Temperature-dependent aggregation of pH-sensitive phosphatidyl ethanolamine-oleic acid-cholesterol liposomes as measured by fluorescent spectroscopy.
pH-sensitive liposomes made of phosphatidyl ethanolamine-oleic acid-cholesterol (4:2:4 molar ratio) at neutral pH values aggregate at approximately 40 degrees C. The aggregation is accompanied by liposome destabilization and by the release of intraliposomal fluorescent marker (calcein). Both aggregation and calcein leakage start at the temperature corresponding to the lipid phase transition into hexagonal phase. In the system studied the phase transition temperature interval is within 45 to 55 degrees C as estimated with the use of the fluorescent probe 1,6-diphenylhexatriene. The presence of cell cultivation medium RPMI 1640 decreases liposome aggregation temperature. The addition of 10% serum to the system decreases the temperature at which the aggregation proceeds still further. The conclusion that serum-free media should be used for cell experiments involving pH-sensitive liposomes is made.
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Center for Imaging and Pharmaceutical Research, Massachusetts General Hospital-East, Charlestown 02129.
Omelyanenko
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Lukyanov
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D002021:Buffers; D002448:Cell Adhesion / Q000502:physiology; D002784:Cholesterol / Q000737:chemistry*; D004161:Diphenylhexatriene; D004337:Drug Carriers; D004355:Drug Stability; D005452:Fluoresceins; D006361:Heating; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D008081:Liposomes / Q000737:chemistry*; D019301:Oleic Acid; D009829:Oleic Acids / Q000737:chemistry*; D010710:Phosphates; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence; D013997:Time Factors
D002021:Buffers; D004337:Drug Carriers; D005452:Fluoresceins; D007202:Indicators and Reagents; D008081:Liposomes; D009829:Oleic Acids; D010710:Phosphates; D010714:Phosphatidylethanolamines; D004161:Diphenylhexatriene; D019301:Oleic Acid; D002784:Cholesterol; C007740:fluorexon