Ute Jacobi

Porcine ear skin: an in vitro model for human skin

Background/purpose: Porcine ear skin is used in studies of percutaneous penetration as a substitute for human skin. The structure of this tissue, including hair follicles, was studied qualitatively and quantitatively in comparison with human skin.

The tape stripping procedure ― evaluation of some critical parameters

Tape stripping is a simple and efficient method for the assessment of quality and efficacy of cosmetical and dermatological formulations. After topical application and penetration of formulations, the cell layers of the stratum corneum are successively removed from the same skin area using adhesive films. The tape strips contain the amount of corneocytes and the corresponding amount of the penetrated formulation, which can be determined by classical analytical chemical methods. Different formulations can strongly influence the amount of stratum corneum removed with every tape strip. Therefore, it is essential for the comparison of the penetration of different formulations that the amount of formulation detected on the single tape strip is not related to the tape strip number as a relative measure of the penetration depths, but to their standardized real position in the stratum corneum. Therefore, different methods are reported for the determination of the amount of stratum corneum removed with every tape strip. The tape stripping method in its standardized form is well-suited to determine the dermatopharmacokinetics of topically applied substances. Additionally, the method can be used to obtain information about the homogeneity and the distribution of formulations on the skin and in the stratum corneum. This is used, e.g., for the determination of the homogeneity of the distribution and the ex vivo determination of a universal sun protection factor (USPF) characterizing the efficacy of sunscreens.

In vivo determination of skin surface topography using an optical 3D device

Background/purpose: Topography of the skin surface is a mirror of the functional skin status. Therefore, its evaluation is of great interest for dermatological research. In the present study, a new optical measuring system was applied to evaluate human skin surface topography in vivo and non‐invasively, in order to determine elastotic and mimic wrinkles dependent on age, body site and therapy.

Gender-Related Differences in the Physiology of the Stratum Corneum

Background: Only few studies on gender-related differences in skin physiology have been performed – and they provided conflicting results. Objective: In the present study, the effect of gender on the physiology of the stratum corneum was studied. Methods: The physiological parameters transepidermal water loss, pH value, hydration and sebum content were determined on the flexor forearms of 6 female and 6 male volunteers. In addition, stratum corneum samples, removed by tape stripping, were studied for amount, spectroscopic properties, protein content, and mass. Results: The skin of women was characterized by a significantly higher pH value (5.6 ± 0.4) than that of men (4.3 ± 0.4, p < 0.05). Protein absorption was the only other parameter significantly dependent on gender (p < 0.05). Both effects might be caused by differences in human biology, such as hormonal status. Conclusion: Therefore, the gender of the volunteers should be considered in dermatologic studies.

Estimation of the relative stratum corneum amount removed by tape stripping.

Background/purpose: The tape stripping procedure is a suitable minimal invasive tool to study, e.g. the penetration and dermatopharmacokinetics of topically applied substances. In the present study, this procedure was used to remove the stratum corneum (SC) completely and to study the penetration of the UVA filter substance butyl methoxydibenzoylmethane after application in two different vehicles.

Follicular Penetration: Development of a Method to Block the Follicles Selectively against the Penetration of Topically Applied Substances

Investigations into the penetration pathways of topically applied substances through the skin play an important role in dermatological science. Recently, the hair follicles have increasingly been recognized as an important pathway for percutaneous penetration, although the role of the follicles has still not been clarified in detail. Therefore, the aim of the present study was to develop an in vivo method for the analysis of the follicular rate of penetration processes. In order to reach this goal, the follicles were excluded from the penetration process of topically applied substances. Different study designs were evaluated, and we were able to show that the application of nail varnish to each follicular orifice represents an effective method of blocking the follicles selectively against the penetration of topically applied substances. In dermatological science, there is new information on the physiology of skin penetration processes, thus allowing examination of the follicular rate of penetration and improvement of the pharmacokinetics of topically applied substances.

Effect of the vehicle on the amount of stratum corneum removed by tape stripping

Background: The penetration of topically applied substances into the stratum corneum can non‐invasively be studied using the tape stripping procedure. This method was applied to investigate in vivo the penetration of a fragrance, vanillin, applied in ethanol and a w/o emulsion.

Influence of nonhomogeneous distribution of topically applied UV filters on sun protection factors

The aim of the present study is the development of a method to determine quantitatively in vivo the influence of homogeneity of the distribution of sunscreen containing UV filters on the sun protection factor (SPF). The SPF of a sunscreen applied either topically or inside an optical cell (pure or in a solvent) fixed above the skin is determined in vivo. In both cases, in vivo measurements using the erythema formation are carried out. Identical optical parameters of the skin are realized in both experiments. In addition, both in vitro (using tape stripping) and in vivo microscopic measurements are performed to analyze the homogeneity of distribution of the topically applied substances. An SPF of 8 is measured in the experiment applying the UV filters topically, whereas this value increases by a factor of 10 if the same amount of filter substances is distributed homogeneously in solution inside the optical cell. Tape strips removed from skin treated with the sunscreen reflect the inhomogeneous distribution of the topically applied substances on the skin. The direct correlation of homogeneity of distribution with the SPF opens up the possibility to increase the SPF by optimizing the formulation.

Determination of penetration profiles of topically applied substances by means of tape stripping and optical spectroscopy: UV filter substance in sunscreens

Penetration profiles of topically applied drugs and cosmetic products provide important information on their efficacy. The application of tape stripping in combination with UV/VIS spectroscopy is checked to determine the local position of topically applied substances inside the stratum corneum, the penetration profile. The amount of corneocytes removed with each tape strip is quantified via the particle-dependent absorption, the pseudoabsorption, in the visible spectral range. The concentration of a typical UV filter substance, 4-methylbenzylidene camphor, is determined by optical spectroscopy using the tape strips removed originally. In this case, a time-dependent increase in the absorbance must be taken into account. Laser scanning microscopic investigations confirm that the nonhomogeneous distribution of the filter substance, on the strips, can explain this spectroscopic behavior. When reaching a homogeneous distribution, the UV spectroscopic signal reflects the correct concentration. These spectroscopic values are compared with high performance liquid chromatography (HPLC) data. The values obtained with both methods for the concentrations of 4-methylbenzylidene camphor are in good agreement. The data obtained are used to illustrate the determination of a penetration profile of a UV filter substance. The results demonstrate that the described protocol is well suited to characterize, in a simple manner, topically applied substances that have a characteristic UV/VIS absorption band.

Cutaneous distribution and localization of dyes affected by vehicles all with different lipophilicity

The penetration of topically applied substances into the stratum corneum (SC) depends on several factors, e.g., the physicochemical properties of the vehicle used for application. The penetration of highly hydrophilic and lipophilic dyes into the skin was studied using a pure oil (o) or water (w) for the application compared to an o/w emulsion. The penetration and localization of both dyes, the lipophilic curcumin and the hydrophilic Patent blue V, was investigated in vivo using the method of tape stripping and microscopy. In addition, histological sections of biopsies, removed from porcine ear skin were studied using microscopy. Differences in the distribution and the localization of both dyes within the SC were observed. These differences depend on the physicochemical properties of both the vehicles and the dyes. The vehicle appears to affect, in particular, the pathways of penetration.