Study of the mechanisms of laser-induced release of liposome-encapsulated dye.

To differentiate the contributing factors (blood or encapsulated dye) leading to the release of encapsulated dyes from liposomes after laser exposure, we initiated an in vitro experimental study. The release of encapsulated calcein was quantified under various experimental conditions in whole blood and in buffered solution containing high-density lipoprotein. Generally, the amount of dye release improved with an increase in laser power, with a maximum release of approximately 80% of encapsulated dye. Because the laser exposure was not continuous, only 80% of each sample was actually exposed. Therefore, 80% release may be thought of as total release. In a lipoprotein/buffer mixture, the 488 nm wavelength caused greater dye release than the 577 nm wavelength, because the maximum absorption of calcein is near 488 nm. The laser wavelength at 577 nm, however, caused greater release in the blood mixture, reflecting the peak absorption of hemoglobin at near 577 nm. At a 3 x higher liposome concentration, the differences in the effects of wavelengths on the release of dye from liposomes were insignificant. Although the 577 nm wavelength is an optimum wavelength for dye and drug delivery in the presence of blood, the 488 nm wavelength might also be suitable for the release of dye from the liposomes.

Assessment of laser-induced release of drugs from liposomes: an in vitro study.

We evaluated the characteristics of laser-induced release of an antimetabolite (cytosine arabinoside) from temperature-sensitive liposomes. Previous work had shown that a laser would induce breakdown of liposomes when a dye was encapsulated within the liposomes. The present investigation was performed to determine if release could be induced from liposomes that did not contain dye. In vitro, dynamic studies of the release of the drug from liposomes diluted in blood (flowing in a capillary tube at 40 microns/min) were conducted using an argon dye laser operating either in the blue-green mode (488/514 nm) or in the dye mode (577 nm). A radio-labeled marker was used to monitor the drug release. The results showed that the drug could indeed be released from liposomes that did not contain dye, at energy levels that are not likely to be harmful to the tissue. At identical power levels, the release of the drug was greater at 577 nm than at 488/514 nm, probably owing to the greater light absorbance of hemoglobin at the longer wavelength. The results indicate the potential for the site-specific release of a variety of molecules in the ocular vasculature.