title: Effect of grafted polyethylene glycol (PEG) on the size, encapsulation efficiency and permeability of vesicles.
abstract: Liposomes have been prepared by the vesicle extrusion method (VETs) from mixtures of dipalmitoylphosphatidylcholine (DPPC), phosphatidylinositol (PI) and dipalmitoylphosphatidylethanolamine with covalently linked poly(ethylene glycol) molecular mass 5000 and 2000 (DPPE-PEG 5000 and DPPE-PEG 2000) covering a range of 0-7.5 mole%. The encapsulation of D-glucose has been studied and found to be markedly dependent on the mole% DPPE-PEG. The permeability of the liposomes to D-glucose has been measured both as a function of temperature and liposome composition. The permeability coefficients for D-glucose increase with mole% DPPE-PEG 5000 and with temperature over the range 25-50 degrees C. The activation energies for glucose permeability range from 90 to 23 kJ mol(-1). The decrease in activation energy with increasing temperature is attributed to an increasing number of bilayer defects as the liposome content of PEG-grafted lipid is increased. The dependence of D-glucose encapsulation as a function of PEG-grafted lipid content is discussed in terms of the conformation of the PEG molecules on the inner surface of the bilayer. For liposomes containing DPPE-PEG 5000 the relative percentage encapsulation of glucose, assuming that the PEG surface layer excludes glucose, is comparable to that predicted from the mushroom and brush conformational models.
authors.affiliation: School of Biological Sciences, University of Manchester, Manchester, UK.
authors.forename: A R
authors.initials: AR
authors.lastname: Nicholas
authors.forename: M J
authors.initials: MJ
authors.lastname: Scott
authors.forename: N I
authors.initials: NI
authors.lastname: Kennedy
authors.forename: M N
authors.initials: MN
authors.lastname: Jones
mesh_terms: D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D004337:Drug Carriers; D005947:Glucose / Q000008:administration & dosage; D066298:In Vitro Techniques; D008081:Liposomes / Q000737:chemistry*; D010316:Particle Size; D010539:Permeability; D010714:Phosphatidylethanolamines / Q000737:chemistry; D010716:Phosphatidylinositols / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D004337:Drug Carriers; D008081:Liposomes; D010714:Phosphatidylethanolamines; D010716:Phosphatidylinositols; D015060:1,2-Dipalmitoylphosphatidylcholine; C007510:1,2-dipalmitoyl-3-phosphatidylethanolamine; D011092:Polyethylene Glycols; D005947:Glucose