Analysis of skin penetration of phytosphingosine by fluorescence detection and influence of the thermotropic behaviour of DPPC liposomes

Phytosphingosine (PS) is a promising compound in skin formulations, considering its application in the treatment of acne and different inflammations as well as in the 'anti age' cosmetics. PS, as an active substance was incorporated in DPPC liposomes intended to standard diffusion experiments, where dermatomed porcine skin was mounted in FRANZ cells. The proved skin retention was about 5.5% (w/w) after 24 h and about 6.8% (w/w) after 48 h of the applied PS amount, whereas only about 0.05% (w/w) and about 0.07% (w/w) PS, respectively, could be observed in the acceptor medium. To increase analytical sensitivity PS was derivatised by o-phtalaldehyde (OPA) reagent and analysed by HPLC with fluorescence detection. The higher amount of PS within the skin symbolised an interaction with lipid structures in skin. Further evaluation of this interaction was accomplished by applying microDSC studies of PS with DPPC as a model membrane. For this purpose liposomes were prepared by increasing PS content. The characteristic endothermic peak observed for the single system was shifted to a slightly higher temperature and broadened as the mole fraction of PS increased. This might be the effect of mixing of PS with DPPC. An addition of 10 mol% PS resulted in more than double sized particles pointing to a possible change in the liposomal shape.