DYE-SENSITIZED DESTABILIZATION OF LIPOSOMES BEARING PHOTOOXIDIZABLE LIPID HEAD GROUPS

Liposomes were prepared from mixtures of dipalmitoyl-L-alpha-phosphati dylcholine and up to 40% mol:mol of N-stearoyl-L-histidine (NSH) in th e presence of the hydrophobic sensitizer DHE. In the dark such liposom es are stable and retain entrapped salts. On photolysis with visible l ight, liposomes leak trapped ions at NSH concentrations greater than 1 0% mol:mol. Up to 15% mol:mol NSH concentration leakage is seen only d uring the illumination period, whereas at higher concentration the lip osomes continue to leak contents after illumination and fuse to form l arger structures. Photolysis of the liposomes is accompanied by oxygen uptake in proportion to the NSH concentration within the bilayer. Pho tocontrol of liposome permeability through oxidation of membrane addit ives such as NSH offers a potential means for controlled drug delivery and might be useful as an adjunct to photodynamic therapy.