Photolabile liposomes as carriers

UV-induced drug release from photoactive REV sensitized by suprofen

In order to achieve local administration of drugs, calcein (CAL) encapsulated reverse phase evaporation vesicles (REV) carrying photoactive destabilization agent suprofen (SPF) in the lipid bilayer were prepared. Effect of both UV-A and UV-B photoactivation of liposomal membrane incorporated SPF on the destabilization of the liposome bilayer and the release of encapsulated CAL was investigated. Standard REV of phosphatidylcholine (PC):cholesterol (CHOL) in 7:3 molar ratio, and photoactive REV of PC:CHOL:SPF, and DPPC:CHOL:SPF in 7:3:3 molar ratio were prepared. CAL encapsulation efficiency (EE (%)) and in situ release was studied. SPF incorporation in the PC REV membrane led to approximately 5% increase in the EE (34%) in comparison to standard REV (29%). EE decreased (21%) when DPPC was used to replace PC. Exposure to UV-B caused the highest CAL release. The lowest release was from the unexposed REV. DPPC led to a higher liposomal membrane stability (lower CAL release) than PC. A linear relationship was observed between UV-B exposure duration and REV permeability. This study revealed that membrane destabilization of SPF incorporated REV was best achieved upon photoactivation of the membrane-localized SPF by a 40 min exposure to UV-B.

Liposomes from novel photolabile phospholipids: light-induced unloading of small molecules as monitored by PFG NMR

A molecular dithiane-based approach to synthesis of novel photolabile phospholipids is developed. These lipids are used in formulations with egg-POPC and cholesterol to prepare light-sensitive liposomes. Irradiation of such liposomes in PBS buffer (medium pressure mercury lamp, Pyrex filter, lambda > 300 nm) significantly increases the bilayer permeability and accelerates the release of entrapped small organic molecules by an order of magnitude. A simple assay, based on (1)H or (19)F PFG NMR measurements of diffusion coefficients, is developed to monitor light-induced unloading of the probe molecules.

A simple method for preparation of immuno-magnetic liposomes

A simple and readily manoeuverable method for preparing immuno-magnetic liposomes that indigenously contain binding sites for attaching other molecules like antibodies on their exterior surface is described. In this method magnetic unilamellar vesicles are prepared from a mixture of phosphatidylcholine, cholesterol, small amounts of a linear chain aldehyde and colloidal particles of magnetic iron oxide, using a reverse phase evaporation technique. The aldehyde (dedecanal) molecules align themselves among the lipid molecules in the bilayer with their aldehyde groups exposed to the aqueous phase, allowing straight attachment of antibody molecules (human-antimouse IgG-FITC in this case) in one single step. The success of this approach is confirmed by fluorescence microscopy as well as binding of the resulting immuno-magnetic liposomes to their corresponding target cells.

Influence of membrane components on the stability and drug release properties of reverse phase evaporation vesicles (REVs): light sensitive all-trans retinal, negatively charged phospholipid dicetylphosphate and cholesterol

Incorporation of a negatively charged phospholipid, dicetylphosphate, initially increased encapsulation efficiency (from 12 to 24%) but beyond 5% (molar) a detrimental effect was observed. Rate of drug release from REVs was, for most cases, found to be bi-phasic implying partitioning between the lipid bilayer and the aqueous compartment. It was not possible to prepare liposomes with more than 1% (molar) all-trans retinal (ATR) as a membrane component. When ATR was reduced to 0.5% (molar), encapsulation efficiency increased to 7.76%. Upon exposure to long wave UV (365 nm), release from ATR containing REVs was increased and this was attributed to the formation of 13-cis isomer as indicated by HPLC and UV spectroscopy data.

Laser mediated release of dye from liposomes

Liposomes made from phospholipids and containing sulforhodamine dye (1-50 mM) have been irradiated with nanosecond and picosecond laser pulses. Individual liposomes were locally heated by laser absorption of dye dimers during a single laser pulse, and heating was sufficient to release the liposome contents. The extent of dye release produced by a single laser pulse was shown to be quantitatively dependent on several interdependent variables, including dye concentration, liposome size, laser excitation parameters and initial temperature of the dye-liposome system. Fluorescence lifetime data having three components have been obtained and analyzed in terms of three dye environments. Quantitative estimates support a photo-induced thermal mechanism for liposome lysis and release of its contents. These results may be useful for laser induced delivery of therapeutic agents or other applications of lasers in biological systems.

Triggered release of hydrophilic agents from plasmalogen liposomes using visible light or acid

Triggered release from liposomes composed of semi-synthetic 1-alk-1'-enyl-2-acyl-sn-glycero-3-phosphocholine (plasmalogen) lipids has been demonstrated using either aerobic visible illumination or low pH to induce leakage. The photodynamic release system consists of three functional components: (1) small (less than 1000 A) unilamellar plasmalogen vesicles (SUVs) containing encapsulated glucose, (2) oxygen and (3) zinc phthalocyanine (ZnPc) incorporated within the hydrophobic region of the SUV membrane. Irradiation (lambda greater than 640 nm) at 37 degrees C of air-saturated 1-alk-1'-enyl-2-palmitoyl-sn-glycero-3-phosphocholine (PlasPPC)/1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) (8:1, mol/mol) liposomes at physiologically relevant temperatures results in glucose release rates that are twice those of the corresponding dark control. Photolysis of argon-saturated PlasPPC/DPPC liposomes or of identical vesicles lacking either ZnPc or the plasmalogen vinyl ether bond exhibit glucose release curves which are indistinguishable from the dark control. Irradiation under identical conditions, but in the presence of 100 mM sodium azide, also results in no increased rate of glucose release above that of the dark control. TLC analysis indicates that oxidized lipid species are produced only in air-saturated, irradiated plasmalogen liposomes. The acid lability of the plasmalogen vinyl ether linkage has also been used to trigger release of entrapped calcein. At pH 4.2, the release rate at 37 degrees C is increased 4-fold over rates observed at pH 8. TLC analysis indicates formation of a lysoplasmalogen product. Taken together, these results indicate that both photodynamic and acid triggering can be used to increase plasmalogen liposome permeability and suggest that these liposomes are potentially useful for drug delivery applications.