Using dual labelled liposome components, the skin deposition of those derived from phospholipid and SCL carriers was studied.
The ratio of radiolabelled components of liposomal preparations was constant throughout the skin strata.
The authors explained this as possible molecular mixing of liposomal bilayers with the SC bilayers (Egbaria et al., 1990).
When [14C] inulin (hydrophilic marker) in liposomes whose lipid bilayer was radiolabelled with [3H] cholesterol was applied, the ratio of inulin to cholesterol was also constant throughout skin strata.
The explanation given by the authors (molecular mixing) would not justify equal ratios of the dual label in the deeper skin strata.
These findings may suggest possible carrier skin penetration.
Similar findings were reported again for both phospholipid and SCL liposomes (Fresta and Puglisi, 1996).
The ratio of [3H] DPPC to [14C] tretinoin deposited into various skin strata of the hairless rat was monitored after application of liposomes (Masini et al., 1993).
This ratio was constant throughout the SC but not in the nucleated epidermis and dermis.
Liposomes and tretinoin co-transport into SC was thus accompanied by independent penetration of free drug, which could have escaped from liposomes on the skin
surface.
This report suggests that vesicles can penetrate only into the stratum corneum.