P1.12 Follicular penetration: Development of a method to block the follicles selectively against the penetration process

A. Teichmann, U. Jacobi, H.J. Weigmann, H. Schaefer, W. Sterry, J. LademannCenter of Experimental and Applied Cutaneous Physiology, Department of Dermatology and Allergology, Charité - Universitätsmedizin, Berlin, Germany

Investigations concerning the penetration pathways of topically applied substances through the stratum corneum (SC) play an important role in dermatologic science, as they make possible the understanding of the pharmacokinetics of topically applied substances. Several penetration pathways are known as transepidermal routes (intercellular and transcellular) and the transappendageal routes (via sweat glands and hair follicles). Recently, the transfollicular penetration has increasingly been recognized as an important pathway for percutaneous penetration.

In order to investigate the influence of the follicular part of penetration, a method was developed to selectively block the follicles against penetration by the application of nail varnish inside defined skin areas. The skin surface was cleaned by removing two tape strips, whereas the follicular orifices were still blocked with nail varnish. Then, two different sunscreens (o/w emulsion containing a chemical UV filter and o/w emulsion containing a physical UV filter) were applied onto these areas and on reference skin areas under in vivo and in vitro conditions. Subsequently, the tape stripping procedure and spectroscopic measurements were utilized in order to determine the amount of UV filters, which had penetrated into the SC.

As a result of the investigation, it was demonstrated that the follicles were closed up for the penetration of the physical UV filter (lower penetration rates in comparison to reference skin areas) while the penetration process of the chemical filter substance was not influenced (no significant difference in penetration rates between treated and reference skin areas). Histological investigations were able to explain this difference. The follicular orifices were not completely closed due to the tape stripping procedure performed after application of the nail varnish. The block was raised allowing the penetration of the small molecules of the chemical UV filter in contrast to the much bigger microparticles of the physical UV filter. Therefore, the follicles were closed by the application of nail varnish directly onto the follicular orifices using a syringe. In this way, the penetration of the chemical UV filter was also reduced.

In summary, a method has been developed to block the follicles to prevent penetration in order to examine the follicular rate of penetration.