P-14   PENETRATION PROFILE OF MICROSPHERES IN SELECTIVE FOLLICULAR TARGETIN OF TERMINAL HAIR FOLLICLES

R. Toll, U. Jacobi, H. Richter, J. Lademann, H. Schaefer, U. Blume-Peytavi Centre of experimental and applied Cutaneous Physiology, Department of Dermatology and Allergy, University Hospital Charité, Berlin, Germany.

The transfollicular administration of drug products is of current therapeutic interest, mainly with regard to delivery to specific sites of the hair follicle and the reduction of hepatic metabolism and systemic toxicity. Hair follicles are privileged pathways for specific molecules and formulations, which enter faster into these shunts than through the stratum corneum. The aim of the present study was to optimize the delivery of fluorescent microspheres into the hair follicles thereby to (1) develop a standardized protocol for follicular targeting with microspheres, (2) find an optimal size of microsphere, (3) investigate the properties of the microspheres on the skin surface as well as in the hair follicle and (4) make a penetration profile regarding the number of hair follicles showing penetration as well as depth of penetration. Skin with terminal hair follicles from freshly excised skin (< 24h) was collected, after cyanocrylate stripping, microspheres in the size from 0.75 µm to 6.0 µm were applied according to a standardized protocol. Skin biopsies were shock frozen and sectioned using a cryostate in thin 5 µm slices. The fluorescent microspheres were localised and evaluated using a fluorescent light microscope. In-vivo investigations on volunteers were also conducted using the standardized protocol for application; subsequent evaluation was performed with the non-invasive technique of confocal laser scanning microscope. We demonstrated a selective penetration route of the microspheres into the hair follicle. Using our standardized protocol, an optimal microsphere size seemed to be ca. 1.5 µm with a maximum penetration depth of >2000 µm.