Retinyl palmitate-loaded vesicles: influence on vitamin light-induced degradation

The therapeutic use of retinoids is still limited because of adverse effects and their chemical instability due to moisture, oxygen, acids, metals and exposure to light. The main purpose of this study is to evaluate the influence of the inclusion in phospholipid and in surfactant (Tween 20 and Span 60) unilamellar vesicles on retinyl palmitate (RetP) light-induced degradation. Vesicles were obtained by means of the “film” technique and were characterized by means of freeze fracture microscopy technique, dynamic light scattering, for size and zeta potential measurements, and collisional quenching experiments, for the characterization of the RetP localization in vesicular structures. RetP stability studies were carried out by means of normal phase HPLC on samples exposed continuously in a darkened room to the light of a filament lamp (400 lux). Under dark conditions and under light irradiation the RetP inclusion in liposomes and in surfactant vesicles does not lead to significantly different degradation rates, comparing vesicle formulations to RetP reference solution in THF:water 9:1.