Hans Schaefer

Investigation of follicular penetration of topically applied substances.

The influence of specific follicle properties, sebum production and hair growth on the follicular penetration of topically applied substances was investigated. The behavior of follicles identified in selected skin areas of volunteers was analyzed by various tape stripping and staining methods in combination with laser scanning microscopy. Furthermore hair growth in the selected skin areas was determined. A correlation between sebum production, hair growth activity and follicular penetration was observed.

Correlation of the local distribution of topically applied substances inside the stratum corneum determined by tape-stripping to differences in bioavailability.

Tape-stripping and optical spectroscopy are used as a suitable combined method to determine the horny layer profile. Firstly, typical ultraviolet filter substances are used as active substances which are fixed inside the horny layer. Secondly, clobetasol propionate was applied topically in two formulations, Temovate® Cream and Temovate Ε Emollient®. The measured changes in the local distribution of the drug inside stratum corneum reflect the observed differences in the biological response visualized as blanching. The concentration of the drug in deeper parts of the horny layer proposes the existence of a small channel available for the percutaneous absorption. The observed low intensity blanching is correlated to the follicle orifices of the skin. After application of Temovate Ε Emollient®, a lateral spreading of the drug must be taken into account.

Evaluation of the Pseudo-Absorption Method to Quantify Human Stratum corneum Removed by Tape Stripping Using Protein Absorption

Tape stripping is a well-known method to study the barrier function of the stratum corneum (SC) and penetration processes of topically applied substances into the horny layer. The quantification of the removed corneocytes for each tape strip is the prerequisite for these studies. The pseudo-absorption of the corneocytes was proposed as a measure for the quantification of the removed corneocyte aggregates. In this study, the pseudo-absorption of the corneocytes in the visible range (430 nm) is compared with the protein absorption in the UV range (278 nm) and an absorption at 652 nm obtained after staining of the SC proteins with Trypan blue. Both the protein absorption and the absorption measured after staining correlate well with the pseudo-absorption measured at 430 nm (R2 = 0.92 ± 0.04 and R2 = 0.95 ± 0.04, respectively).

Quantification of the horny layer using tape stripping and microscopic techniques

Tape stripping is a method well suited for studying the penetration of topically applied substances into the upper part of the skin, the stratum corneum (SC). The amount of topically applied substances removed by each tape strip can be determined by common analytical methods. These amounts have to be correlated with their location within the horny layer in order to determine penetration profiles. Therefore the amount of SC on each removed strip must be determined. In the study reported, this amount was derived from the covering density of the SC cells, the corneocytes, on tape strips using classic microscopic techniques and laser scanning microscopy. The amount of corneocytes determined by both microscopic methods shows a good correlation (R2 +/- S.D.= 0.95 +/- 0.02) with the pseudoabsorption of the corneocytes, a method usually used to determine the SC amount on the removed strips. These measurements require the application of a special spectrometer, whereas the covering density can easily be determined using widely available microscopic equipment. The penetration of a typical UV filter, butyl methoxydibenzoylmethane, applied at two different formulations, was studied using the microscopic method developed. The calculated penetration profiles show that the applied formulation influences the amount of corneocytes on the removed strips.

Determination of the formation of the stratum corneum reservoir for two different corticosteroid formulations using tape stripping combined with UV/VIS spectroscopy

Background: The stratum corneum, the outermost layer of the skin, not only represents a barrier, but also a reservoir for topically applied substances. Both properties influence the penetration process, as does the vehicle. It determines the penetration pathway and the retention time of the topically applied substances.

Analysis of the penetration process of drugs and cosmetic products into the skin by tape stripping in combination with spectroscopic measurements

A new method is described for analyzing the penetration of drugs and cosmetic products into the skin. This method combines the tape stripping procedure with UV/VIS spectroscopic measurements to determine the amount of corneocytes on the tapes removed by their scattering properties. The UV/VIS spectroscopic measurements were made using a Perkin Elmer Lambda 20 double beam spectrophotometer, which had been modified to obtain a rectangular beam diameter of 10 times 10 mm2. The absorbance measured at 430 nm was taken as measure for the mass of the corneocyte aggregates placed on the individual tapes. It was proven by weighing, laser scanning microscopy and spatial-spectral density analysis, that the absorbance in the visible range is better suited than the weight to quantify the amount of corneocyte aggregates removed by a single strip. This novel combination method permits to determine the actual position of sunscreen components in the stratum corneum.