioleoylphosphatidylethanolamine/cholesterylhemisuccinate liposomes and evaluated their potential to deliver entrapped tracers in cultured macrophages. Membrane permeability was determined by the release of entrapped calcein or hydroxypyrene-1,3,6-trisulfonic acid (HPTS)-p-xylene-bis-pyridinium bromide (DPX); membrane fusion, by measuring the change in size of the liposomes and the dequenching of octadecylrhodamine-B fluorescence; and change in lipid organization, by 31P nuclear magnetic resonance spectroscopy. Measurement of cell-associated fluorescence and confocal microscopy examination were made on cells incubated with liposomes loaded with HPTS or HPTS-DPX. The biophysical studies showed (i) a lipid reorganization from bilayer to hexagonal phase progressing from pH 8.0 to 5.0, (ii) a membrane permeabilization for pH <6.5, (iii) an increase in the mean diameter of liposomes for pH <6.0, and (iv) a mixing of liposome membranes for pH <5.7. The cellular studies showed (i) an uptake of the liposomes that were brought from pH 7.5-7.0 to 6.5-6.0 and (ii) a release of approximately 15% of the endocytosed marker associated with its partial release from the vesicles (diffuse localization). We conclude that the permeabilization and fusion of pH-sensitive liposomes occur as a consequence of a progressive lipid reorganization upon acidification. These changes may develop intracellularly after phagocytosis and allow for the release of the liposome content in endosomes associated with a redistribution in the cytosol.
Van Bambeke
F
F
Unité de Pharmacologie Cellulaire et Moléculaire, Brussels, Belgium. vanbambeke@facm.ucl.ac.be
Kerkhofs
A
A
Schanck
A
A
Remacle
C
C
Sonveaux
E
E
Tulkens
P M
PM
Mingeot-Leclercq
M P
MP
D000818:Animals; D001190:Arylsulfonates / Q000378:metabolism; D001703:Biophysics / Q000379:methods*; D002478:Cells, Cultured; D002788:Cholesterol Esters / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008081:Liposomes / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D010316:Particle Size; D010539:Permeability; D010713:Phosphatidylcholines / Q000737:chemistry; D010714:Phosphatidylethanolamines / Q000737:chemistry
D001190:Arylsulfonates; D002788:Cholesterol Esters; D008081:Liposomes; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; C094877:dioleoyl phosphatidylethanolamine; C017251:1,2-oleoylphosphatidylcholine; C005047:pyranine; C013440:cholesteryl succinate