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.