ABSTRACT
Complexation-triggerable liposomes were prepared by modifying the surface of egg phosphatidylcholine (EPC) liposomes with hydrophobicized silk fibroin (HmSF) and hydrophobicized chitosan (HmCh). Maximum complexation, determined by measuring the diameter of complexation, was found when the ratio of HmSF to HmCh was 14:1, so they were immobilized on the surface of liposomes at the same ratio. The degree of fluorescence quenching of calcein in liposomal suspension was as high as 68% when the ratio of surface modifier (HmSF + HmCh) to EPC was 1:15. When the ratio was increased to 1:5, the degree of quenching decreased to 32%, indicating the inefficient formation of liposome. Liposome mixed with the surface modifier was multi-lamellar vesicle on TEM photo. And, the mean diameter was larger than those of liposome mixed with either HmSF or HmCh, possibly due to insoluble complex on the liposomal surface. The liposome exhibited a pH-sensitive release and triggered the release at pH 5.5 and 6.0. It is believed that complexation is responsible for the promoted release at those pH values.
Subject(s)
Chitosan/chemistry , Liposomes/chemistry , Silk/chemistry , Drug Liberation , Fluoresceins/chemistry , Hydrophobic and Hydrophilic Interactions , Immobilized Proteins/chemistry , Phosphatidylcholines/chemistry , Surface PropertiesABSTRACT
Egg phosphatidylcholine (EPC) liposomes incorporating hydrophobically modified chitosan (HmCh) were prepared by a sonication method. In order to immobilize chitosan on the surface of EPC liposomes, pentyl chains were covalently attached to chitosan. Following the proton NMR spectrum, the number of pentyl chains per chitosan molecule was calculated to be 2.5. Once the ratio of HmCh to EPC was kept below 1:5, the degrees of fluorescence quenching in the liposomal suspension were greater than 70%, indicating a high yield of liposome formation. No significant release from the liposome was observed in neutral and akali condition. The liposomes started to release their content at pH 6.5, and the release became more extensive as the pH of release medium decreased. The pH-sensitivity of the liposomes in terms of the release strongly depended on the amount of HmCh incorporated in liposomes.
Subject(s)
Chitosan/chemistry , Fluoresceins/chemistry , Liposomes/chemistry , Phosphatidylcholines/chemistry , Drug Stability , Eggs , Hydrogen-Ion Concentration , Hydrophobic and Hydrophilic Interactions , SonicationABSTRACT
Liposomes, which release their contents in response to change in environmental pH and Ca2+ concentration, were prepared by modifying the surface of egg phosphatidylcholine (EPC) liposome with hydrophobically modified alginate (Hm AL). The liposomes prepared using the ratio of 1:7 (Hm AL:EPC) was stable when the pH of release medium was higher than 6.5. They started to release at pH 6.0, and the degree of release in 300 sec was more than 80% at pH 4.5. The collapse of Hm AL chains, caused by the lack of intramolecular electrostatic repulsion, would impose a mechanical energy on the liposomal membrane, promoting a release from the liposomes. Liposomes bearing less amount of Hm AL exhibited less degree of release, but the release profiles were found similar whatever Hm AL to EPC ratio was. On the other hand, the liposomes bearing Hm AL released calcein significantly (10-30%) in 300 sec when Ca2+ was contained in the release medium (5 mM and 10 mM). The collapse or the gellation of Hm AL, caused by an electrostatic interaction between Ca2+ and the polysaccharide, would be responsible for the release.
Subject(s)
Alginates/chemistry , Calcium/metabolism , Liposomes/chemistry , Phosphatidylcholines/chemistry , Alginates/metabolism , Animals , Calcium/chemistry , Chickens , Egg Yolk/chemistry , Fluoresceins/chemistry , Fluoresceins/pharmacokinetics , Glucuronic Acid/chemistry , Glucuronic Acid/metabolism , Hexuronic Acids/chemistry , Hexuronic Acids/metabolism , Hydrogen-Ion Concentration , Hydrophobic and Hydrophilic Interactions , Liposomes/metabolism , Liposomes/ultrastructure , Microscopy, Electron, Transmission , Static Electricity , Surface TensionABSTRACT
pH-sensitive liposomes were prepared by modifying the surface of egg phosphatidylcholine (EPC) liposomes with hydrophobically modified silk fibroin (HmSF). For the hydrophobic modification of SF, palmitic acid residues were covalently attached to SF through amide bond. According to the result of TNBS assay, about 90% of amino groups of SF participated in the conjugation reaction with palmitic acid N-hydroxysuccinimide ester, and the number of palmitic acid residue per SF molecule was calculated to be 15.3. The fluorescence quenching of calcein in liposomal suspension decreased from about 80-50%, when the ratio of HmSF to phospholipid increased from 1:20 to 1:5. The maximum degree of release from liposomes incorporating HmSF (of which HmSF to phospholipid ratio was 1:20) for 5 min was about 95% at pH 4.5, 25% at pH 5.0, and 5% at pH 5.5, and no appreciable amount of release was observed in the range of pH 6.5 to pH 8.0. Under acidic conditions, HmSF is likely to perturb the packing of phospholipid in liposomal membrane, possibly due to the unionization of the carboxylic groups of the silk protein.
